The Swedish Hip Arthroplasty Register

AC­TA OR­THO­PA­E­DI­CA

The Swedish Hip Arthroplasty Register 40-year anniversary

Ezine edition: The Swedish Hip Arthroplasty Register — 40-year anniversary

Cover illustration: Pontus Andersson, Pontus Art Production

Ezine edition, May 2019

© LINK 643_SPII_Ad_en_2019-04_001 Waldemar Link GmbH & Co. KG · www.linkorthopaedics.com · info@linkhh.de · Germany

ODEP

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13A* The LINK® Lubinus SP II® is one of the most used anatomical hip stems in the world.2 Successfull for 40 years proven through profound clinical data3,4 1 www.odep.org.uk; Orthopaedic Data Evaluation Panel 2 S . Sesselmann, Y. Hong, F. Schlemmer, K. Wiendieck, S. Söder, I. Hussnaetter, L. A. Müller, R. Forst, T. Wierer; Migration measurment oft he cemented Lubinus SPII hip stem – a 10-year follow-up using radiostereometric analysis; Biomed. Eng.Biomed. Tech. 2017; 62(3): 271-278 3 K ärrholm, Lindahl, Malchau, Mohaddes, Rogmark, Rolfson, ANNUAL REPORT 2015; The Swedish Hip Arthroplasty Register 4 G arellick, Kärrholm, Rogmark, Rolfson, Herberts, ANNUAL REPORT 2014; The Swedish National Hip Arthroplasty Register.; p. 75

643_SP II_Ad_en_A4_2019-04_001_SWEDEN210x280mm.indd 1

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CORAIL® PINNACLE® Your cementless solution, with a 17% lower risk of revision when compared to all other uncemented contructs on the NJR.1 The standard CORAIL® Femoral Stem is available both with and without a collar. Proponents of the use of a collared prosthesis claim that it provides advantages in the early stability of the implant, allowing for earlier post-operative weight bearing, protection against subsidence, and a positive dispersion of the vertical forces via the collar into the medial calcar.2,3

The CORAIL STD Collared femoral stem has been shown to have a 29% lower risk of revision when compared to all other cementless stems on the NJR.4 The NJR has produced a new report analyzing the performance of the CORAIL® PINNACLE® Cementless Construct. This analysis was commissioned by DePuy Synthes, but conducted and validated by the NJR. The reports details 123,536 CORAIL PINNACLE Cementless implantations (mean age 65.7, 44.4% male). All metal-on-metal was excluded.

Patients receiving a CORAIL PINNACLE Cementless Construct are 17% less likely to be revised when compared to all other uncemented constructs on the NJR (HR 0.83 (0.79, 0.87) p<0.001).

Please visit www.corailpinnacle.net for more information

References 1. According to NJR data from 2003 to 2017 where 123,356 CORAIL PINNACLE Cementless implantations were used in primary THR and compared to all other cementless constructs in NJR. Hazard ratio adjusted for age, gender, year cohort and indications. Bespoke Report: Corail - Pinnacle vs. All other Cementless hips DSEM/JRC/0518/1040. Report can be accessed at http://www.corailpinnacle.net/supportingevidence/overview. 2. H. Strom, O. Nilsson, J. Milbrink, et al. The effect of early weight bearing on migration pattern of the uncemented CLS stem in total hip arthroplasty. J Arthroplasty, 22 (2007), p. 1122 3. Demey G, Fary C, Lustig S, Neyret P, Aït si Selmi T. Does a Collar Improve the Immediate Stability of Uncemented Femoral Hip Stems in Total Hip Arthroplasty? A Bilateral Comparative Cadaver Study. J Arthroplasty 26 (2011), No.8, p. 1549 4. According to NJR data from 2003 to 2017 where 65,545 CORAIL STD Collared femoral stems were used in primary THR and compared to all other cementless stems in NJR. Hazard ratio adjusted for age, gender, year cohort and indications. Bespoke Implant report CORAIL Stem (Standard Offset Collared) NJR, DSEM/JRC/0118/0999. Report can be accessed at http://www.corailpinnacle.net/supportingevidence/overview

www.depuysynthes.com This publication is not intended for distribution in the USA © DePuy Synthes Joint Reconstruction, a division of Johnson & Johnson Medical Limited. 2018. All rights reserved. DSEM/JRC/0618/1056

40 years with the Swedish Hip Arthroplasty Register Abstract — The Swedish Hip Arthroplasty Register started in 1979 and celebrates its 40th anniversary this year. The register is not primarily a device register or research database; we strive to provide an overall assessment of the care provided with a multidimensional approach, and to disseminate knowledge on best practices in our network of participating hospitals. The completeness of registrations has been 97–99% for primary total hip arthroplasty, 93–95% for revisions, and 95–98% for hemiarthroplasty over the last 10 years. The register currently contains 470,000 primary arthroplasties, 85,000 reoperations, and 450,000 PROM responses registered in more than 370,000 unique patients. Since the inception of the register, there has been a marked change in trends and outcomes. All outcome measures have improved over time; primary THA has 95% 10-year implant survival, and 2.2% 2-year reoperation rate. At 1-year follow up, 92% of patients report pain reduction, 83% report improvement in health-related quality of life, and 87% are satisfied with the result of the operation. The trends and changes in Swedish arthroplasty practice have largely been promoted and facilitated by the register over the last 40 years. Moving forward, we are developing enhanced online applications for surgeons, patients and the implant industry to access real-time information. This work involves constructing a shared decision-making tool that helps clinicians assessing the future benefits and risks of THA by offering individualized outcome predictions. Further steps forward include randomized clinical trials, nested studies through the registry’s platform and consolidation with other orthopaedic registers.

Initiated in 1979, the Swedish Hip Arthroplasty Register is a national quality register with the overall aim of improving hip arthroplasty care in Sweden. Intentionally, we register all hip arthroplasty procedures regardless whether the operation takes place in a public or private establishment and regardless of the diagnostic indication for surgery.

Figure 2. Peter Herberts led the development of the Swedish Hip Arthroplasty Register and was the director until 2006. Photo: Åke Sjöstedt

We collect data longitudinally to ascertain implant survival, causes of revisions and other reoperations, and patient-reported endpoints pertaining to hip pain, general health status and satisfaction with the result of surgery. These data allow us to report back to health care professionals involved in arthroplasty care, with a concerted aim of stimulating quality-improvement interventions at the local level and improving patient care. Importantly, the Swedish Hip Arthroplasty Register is not primarily a device register or research database; we strive to provide an overall assessment of the care provided with a multidimensional approach, and to disseminate knowledge on best practices in our network of participating hospitals. This narrative review covers the history of the register and important milestones (Figure 1), summarizes some major findings and discusses future directions of the register. World’s 1st national hip arthroplasty register What later became the Swedish Hip Arthroplasty Register, started as a pilot projected initiated by Peter Herberts (Figure 2) in the mid 70’s (Ahnfelt et al. 1980). Retrospective by its

Figure 1. Milestones in the history of the Swedish Hip Arthroplasty Register

nature, the pilot study focused on what variables to include in a national register and the feasibility of collecting those. Most Swedish orthopaedic departments contributed to the pilot study. The lessons learned were used to set up the register and the prospective data collection started in 1979 as the world’s 1st national quality register on total hip arthroplasty (THA). When the register started, primary THAs were recorded on aggregate hospital level while registration of reoperations was based on personal identity number. In 1992, we started recording primary THAs based on personal identity number as well. A few years after its inception, all hospitals performing THA in Sweden participated. The profession soon learnt to appreciate the feed-back of results and adhere to recommendations. The 1st large mid- to long-term follow-up study of the register identified several implants associated with worse implant survival, which resulted in change of practice and abandoning of underperforming implants (Malchau et al. 1993). This study highlighted the importance of implant selection and cementing technique and demonstrated the importance of systematic implant surveillance through an arthroplasty register. Annual user meetings In 1992, together with the Swedish Knee Arthroplasty Register, we started organizing annual meetings for orthopaedic surgeons responsible for the local collection of register information at each hospital. These user meetings have been instrumental in communicating with the profession and implementing recommendations based on our findings. We dare to state that the register has contributed to foster generations of Swedish arthroplasty surgeons in a tradition to adhere to the concept of staged introduction of new implant technology (Malchau 1995). The cautious attitude towards undocumented new concepts has helped avoid catastrophes such as those associated with metal-on-metal implants experienced in other countries. Today, 6 different stem designs account for more than 92% of all femoral components used in THA in Sweden. Likewise for acetabular components, 10 different cup designs account for more than 82% of the production (Kärrholm et al. 2017). Platform designers The register database was digitalized in 1990 and, as the 1st national quality register, we launched a web-based system for data collection in 1999. The original platform, designed by Roger Salomonsson, was used up to 2017 when we transitioned all data to a modern platform developed by the same designer. Today, more than 20 national quality registers use this new generic register platform named Stratum. Completeness of registrations Completeness analysis on the individual level are yearly being undertaken by linkage with the Patient Register at the National Board of Health and Welfare since 2006. This is an important step to ensure that the results reflect the entire arthroplasty population and are generalizable. The completeness of regis-

trations has been 97–99% for primary THA, 93–95% for revisions, and 95–98% for hemiarthroplasty over the last 10 years (Kärrholm et al. 2017). The PROMs program The 1st 20 years of the register activities focused on implant survival as the main outcome measure. However, an implant still in place is not the only indicator of success (Söderman et al. 2001, Rolfson et al. 2011). The quality of hip arthroplasty is ultimately defined by whether it has helped the patients in terms of pain relief, functional gains and improved health-related quality of life as judged by the patient. Consequently, the register started a patient-reported outcome measures (PROMs) program in 2002. The development was led by Göran Garellick and the program was gradually adopted by all hospitals performing THA in Sweden. To include PROMs in a nationwide quality register was demanding and it required a rigorous organization and technological support system in place to collect the large volumes of data. The brief standardized protocol includes items on pain, health status (EQ-5D), patient-reported Charnley category, smoke habits, prior physiotherapy and patient education interventions. At the 1-, 6- and 10-year follows-ups, the same questions are asked (except prior interventions and smoking) with the addition of an item addressing satisfaction with the outcome of the intervention. The response frequency has been reported at 86% preoperatively and 90% at the 1-year follow-up (Rolfson et al. 2011). Findings from the PROMs program The mere act of measuring patient-reported outcomes has corroborated that elective THA in Sweden is successful in alleviating pain and improve health status treatment in patients with degenerative hip disorders in general. Among patients operated in 2017, 92% of patients reported pain reduction, 83% reported improvement in health-related quality of life, and 87% were satisfied with the result of the operation 1 year after surgery. However, the program has also recognized an important minority of patients who do not reach the expected improvements or who express dissatisfaction with the result of the surgery. To investigate this further, several patientrelated determinants such as emotional health (Rolfson et al. 2009, Greene et al. 2016), the presence of other comorbidities (Gordon et al. 2014, Greene et al. 2015), and socioeconomic status (Greene et al. 2014) have been identified as being associated with patient-reported outcomes. We have also identified associations between surgical factors, such as the surgical approach and fixation method, and outcomes (Lindgren et al. 2014, Rolfson et al. 2016). In addition, we have demonstrated poor PROMs at 1 year after THA to be a risk factor of subsequent reoperations (Eneqvist et al. 2018). Importantly, there is variation between hospitals; despite adjustment for patient case-mix, patient-reported outcomes differ considerably between providers (Garellick et al. 2015). Gratifyingly, we

have observed a significant nationwide trend of improvement in PROMs over the last decade (Garellick et al. 2015). Pioneers in hemiarthrolasty registration Cecilia Rogmark took the initiative and led the work on including hemiarthroplasties in the Swedish Hip Arthroplasty Register in 2005. This was yet another pioneering work and still very few national arthroplasty registers comprise hemiarthroplasties. Because of the established data collection routines, it was easy for hospitals to join and the national completeness at case level reached 95% from the start (Kärrholm et al. 2018). The early results indicated that direct lateral approach was associated with reduced risk of dislocation which dramatically influenced the choice of surgical technique in Sweden (Leonardsson et al. 2012). The exceptionally high use of cemented fixation in hemiarthroplasties is well-supported by our findings. Without differences in mortality, uncemented stem fixation carries an increased risk of all-cause reoperation mainly explained by increased risk of periprosthestic fractures in particular without differences in mortality (Leonardsson et al. 2012). We believe these register findings have contributed to maintain cemented fixation as the method of choice in hemiarthroplasty and avoided the international trend towards uncemented fixation for this frail patient group. Up to 2012, hemiarthroplasties were presented separately from THAs. Since the annual report of 2012, all results of arthroplasty due to hip fracture or failed hip fracture treatment, regardless if it was a total or hemiarthroplasty, have been presented together. The homogeneity of implants used for fracture patients is considerable; 3 stems account for more than 90% of the operations (Kärrholm et al. 2018). Research in the Swedish Hip Arthroplasty Register During the last decade, we have carried out strategic work within the register to improve the infrastructure with the purpose of increasing and reinforcing research activities. This has been successful, which can be noted in the fact that currently more than 20 PhD students, representing 7 universities, base the whole or part of their research on data from the register. During the last 10 years, 150 scientific articles from the register were published, and only in 2018, we gave more than 80 presentations at national and international meetings. Since 1986, when Lennart Ahnfelt defended the 1st thesis based on the Swedish Hip Arthroplasty Register, a further 24 PhD students have produced theses based on data from the register. Future directions – consolidation efforts The impact of the Swedish Hip Arthroplasty Register on arthroplasty practice in Sweden is not attributable to isolated major discoveries. It is based on continuous in-depth analyses, persistent communication with the profession, and open reporting of results at hospital unit level. The resulting homo-

geneous use of well-documented implants and methods has yielded outstanding long-term implant survivorship. These endeavors will persist in the future, but perhaps in a new shape. Moving forward, we are developing enhanced online applications for surgeons, patients and the implant industry to access real-time information. This work involves constructing a shared decision-making tool that helps clinicians assessing the future benefits and risks of THA by offering individualized outcome predictions. In a near future, we will increase the register’s utility by developing the infrastructure necessary to conduct randomized and nested clinical trials based on the register platform (Malchau et al. 2015). There are today 13 national quality registers with orthopaedic focus. Each register stems from enthusiasts within the respective sub-field and the registers have largely been developed independent of each other. This has resulted in heterogeneous methods for how the registers operate, capture data, and present results. On the one hand, this has driven progression and kept the primary target group, i.e. health care professionals, involved in the development of the different registers. On the other hand, the plethora of methods used by registries makes it complicated for stakeholders (caregivers, health care providers, decision-makers, politicians and patients) to use and contribute to the registers. Now, the sectioning prevents from eliciting the full potential of the orthopaedic registers. We have reached a critical point where we are limited by the diversity and realize the potential benefits of consolidation. Representatives from all orthopaedic registers have formed a steering group and started a consolidation project. The overall purpose is to consolidate musculoskeletal national quality registries into 1 common organization with different sub-registers. We aim to lay the foundation for a powerful registerbased research and health-care quality improvement environment in the musculoskeletal field. Expectedly, the 1st important step of the consolidation project will be the formation of a Swedish Arthroplasty Register combining the Swedish Knee and Hip Arthroplasty Registers into 1 register. The directors of the 2 registers plan to launch the new merged Swedish Arthroplasty Register in the beginning of 2020. Thus, the 40-year anniversary of the Swedish Hip Arthroplasty Register is probably the last anniversary of the register. The two oldest national quality registers in Sweden will make history, once again. Ola ROLFSON Swedish Hip Arthroplasty Register Department of Orthopaedics, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Sweden Department of Orthopaedics, Sahlgrenska University Hospital Correspondence: ola.rolfson@vgregion.se

Ahnfelt L, Andersson G, Herberts P. [Re-operation of total hip arthroplasties]. Läkartidningen 1980; 77(30-31): 2604-7. Eneqvist T, Nemes S, Bulow E, Mohaddes M, Rolfson O. Can patientreported outcomes predict re-operations after total hip replacement? Int Orthop 2018; 42(2): 273-9. Garellick G, Kärrholm J, Lindahl H, Malchau H, Rogmark C, Rolfson O. The Swedish Hip Arthroplasty Register Annual Report 2014. The Swedish Hip Arthroplasty Register; 2015. Gordon M, Frumento P, Sköldenberg O, Greene M, Garellick G, Rolfson O. Women in Charnley class C fail to improve in mobility to a higher degree after total hip replacement. Acta Orthop 2014; 85(4): 335-41. Greene M E, Rolfson O, Gordon M, Annerbrink K, Malchau H, Garellick G. Is the use of antidepressants associated with patient-reported outcomes following total hip replacement surgery? Acta Orthop 2016; 87(5): 444-51. Greene M E, Rolfson O, Gordon M, Garellick G, Nemes S. Standard comorbidity measures do not predict patient-reported outcomes 1 year after total hip arthroplasty. Clin Orthop Relat Res 2015; 473(11): 3370-9. Greene M E, Rolfson O, Nemes S, Gordon M, Malchau H, Garellick G. Education attainment is associated with patient-reported outcomes: findings from the Swedish Hip Arthroplasty Register. Clin Orthop Relat Res 2014; 472(6): 1868-76. Kärrholm J, Lindahl H, Malchau H, Mohaddes M, Nemes S, Rogmark C, et al. The Swedish Hip Arthroplasty Register Annual Report 2016. The Swedish Hip Arthroplasty Register; 2017. Kärrholm J, Mohaddes M, Odin D, Vinblad J, Rogmark C, Rolfson O. The Swedish Hip Arthroplasty Register Annual Report 2017. The Swedish Hip Arthroplasty Register; 2018. Leonardsson O, Garellick G, Kärrholm J, Åkesson K, Rogmark C. Changes in implant choice and surgical technique for hemiarthroplasty. 21,346 procedures from the Swedish Hip Arthroplasty Register 2005-2009. Acta Orthop 2012; 83(1): 7-13.

Leonardsson O, Kärrholm J, Åkesson K, Garellick G, Rogmark C. Higher risk of reoperation for bipolar and uncemented hemiarthroplasty. Acta Orthop 2012; 83(5): 459-66. Lindgren J V, Wretenberg P, Kärrholm J, Garellick G, Rolfson O. Patientreported outcome is influenced by surgical approach in total hip replacement: a study of the Swedish Hip Arthroplasty Register including 42,233 patients. Bone Joint J 2014; 96-b(5): 590-6. Malchau H. On the importance of stepwise introduction of new hip implant technology: assessment of total hip replacement using clinical evaluation, radiostereometry, digitised radiography and a national hip registry. Thesis. Sahlgrenska Academy. Gothenburg: University of Gothenburg; 1995. Malchau H, Graves S E, Porter M, Harris W H, Troelsen A. The next critical role of orthopedic registries. Acta Orthop 2015; 86(1): 3-4. Malchau H, Herberts P, Ahnfelt L. Prognosis of total hip replacement in Sweden. Follow-up of 92,675 operations performed 1978-1990. Acta Orthop Scand 1993; 64(5): 497-506. Rolfson O, Dahlberg L E, Nilsson J Å, Malchau H, Garellick G. Variables determining outcome in total hip replacement surgery. J Bone Joint Surg (Br) 2009; 91(2): 157-61. Rolfson O, Kärrholm J, Dahlberg L E, Garellick G. Patient-reported outcomes in the Swedish Hip Arthroplasty Register: results of a nationwide prospective observational study. J Bone Joint Surg (Br) 2011; 93(7): 867-75. Rolfson O, Donahue G S, Hallsten M, Garellick G, Kärrholm J, Nemes S. Patient-reported outcomes in cemented and uncemented total hip replacements. Hip Int. 2016 Sep 29;26(5):451-457.) Söderman P, Malchau H, Herberts P, Zugner R, Regner H, Garellick G. Outcome after total hip arthroplasty: Part II. Disease-specific follow-up and the Swedish National Total Hip Arthroplasty Register. Acta Orthop Scand 2001; 72(2): 113-9.

Introduction to the articles reproduced from Acta Orthopaedica

40-year anniversary of the Swedish Hip Arthroplasty Register The Swedish Hip Arthroplasty Register was established in 1979 and celebrates its 40th anniversary this year. The success of the register largely depends on the now retiring professors Johan Kärrholm and Henrik Malchau. To acknowledge their important contributions to orthopaedics and to celebrate the anniversary, we are organizing a jubilee symposium June 13-14th, 2019 in Gothenburg. This collection of articles has been compiled for the anniversary jubilee. The articles have recently been published in Acta Orthopaedica and they demonstrate the diversity of endeavors the register-associated researchers undertake. We, the register direction, are utterly pleased with the large national and international interest in working with the Swedish Hip Arthroplasty Register; the authors of the papers in this collection represent 6 universities in Sweden and 9 countries. Although the register is administered from Gothenburg and governed by Region Västra Götaland, we emphasize that the register is a national concern and a source open for all researchers. Using the register data for research and quality improvement work with the ultimate goal of improving care for hip arthroplasty patients completely aligns with the overall aim of the register. For practical reasons, several of the research questions investigated here, can be answered only in the setting of large, national registries. Otten et al. (2019), who investigated the influence of screw holes in acetabular components on implant survival, and Chatziagorou et al. (2019), who investigated 2 different commonly used stem designs and the risk of periprosthetic fractures, are good examples of studies that practically only can be done using registry data. From start, Swedish Hip Arthroplasty Register has registered all types of reoperations following arthroplasty, not only revisions where implant components are removed, replaced or added. Most other hip arthroplasty registers only cover revisions. From a patient’s perspective, any reoperation could be regarded as a failure. Among the articles in this collection, there are 2 with special focus on reoperations. Posterior surgical approach has previously been shown to increase the risk of reoperation due to dislocation. However, in contemporary Swedish practice, Skoogh et al. (2019) demonstrated similar risks for posterior and direct lateral approaches. Among all indications for reoperation, dislocation and periprosthetic fracture had the worse relative patient survival (Cnudde et al. 2019). Several articles investigated patient factors such as age, BMI, ASA class, and socioeconomic status, which may be associated with arthroplasty outcomes (Mohaddes et al. 2019,

Sayed-Noor et al. 2019, Ferguson et al. 2019, Weiss et al. 2019). For obvious reasons, such “exposures” cannot be allocated by randomization. The studies employed different strategies to adjust for confounders and interactions to investigate the exposure of interest. In particular, the study of Mohaddes et al. (2019) is a good example of how propensity score matching may be applied to select a control group in order to level out confounding factors between study groups. 2 papers utilized hip arthroplasty register data from 2 or more countries (Ferguson et al. 2019, Paxton et al. 2019). An important strength of these studies is the confirmation of results in different populations. To avoid the difficulties in sending data outside the country, these studies use a meta-analytic approach, which has demonstrated effective and to yield practically identical results as when merging data (Paxton el al. 2018). The 2 studies from the Finnish Arthroplasty Register demonstrate how research emerged the Swedish Hip Arthroplasty Register may be further expanded and externally validated in another register (Hemmilä et al. 2019, Ekman et al. 2019). The Swedish Hip Arthroplasty Register pioneered in collecting patient-reported outcomes measures (PROMs) in a national quality register. Torisho et al. (2019) investigated the influence of patient education and physiotherapy interventions and found only marginal effect on the 1-year PROMs after THA. Oxblom et al. (2019) demonstrated similar PROMs between resurfacing and conventional THA, albeit resurfacing patients reported better function in sport and recreation subscales. The register’s PROMs questionnaire has been kept short to maximize response rate and minimize workload for those involved in entering the data. However, except for the hip pain item collected, we lack a condition-specific measure in the PROMs program. Larsson et al. (2019) undertook a study to evaluate the Forgotten Joint Score in comparison to Oxford Hip Score, which provides important information for future decisions on adding new items to the survey. Gromov et al. (2019) undertook a survey of the orthopaedic departments in Denmark, Finland, Norway and Sweden to investigate the use of postoperative mobilization restriction after primary THA. Each national register used their network of participating hospitals to distribute the survey, which turned out to yield high response rates – an indication of the high impact of the registers in the Nordic countries. In a technical note, Vinblad et al. (2019) describe the development of an application for manufacturers to assess

implant survival in the Swedish hip arthroplasty population. We hope the application will help manufacturers to identify products with suboptimum performance and facilitate regulatory reporting. The application could also help stimulate an even closer dialogue between manufacturers and the profession to potentially initiate in-depth analyses and if necessary improvement work. Jolbäck et al. (2019) investigated the relationship between surgical volume and risk of adverse events following THA. The finding that higher surgical volume markedly reduces risk for early adverse events should guide healthcare decisionmaking on future organization of THA surgery. Lastly, we would like to express our greatest thanks to all contact orthopaedic surgeons and contact secretaries of all times and all around the country for their devoted work on delivering high quality data to the register. Without their loyalty, dedication, and hard work, the register would not have succeeded in its mission over the 40 years. Ola ROLFSON Swedish Hip Arthroplasty Register Department of Orthopaedics, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Sweden Department of Orthopaedics, Sahlgrenska University Hospital Correspondence: ola.rolfson@vgregion.se

Chatziagorou G, Lindahl H, Kärrholm J. The design of the cemented stem influences the risk of Vancouver type B fractures, but not of type C: an analysis of 82,837 Lubinus SPII and Exeter Polished stems. Acta Orthop 2019; 90(2): 135-42. Cnudde P, Bülow E, Nemes S, Tyson Y, Mohaddes M, Rolfson O. Association between patient survival following reoperation after total hip replacement and the reason for reoperation: an analysis of 9,926 patients in the Swedish Hip Arthroplasty Register. Acta Orthop 2019; 90 (3): 226-30. Ekman E, Palomäki A, Laaksonen I, Peltola M, Häkkinen U, Mäkelä K. Early postoperative mortality similar between cemented and uncemented hip arthroplasty: a register study based on Finnish national data. Acta Orthop 2019; 90 (1): 6-10. Ferguson R J, Silman AJ, Combescure C, Bulow E, Odin D, Hannouche D, Glyn-Jones S, Rolfson O, Lübbeke A. ASA class is associated with early revision and reoperation after total hip arthroplasty: an analysis of the Geneva and Swedish Hip Arthroplasty Registries. Acta Orthop 2019; Apr 30: 1-13. [Epub ahead of print] Gromov K, Troelsen A, Modaddes M, Rolfson O, Furnes O, Hallan G, Eskelinen A, Neuvonen P, Husted H. Varying but reduced use of postopera-

tive mobilization restrictions after primary total hip arthroplasty in Nordic countries: a questionnaire-based study. Acta Orthop 2019; 90(2): 143-7. Hemmilä M, Karvonen M, Laaksonen I, Matilainen M, Eskelinen A, Haapakoski J, Puhto A P, Kettunen J, Manninen M, Mäkelä K T. Survival of 11,390 Continuum cups in primary total hip arthroplasty based on data from the Finnish Arthroplasty Register. Acta Orthop 2019; Apr 17:1-10. [Epub ahead of print] Jolbäck P, Rolfson O, Cnudde P, Odin D, Malchau H, Lindahl H, Mohaddes M. High annual surgeon volume reduces the risk of adverse events following primary total hip arthroplasty: a registry-based study of 12,100 cases in Western Sweden. Acta Orthop 2019; 90(2): 153-8. Larsson A, Rolfson O, Kärrholm J. Evaluation of Forgotten Joint Score in total hip arthroplasty with Oxford Hip Score as reference standard. Acta Orthop 2019; 90(3): 253-7. Mohaddes M, Nauclér E, Kärrholm J, Malchau H, Odin D, Rolfson O. Implant survival and patient-reported outcome following total hip arthroplasty in patients 30 years or younger: a matched cohort study of 1,008 patients in the Swedish Hip Arthroplasty Register. Acta Orthop 2019; 90(3): 249-52. Otten V, Mukka S, Nilsson K, Crnalic S, Kärrholm J. Uncemented cups with and without screw holes in primary THA: a Swedish Hip Arthroplasty Register study with 22,725 hips. Acta Orthop 2019; 90(3): 258-63. Oxblom A, Hedlund H, Nemes S, Brismar H, Felländer-Tsai L, Rolfson O. Patient-reported outcomes in hip resurfacing versus conventional total hip arthroplasty: a register-based matched cohort study of 726 patients. Acta Orthop 2019; April 18: 1-6. [Epub ahead of print] Paxton E W, Mohaddes M, Laaksonen I, Lorimer M, Graves SE, Malchau H, Namba R S, Kärrholm J, Rolfson O, Cafri G. Meta-analysis of individual registry results enhances international registry collaboration. Acta Orthop 2018; 89(4): 369-73. Paxton EW, Cafri G, Nemes S, Lorimer M, Kärrholm J, Malchau H, Graves SE, Namba RS, Rolfson O. An international comparison of THA patients, implants, techniques, and survivorship in Sweden, Australia, and the United States. Acta Orthop 2019; 90(2): 148-152. Sayed-Noor AS, Mukka S, Mohaddes M, Kärrholm J, Rolfson O. Body mass index is associated with risk of reoperation and revision after primary total hip arthroplasty: a study of the Swedish Hip Arthroplasty Register including 83,146 patients. Acta Orthop 2019; 90(3): 220-5. Skoogh O, Tsikandylakis G, Mohaddes M, Nemes S, Odin D, Grant P, Rolfson O. Contemporary posterior surgical approach in total hip replacement: still more reoperations due to dislocation compared with direct lateral approach? An observational study of the Swedish Hip Arthroplasty Register including 156,979 hips. Acta Orthop 2019; May 1: 1-6. [Epub ahead of print] Torisho C, Mohaddes M, Gustafsson K, Rolfson O. Minor influence of patient education and physiotherapy interventions before total hip replacement on patient-reported outcomes: an observational study of 30,756 patients in the Swedish Hip Arthroplasty Register. Acta Orthop 2019; Apr 17: 1-9. [Epub ahead of print] Weiss R J, Kärrholm J, Rolfson O, Hailer N P. Increased early mortality and morbidity after total hip arthroplasty in patients with socioeconomic disadvantage: a report from the Swedish Hip Arthroplasty Register. Acta Orthop 2019; 90(3); 264-9. Vinblad J, Odin D, Kärrholm J, Rolfson O. The development of an online implant manufacturer application: a knowledge-sharing platform for the Swedish Hip Arthroplasty Register. Acta Orthop 2019; Apr 30: 1-5. [Epub ahead of print]

A tribute to Professor Johan Kärrholm on his retirement

Johan Kärrholm, well-renowned and highly appreciated professor at the department of Orthopaedics at Sahlgrenska Academy in Gothenburg, has retired. During his extraordinary career, he has made several significant contributions to the orthopaedic research field. Meantime, while working harder than most of us, he has always had time and energy for a friendly chat at the coffee machine before returning to his office. We, who have the honor of working with Johan, may have had trouble assimilating that this day would eventually come. As consolation for us, for Johan retirement translates into cutting down on work hours instead of leaving completely, at least for now. Milestones in life usually calls for retrospection and therefore, as a tribute to Johan, we will attempt to depict some of the events in his career in the following paragraphs. Johan’s parents were both Professors at Chalmers University of Technology in Gothenburg, and therefore, it was natural for him to enter upon an academic career. He undertook his basic medical training at Lund University and got his license to practice in 1978. During orthopaedic residency at Lund University Hospital, he completed his doctoral thesis in 1982 (Kärrholm 1982). 6 of 11 included papers made use of radiostereometric analysis (RSA), introduced to him by one of his tutors and the inventor of the method, Göran Selvik. RSA, in those days an extremely time-consuming and laborious method, has become much more efficient. It is repeatedly proven, by Johan and other workers, to be a cornerstone in the evaluation of new orthopaedic implants (Kärrholm 1989, Kärrholm et al. 1997, Nelissen et al. 2011). Also, with later modifications, it enables us to measure joint kinematics with unsurpassed resolution. In 1983, soon after receiving his PhD degree, Johan, his wife Evy and their children moved up north. He had been recruited to Umeå University Hospital by another of his former tutors, professor Lars-Ingvar Hansson. Besides discovering the whereabouts of Swedish Norrland treasures like cloudberries and morels, he continued doing RSA research. After a few years he established an independent RSA laboratory in Umeå and subsequently evolved the RSA toolbox further, now in collaboration with new co-workers from the technological community in Umeå. The advent of the personal computer in the mid-80’s offered a more efficient way of handling and analyzing RSA data. The first MS-DOS-based software package for RSA measurement and analysis was the first step towards the contemporary widespread use of the method. With gradually

increasing computational power it was also possible to realize his early idea of using basic geometrical shapes of implants to accurately measure implant positions, thereby decreasing the need for implant modification by inserting and attaching metal markers. Alongside methodological progress and greater feasibility, there was also an increased need for RSA education. Johan organized and was the main lecturer of 10 RSA courses held between 1990 and 2008. The courses effectively spread the knowledge of how to set up and run the method. Nowadays RSA laboratories are found all around the globe. In 1993, after 10 successful years in Umeå, Johan returned to Gothenburg, where he joined the Orthopaedic Department at the Sahlgrenska University Hospital. During these years, he also inherited his family’s beautifully situated summer house, which since then has filled his summer vacations with work and joy. He depicts the 90’s as “the golden years” as he and his research group continued to produce publications, mainly RSA-based, covering the hip, knee, foot and spine regions. In 1999, he became Professor of Orthopaedics at the Faculty of Medicine, Gothenburg University. Johan’s well-renowned reputation in register research was initiated in the mid 90’s as he became a co-tutor of Professor Henrik Malchau’s doctoral work. In 2005, Johan became the Director of the Swedish Hip Arthroplasty Register (SHAR). In this position he facilitated the founding of the Swedish Hemiarthroplasty Register, now an incorporated part of SHAR. He also developed the way that register data are displayed. At the

time, the hip arthroplasty register had taught Swedish orthopaedic surgeons to be aware of possible downsides to early adoption of new implants and techniques. Johan aimed to further employ the benefits of register data by including statistical analyses unprecedented in register reports at the time. Such extended analyses are now commonly seen in the reports of prominent registers worldwide. Additionally, in order to facilitate comparability between orthopaedic units operating patients with different demographics and co-morbidity patterns, Johan developed the simple but effective concept of the Standard Patient, presented for the first time in the 2012 Annual Report from SHAR. In 2006, as a team manager, Johan lead the Joint Arthroplasty Unit through a complex reorganization of the Orthopaedic Department. After four years of combining register work, research and team management he handed over the latter to his successor. Subsequently he has continued to produce scientific papers and other contributions at a steadily high pace. In addition to his academic accomplishments, he is also a very skilled orthopaedic surgeon, especially in the field of advanced revision arthroplasty. His inherent and pronounced manual skill and the ability to promptly translate considerable theoretical knowledge into surgical practice are admirable qualities. During his career, he has held several prestigious positions; scientific secretary of the Swedish Orthopaedic Society and scientific board member of European Hip Society, among others. He has received several scientific awards, the two most recent being H-G Willert Award for outstanding research on hip arthroplasty in Hamburg 2015 and the 2017 OREF Clinical Research Award (Kappa Delta Award) in San Diego (Malchau et al. 2018). Johan is also a role model as supervisor for students at all levels, imprinting his motto: “It has to be right”. An inquiry among his 45 PhD students, ongoing or terminated, asking for their perceptions of Johan, rendered attributes such as: proficient; wise; smart; unsurpassed scientific clear-sight; never giving up; impressive working capacity; supportive; kindly yet firmly pushing forward.

In addition to all this - professor Kärrholm is a warm, humoristic and caring man that besides all aforementioned has other capabilities, exemplified by but not restricted to both elegantly renovating and fixing cars as well as creating gourmet food. On the behalf of the Swedish Hip Arthroplasty Register and the Sahlgrenska Academy, we would like to conclude this tribute by paying our deepest respect to Johan Kärrholm as one of the most prominent and honorable orthopaedic professors in Sweden. We wish him all the best for the future, and hope he will still spend some time with research but also enjoy more time with his family. Per-Erik Johanson 1 and Ola Rolfson 2 Swedish Hip Arthroplasty Register, Gothenburg, Sweden Department of Orthopaedics, Institute of Clinical Sciences, the Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden 1 Department of Orthopedics, Södra Älvsborg Hospital, Borås, Sweden 2 Department of Orthopedics, Sahlgrenska University Hospital, Gothenburg, Sweden Correspondence: per-erik.johanson@vgregion.se

Kärrholm J. Ankle fractures in children : incidence, fracture anatomy, and treatment with special reference to post-traumatic growth patterns, Lund 1982. Kärrholm J. Roentgen stereophotogrammetry. Review of orthopedic applications. Acta Orthop Scand 1989; 60 (4): 491-503. Kärrholm J, Herberts P, Hultmark P, Malchau H, Nivbrant B, Thanner J. Radiostereometry of hip prostheses. Review of methodology and clinical results. Clin Orthop Relat Res 1997; (344): 94-110. Malchau H, Garellick G, Berry D, Harris W H, Robertson O, Kärrholm J, Lewallen D, Bragdon C R, Lidgren L, Herberts P. Arthroplasty implant registries over the past five decades: Development, current, and future impact. J Orthop Res 2018; 36 (9): 2319-30. Nelissen R G, Pijls B G, Kärrholm J, Malchau H, Nieuwenhuijse M J, Valstar E R. RSA and registries: the quest for phased introduction of new implants. J Bone Joint Surg Am 2011; 93 Suppl 3: 62-5.

A tribute to Professor Henrik Malchau on his retirement new orthopaedic implants in a controlled fashion may have been ahead of his time. One may rightly argue that the adoption of his principles has saved enormous costs and prevented suffering. Sadly, we have repeatedly been reminded of how deviating from the principles of stepwise introduction may lead to catastrophes. During years 1994 and 2004, Henrik was the head of the orthopaedic department at Sahlgrenska University Hospital before he moved to Boston as visiting professor at Harris Orthopaedic Laboratory at Massachusetts General Hospital and Harvard Medical School in 2004. Henrik was headhunted by professor William Harris to take over the directorship of the Harris Orthopaedic Laboratory. Sharing the same office for 10 years and daily discussions resulted in a very close relationship and further advancements in arthroplasty care. Because of his successful research and clinical activity in Boston, Henrik was appointed the Alan Gerry Professor of Orthopaedic Surgery at Harvard Medical School in 2010. Through his career, Henrik has emphasized and focused on keeping a close relationship between academia and clinical work. In all his activities and in every decision, he has the patients’ best on his mind. Henrik is not only a prominent researcher, he is also a very skilled surgeon. During his years in Boston, Henrik took on the most complex hip revision cases; cases that few consultants on the team at the hospital would ever take on. His research has followed the principles of stepwise introduction and the studies cover all steps described in his thesis. The development and testing of vitamin E diffused polyethylene is a good example. It was first evaluated in preclinical studies (Jarrett et al. 2010), then within a randomized radiostereometric study (Nebergall et al. 2016 and 2017), followed by a multicenter study (Sillesen et al. 2016) and finally monitored in arthroplasty registries (ongoing studies). “Sit-down meetings are waste of time” Henrik uses to say. Despite his aversion to long meetings, Henrik has served on numerous national and international committees and boards. Many organizations are in debt of Henrik’s contributions over the years. To mention some, he is currently president of the International Hip Society and treasurer of the InternaFigure 1. Henrik Malchau practicing prophylactic medicine in Botswana 1975. tional Society of Arthroplasty RegisOn February 27th 2019, Professor Henrik Malchau celebrated his 68th birthday. He will retire from his current position as the head of the Orthopaedic Department at Sahlgrenska University Hospital at the end of the year. Henrik has had an impressive career and made enormous contributions to orthopaedics internationally. This tribute is to honor one of the most prominent orthopaedic professors ever in Sweden. Henrik was born and raised in Denmark. After graduating from medical school at University of Aarhus, Henrik started his professional medical career in Africa. In 1975, he practiced prophylactic medicine in Botswana (Figure 1). Henrik likes to tell stories about the adventurous travels forth and back to Africa and India in a classic Volkswagen van. Safely back, he did his internship and orthopaedic residency at Uddevalla Hospital and transitioned to Sahlgrenska University Hospital in 1983 to begin fellowship with professors Peter Herberts and Alf Nachemsson. A few years earlier, the Swedish Hip Arthroplasty Register had been established and upon starting his fellowship, he involved in the early development of the register. In 1989, he became the co-director and has since successfully promoted the benefits of arthroplasty registries internationally. Supervised by Peter Herberts, Henrik defended his thesis entitled “Stepwise introduction of implant technology” in 1995 at Sahlgrenska Academy, University of Gothenburg (Malchau 1995). The thesis has made an enormous impact in the field of arthroplasty. The proposed strategy for introducing

his always so supportive wife Inger, are outermost generous, welcoming and warm-hearted. Representing the Swedish Hip Arthroplasty Register and University of Gothenburg, we celebrate Henrik’s astonishing career. Despite his formal retirement, we hope he will stay engaged for many years to come and guide us towards the next critical role for orthopaedic registers (Malchau et al. 2015). Ola ROLFSON and Maziar MOHADDES Swedish Hip Arthroplasty Register, Gothenburg, Sweden Department of Orthopaedics, Institute of Clinical Sciences, the Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden Department of Orthopedics, Sahlgrenska University Hospital Gothenburg, Sweden Correspondence: ola.rolfson@vgregion.se

ters. Henrik has initiated important organizations such as the International Society of Arthroplasty Registers and the Nordic Arthroplasty Register Association. Over the years, Henrik has received several prestigious awards. In 2017, he received the OREF Clinical Research Kappa Delta Award (Malchau et al. 2018); a great acknowledgement for his register-promoting endeavors. Perhaps the most dominating quality of Henrik is his ability to inspire people and let them grow. He is a visionary leader, an entertaining and provocative educator, a trustworthy supervisor, and a supportive colleague. He recognizes the opportunities and nothing is impossible for Henrik. Lastly, Henrik and

Jarrett B T, Cofske J, Rosenberg A E, Oral E, Muratoglu O, Malchau H. In vivo biological response to vitamin E and vitamin-E-doped polyethylene. J Bone Joint Surg Am 2010; 92(16): 2672-81. Malchau H. On the importance of stepwise introduction of new hip implant technology: assessment of total hip replacement using clinical evaluation, radiostereometry, digitised radiography and a national hip registry. Thesis. University of Gothenburg. 1995. Malchau H, Graves S E, Porter M, Harris W H, Troelsen A. The next critical role of orthopedic registries. Acta Orthop 2015; 86(1): 3-4. Malchau H, Garellick G, Berry D, Harris W H, Robertson O, Kärrlholm J, Lewallen D, Bragdon C R, Lidgren L, Herberts P. Arthroplasty implant registries over the past five decades: Development, current, and future impact. J Orthop Res 2018; 36(9): 2319-30. Nebergall A K, Troelsen A, Rubash H E, Malchau H, Rolfson O, Greene M E. Five-year experience of vitamin E-diffused highly cross-linked polyethylene wear in total hip arthroplasty assessed by radiostereometric analysis. J Arthroplasty 2016; 31(6): 1251-5. Nebergall A K, Greene M E, Laursen M B, Nielsen P T, Malchau H, Troelsen A. Vitamin E diffused highly cross-linked polyethylene in total hip arthroplasty at five years: a randomised controlled trial using radiostereometric analysis. Bone Joint J 2017; 99-B(5): 577-84. Sillesen N H, Greene M E, Nebergall A K, Huddleston J I, Emerson R, Gebuhr P, Troelsen A, Malchau H. 3-year follow-up of a long-term registry-based multicenter study on vitamin E diffused polyethylene in total hip replacement. Hip Int 2016; 26(1): 97-103.

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Uncemented cups with and without screw holes in primary THA: a Swedish Hip Arthroplasty Register study with 22,725 hips Volker OTTEN 1, Sebastian MUKKA 1, Kjell NILSSON 1, Sead CRNALIC 1, and Johan KÄRRHOLM 2 1 Department

of Surgical and Perioperative Sciences (Orthopaedics), Umeå University, Umeå; 2 Department of Orthopaedics, Institute of Surgical Science, Sahlgrenska University Hospital, Gothenburg University, Mölndal, Sweden Correspondence: volker.otten@umu.se Submitted 2018-11-21. Accepted 2019-02-15.

Background and purpose — Uncemented cups in total hip arthroplasty (THA) are often augmented with additional screws to enhance their primary stability. We investigated whether there is a difference in the risk for revision between cups with screw holes and cups without screw holes. Patients and methods — We analyzed the risk for cup revision of uncemented cups registered in the Swedish Hip Arthroplasty Register (SHAR) between 2000 and 2017 with respect to the presence of screw holes. Only patients with primary osteoarthritis (OA) were included. 22,725 cups, including 12,354 without screw holes and 10,371 with screw holes, were evaluated. Revision rates at 2 and 10 years after the primary operation were analyzed. Results — At a median follow-up time of 3.4 years (0–18), 459 cup revisions were reported. The main reasons for cup revision during the whole observation time were infection, 52% of all cup revisions, and dislocation, 26% of all cup revisions. The survival rate with cup revision due to aseptic loosening as endpoint was 99.9% (95% CI 99.8–99.9) at 2 years for both cups with and cups without screw holes, and the survival rates at 10 years were 99.5% (CI 99.3–99.7) and 99.1% (CI 98.6–99.5), respectively. Cups without screw holes showed a decreased risk of revision due to any reason at both 2 years (adjusted hazard ratio [HR] 0.6, CI 0.5–0.8) and 10 years (HR 0.7, CI 0.5–0.9). Interpretation — We found a very low revision rate for aseptic loosening with modern, uncemented cup designs. Cups with screw holes had an increased risk of revision due to any reason in patients with primary OA

Uncemented cups have gained popularity in recent years, even in countries traditionally using cemented fixation (Kärrholm et al. 2017). Initial stability is essential for good long-term results. Therefore, uncemented cups are often augmented with screws or pegs. However, screw holes in acetabular cups have also been discussed as potential routes for synovial fluid, which might lead to osteolysis (Aspenberg and van der Vis 1998, Iorio et al. 2010). Additionally, using screws for cup fixation increases the cost and operation time. Hence, the surface of uncemented cups has been further developed towards a rougher finish to improve primary stability and long-term bone ingrowth even without any extra augmentation. In a recently published randomized controlled study with a minimum follow-up of 14 years comparing cups with and without screw holes, we found no difference in implant migration (Otten et al. 2016). To our knowledge, there has not been any published study investigating the risk for cup revision depending on the use of cups with or without screws. We analyzed the survival of uncemented cups with or without screw holes in the Swedish Hip Arthroplasty Register (SHAR). Our hypothesis was that screw fixation reduces the risk for early aseptic loosening but increases the risk for late failure because of potentially increased risk for osteolysis due to screw holes (Iorio et al. 2010). Revision rates due to aseptic loosening and for any reason at 2 and 10 years after primary operation were analyzed.

Patients and methods Study design, source of data, and terminology This study is based on data obtained from the SHAR. Primary and revision hip arthroplasties performed in Sweden have been registered since 1979. During the last decade, the completeness of primary surgeries has been approximately 98–99% and 94% for revisions. Since 1999, detailed informa-

© 2019 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group, on behalf of the Nordic Orthopedic Federation. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits ­unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. DOI 10.1080/17453674.2019.1599777

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Number or operations

Primary THA procedures 2000–2017 using uncemented cups (SHPR database) n = 46,047 Excluded (n = 23,322): – resurfacing arthroplasty, 2,806 – dual mobility cups, 217 – cups designs used less than 500 times, 3,199 – registration about screw holes missing, 178 – cup designs with screw holes used < 100 times or without screw holes used < 100 times, 8,500 – liner material or design unknown, 76 – ceramic liner, 444 – metal liner, 164 – standard PE liner, 2,295 – head size unknown, 42 – head size < 28 mm, 160 – head size > 36 mm, 181 – other diagnosis than primary OA or unknown, 5,060 Analyzed n = 22,725 Without screw holes, 12,354 With screw holes, 10,371

Figure 1. Procedures not included in the final analysis.

tion regarding the prosthesis design, such as the presence of screw holes, has been registered in the SHAR. The guidelines of the STROBE statement were followed. In this study, we classified cups without any holes and cups with 1 central hole, used for the cup impactor, into the category referred to as “cups without screw holes.” Cups with holes placed in a sector of the shell or over the whole cup area (multi-hole cups) were classified into “cups with screw holes” regardless of whether the holes were intended for screws or pegs, as long as the holes penetrated the entire thickness of the shell. Cup revision is defined as any reoperation of the hip where 1 or more components of the cup (shell, liner, or both) were removed or exchanged. “Aseptic loosening” as the reason for revision includes aseptic loosening, osteolysis, liner instability, technical reasons (explain), and wear. Failure due to insufficient primary stability most often occurs within the first 2 years. Hence, survival of the cups up to a 2-year follow-up was analyzed. Aseptic loosening due to osteolysis is a late complication that might be influenced by the presence of screw holes. Therefore, we also evaluated the 10-year survival. Characteristics of the study population Between January 1, 2000, and December 31, 2017, 46,047 uncemented cups used in primary total hip arthroplasty (THA) were reported to the SHAR, including 63 different cup designs. During the 18-year study period, 30 of these cup designs were reported in less than 100 cases and for 17 cup designs in even less than 10 cases. Only cases using cups that have been frequently used both with and without screw holes and that are still available today were included in this study. After applying the exclusion criteria described in Figure 1, 22,725 hips

3,000 CUPS without screw holes with screw holes

2,000

1,000

0 2000 2002 2004 2006 2008 2010 2012 2014 2016

Year of operation

Figure 2. Number of operations per year.

Table 1. Baseline characteristics of the study population

Screw holes No Yes n (%) n (%)

Totals n (%) p-value a

Sex Male 6,916 (56) 5,405 (52) 12,321 (54) < 0.001 Female 5,438 (44) 4,966 (48) 10,404 (46) Age < 45 403 (3.3) 406 (3.9) 809 (3.6) < 0.001 45–64 7,428 (60) 6,395 (62) 13,823 (61) 65–74 3,662 (30) 2,607 (25) 6,269 (28) ≥ 75 861 (7.0) 963 (9.3) 1,824 (8.0) Side Right 6,550 (53) 5,572 (54) 12,122 (53) 0.3 Left 5,804 (47) 4,799 (46) 10,603 (47) Approach b Posterolateral 7,769 (63) 3,252 (31) 11,021 (49) < 0.001 Direct lateral 4,016 (33) 7,008 (68) 11,024 (49) Other 464 (3.8) 97 (0.9) 561 (2.5) Type of stem: Uncemented 10,580 (86) 8,715 (84) 19,295 (85) 0.001 Cemented 1,774 (14) 1,656 (16) 3,430 (15) Cup coating No HA 6,662 (54) 3,483 (34) 10,145 (45) < 0.001 HA 5,692 (46) 6,888 (66) 12,580 (55) Head size 28 mm 1,385 (11) 2,434 (24) 3,819 (17) < 0.001 32 mm 7,585 (61) 7,128 (69) 14,713 (65) 36 mm 3,384 (27) 809 (7.8) 4,193 (19) Head material Metal 9,260 (75) 9,542 (92) 18,802 (83) < 0.001 Ceramic 3,094 (25) 828 (8.0) 3,922 (17) Sum

12,354 (100) 10,371 (100) 22,725 (100)

Distribution of possible confounding factors between cups with and without screw holes a Pearson’s chi-square. b Missing data in 119 cases.

in 19,840 patients were used for analysis (Table 1), including 8 different cup designs, 12,354 cups without screw holes and 10,371 cups with screw holes (Table 2, see Supplementary data). Both hips were included in 2,885 patients. Cups without screw holes were used in 1,305 of these bilateral THA patients,

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and cups with screw holes were used in 1,217 bilateral THA patients. The remaining 363 patients had 1 of each type of cup used on each on the 2 sides. The median follow-up time for cups without screw holes was 2.6 years (0–16) and for cups with screw holes was 5.2 years (0–18) (Table 2, see Supplementary data). The number of procedures and the proportion of cups without screw holes increased over time (Figure 2). Operations from 81 different hospitals are included, of which 30 hospitals used cups with screw holes in more than 90% of cases, and 30 hospitals used cups with screw holes in less than 10% of cases. Adjusting for confounders Poor bone quality or abnormal anatomy could lead to the use of cups with screws in primary THA. Neither of these factors is registered in the SHAR. We assumed that older patients and women, in general, have poorer bone quality and patients who had dysplasia or sequelae after hip diseases, as well as patients with other secondary arthrosis, are more likely to have abnormal anatomy. Therefore, we used the patient’s age and sex to adjust the dataset and excluded all diagnoses other than primary osteoarthritis (OA). To various extents, the presence of a hydroxyapatite (HA) coating, the head size, and the head material will contribute to the revision risk (Lazarinis et al. 2010, Cross et al. 2012, Dahl et al. 2012), and these factors were used as covariates in a Cox regression. Liner material influences the amount of wear. During the last few years, almost exclusively PE liners with x-linked polyethylene (PE) have been used in uncemented cups in Sweden. Hence, only cups with the x-linked PE liner were included in the analysis. Statistics Continuous variables are described as the means, medians, and ranges. Comparisons between groups were performed using independent Student’s t-tests, Welch’s t-tests, or 1-way ANOVA. Categorical data were analyzed with chi-square tests. Survival of the cup was calculated using life tables with 95% confidence intervals (CIs). For comparison of the survival of cups with and without screw holes, the log-rank test was used. Adjusted hazard ratios (HRs) with CIs were calculated using multivariable Cox regression models. The total observation time comprised 18 years (2000–2017). However, the number of cups at risk for revision after 10 years was only 1,846, and the distribution of cups with and cups without screw holes was unequal between cup design (Table 4, see Supplementary data); therefore, the risk for revision was not calculated beyond 10 years. The E-value was calculated to define the minimum strength of association of the HR that an unmeasured confounder would need to have with both the treatment and the outcome to fully explain away the association between screw holes and cup revision on the measured covariates (VanderWeele and Ding 2017).

A p-value < 0.05 was considered statistically significant. Statistical analysis was performed using SPSS Statistics software, version 24.0 (IBM Corp, Armonk, NY, USA). Ethics, funding, and potential conflicts of interest The study was approved by the Regional Ethics Committee in Gothenburg (dnr 348-17). No competing interests are declared. The research was funded by SHAR and grants from the regional agreement on medical training and clinical research (ALF) between Västerbotten County Council and Umeå University.

Results Early revisions within 2 years after primary operation The survival rate with cup revision for aseptic loosening within 2 years was 99.9% (CI 99.8–99.9) for both groups (Table 3). When including all reasons for cup revision, the survival rate for cups without screw holes was 98.6% (CI 98.4–98.8) and for cups with screw holes was 98.4% (CI 98.2–98.7). The crude HR for the risk of cup revision due to aseptic loosening of cups without screw holes compared with cups with screw holes was 0.8 (CI 0.4–1.7). After adjusting for sex, age, surgical approach, type of stem fixation, presence of HA coating, head size, head material, and cup design, we found that screw holes had no influence on cup revision due to aseptic loosening (HR = 0.6, CI 0.2–1.8). The crude HR for cup revision for any reason was 0.8 (CI 0.7–1.0) for cups without screw holes. After adjustment for the covariates, cups without screw holes showed a lower risk for cup revision for any reason with an HR of 0.6 (CI 0.5–0.8) (Table 3) and an E-value of 2.7 (CI 1.8–3.4). The influence of other patient- or prothesis-related factors on the revision rate is presented in Table 5 (see Supplementary data). In 293 out of 22,725 hips, cup revision, including exchange (or extraction) of the cup, the liner, or both, was performed within the first 2 years after the primary operation. These early revisions were caused by infection in 58% of cases, dislocation in 27%, and aseptic loosening in 9%. Other complications, such as fracture, implant failure, or pain, caused less than 6% of early cup revisions. The proportion of various reasons for early revision did not differ significantly between cups with and without screw holes (p = 0.2) but differed significantly between cup designs (p = 0.03). For example, all revisions of the Tritanium cup were performed due to infection, while the main reason for revision of the Continuum cup was dislocation (47%). Revisions within 10 years after primary operation The overall 10-year survival rate for aseptic loosening was 99.1% (CI 98.6–99.5) for cups without screw holes and 99.5% (CI 99.3–99.7) for cups with screw holes (Table 3). However, the risk for cup revision due to any reason was still lower for

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Table 3. Survival after 2 and 10 years and hazard ratio for revision Endpoint

2-year survival (95% CI)

Cup revision for aseptic loosening Without screw holes 99.9 (99.8–99.9) With screw holes 99.9 (99.8–99.9) Cup revision for any reason Without screw holes 98.6 (98.4–98.8) With screw holes 98.4 (98.2–98.7) Revision (cup or stem) for any reason Without screw holes 98.0 (97.7–98.2) With screw holes 97.7 (97.4–98.0)

10-year survival (95% CI)

Crude HR Adjusted HR Crude HR Adjusted HR (0–2 years) (0–2 years) (0–10 years) (0–10 years) (95% CI) p-value (95% CI) p-value (95% CI) p-value (95% CI) p-value

99.1 (98.6–99.5) 99.5 (99.3–99.7)

0.8 (0.4–1.7) 0.6 1.0 (ref)

0.6 (0.2–1.8) 0.4 1.0 (ref)

1.2 (0.7–2.1) 0.5 1.0 (ref)

0.9 (0.5–1.8) 0.8 1.0 (ref)

96.5 (95.8–97.2) 96.8 (96.3–97.2)

0.8 (0.7–1.0) 0.09 0.6 (0.5–0.8) 0.002 1.0 (0.8–1.2) 0.7 1.0 (ref) 1.0 (ref) 1.0 (ref)

0.7 (0.5–0.9) 0.004 1.0 (ref)

95.0 (94.1–95.9) 95.4 (94.9–95.9)

0.9 (0.7–1.0) 0.09 0.6 (0.5–0.8) 0.001 1.0 (0.8–1.1) 0.6 1.0 (ref) 1.0 (ref) 1.0 (ref)

0.7 (0.6–0.8) < 0.001 1.0 (ref)

The adjusted hazard ratio was calculated based on a Cox regression model with gender, age, surgical approach, type of stem fixation, cup coating, head size, head material, and cup design as covariates. Number of cups at risk for revision in cups without/with screw holes was 12,354/10,371 at 0 years, 7,228/7,984 at 2 years and 3,47/1,499 at 10 years after primary operation.

cups without screw holes, with an adjusted HR of 0.7 (CI 0.5– 0.9) of E-value of 2.2 (CI 1.5–3.4) (Table 3). Between the 2- and 10-year follow-up, 152 cup revisions were registered. 41% of these revisions were caused by infection, 26% by dislocation, and 20% because of aseptic loosening. The distribution of these revisions did not differ statistically significantly between patients who underwent unilateral or bilateral operations.

Discussion We found similar risk both at 2 years and 10 years for revision because of aseptic loosening between cups with and without screw holes in patients with primary OA. However, the risk for cup revision for any reason at both 2 and 10 years was higher when a cup with screw holes was used. Screw fixation of uncemented cups increases stability in simulated models (Hsu et al. 2007) and cadaver studies (Won et al. 1995) and is therefore used with the intention to reduce the risk for loosening. This theory might still hold true for patients with abnormal anatomy, fractures, revision settings, and cups without porous coating or trabecular surfaces. Additional screw fixation of cups with a porous coating or trabecular surfaces has previously been investigated in small populations and did not reduce migration in radiostereometric analysis (RSA) studies (Minten et al. 2016, Otten et al. 2016). A review of 5 articles with a total of more than 1,000 patients and a follow-up time of up to 5 years also did not show any difference in revision rate or osteolysis between cups with and without screw fixation (Ni et al. 2013). Even in the present study with a substantially larger population and operations performed in more than 80 different hospitals, the cups without screw hole did not show a higher risk for early revision due to aseptic loosening. In contrast, we found a higher risk for revision due to any reason for cups with screw holes.

Using screws has some potential risks. Both prolonged operation time (Pepe et al. 2017) and increased likelihood of receiving a blood transfusion (Colacchio et al. 2017) have been reported in recent studies. Inserting screws in the acetabulum might even be a risk for damaging intrapelvic vessels (Ohashi et al. 2017). A report from a smaller group of patients describe a higher risk for osteolysis around cups with screw holes (Iorio et al. 2010). During the last 2 decades, the number of uncemented cups used per year in Sweden has substantially increased. In the last decade, cups designed without screw holes have been used more often in operations for primary OA than have cups with holes. Data from the current study show that this development did not increase the risk of aseptic loosening. In contrast, we found a higher HR for cup revision for any reason if the cup had screw holes, at both 2 and 10 years. The main reason for both early and late revision was infection. A longer operation time when using screws might have caused a higher risk for infection, and there might also have been differences related to patient selection, which are not possible to adjust for in a register study. The E-value shows that unmeasured confounders need to increase the risk for revision by 2.7 times and must be 2.7 times more common in the group of patients who received a cup with screw hole to fully explain away the differences at 2 years. Of the possible confounding factors available, female sex, the use of cemented stems, and HA coating of the cups reduced the risk for cup revision for any reason. However, these 3 risk-reducing factors were overrepresented in the group of cups with screw holes. Nevertheless, cups with screw holes showed a higher risk for revision due to any reason both at 2 years and 10 years after operation. The second most common reason for revision in this study was dislocation. The larger the head size, the lower the risk for revision due to dislocation (Hailer et al. 2012). In particular, 22 mm heads, which were used as standard size in the early days of modern hip arthroplasty to reduce wear (Charn-

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ley et al. 1969), had a higher risk for dislocation. In cups with cross-linked PE liners, head sizes up to 36 mm do not seem to increase wear (Howie et al. 2016). Therefore, a head size of 28–36 mm, depending on the cup size, seems to be the optimal size when using metal or ceramic heads and a cross-linked PE liner. In this study, only head sizes 28, 32, and 36 mm were included. We did not find any difference in the risk for cup revision for any reason between these 3 head sizes. However, a larger proportion of 28 mm heads was used in the group of cups with screw holes, and this might still have influenced the risk for revision. TMT cups have been reported to have a higher revision rate due to dislocation (Hailer 2018, Laaksonen et al. 2018). Our results are concurrent with these reports. HA coating has been discussed in several other papers. There is still no consensus on how HA coating influences the risk for cup revision. Several studies have shown an increased revision rate for HA-coated cups (Stilling et al. 2009, Lazarinis et al. 2010). The main reason for the higher revision rate of cups with HA coating seems to be failure of the liner (Lazarinis et al. 2012). Older cup designs have more often been used with HA coating and, at the same time, with standard but not crosslinked PE liners. When adjusting for potential confounders, including the type of liner, in a larger register-based study, a similar risk of aseptic loosening was found for cups with or without HA coating (Lazarinis et al. 2017). Unadjusted data from our study show a slight advantage for cups with HA coating, but when adjusting for several potential confounders, including cup design, there was no statistically significant difference in the risk for revision. The main limitation of this study is the lack of detailed patient- or surgeon-related information that might have influenced the decision to use screws. Register data do not provide any information regarding the reason why a specific implant was chosen in the individual case. Perhaps surgeons chose cups with the possibility of augmentation with screws in more difficult cases. Excluding all diagnoses other than primary OA reduces the variety of some of these factors. A comparison of the included hospitals showed significant differences in the use of cups with screw holes. It is unlikely that these differences between hospitals can be explained fully by case mix. Another limitation of our study is that only 2 of the cup designs, with unequal distribution between the groups, had a follow-up time of more than 10 years. Therefore, no reliable analysis was possible beyond 10 years of follow-up, and general conclusions about the long-term consequences of using cups with screw holes should be made with caution. A new analysis of the registry data will be necessary when a sufficient number of cases with several different cup designs have been followed for more than 10–15 years to obtain robust long-term data. 17% of patients were registered with bilateral cups. This subgroup decreases the variance within the groups and can increase the risk for type 1 errors. However, we did not find a statistically significant difference in HR for revision between

Acta Orthopaedica 2019; 90 (3): 258–263

cups in patients with unilateral THA and cups in patients with bilateral THA. The incidence of aseptic loosening was very low, making it statistically uncertain to adjust for a large number of potential confounders. The larger number of revisions for any reason gives better statistical strength. In conclusion, we found that the revision rate for modern and frequently used uncemented cups was very low, and cup revision due to aseptic loosening within 2 years was extremely rare. We could not show that the use of cups designed for additional fixation with screws had any advantages in standard patients. In contrast, cups with screw holes increased the risk of cup revision for any reason. Notably, our study mainly embraces the first decade after the operation. Longer followup is needed to evaluate whether this conclusion remains valid during the second decade. Supplementary data Tables 2, 4–5 are available as supplementary data in the online version of this article, http://dx.doi.org/10.1080/17453674. 2019.1599777

VO: study design, data collection, statistical analysis, data analysis, manuscript writing. SM: statistical analysis, data analysis, manuscript writing. KN and SC: data analysis, manuscript writing. JK: study design, data collection, statistical analysis, data analysis, manuscript writing, study supervision. Acta thanks Ross W Crawford for help with peer review of this study.

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Iorio R, Puskas B, Healy W L, Tilzey J F, Specht L M, Thompson M S. Cementless acetabular fixation with and without screws: analysis of stability and migration. J Arthroplasty 2010; 25(2): 309-13. doi: http://dx.doi. org/10.1016/j.arth.2009.01.023. Kärrholm J, Lindahl H, Malchau H, Mohaddes M, Nemes S, Rogmark C, Rolfson O. The Swedish Hip Arthroplasty Register Annual Report 2016; 2017. Laaksonen I, Lorimer M, Gromov K, Eskelinen A, Rolfson O, Graves S E, Malchau H, Mohaddes M. Trabecular metal acetabular components in primary total hip arthroplasty: higher risk for revision compared with other uncemented cup designs in a collaborative register study including 93,709 hips. Acta Orthop 2018; 89(3): 259-64. Lazarinis S, Karrholm J, Hailer N P. Increased risk of revision of acetabular cups coated with hydroxyapatite. Acta Orthop 2010; 81(1): 53-9. doi: 10.3109/17453670903413178. Lazarinis S, Karrholm J, Hailer N P. Effects of hydroxyapatite coating of cups used in hip revision arthroplasty. Acta Orthop 2012; 83(5): 427-35. doi: 10.3109/17453674.2012.720117. Lazarinis S, Mäkelä K T, Eskelinen A, Havelin L, Hallan G, Overgaard S, Pedersen A B, Kärrholm J, Hailer N P. Does hydroxyapatite coating of uncemented cups improve long-term survival? An analysis of 28,605 primary total hip arthroplasty procedures from the Nordic Arthroplasty Register Association (NARA). Osteoarthritis Cartilage 2017; 25: 1980-7. Minten M J, Heesterbeek P J, Spruit M. No effect of additional screw fixation of a cementless, all-polyethylene press-fit socket on migration, wear, and clinical outcome: a 6.5-year randomized radiostereometric analysis followup report. Acta Orthop 2016; 87(4): 363-7.

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Ni S H, Guo L, Jiang T L, Zhao J, Zhao Y G. Press-fit cementless acetabular fixation with and without screws. Int Orthop 2013. doi: 10.1007/s00264013-2075-2. Epub 2013 Aug 28. Ohashi H, Kikuchi S, Aota S, Hakozaki M, Konno S. Surgical anatomy of the pelvic vasculature, with particular reference to acetabular screw fixation in cementless total hip arthroplasty in Asian population: a cadaveric study. J Orthop Surg (Hong Kong) 2017; 25(1): 2309499016685520. doi: 10.1177/2309499016685520. Otten V T, Crnalic S, Röhrl S M, Nivbrant B, Nilsson K G. Stability of uncemented cups—long-term effect of screws, pegs and HA coating: a 14-Year RSA follow-up of total hip arthroplasty. J Arthroplasty 2016; 31(1): 15661. Pepe M, Kocadal O, Erener T, Ceritoglu K, Aksahin E, Aktekin C N. Acetabular components with or without screws in total hip arthroplasty. World J Orthop 2017; 8(9): 705. Stilling M, Rahbek O, Søballe K. Inferior survival of hydroxyapatite versus titanium-coated cups at 15 years. Clin Orthop Relat Res 2009; 467(11): 2872-9. VanderWeele T J, Ding P. Sensitivity analysis in observational research: introducing the e-value. Ann Intern Med 2017; 167(4): 268-74. doi: 10.7326/ M16-2607. Won C H, Hearn T, Tile M. Micromotion of cementless hemispherical acetabular components. Does press-fit need adjunctive screw fixation? Bone Joint J 1995; 77(3): 484-9.

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The design of the cemented stem influences the risk of Vancouver type B fractures, but not of type C: an analysis of 82,837 Lubinus SPII and Exeter Polished stems Georgios CHATZIAGOROU 1,2, Hans LINDAHL 1,3, and Johan KÄRRHOLM 1,2 1 The Swedish Hip Arthroplasty Register, Gothenburg; 2 Department of Orthopaedics, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg; 3 Department of Orthopaedics, Lidköping Hospital, Sweden Correspondence: g.chatziagorou@gmail.com Submitted 2018-09-30. Accepted 2019-01-07.

Background and purpose — In total hip replacements, stem design may affect the occurrence of periprosthetic femoral fracture. We studied risk factors for fractures around and distal to the 2 most used cemented femoral stems in Sweden. Patients and methods — This is a register study including all standard primary Lubinus SPII and Exeter Polished stems operated in Sweden between 2001 and 2009. The outcome was any kind of reoperation due to fracture around (Vancouver type B) or distal to the stem (Vancouver type C), with use of age, sex, diagnosis at primary THR, and year of index operation as covariates in a Cox regression analysis. A separate analysis of the primary osteoarthritis patient group was done in order to evaluate eventual influence of the surgical approach (lateral versus posterior) on the risk for Vancouver type B fractures. Results — The Exeter stem had a 10-times (95% CI 7–13) higher risk for type B fractures, compared with the Lubinus, while no statistically significant difference was noticed for type C fractures. The elderly, and patients with hip fracture or idiopathic femoral head necrosis, had a higher risk for both fracture types. Inflammatory arthritis was a risk factor only for type C fractures. Type B fractures were more common in men, and type C in women. A lateral approach was associated with decreased risk for Type B fracture. Interpretation — Stem design influenced the risk for type B, but not for type C fracture. The influence of surgical approach on the risk for periprosthetic femoral fracture should be studied further.

Periprosthetic femoral fracture (PPFF) is more common in uncemented stems (Hailer et al. 2010, Thien et al. 2014, Abdel et al. 2016). In cemented stems, higher risk for fracture has been reported for “force-closed” (e.g., Exeter Polished, CPT), compared with “shape-closed” stems like Lubinus SPII and Charnley (Lindahl et al. 2005, Thien et al. 2014, Broden et al. 2015, Palan et al. 2016). However, most of the previous studies have focused on fractures treated with stem revision (Thien et al. 2014, Palan et al. 2016), and hence mainly fractures around a loose stem. It is probable that the shape and the surface finish of the stem contribute to the risk for Vancouver type B fractures (fractures around or close to a femoral stem) (Broden et al. 2015, Palan et al. 2016). Little research has been done to investigate whether the design of the stem can affect the risk for suffering a fracture distal to the stem (Vancouver type C) (Lowenhielm et al. 1989). The majority of hip arthroplasty registries report only primary procedures and revisions. Therefore, type C fractures, treated in principle with open reduction and internal fixation (ORIF) without revision, are not reported. A recent register study from Sweden (Chatziagorou et al. 2018), revealed that only 17% of these fractures were reported to the Swedish Hip Arthroplasty Register (SHAR). Type C fractures were numerically more common among Lubinus SPII stems, while type B fractures predominated after insertion of an Exeter stem. These figures were, however, not related to the numbers at risk in each group. We are not aware of any study where the majority of type C fractures treated without revision were included. Nothing is known regarding the influence of surgical approach on the risk for postoperative periprosthetic fracture around a total cemented hip prosthesis. Both the Exeter and the Lubinus stems are frequently used in Sweden. Between 2000 and 2016, 104,081 Lubinus

© 2019 The Author(s). Published by Taylor & Francis on behalf of the Nordic Orthopedic Federation. This is an Open Access article distributed under the terms of the Creative Commons Attribution-Non-Commercial License (https://creativecommons.org/licenses/by/4.0) DOI 10.1080/17453674.2019.1574387

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Eligible primary THRs n = 82,837 Lubinus SP II stems, n = 55,026 (66%) Exeter polished stems, n = 27,811 (34%) Excluded THRs (n = 3,024): – with primary diagnosis of tumor, 548 – stems shorter or longer than standard length, 844 – previous history of hemiarthroplasty, 30 – THRs with uncemented cups, 1,602 Analyzed THRs n = 79,813 Lubinus SP II stems, n = 52,625 (66%) Exeter polished stems, n = 27,188 (34%)

Table 1. Periprosthetic fractures (n = 31) primarily excluded Intraoperative fracture Malignancy at the time of reoperation Active deep infection Perforation only Fracture occurred during TKR surgery Vancouver type A Sawing (non-iatrogenic)

10 5 5 3 3 4 1

length is one of these parameters, and during the study period (2001–2011), the standard length for both involved stems was 150 mm. Stem lengths other than 150mm were excluded. Further excluFigure 1. Flow chart. Of the 73,630 originally included patients, 70,981 remained for analysis. Standard stem length was 150 mm for both Exeter and Lubinus SPII. sion criteria are presented in a flow chart (Figure . 1). Surgical treatment of fracture types excluded SPII and 53,358 Exeter stems were used in primary total hip for various reasons was labelled as reoperation due to causes replacements (THR) (Karrholm et al. 2017). This corresponds other than PPFF in the analyses (Table 1). Data for the primary THRs and the reoperations were to two-thirds of all primary THRs during this period. Previous studies have shown that Exeter stems run increased risk of derived from the SHAR. The reporting of primary hip arthrorevision due to periprosthetic fractures, whereas less is known plasties is almost complete (98%) (Karrholm et al. 2017), about the risk for reoperation including also operative treat- whereas the reporting of reoperations is poorer (Söderman et al. 2000, Lindgren et al. 2014). Therefore, data linking was ment with osteosynthesis and without stem exchange. We compared the Lubinus SPII and the Exeter Polished done between the SHAR and the National Patient Register stem as risk factors for Vancouver type B and C fractures. (NPR), in order to detect even PPFFs not registered with the Other risk factors studied were age, sex, diagnosis at the pri- SHAR. Cross-matching for the other types of reoperations mary THR, year of index operation, and surgical approach. was not done. The NPR holds information on all inpatient care We hypothesized that Lubinus stems might run an increased since 1987, and all outpatient care since 2001. Both private risk of type C fractures because of the high resistance of this and public healthcare providers have had to report to the NPR stem to undergoing type B fractures ending up in a revision. since 2001. All medical records of reoperations due to fracture To include all types of surgical procedures of the operated were collected and scrutinized to detect all femoral fractures femur with relation to the hip prosthesis inserted, our primary in patients with a primary THR. The information provided in the case records was also used for fracture classification by outcome was any reoperation due to periprosthetic fracture. GC, according to the Vancouver classification system (Brady et al. 1999). A detailed description of the classification process, as well as its validation, is described in a previous publiPatients and methods cation (Chatziagorou et al. 2018). Bilateral observations were All primary standard Lubinus SPII and Exeter Polished included as previous studies have indicated that this will not stems used in THRs between 2001 and 2009, and reported cause significant problems related to dependency (Ranstam et to the SHAR, were included. We studied reoperations for al. 2011). any reason, and specifically due to PPFF between 2001 and 2011, to include a minimum of 2 years’ follow-up (maximum Statistics follow-up 11 years). Follow-up ended at the date of reopera- Statistical calculations were done using IBM SPSS statistion for any reason, death, emigration, or on December 31, tics 23 (IBM Corp, Armonk, NY, USA). To identify eventual 2011, whichever came first. Reoperation was defined as any demographic differences between the Lubinus and the Exeter further surgical intervention related to the index hip arthro- group, a chi-squared test and Mann–Whitney test were used. plasty irrespective of whether the prosthesis or parts of it have The 10-year survival was calculated with Kaplan–Meier analbeen exchanged, extracted, or left untouched. All type A frac- ysis (log rank test). We plotted survival curves for the covaritures (fractures of the greater and lesser trochanter), conserva- ates included, and log–log plots to test that the Cox proportively treated periprosthetic fractures, and fractures occurring tional hazard model was fulfilled. A Cox regression model during insertion of a primary stem (intraoperative fractures) was used to analyze the relative risk for reoperation due to were excluded. The SHAR records stem characteristics pro- PPFF. Adjustment for age, sex, type of stem, and diagnosis at spectively, for all primary and secondary arthroplasties. Stem the time of primary THR, as well as the year of index opera-

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tion, was performed. The distribution of the population into age groups was done according to the age at the time of the primary operation. The aim was to have as equally sized groups as possible. Diagnosis was separated into primary osteoarthritis (OA), inflammatory arthritis, hip fracture, idiopathic femoral head necrosis, and various (including sequel to childhood hip disease). Censored were cases with cause of reoperation other than PPFF, excluded cases (Table 1), patients who died without any reoperation, or those who had not been reoperated until the end of 2011. The surgical approach (lateral versus posterior), as a risk factor for Vancouver type B fracture, was studied in a subgroup analysis. Complete information on surgical approach was available in 43,639 Lubinus and in 22,271 Exeter cases with primary OA. Missing data were 9 cases for each stem (Table 6). In the other groups of diagnoses, up to 97.5% (hip fracture) had missing information. Therefore, we chose to include only those patients operated due to primary OA and with a lateral or posterior incision. P-values were 2-sided with a significance level < 0.05, and 95% confidence intervals (CI) were calculated.

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Table 2. Patient demographics and reoperations Item

Lubinus SPII

Exeter

All

p-value

Primary THRs, n (%) 52,625 (66) 27,188 (34) 79,813 (100) Male sex, n (%) a 20,870 (40) 10,322 (38) 31,192 (39) < 0.001 b Median age (interquartile range): at primary THR 72.2 (13) 72.1 (13) 72.1 (13) at reoperation for any reason 73.0 (13) 74.7 (14) 74.0 (13) 0.001 c at reoperation due to PPFF 80.3 (14) 79.8 (13) 79.9 (13) Age group, n (%) a < 64 10,613 (20) 5,824 (22) 16,437 (20) 64–69 11,015 (21) 5,502 (20) 16,517 (21) 70–74 10,826 (21) 5,505 (20) 16,331 (20) 75–79 10,451 (20) 5,172 (19) 15,623 (20) 80–100 9,720 (18) 5,185 (19) 14,905 (19) Diagnoses, n (%) a < 0.001 b Primary OA 43,648 (83) 22,280 (82) 65,928 (83) Hip fracture 6,181 (12) 2,794 (10) 8,975 (11) Idiopathic femoral head necrosis 1,148 (2) 968 (4) 2,116 (3) Inflammatory arthritis 1,162 (2) 654 (2) 1,816 (2) Various d 486 (1) 492 (2) 978 (1) Reoperations, n (%) a All reasons 1,660 (3.2) 966 (3.6) 2,626 (3.3) 0.003 b Due to PPFFs 167 (0.3) 298 (1.1) 465 (0.6) < 0.001 b Revisions, n (%) a All reasons (revision of any part) 1,095 (2.1) 595 (2.2) 1,690 (2.1) All reasons (revision of the stem) 544 (1.0) 343 (1.3) 887 (1.1) 0.004 b Due to PPFFs e 18 (0.03) 131 (0.5) 149 (0.2) < 0.001 b P-value is referred to only in cases with statistically significant difference. a % of all primary Lubinus, Exeter, and both stems, respectively. b Pearson chi-squared test. c Mann–Whitney test. d Other reasons including sequel after childhood hip disease. e The number of revisions of any part due to fracture was the same as the number of stem revisions due to fracture.

Ethics, funding, and potential conflicts of interest The study was approved by the Central Ethical Review Board in Gothenburg (Entry number: 198-12, Date: 2012-04-05). There was no financial support for this research. The authors declare no conflict of interest.

Results Study population Between 2001 and 2009, 82,837 primary Lubinus SPII and Exeter Polished femoral stems were inserted in 73,630 patients. The data linking with the NPR resulted in a total of 626 PPFFs (295 of these were registered only in NPR), giving 4,233 reoperations between 2001 and 2011. After the exclusions (Figure 1 and Table 1), there were 79,813 primary THRs (70,981 patients), with 2,626 first-time reoperations (2,597 patients) left for analysis. 465 of the reoperations (462 patients) were due to periprosthetic femoral fracture. The mean follow-up time was 5.6 years. A slightly higher proportion of men was noted in the Lubinus SPII group (Table 2). The Exeter group had, proportionally, more patients classified as idiopathic femoral head necrosis and “various.” The cups

used with the Lubinus and the Exeter stems are presented in Table 3. Vancouver type and risk factors The proportion of reoperations due to PPFF was higher in the Exeter than in the Lubinus group, as reflected in the survival analyses (Table 2, Figure 2). The commonest fracture type observed after insertion of a Lubinus SPII stem was Vancouver type C (74%), whereas type B fractures were more common after use of Exeter Polished stems (73%, Table 4). The Exeter stem had a 3.5-times higher risk for PPFF (B or C), and a 9.6times higher risk for type B fracture when compared with the Lubinus SPII (Table 5). There was no statistically significant difference between the 2 groups regarding the risk of type C fracture. Overall, women more frequently sustained fractures distally to the stem, whereas men had a higher risk for fracture around the stem, and a slightly higher risk for PPFF in general (type B or C). The risk for fracture increased with age, irrespective of whether age was studied as a continuous or a categorical variable. Patients aged 80 years and older had the highest risk for both type B and C fractures, compared with patients younger than 64 years (Table 5).

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Figure 2. Cumulative survival (unadjusted) for periprosthetic femoral fracture. Numbers at risk at the end of 10 years’ follow-up were: 2,903 for the Lubinus SPII group, and 1,518 for the Exeter Polished group. 2(a): All fractures studied (Type B and C fractures). Mean survival at 10 years was 99.4% (SE 0.06) for the Lubinus SPII, and 97.9% (SE 0.17) for the Exeter Polished (log rank test p < 0.001). 2(b): Type B fractures. Mean survival at 10 years was 99.8% (SE 0.04) for the Lubinus SPII, and 98.6% (SE 0.11) for the Exeter Polished (log rank test p < 0.001). 2(c): Type C fractures. Mean survival at 10 years was 99.6% (SE 0.05) for the Lubinus SPII, and 99.3% (SE 0.11) for the Exeter Polished (log rank test p = 0.08).

Table 3. Type of cups (all cemented) used with Lubinus SPII and Exeter Polished stems. Values are frequency (%) Cups used with Lubinus SPII stems, total number Lubinus FAL Charnley Elite ZCA XLPE Exeter Duration OPTICUP Contemporary Hooded Duration Avantage Cemented Reflection Various Exeter Polished stems, total number Exeter Duration Charnley Elite Contemporary Hooded Duration Charnley Marathon XLPE Cenator ZCA XLPE Exeter Various

All THRs

PPFFs

52,625 (100) 44,620 (85) 5,075 (9.6) 943 (1.8) 809 (1.5) 674 (1.3) 158 (0.3) 111 (0.2) 93 (0.2) 55 (0.1) 87 (0.2) 27,188 (100) 9,157 (34) 8,308 (31) 6,454 (24) 2,041 (7.5) 714 (2.6) 194 (0.7) 168 (0.6) 68 (0.3) 84 (0.3)

167 (100) 139 (83) 16 (9.6) 5 (3) 0 2 (1.2) 3 (1.8) 0 1 (0.6) 0 1 (0.6) 298 (100) 110 (37) 97 (33) 48 (16) 22 (7.4) 12 (4.0) 4 (1.3) 1 (0.3) 1 (0.3) 3 (1.1)

22 different types of cups were used in conjunction with Lubinus SPII, and 17 with Exeter Polished stems.

Table 4. Distribution of periprosthetic femoral fractures according to the Vancouver classification system. Values are frequency (%) Vancouver Lubinus B1 B2 B3 C Total

27 (16) 15 (9) 2 (1) 123 (74) 167 (100)

Exeter 55 (19) 157 (53) 4 (1) 82 (28) 298 (100)

Type A fractures were excluded from this study.

All 82 (18) 172 (37) 6 (1) 205 (44) 465 (100)

Table 5. Risk factors, adjusted hazard ratios (HR), and 95% confidence intervals (CI) for reoperation due to periprosthetic femoral fracture Risk factors

Vancouver B&C Vancouver B Vancouver C HR (CI for HR) HR (CI for HR) HR (CI for HR)

Stem Lubinus SPII (ref.) 1 1 1 Exeter Polished 3.5 (2.9–4.2) 9.6 (7.0–13) 1.3 (0.95–1.7) Sex Men (reference) 1 1 1 Women 0.7 (0.6–0.8) 0.4 (0.3–0.5) 2.0 (1.4–2.8) Age groups < 64 (reference) 1 1 1 64–69 1.1 (0.8–1.5) 1.0 (0.6–1.5) 1.3 (0.7–2.2) 70–74 1.5 (1.1–2.1) 1.4 (0.9–2.2) 1.7 (1.0–2.8) 75–79 2.0 (1.5–2.7) 2.1 (1.4–3.1) 1.9 (1.2–3.1) 80–100 3.1 (2.3–4.2) 2.9 (2.0–4.3) 3.4 (2.1–5.4) Diagnoses Primary OA (ref.) 1 1 1 Inflam. arthritis 3.6 (2.3–5.5) 1.9 (0.9–4.2) 5.6 (3.3–9.6) Hip fracture 3.6 (2.9–4.5) 3.3 (2.4–4.4) 4.2 (3.0–5.7) Idiopathic femoral head necrosis 3.5 (2.4–5.0) 3.0 (1.9–5.0) 4.1 (2.4–7.1) Various a 2.0 (1.02–3.9) 1.6 (0.6–3.9) 2.8 (1.01–7.6) Calendar year for primary THR 1.1 (1.0–1.1) 1.1 (1.1–1.2) 1.0 (0.97–1.1) a Other

reasons including sequel after childhood hip disease.

Inflammatory arthritis, when compared with primary OA, did not affect the risk for fracture around a stem, but distal to it. Patients with hip fracture or idiopathic femoral necrosis had approximately 3 times higher risk for type B fractures, and 4 times for type C (Table 5). The later the year for the index operation, the more likely the patient would suffer a type B fracture. No corresponding time-related change in risk was observed as regards type C fractures. The subgroup analysis (lateral versus posterior approach) was done in 43,271 Lubinus SPII stems and 21,562 Exeter Polished stems, inserted

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Table 6. Distribution of surgical approach among hips with primary OA. Values are frequency (%) Approach a Item Lateral Posterior Other

All

Lubinus SPII Primary THRs 12,540 (100) 30,731 (100) 368 (100) 43,639 (100) Type B fractures 6 (0.05) 21 (0.07) 0 27 (0.06) Type C fractures 16 (0.13) 47 (0.15) 1 (0.27) 64 (0.15) Exeter Polished Primary THRs 10,471 (100) 11,091 (100) 709 (100) 22,271 (100) Type B fractures 49 (0.47) 89 (0.80) 8 (1.13) 146 (0.66) Type C fractures 14 (0.13) 27 (0.24) 2 (0.28) 43 (0.19) a9

Exeter and 9 Lubinus stems with unknown approach were excluded. Only patients operated with lateral or posterior approach were included in the separate regression analysis.

due to primary OA (Table 6). 1,077 stems operated with other surgical approaches were excluded from this analysis. Stems inserted with the posterior approach had a 1.6-times higher risk for suffering a Vancouver type B fracture compared with those inserted with a lateral approach (Table 7).

Discussion Several previous studies have demonstrated an increased risk for periprosthetic fracture of the Exeter when compared with the Lubinus stem (Lindahl et al. 2005, Thien et al. 2014). To our knowledge, this is the first study that distinguished between Vancouver type B and type C fractures, based on extensive research to include all reoperations. Earlier studies have either looked at the overall risk for periprosthetic fracture (Lindahl et al. 2005, Palan et al. 2016), or the risk for revision due to fracture (Cook et al. 2008, Thien et al. 2014) (mainly Vancouver type B2 and type B3 fractures), for one or both of these stems. Our main finding is that the Lubinus SPII did not have a higher risk for type C fractures, despite the fact that almost 3 out of 4 fractures around this stem were located distal to it (see Table 4). The finding that the Exeter Polished stem had a higher risk for fracture (type B and overall), confirms earlier publications (Lindahl et al. 2005, Thien et al. 2014). The commonest fracture type in this material was, however, type C (see Table 4). This observation results from an almost complete registration of fractures treated with osteosynthesis only, and without any stem revision (Chatziagorou et al. 2018). In Sweden, type B fractures are more common in uncemented stems, and type C fractures in cemented stems (Chatziagorou et al. 2018), in contrast to a previous study from the Mayo Clinic (Abdel et al. 2016). The cemented Lubinus SPII stem (Waldemar Link, Hamburg, Germany) is a shape-closed, CoCrMo, tapered, and anatomically s-shaped stem, with a collar, a matte finish, and a 19° built-in anteversion of the femoral neck. Its shape allows

Table 7. Risk factors, adjusted hazard ratios (HR), and 95% confidence intervals (CI) for reoperation due to Vancouver type B fracture Risk factors

Vancouver B HR (CI for HR)

Stem Lubinus SPII (reference) 1 Exeter Polished 11.4 (7.5–17) Sex Men (reference) 1 Women 0.4 (0.3–0.5) Age groups < 64 (reference) 1 64–69 1.3 (0.7–2.4) 70–74 1.9 (1.1–3.3) 75–79 3.1 (1.8–5.3) 80–100 4.5 (2.7–7.7) Calendar year for primary THR 1.1 (1.04–1.2) Surgical approach: Lateral (reference) 1 Posterior 1.6 (1.2–2.2) Only patients with the diagnosis of primary OA, and a lateral or posterior approach were included in this analysis.

neutral positioning in the femoral canal and resists rotational forces (Sesselmann et al. 2017), while the collar is claimed to restrict the distal migration of the stem (Catani et al. 2005). The anatomical shape of this stem probably facilitates an adequate cement mantle (Broden et al. 2015). The cemented Exeter stem (Stryker Howmedica, Mahwah, NJ, US) is a forceclosed, straight, collarless, double-wedge tapered, highly polished stem. It does not bond to the cement and is designed to subside into the cement mantle as a wedge (Palan et al. 2016). Both stems are well documented with excellent outcomes in the short and long term (Murray et al. 2013, Prins et al. 2014, Sesselmann et al. 2017, Westerman et al. 2018). It is postulated that the subsidence of the Exeter stem into the cement mantle will create an axial loading effect within the cement mantle, resulting in hoop stresses in the adjacent bone, which might increase the risk of sustaining a PPFF. As soon as a periprosthetic fracture occurs close to an Exeter stem, the stem is by definition loose (Broden et al. 2015). The reason why forceclosed cemented stems have a higher risk for periprosthetic fractures has been reported previously (Broden et al. 2015, Palan et al. 2016). The higher percentage of type C fractures within Lubinus SPII stems possibly has to do with the relative lower risk for fractures close to it (type B). We assume that these fractures are, rather, secondary to an osteoporotic femur (elderly, women, inflammatory arthritis, and previous history of hip fracture), than secondary to the stem’s design. Previous comparisons between the posterior and the lateral approach showed superior results for the former regarding the thickness of the cement mantle (Hank et al. 2010), the alignment of the stem (Vaughan et al. 2007, Broden et al. 2015), and revision risk due to aseptic loosening of the stem (Lind-

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gren et al. 2012). Femurs with a loose stem are more prone to suffer a periprosthetic fracture (Lindahl et al. 2005). Thus, the posterior surgical approach should be beneficial regarding the risk for aseptic loosening and, hence, the risk for type B fractures around a loose stem. We are not aware of any publication where the surgical approach is studied as a risk factor for postoperative periprosthetic femoral fractures, secondary to a primary cemented THR. Berend et al. (2006) found that an anterolateral approach was associated with intraoperative fracture of the proximal femur, in both cemented and uncemented stems. A more recent study showed that patients older than 85 years, with hemiarthroplasty, had 2 times higher risk for postoperative PPFF if operated with a posterior approach, compared with those operated via a direct lateral approach (Rogmark et al. 2014), but this observation might have been confounded by inclusion of both cemented and uncemented stems of various designs. Our finding, that use of a posterior approach is associated with a higher risk for PPFF, is difficult to explain. A radiostereometric study (Glyn-Jones et al. 2006) observed slightly increased retrotorsion of the Exeter stem if inserted through a posterior compared with an anterolateral approach, suggesting a less secure stem fixation in the former group. Gore et al. (1982) showed less prosthetic femoral anteversion and more inward rotation of the operated hip with the posterior approach. A Cochrane review (Jolles and Bogoch 2006) also reported increased internal rotation of the hip joint in extension with use of the posterior approach, suggesting that implant loading might differ depending on the approach used. The influence of potential risk factors for PPFF such as age, sex, and diagnosis at the time of primary THR vary depending on the type of the stem (cemented/uncemented, primary/ secondary), the outcome measure (revision, reoperation, nonoperative treatment), and whether the fracture is intra- or postoperative (Berend et al. 2006, Cook et al. 2008, Meek et al. 2011, Abdel et al. 2016). We studied risk factors in patients with cemented Lubinus or Exeter stems and only those suffering a postoperative PPFF on the same side, and without any history of previous reoperation. Therefore, a generalization of our results for the whole population of patients with THR would be unreliable. High age, as well as the diagnosis of hip fracture or idiopathic femoral head necrosis, implied an increased risk for both type B and C fracture. Men had a higher risk for type B fractures, probably because of younger age with increased daily activity level (Witte et al. 2009) and higher risk for aseptic loosening than women (Hailer et al. 2010). Conversely, women, with more osteoporotic femoral bone and higher mean age at the time of primary THR, more frequently suffered type C fractures. The year of index operation influenced the risk for type B and not for type C fractures. This is probably the result of the increasing mean age at the index operation during the study period, from 71 years in 2001 to 72 years in 2009. Another reason could, theoretically, be a trend toward a decrease in

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postoperative clinical and radiological controls after primary THR. This could lead to more cases with “unknown stem loosening,� and thus an increased risk for Vancouver type B fractures. The addition of the surgical approach in the subgroup analysis did not alter the relation of the other risk factors (age, sex, stem type, and year of primary THR). Inflammatory arthritis did not have a higher risk for fractures around the stem when compared with primary OA. This finding is in line with a previous report (Thien et al. 2014). On the other hand, femurs with inflammatory arthritis run a 6-times higher risk for distal femoral fractures. This is in accordance with a previous publication that reported a higher risk for osteoporotic fractures (Yamamoto et al. 2015) in patients with rheumatoid arthritis. There are limitations to our study. The linkage between the SHAR and the NPR included only reoperations due to periprosthetic fracture and not all other reasons for reoperation (aseptic loosening, infection, dislocation, other). These reoperations are recorded in the SHAR, but could be underreported, especially those performed owing to infection (Lindgren et al. 2014). Therefore, the real number of all reoperations could be slightly higher than found by us. Reoperations that took place before the PPFF were detected when the case records were scrutinized. All other reoperations not reported to the SHAR could most probably be expected to be equally distributed between the 2 groups studied. Another limitation, however, is that we did not include the presence of a total knee replacement (TKR) as a risk factor. Total hip replacements with an ipsilateral TKR have a higher risk for proximal femoral fracture (Katz et al. 2014), and total knee replacement is associated with distal femoral fracture (McGraw and Kumar 2010). We do not, however, think that the relative number of patients with TKR differs between those who have been operated with a Lubinus and those who have received an Exeter stem. Hips with primary osteoarthritis and inflammatory arthritis had almost the same share in the 2 groups. It is also important to underline that the classification process was based on reading of medical records. A better optimized way would be to define the fracture type based on information from both the medical records and the radiographs. In a previous validation of the classification process (Chatziagorou et al. 2018) we did, however, observe good agreement corresponding to previous validations of the Vancouver classification (Brady et al. 2000, Rayan et al. 2008). In addition, our analysis was based only on fractures classified as either B or C, without any further analyses of the sub-categories in the type B group. The methodological strength of this study was the relatively good data quality of a large volume of material, and its high external validity regarding PPFFs in the Swedish population. The hip prostheses studied in our report have a long tradition in Sweden with excellent implant survival (Junnila et al. 2016). The volume of our data was big enough to analyze only stems of the same length (150 mm). A difference in stem length can potentially affect the risk of periprosthetic fracture and its classification into type B or C. We also excluded unce-

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mented cups, since use of such implants was shown to result in a higher rate of femoral lysis when used with Exeter V40 stems (Westerman et al. 2018). Furthermore, we investigated all kind of reoperations due to PPFF, and not only revisions, which is the contemporary standard in other arthroplasty registries. This, in addition to the cross-matching with the NPR, gave us the unique opportunity to study an almost complete data set of fractures treated surgically with other methods such as ORIF and without concomitant revision of the stem (mostly type B1 and C fractures). Overall, the Exeter stem had almost an 3.5-times increased risk to suffer a periprosthetic fracture and about 10 times increased risk to suffer a PPFF leading to revision, which for the patient usually is a more demanding procedure than operation with osteosynthesis. According to our findings and previous studies the difference in risk ratio will increase further with increasing age and in patients with secondary OA. Lindahl et al. reported 23% reoperation rate (235 of 1,002) in patients treated surgically for type B and C fractures (Lindahl et al. 2005). We therefore think that our findings have clinical relevance and especially in the older population with a high incidence of osteoporosis. In summary, the Exeter Polished stem had a higher risk for postoperative periprosthetic femoral fractures of type B compared with the Lubinus SPII. As regards type C fractures there was no difference. The relative increased proportion of type C versus type B fractures in the Lubinus group might indicate that, after the insertion of a Lubinus stem, the distal femur will constitute the weakest part as long as the stem has not loosened. Our study suggested that the posterior approach may not be beneficial regarding the risk of PPFF in cemented THRs, but this observation needs to be studied further.

GC: Planning of the research, collection of the material, analysis of the material, manuscript. HL: Planning of the research, collection of the material, manuscript. JK: Planning of the research, analysis of the material, manuscript. Acta thanks Søren Overgaard for help with peer review of this study.

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Survival of 11,390 Continuum cups in primary total hip arthroplasty based on data from the Finnish Arthroplasty Register Matias HEMMILÄ 1, Mikko KARVONEN 1, Inari LAAKSONEN 1, Markus MATILAINEN 2, Antti ESKELINEN 3, Jaason HAAPAKOSKI 4, Ari-Pekka PUHTO 5, Jukka KETTUNEN 6, Mikko MANNINEN 7, and Keijo T MÄKELÄ 1 1 Department

of Orthopaedic Surgery, University of Turku and Turku University Hospital, Turku; 2 Department of Biostatistics, University of Turku, Turku; 3 Coxa Hospital for Joint Replacement, Tampere; 4 National Institute for Health and Welfare, Helsinki; 5 Department of Orthopaedics and Traumatology, Oulu University Hospital, Oulu; 6 Department of Orthopaedics and Traumatology, Kuopio University Hospital, Kuopio; 7 Orton Hospital, Helsinki, Finland Correspondence: matias.hemmila@utu.fi Submitted 2018-11-29. Accepted 2019-03-12.

Background and purpose — The use of trabecular metal (TM) cups for primary total hip arthroplasty (THA) is increasing. Some recent data suggest that the use of TM in primary THA might be associated with an increased risk of revision. We compared implant survival of Continuum acetabular cups with other commonly used uncemented cups. Patients and methods — Data on 11,390 primary THAs with the Continuum cup and 30,372 THAs with other uncemented cups (reference group) were collected from the Finnish Arthroplasty Register. Kaplan–Meier survival estimates were calculated; the endpoint was revision for any reason, for infection, or for dislocation. Revision risks were assessed with adjusted Cox multiple regression models. A subgroup analysis on the use of neutral or elevated liners in the Continuum group was made. Results — The 7-year survivorship of the Continuum group was 94.6% (95% CI 94.0–95.2) versus 95.6% (CI 95.3–95.8) in the reference group for revision for any reason. The risk for revision was higher in the Continuum group than in the reference group both for revision for any reason (HR 1.3 [CI 1.2–1.5)]) and for revision for dislocation (HR 1.9 [CI 1.5–2.3]). There was no difference in the rates of revision because of infection (HR 0.99 [CI 0.78–1.3]). Use of a neutral liner increased the risk for revision due to dislocation in comparison with the use of an elevated rim liner in the Continuum group (HR 1.7 [CI 1.2–2.5]). Interpretation — THA with Continuum cups is associated with an increased risk of revision compared with other uncemented cups, mainly due to revisions because of dislocation. Our results support the use of an elevated liner when Continuum cups are used for primary THA.

Trabecular metal (TM) acetabular components were initially indicated in particular for cup revisions after total hip arthroplasty (THA) (Levine et al. 2006). TM cups provide increased bone ingrowth, better modulus of elasticity, and better stability due to their porous structure compared with conventional uncemented cup devices made of titanium alloy (Meneghini et al. 2010). Currently, TM revision cups are used frequently worldwide. Besides revision surgery, TM cups have demonstrated promising mid- to long-term survivorship in primary THA (Baad-Hansen et al. 2011, Howard et al. 2011) and hence the use of Continuum (ZimmerBiomet, Warsaw, IN, USA) TM cups in primary THA increases (Wegrzyn et al. 2015, De Martino et al. 2016). However, a recent register study showed that the early and mid-term revision rate of TM cups was slightly higher compared with other uncemented cups when used in primary THA in Sweden and Australia (Laaksonen et al. 2018). The revision rate due to periprosthetic joint infection has been slightly increasing during recent decades (Dale et al. 2012). Some data suggest that the use of a TM acetabulum component in hip revision arthroplasty might be associated with a lower infection rate (Tokarski et al. 2015), but this finding has not been confirmed by register data and thus far there is, to our knowledge, no other evidence that the material of TM would protect patients from prosthetic joint infection (PJI) (Laaksonen et al. 2017, 2018). It has also been suggested that there might be an increased risk of dislocations associated with the use of Continuum cups due to a decreased jumping distance of the femoral head (Pakarinen et al. 2018). To compensate for this circumstance, elevated or hooded acetabular liners are currently widely

© 2019 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group, on behalf of the Nordic Orthopedic Federation. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits ­unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. DOI 10.1080/17453674.2019.1603596

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Table 1. Acetabular cups included in the study Cup design

n (%)

Continuum (ZimmerBiomet, Warsaw, IN, USA) 11,390 (27) Reference group 30,372 (73) Exceed (ZimmerBiomet, Warsaw, IN, USA) 1,550 (4) G7 (ZimmerBiomet, Warsaw, IN, USA) 1,121 (3) Pinnacle (DePuy, Warsaw, IN, USA) 14,844 (36) R3 (Smith & Nephew, Andover, MA, USA) 7,289 (18) Trident (shell) (Stryker, Mahwah, NJ, USA) 4,279 (10 Vision Ringloc (ZimmerBiomet, Warsaw, IN, USA) 1,280 (3)

available for the purpose of decreasing the dislocation rate. The use of elevated liners may, in theory, improve hip stability and decrease the revision rate (Insull et al. 2014), but the routine use of elevated liners has been questioned (Krushell et al. 1991, Insull et al. 2014). We compared the revision rate of Continuum cups used in primary THA with the most commonly used uncemented cups made of titanium alloy. We specifically compared the revision rates (1) for any reason, (2) for infection, and (3) for dislocation. We also studied whether use of elevated liners in primary THA decreases the revision rate due to dislocations compared with the Continuum cup with neutral liners.

Patients and methods This study is based on data from the Finnish Arthroplasty Register (FAR). The FAR data include nearly all hip and knee implants operated in Finland since 1980 (Paavolainen et al. 1991). Orthopedic units are obligated to provide all information essential for maintenance of the register to the Finnish National Institute for Health and Welfare. The register gathers information from most total hip implantations in the entire country and data coverage on primary THA exceeds 95% and on revision THA coverage is 81% (FAR 2018). Dates of death are obtained from the Population Information System maintained by the Population Register Centre. The data content of the register was scrutinized and revised in May 2014. The updated data now include detailed information on items like ASA class, BMI, and surgical approach. Study population Between January 2009 and December 2017, 133,488 primary THAs were reported to FAR. In 11,390 of these the Continuum primary cup was used. The reference group consisted of the 6 most commonly used other uncemented cups made of titanium alloy (n = 30,372) (Table 1). A head size other than 28 mm, 32 mm, or 36 mm, dual mobility, and constrained liners were excluded. The number of patients with bilateral hip prostheses was 4,407 and in 658 patients both hips were operated simultaneously. 498 patients had the Continuum cup in one hip and a control group cup component in the contra-

Table 3. Demographic data of the time period after data content revision in the Finnish Arthroplasty Register starting May 15, 2014. Values are frequency (%) unless stated otherwise Data

Continuum Reference group group

Mean age (SD) 67 (11) 66 (11) BMI (SD) 28 (5) 28 (5) Male sex 3,609 (42) 7,547 (46) Diagnosis Primary osteoarthritis 7,324 (85) 13,852 (85) Rheumatoid arthritis 137 (2) 195 (1) Other a 1,113 (13) 2,278 (14) Femoral head size of prosthesis 28 mm 29 (0.3) 107 (1) 32 mm 1,832 (21) 3,369 (21) 36 mm 6,713 (78) 12,849 (79) Status at end of follow-up Not revised 8,202 (96) 15,792 (97) Revised 372 (4) 533 (3) Liner material Ceramic 619 (7) 2,249 (14) Highly cross-linked polyethylene 7,955 (93) 14,041 (86) Elevated liner No 4,385 (55) 8,648 (62) Yes 3,570 (45) 5,393 (38) Approach Posterior 6,654 (78) 12,884 (81) Anterolateral (modified Hardinge) 1,667 (20) 2,864 (18) Anterior (Watson-Jones) 15 (0.2) 11 (0.1) Anterior (Smith-Peterson) 143 (2) 137 (1) Trochanteric osteotomy performed 1 (0.01) 1 (0.01) ASA class 1 1,281 (15) 2,163 (14) 2 4,132 (49) 8,260 (52) 3 2,992 (35) 5,308 (33) 4 104 (1) 189 (1) Femoral stem fixation Uncemented 5,502 (65) 13,209 (81) Cemented 3,030 (36) 3,057 (19) a

Fractures (5% Continuum group vs. 4% control group), avascular necrosis (3% vs. 3 %), osteoarthritis due to hip dysplasia (2% vs. 2 %), tumors (1% vs. 1 %), congenital hip dislocation (0.5% vs. 0.3%), inflammatory arthritis (0.3% vs. 0.4%), Legg–Perthes–Calve disease (0.3% vs. 0.2%), femoral head epiphyseolysis (0.2% vs. 0.1%), status post purulent arthritis (0.1% vs. 0%).

lateral hip. Tables 2 (see Supplementary data) and 3 show the demographic data hip-wise separately for the whole study period and after the data content revision in May 2014. Mortality during the study period in the Continuum group was 4% and 5% in the control group. Surgery In the Continuum group, 36 mm femoral heads were used in 79% of cases. The corresponding proportion in the reference group was 80%. A ceramic liner was used in 14% of cases in the Continuum group and in 27% of cases in the reference group. The rest were highly cross-linked polyethylene liners in both groups. From May 2014 surgical approach data have been available from the register. Since then the majority of the operations have been performed via the posterior approach in

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Table 4. Indication for revision prior to data content revision (May 15, 2014) of the Finnish Register. Values are frequency (%) Continuum Reference Main reason for revision a group group Aseptic loosening Cup and stem 0 (0) 2 (1) Cup 2 (4) 15 (5) Stem 3 (6) 17 (5) Infection 7 (13) 56 (18) Dislocation 21 (39) 88 (28) Component malposition 3 (6) 31 (10) Fracture 13 (24) 72 (23) Component breakage 0 ( 4 (1) Other 5 (9) 28 (9) a

No data available concerning indication for revision from 83 revisions.

both groups (79% in the Continuum group and 81% in the reference group). Uncemented femoral stems were used in 71% in the Continuum group compared with 83% in the reference group. The average follow-up time was 3 years (0–9) in the TM group and 4 years (0–10) in the reference group. Statistics Kaplan–Meier survival estimates were calculated for both groups and the log rank test was used to compare the survival curves. Revision was described as change or removal of at least 1 component (Tables 4 and 5). To reduce the risk of selection bias we adjusted the estimated revision risks in the Cox multiple regression model by sex, age group, diagnosis, femoral head size, operated side, operation year, and fixation of the femoral stem. An additional cup revision analysis was performed and the type of approach, ASA, BMI, and elevation status of the liner were added to the Cox model as possible confounders for cup revision for any reason as the endpoint. The analysis was done with the data of primary operation after register update in May 2014. In the Continuum elevation subgroup analysis sex, age group, diagnosis, side, stem fixation, and operation year were added to the Cox model (head size was stratified) and other than polyethylene liners were excluded. If the proportional hazards assumption for a variable was not fulfilled in the Cox model, the model was stratified by it instead. Stratification in Cox models means that the hazard functions can be estimated for all level combinations of the stratified variables, and the hazard ratios for the other variables (those that meet the proportional hazard assumption) are then optimized for all these hazard functions. Without stratification we would assume that hazards were the same for all levels of such variables. The primary outcome was revision for any reason and the secondary outcomes were revision for periprosthetic infection, revision for dislocation, and cup revision for any reason. Patients were censored for any event other than the outcome, or at the end of the follow-up. After the register update in May 2014 it has been possible to assess separately which component has been changed or removed in connection with the revi-

3

Table 5. Indication for revision after new indications for revision were added at the data content revision (May 15, 2014) of the Finnish Register. Values are frequency (%) Continuum Reference Main reason for revision a group group Aseptic loosening Cup 5 (1) 10 (2) Stem 15 (4) 26 (4) Osteolysis Cup 2 (1) 8 (1) Stem 1 (0.3) 11 (2) Liner wear 0 (0) 2 (2) Component breakage Cup 0 (0) 1 (0.2) Liner 1 (0.3) 11 (2) Head 1 (0.3) 1 (0.2) Modular neck 0 (0) 1 (0.2) Infection 100 (26) 194 (30) Dislocation 132 (34) 153 (24) Component malposition Cup 12 (3) 23 (4) Stem 1 (0.3) 14 (2) Periprosthetic fracture Acetabulum 6 (2) 2 (0.3) Femur 73 (19) 105 (17) Adverse reaction to metal debris 2 (1) 5 (1) Squeaking 2 (1) 5 (1) Unexplained pain 10 (3) 32 (5) Leg length discrepancy repair 4 (1) 10 (2) Other 17 (4) 24 (4) a

No data available concerning indication for revision from 83 revisions.

sion. Therefore, a subgroup analysis for cup-only-revisions was performed only for the newest FAR data. In addition, a subgroup analysis was performed for Continuum cups by liner type (neutral or elevated liner) with dislocation revision as the endpoint. Survival data are presented as percentages with the 95% confidence interval (CI). Cox regression analysis is presented with the hazard ratio (HR) and the CI. All analyses were performed using the SAS software (Version 9.3; SAS Institute, Cary, IN, USA). Ethics, funding, and potential conflicts of interest Ethical approval: June 13, 2017, Dnor THL/926/5.05.00/2017. This research received no funding. The authors declare no conflicts of interest.

Results Revision for any reason The up to 7-year survivorship for the Continuum group was 94.6% (CI 94.0–95.2) and the survival for the reference group was 95.6% (CI 95.3–95.8) for revision for any reason as an endpoint (Figure 1, Table 6; see Supplementary data). By Cox regression analysis the Continuum group had an increased risk of revision for any reason compared with the reference group (HR 1.3, CI 1.2–1.5).

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4

Revisionfree survival probablity

Survival probablity – endpoint revision for infection

Survival probablity – endpoint revision for dislocation

Survival probablity – endpoint revision for dislocation

1.00

1.000

1.000

1.000

CUP TYPE Continuum Others

CUP TYPE Continuum Others

0.998

0.98

CUP TYPE Continuum Others

Elevation Yes No

0.995

0.995

0.996

0.990 0.994 0.990

0.96

0.985

0.992 0.980

0.990

0.985

0.94

0.975

0.988

0.986

0.92 0

2

4

6

8

10

Years after index operation

Figure 1. Kaplan–Meier survival for Continuum group and reference group with revision for any reason as the endpoint. 95% CI levels presented in blue and red.

0.980 0

2

4

6

8

10

Years after index operation

Figure 2. Kaplan–Meier survival for Continuum group and reference group with revision for infection as endpoint. 95% CI levels presented in blue and red.

Cup revision for any reason In the cup-only-revision analysis performed with the data from May 15, 2014 to December 31, 2017, the 3-year survivorship was the same in the Continuum group as in the reference group: 99.4% vs. 99.6% (CI 99.2–99.6 vs. 99.5–99.7). These figures are not statistically different (Cox regression analysis HR 1.3, Cl 0.8–2.0). Revision due to infection The 7-year survivorship for the Continuum group was 98.9% (CI 98.6–99.1) and for the reference group 99.1% (CI 99.0– 99.2), when revision because of infection was the endpoint (Figure 2). The risk of revision for infection was the same in the groups (HR 1.0, CI 0.8–1.3) (Table 7; see Supplementary data). Revision due to dislocation The 7-year survivorship for the Continuum group was 98.3% (CI 98.0–98.6) and for the reference group 99.0% (CI 98.8– 99.1), when revision because of dislocation was the endpoint (Figure 3). The Continuum group had an increased risk of revision for dislocation (HR 1.9, CI 1.5–2.3) compared with the reference group (Table 7; see Supplementary data). Subgroup analysis: Continuum THA with or without liner elevation The 5-year survivorship for the Continuum group with elevated liners was 98.9% (CI 98.4–99.2) and for the Continuum group with neutral liners 97.8% (CI 97.3–98.2), when revision because of dislocation was the endpoint (Figure 4). After adjustments of the statistical data, the Continuum group with neutral liners had a higher risk of revision for dislocation compared with the Continuum group with elevated liners (HR 1.7, CI 1.2–2.5).

0.970 0

2

4

6

8

10

Years after index operation

Figure 3. Kaplan–Meier survival for Continuum group and reference group with revision for dislocation as endpoint. 95% CI levels presented in blue and red.

0

2

4

6

8

10

Years after index operation

Figure 4. Kaplan–Meier survival by subgroup analysis of Continuum THA with or without elevated liner. Endpoint: revision for dislocations. 95% CI levels presented in blue and red.

Discussion This study shows that use of the Continuum THA is associated with a slightly higher risk of revision than use of other uncemented titanium alloy cups. The Continuum study group and the reference group had a similar risk of revision due to infection, but the risk of revision due to dislocation was higher in the Continuum group. Further, the use of elevated liners in the Continuum THA reduced the risk of revision for dislocation compared with neutral liners. Trabecular metal was first introduced to the market in 1997. Since then, TM cups have shown reliable results when used for hip revision arthroplasty and are currently used routinely worldwide (Davies et al. 2011, Mohaddes et al. 2015). Their routine use in primary THA is increasing. Implant survival of primary TM cups has been comparable or even superior compared with uncemented devices made of titanium alloy (Baad-Hansen et al. 2011, Howard et al. 2011, Wegrzyn et al. 2015, De Martino et al. 2016). However, a recent collaborative register study reported that TM cups have a 1.5 times higher risk for revision than other frequently used uncemented cups in primary THA (Laaksonen et al. 2018). These results were somewhat surprising and at variance with previous literature. Our study supports the previous finding from the Swedish and Australian registries of a higher risk of revision of TM cups. The use of TM cups in primary THA is increasing in Sweden and Australia (Laaksonen et al. 2018). Continuum was the 2nd most common cup design in the FAR data of the present study. Due to the good gription of and high primary stability of TM, Continuum cups have been preferred in more demanding THAs. To reduce the risk of selection bias towards more difficult cases being treated with Continuum cups, we adjusted the revision risks in the Cox regression models. Our data suggest that the use of the Continuum cup in primary THA does not give superior results compared with other uncemented devices. However, TM cups are a reliable option when

Acta Orthopaedica 2019; 90 (x): x–x

treating large bone defects in revision or complex primary THA and results in these cases have been excellent (Weeden and Schmidt 2007, Macheras et al. 2010). The revisions in the Continuum group in the current study were mainly due to dislocations, and the number of revisions for early lack of osteointegration or aseptic loosening was low. PJIs are a growing challenge as an increasing number of joint replacements are being performed and the life expectancy of patients is increasing (Huotari et al. 2015). Indeed, the cumulative incidence of PJI in USA and the Nordic countries is reportedly growing (Dale et al. 2012, Kurtz et al. 2012). A recent study presented promising results of TM components possibly having a protective effect against PJI (Tokarski et al. 2015). These results were not confirmed in a register study (Laaksonen et al. 2018), and were similar to our results: the risk for revision due to PJI was similar in the Continuum and in the reference group (Table 7; see Supplementary data). Continuum cups with the neutral liner used have been associated with a reduced jumping distance of the femoral head and possibly with a higher dislocation risk due to this circumstance (Pakarinen et al. 2018). In an earlier large register study based on Australian and Swedish data, the revision risk due to dislocation was not assessed separately, although the overall revision risk of TM cups was increased compared with the other uncemented cups (Laaksonen et al. 2018). We found that the risk of revision due to dislocation of the Continuum THA is increased compared with reference THAs. This difference is largely explained by the difference in the revision rate due to dislocation. In the subgroup analysis of the Continuum group we found that cups with a neutral polyethylene liner are associated with 1.7-fold dislocation revision risk compared with Continuum cups with an elevated liner. This is in line with the previous finding by Pakarinen et al. (2018). Elevated liners were first introduced by Charnley in the early 1970s to decrease the tendency for posterior dislocation by providing more coverage (Charnley 1979). The improved stability in primary THA while using an elevated rim liner was first reported in 1996 and, although these liners are widely used, there is only limited clinical evidence to support their use (Cobb et al. 1996, Sultan et al. 2002, Carter et al. 2011). Also, the benefit of routine use of elevated-rim liners in instances in which the acetabular component otherwise is positioned satisfactorily has been questioned (Krushell et al. 1991). In addition, there might be potentially harmful side effects. The elevated liners may predispose the neck of the prosthesis to impinge on the acetabular rim, forcing the head out of the cup anteriorly, but such a risk has not been confirmed in clinical studies (McCollum and Gray 1990, Sultan et al. 2002). Despite these suspicions, elevated liners have not been associated with increased revision rates during 5 years of follow-up (Cobb et al. 1997). Also, the use of lipped liners with modular uncemented acetabular components has been associated with a decreased rate of revision due to instability after primary THA, according to a register study from New Zealand

5

(Insull et al. 2014). Our data support these findings: we did not observe any trend toward an elevated risk of revision due to increased wear. It is nevertheless prudent to remember that these problems may appear in a longer follow-up. Our study has some limitations. First, we were not able to assess radiographs to evaluate preoperative bone loss. It is possible that Continuum cups have been used in more demanding cases. However, Continuum being the second most used uncemented cup during our study time does suggest that it is used routinely for primary THA. Second, we were able to analyze only factors included in the register dataset. It is possible that patients might have comorbidities that could influence their dislocation risk that we are not aware of. Third, we were only able to use revision as the outcome. Some of the patients might have experienced pain, dislocations, or other implant-related problems without having a revision, for example, due to poor general health contraindicating risky revision surgery. In summary, this large nationwide study shows that the use of the Continuum cup for primary THA does not provide an advantage over traditional uncemented cups. On the contrary, the use of Continuum cups was associated with an increased revision risk compared with other uncemented cups. This enhanced risk was largely due to revisions for dislocations. If the Continuum cup is used, our results support the use of the elevated rim liner, rather than the neutral rim liner, as the primary choice. Supplementary data Tables 2 and 6–9 are available as supplementary data in the online version of this article, http://dx.doi.org/10.1080/1 7453674.2019.1603596

MH, IL, KM: planning the study, analysis of the data, and writing the manuscript; MK: analysis of the data and revision of the manuscript; MaM and JH: calculating the statistics and revision of the manuscript; AE, A-PP, MiM, and JK: analysis of the data and revision of the manuscript. Acta thanks Henrik Bodén and Ola Rolfson for help with peer review of this study.

Baad-Hansen T, Kold S, Nielsen P T, Laursen M B, Christensen P H, Soballe K. Comparison of trabecular metal cups and titanium fiber-mesh cups in primary hip arthroplasty: a randomized RSA and bone mineral densitometry study of 50 hips. Acta Orthop 2011; 82(2): 155-60. Carter A H, Sheehan E C, Mortazavi S M J, Purtill J J, Sharkey P F, Parvizi J. Revision for recurrent instability: what are the predictors of failure? J Arthroplasty 2011; 26(6): 46-52. Charnley J. Low friction arthroplasty of the hip: theory and practice. New York: Springer Verlag; 1979. Cobb T K, Morrey B F, Ilstrup D M. The elevated-rim acetabular liner in total hip arthroplasty: relationship to postoperative dislocation. J Bone Joint Surg Am 1996; 78(1): 80-6. Cobb T K, Morrey B F, Ilstrup D M. Effect of the elevated-rim acetabular liner on loosening after total hip arthroplasty. J Bone Joint Surg Am 1997; 79(9): 1361-4.

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Dale H, Fenstad A M, Hallan G, Havelin L I, Furnes O, Overgaard S, Pedersen A B, Kärrholm J, Garellick G, Pulkkinen P, Eskelinen A, Mäkelä K, Engesæter L B. Increasing risk of prosthetic joint infection after total hip arthroplasty. Acta Orthop 2012; 83(5): 449-58. Davies J H, Laflamme GY, Delisle J, Fernandes J. Trabecular metal used for major bone loss in acetabular hip revision. J Arthroplasty 2011; 26(8): 1245-50. De Martino I, De Santis V, Sculco P K, D’Apolito R, Poultsides L A, Gasparini G. Long-term clinical and radiographic outcomes of porous tantalum monoblock acetabular component in primary hip arthroplasty: a minimum of 15-year follow-up. J Arthroplasty 2016; 31(9): 110-14. FAR. Finnish Arthroplasty Register. www.thl.fi/far; 2018. Howard J L, Kremers H M, Loechler Y A, Schleck C D, Harmsen W S, Berry D J, Cabanela M E, Hanssen A D, Pagnano M W, Trousdale R T, Lewallen D G. Comparative survival of uncemented acetabular components following primary total hip arthroplasty. J Bone Joint Surg Am 2011; 93(17): 1597-604. Huotari K, Peltola M, Jämsen E. The incidence of late prosthetic joint infections. Acta Orthop 2015; 86(3): 21-5. Insull P J, Cobbett H, Frampton C M, Munro J T. The use of a lipped acetabular liner decreases the rate of revision for instability after total hip replacement: a study using data from the New Zealand joint registry. Bone Joint J 2014; 96-B(7): 884-8 Krushell R J, Burke D W, Harris W H. Elevated-rim acetabular components: effect on range of motion and stability in total hip arthroplasty. J Arthroplasty 1991; 6 Suppl: S53-8. Kurtz S M, Lau E, Watson H, Schmier J K, Parvizi J. Economic burden of periprosthetic joint infection in the United States. J Arthroplasty 2012; 27(8 Suppl): 61–5.e1. Laaksonen I, Lorimer M, Gromov K, Rolfson O, Mäkelä K T, Graves S E, Malchau H, Mohaddes M. Does the risk of rerevision vary between porous tantalum cups and other cementless designs after revision hip arthroplasty? Clin Orthop Relat Res 2017; 475(12): 3015-22. Laaksonen I, Lorimer M, Gromov K, Eskelinen A, Rolfson O, Graves S E, Malchau H, Mohaddes M. Trabecular metal acetabular components in primary total hip arthroplasty: higher risk for revision compared with other uncemented cup designs in a collaborative register study including 93,709 hips. Acta Orthop 2018; 89(3): 259-64.

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Levine B, Della Valle C J, Jacobs J J. Applications of porous tantalum in total hip arthroplasty. J Am Acad Orthop Surg 2006; 14(12): 646-55. Macheras G A, Kateros K, Koutsostathis S D, Tsakotos G, Galanakos S, Papadakis S A. The trabecular metal monoblock acetabular component in patients with high congenital hip dislocation: a prospective study. J Bone Joint Surg Br 2010; 92(5): 624-8. McCollum D E, Gray W J. Dislocation after total hip arthroplasty: causes and prevention. Clin Orthop Relat Res 1990; (261): 159-70. Meneghini R M, Ford K S, McCollough C H, Hanssen A D, Lewallen D G. Bone remodeling around porous metal cementless acetabular components. J Arthroplasty 2010; 25(5): 741-7. Mohaddes M, Rolfson O, Kärrholm J. Short-term survival of the trabecular metal cup is similar to that of standard cups used in acetabular revision surgery: analysis of 2,460 first-time cup revisions in the Swedish Hip Arthroplasty Register. Acta Orthop 2015; 86(1): 26-31. Paavolainen P, Hämäläinen M, Mustonen H, Slätis P. Registration of arthroplasties in Finland. Acta Orthop 1991; 241: 27-30. Pakarinen O, Neuvonen P, Eskelinen A. Luksaatioiden ilmaantuvuus ja riskitekijät lonkan ensitekonivelleikkauksissa—1381 leikkauksen aineisto Tekonivelsairaala Coxasta [article in Finnish, abstract in English]. Suom Ortop ja Traumatol 2018; 41(2): 142-8. Sultan P G, Tan V, Lai M, Garino J P. Independent contribution of elevatedrim acetabular liner and femoral head size to the stability of total hip implants. J Arthroplasty 2002; 17(3): 289-92. Tokarski A T, Novack T A, Parvizi J. Is tantalum protective against infection in revision total hip arthroplasty? Bone Joint J 2015; 97-B(1): 45-9. Weeden S H, Schmidt R H. The use of tantalum porous metal implants for Paprosky 3A and 3B defects. J Arthroplasty 2007; 22(6 Suppl.): 151-5. Wegrzyn J, Kaufman K R, Hanssen A D, Lewallen D G. Performance of porous tantalum vs. titanium cup in total hip arthroplasty: randomized trial with minimum 10-year follow-up. J Arthroplasty 2015; 30(6): 1008-13.

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Contemporary posterior surgical approach in total hip replacement: still more reoperations due to dislocation compared with direct lateral approach? An observational study of the Swedish Hip Arthroplasty Register including 156,979 hips Oscar SKOOGH 1, Georgios TSIKANDYLAKIS 1–3, Maziar MOHADDES 1–3, Szilard NEMES 2,3, Daniel ODIN 2, Peter GRANT 1, and Ola ROLFSON 1–3 1 Department

of Orthopaedics, Sahlgrenska University Hospital; 2 Swedish Hip Arthroplasty Register; 3 Department of Orthopaedics, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Sweden Correspondence: ola.rolfson@vgregion.se Submitted 2018-12-03. Accepted 2019-04-11.

Background and purpose — The direct lateral approach (DLA) and the posterior approach (PA) are the most common surgical approaches in total hip replacement (THR) in Sweden. We investigated how the relationship between surgical approach and risk of reoperation due to dislocation has evolved over time. Patients and methods — Data were extracted from the Swedish Hip Arthroplasty Register from 1999 to 2014. We selected all THRs due to osteoarthritis with head sizes 28, 32, and 36 mm that were performed with either the DLA or the PA. Resurfacing prostheses were excluded. Kaplan– Meier curves for risk of reoperation due to dislocation and all-cause for the 2 surgical approaches were compared for 2 periods (1999–2006 and 2007–2014) up to 2 years postoperatively. We used Cox regression for sex, age, type of fixation, and head size to determine hazard ratios (HR) with DLA set as reference. Results — 156,979 THRs met the selection criteria. In 1999–2006, the PA was associated with increased risk of reoperation due to dislocation (HR 2.3, 95% CI 1.7–3.0) but there was no difference in the risk of all-cause reoperation (HR 1.1, CI 0.9–1.2). In 2007–2014 there was no statistically significant difference in the risk of reoperation due to dislocation (HR 1.2, CI 0.9–1.6) but the risk of all-cause reoperation was lower (HR 0.8, CI 0.7–0.9) for the PA. Interpretation — This study confirms historic reports on the increased risk of early reoperations due to dislocations using the PA compared with the DLA. However, in contemporary practice, the higher risk of reoperation due to dislocation associated with PA has declined, now being similar to that after DLA. We believe improved surgical technique for the PA may explain the results. Surprisingly, the PA was associated with lower risk of all-cause reoperation in 2007– 2014. This finding warrants further investigation.

The posterior approach (PA) and the direct lateral approach (DLA) are the 2 principal surgical approaches for total hip replacement (THR) in Sweden (Kärrholm et al. 2017). There is no consensus regarding the optimum surgical approach to be used in primary THR (Jolles and Bogoch 2006). A majority of the dislocations occurs within the first 2 years postoperatively and is 1 of the most common early complications following THR (Hailer et al. 2012, Gausden et al. 2018). Multiple risk factors for dislocation have been identified such as surgical approach, orientation of components, femoral head size, previous surgery, age, sex, BMI, indication for surgery, and comorbidities such as neurological disability and spinal disease (Bystrom et al. 2003, Berry et al. 2005, Patel et al. 2007, Hailer et al. 2012, Fessy et al. 2017, Seagrave et al. 2017, Gausden et al. 2018). The PA has been associated with higher dislocation rate in comparison with the DLA (Robinson et al. 1980, Woo and Morrey 1982, Demos et al. 2001, Masonis and Bourne 2002, Bystrom et al. 2003, Jolles and Bogoch 2006, Hailer et al. 2012, Lindgren et al. 2012). However, enhanced soft tissue repair and improved surgical technique for the PA lower dislocation rates (Pellicci et al. 1998, White et al. 2001, Soong et al. 2004, Suh et al. 2004, Kwon et al. 2006, Kim et al. 2008, Zhou et al. 2017). According to the Swedish Hip Arthroplasty Register (SHAR), the PA and the DLA are used in 95% to 99% of the primary THRs in Sweden. The DLA that has increased from 37% in 1999 to 48% in 2014 at the expense of the PA, which has decreased from 60% in 1999 to 51% in 2014 (Figure 1). To our knowledge there are no studies comparing trends for the risk of reoperation due to dislocation for the PA and the DLA over a long period of time. In the light of improvements in surgical technique, we investigated how the relationship between surgical approach and risk of reoperation due to dislocation has evolved over time.

© 2019 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group, on behalf of the Nordic Orthopedic Federation. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits ­unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. DOI 10.1080/17453674.2019.1610269

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2

Distribution of approaches (%)

Table 1. Study demographics. Direct lateral and posterior approaches compared

100

1999–2006 2007–2014 Lateral Posterior Lateral Posterior n = 22,507 n = 37,691 p-value n = 44,933 n = 51,848 p-value

80

60

40

20

0

Posterior Lateral Other 2000 2002 2004 2006 2008 2010 2012 2014

Year of index operation

Figure 1. Distribution of posterior, direct lateral and other approaches among THRs performed in Sweden from 1999 to 2014.

Age, mean (SD) 68.7 (9.9) 69.6 (9.5) < 0.001 a 68.8 (9.7) 69.2 (9.5) < 0.001 a Female sex, n (%) 12,829 (57) 21,297 (57) 0.2 b 26,329 (59) 29,401 (57) < 0.001 b ASA-class, n (%) < 0.001 b I 9,994 (22) 10,160 (20) II 23,902 (53) 26,474 (51) III 5,599 (13) 7,069 (14) IV 143 (0.3) 168 (0.3) V 0 (0) 3 (0.0) Missing 5,295 (12) 7,974 (15) BMI, mean (SD) 27.3 (5.1) 27.5 (5.2) < 0.001 a Missing, n (%) 6,236 (14) 8,451 (16) a ANOVA, b Chi-squared

test

All THRs in Sweden 1999–2014 n = 226,254 Excluded (n = 69,275): – not osteoarthritis, 48,116 – resurfacing prosthesis, 2,258 – missing head size or not 28, 32, 36 mm, 10,838 – not posterior or lateral, 8,063 Study population n = 156,979

Figure 2. Patient selection flowchart. In order to reduce heterogeneity, the study population was defined according to preset selection criteria. Starting with all THRs in Sweden between 1999–2014 we applied the selection criteria to step-wise filter out relevant surgeries.

Patients and methods Since 1979, the SHAR has collected data from all units in Sweden performing THR. The completeness of primary registrations to the SHAR is 98% to 99%, and 93% for revisions (Kärrholm et al. 2017). Data we extracted from the Register included all patients who had primary THR due to osteoarthritis between 1999 and 2014. Resurfacing prostheses and head sizes other than 28, 32, and 36 mm were excluded. Only patients operated with PA or DLA were included (Figure 2). 156,979 hips met the selection criteria. SHAR started collecting data on ASA class and BMI in 2008 (Table 1). Outcome measures Primary outcome measure was first reoperation due to dislocation as reported to the register within 2 years following index surgery. Secondary outcome was all-cause reoperation within 2 years. A reoperation was defined as any further open surgery to the hip, regardless of implant components being removed, exchanged, added, or not. Thus, surgeries such as gluteus

maximus repair, tenotomy, and hip arthroscopy were included among reoperations. Statistics We used 1-way ANOVA test (with equal variance assumption) for continuous demographic variables (age and BMI) and chi-square test (with continuity correction) for categorical variables (sex, fixation, head size, ASA, and cause of reoperation). Kaplan–Meier curves for posterior and direct lateral surgical approaches were compared for 2 different time periods (1999–2006 and 2007–2014) until 2 years follow-up. We used data from both operations if patients were bilaterally operated during the study period; the violation of the assumption of independent observations was considered not to have any practical implications (Ranstam et al. 2011). Each hip was followed from primary THR to first reoperation. Hips were censored at death, reoperation, or at 2 years after primary surgery, whichever came first. For the dislocation analyses, all other first reoperations were censored. Cox regression analyses were used to compare hazard ratios (HR) with and without adjustments with 95% confidence intervals (CI). We adjusted for sex, age, fixation method (cemented, uncemented, hybrid, and reversed hybrid) and head size (except for 1999–2006 as 99% of hips had 28-mm head size). Proportional assumption was checked graphically. Divided by year of surgery and for PA and DLA separately, we calculated Kaplan–Meier survival estimates with reoperation due to dislocation at 2 years as endpoint. The uncertainty of the Kaplan–Meier estimates was indicated by CIs. Linear regression was used to determine whether the linear trend was statistically significant. A p-value of less than 0.05 indicated statistical significance. R software version 3.4.2 (R Core Team 2017) was used for all analyses with “survival” packages “A Package for Survival Analysis in S” and “ggplot2” (Therneau 2015, Wickham 2016).

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Figure 3. Kaplan Meier estimates for not being reoperated due to dislocation within 2 years for posterior and direct lateral surgical approaches during 1999–2006 and 2007–2014. Shaded area are 95% confidence intervals.

Ethics, funding, and potential conflicts of interest The Regional Ethical Review Board in Gothenburg approved the study (entry number 804-17). The study received grants from the Handlaren Hjalmar Svensson fund. Grants from the Swedish state under the agreement between the Swedish government and the county councils, the ALF-agreement (ALFGBG–522591) also contributed to the study. The authors have no conflicts of interest.

Results

Figure 4. Kaplan-Meier estimates for not being reoperated up to 2 years (all causes) for posterior and direct lateral surgical approaches during 1999–2006 and 2007–2014. Shaded area are 95% confidence intervals.

Table 2. Cox regression analyses were used to compare hazard ratio (HR) for reoperation due to dislocation and reoperation due to all causes within 2 years with and without adjustments for time periods 1999–2006 and 2007–2014 Reoperation cause

1999–2006 2007–2014 HR (95% CI) p-value HR (95% CI) p-value

Dislocation Unadjusted Adjusted Posterior approach (ref. direct lateral approach) Age Female (ref. male) Hybrid (ref. cemented) Reverse hybrid (ref. cemented) Uncemented (ref. cemented) 32-mm head (ref. 28-mm head) 36-mm head (ref. 28-mm head) All causes Unadjusted Adjusted Posterior approach (ref. direct lateral approach) Age Female (ref. male) Hybrid (ref. cemented) Reverse hybrid (ref. cemented) Uncemented (ref. cemented) 32-mm head (ref. 28-mm head) 36-mm head (ref. 28-mm head)

As indicated in the Kaplan–Meier curves, the risk of reoperation due to dislocation in 1999–2006 was statistically significantly higher for the PA almost directly postoperatively (Figure 3). PA was associated with higher risk of reoperation due to dislocation in 1999–2006 (HR 2.3, CI 1.7–3.0) but not in 2007–2014 (HR 1.2, CI 0.9–1.6) compared with the DLA (Table 2). All-cause reoperation Kaplan–Meier estimates for the 2 approaches were similar for the first period. For the period 2007–2014, however, the Kaplan– Meier curves indicated a higher risk of reoperation due to all causes for the DLA starting at approximately 1 year postoperatively (Figure 4). PA was associated with similar risk of all-cause reoperation in 1999–2006 (HR 1.1, CI 0.9–1.2) compared with the DLA (Table 2). In 2007–2014, PA was associated with statistically significantly lower risk of reoperation due to all causes (HR 0.8, CI 0.7–0.9) compared with the DLA (Table 2).

2.2 (1.7–2.9) < 0.001

1.1 (0.9–1.5)

2.3 (1.7–3.0) < 0.001 1.0 (1.0–1.0) < 0.001 0.8 (0.6–1.0) 0.03 1.1 (0.5–2.4) 0.8 1.6 (0.8–3.1) 0.2 1.8 (1.0–3.3) 0.07 N/A N/A

1.2 (0.9–1.6) 0.2 1.0 (1.0–1.0) 0.004 0.9 (0.7–1.1) 0.4 2.0 (0.9–4.6) 0.1 0.9 (0.6–1.5) 0.8 2.7 (1.9–3.9) < 0.001 0.7 (0.5–0.9) 0.01 0.6 (0.4–1.1) 0.09

1.0 (0.9–1.2)

0.8 (0.7–0.9) < 0.001

0.8

1.1 (0.9–1.2) 0.4 1.0 (1.0–1.0) 0.002 0.8 (0.7–0.9) < 0.001 1.1 (0.8–1.6) 0.6 1.9 (1.4–2.6) < 0.001 1.5 (1.1–2.0) 0.02 N/A N/A

0.8 (0.7–0.9) 1.0 (1.0–1.0) 0.7 (0.7–0.8) 1.0 (0.7–1.6) 1.5 (1.3–1.7) 1.9 (1.6–2.2) 1.0 (0.9–1.1) 1.1 (0.9–1.4)

0.3

< 0.001 < 0.001 < 0.001 1.0 < 0.001 < 0.001 0.9 0.5

Split by year for primary surgery, the trend analysis of Kaplan–Meier estimates for not being reoperated due to dislocation at 2 years demonstrated positive linear trends for both the DLA (p < 0.05) and the PA (p < 0.01) (Figure 5).

Discussion This study confirms historic reports on the increased risk of early reoperations due to dislocations using the PA compared

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Table 3. Distribution of method of fixation, head size and different causes for reoperation within 2 years for direct lateral and posterior approaches during 1999–2006 and 2007–2014. Chi-squared test was used. Values are frequency (%)

Dislocation survival at 2 years (%) 100

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1999–2006 2007–2014 Lateral Posterior Lateral Posterior 98 n = 22,507 n = 37,691 p-value n = 44,933 n = 51,848 p-value Method of fixation < 0.001 < 0.001 Cemented 18,171 (81) 35,050 (93) 30,919 (69) 37,532 (72) Hybrid 1,219 (5.4) 869 (2.3) 609 (1.4) 933 (1.8) Reverse hybrid 1,002 (4.5) 908 (2.4) 5,975 (13) 6,272 (12) Uncemented 2,115 (9.4) 864 (2.3) 7,430 (17) 7,111 (14) Head size (mm) < 0.001 < 0.001 28 22,386 (99) 37,479 (99) 22,239 (50) 19,799 (38) 32 119 (0.5) 179 (0.5) 21,885 (49) 27,586 (53) 36 2 (0.0) 33 (0.1) 809 (1.8) 4,463 (8.6) Reoperations within 2 years < 0.001 < 0.001 Aseptic loosening 43 (0.2) 37 (0.1) 111 (0.2) 81 (0.2) Fracture 41 (0.2) 70 (0.2) 96 (0.2) 147 (0.3) Infection 124 (0.6) 180 (0.5) 486 (1.1) 441 (0.9) Dislocation 60 (0.3) 220 (0.6) 136 (0.3) 185 (0.4) Other 52 (0.2) 42 (0.1) 138 (0.3) 68 (0.1) Not reoperated 22,187 (99) 37,142 (99) 43,966 (98) 50,926 (98)

with the DLA in primary THR due to OA. However, in contemporary practice, the higher risk associated with PA had declined and did not entail a statistically significant increased risk of reoperation due to dislocation within 2 years from primary surgery compared with DLA. Surprisingly, the PA was associated with lower risk of reoperation due to all causes. Despite differences in head size, fixation type, and demography between groups, adjusting for confounders did not alter the results. In this nationwide observational study, the rate of reoperations due to dislocation within 2 years following THR for OA was 0.6% in 1999–2006 and 0.4% in 2007–2014 for the PA, and 0.3% in 1999–2006 and 0.3% in 2007–2014 for the DLA. In the meta-analyses by Kwon et al. (2006) regarding 11 papers between 1997 and 2004 the dislocation rate for the DLA was 0.4% while it was 1.0% for the PA. In the review by Masonis and Bourne (2002) of 14 studies between 1976 and 2001 involving 13,203 primary THRs the dislocation rate was estimated as 6 times higher for the PA (3%) than the DLA (0.5%). According to a study by Hailer et al. (2012) with data from the SHAR on 78,098 THRs in 61,743 patients performed between 2005 and 2010 there was a 1.3 times increased relative risk of revision due to dislocation for the PA compared with the DLA with mean follow-up of 2.7 (0–6) years. However, in our study PA was not associated with higher risk of reoperation due to dislocation in 2007–2014. There are important differences between ours and other studies when it comes to, e.g., selection criteria, time period, follow-up time, and use of components that have to be considered when comparing. We believe there has been an ongoing refinement of the surgical technique in THR over the years. For instance, in our study we found an extensive increase in head sizes larger than 28 mm in 2007–2014 compared with

97

96

Lateral Posterior 2000 2002 2004 2006 2008 2010 2012 2014

Year of index operation

Figure 5. Annual Kaplan Meier estimates (and 95% confidence intervals) for not being reoperated due to dislocation at 2 years after primary THR for posterior and direct lateral approach. Linear regression was used to investigate if the linear trend was statistically significant. Lateral, p < 0.05 and posterior, p < 0.001.

1999–2006 (Table 3). According to a study by Berry et al. (2005) including 21,047 primary THRs performed in a single institution between 1969 and 1999, the relative risk of dislocation was 1.3 for 28 mm heads compared with 32 mm heads. This is consistent with our study where the 32 mm heads were associated with a statistically significantly lower risk of reoperation due to dislocation up to 2 years (HR 0.7, CI 0.5–0.9) compared with 28 mm heads (Table 2). However, 36 mm heads were not associated with lower risk of reoperation due to dislocation (HR 0.6, CI 0.4–1.1) in our study (Table 2). Larger head size and implant use may certainly explain some of the overall improvement in reoperation rates within 2 years for the 2 approaches investigated. However, we believe it is unlikely that the use of larger head size accounts for all the improvement. In 1999–2006, more than 99% of the THRs in Sweden were performed with 28 mm heads for both DLA and PA. Divided by year of primary surgery, improvement trend in annual Kaplan–Meier estimates was much more pronounced for PA compared with DLA (Figure 5). The increased reoperation-free survival for PA was evident already in 1999–2006. In those years, more than 99% of THRs were operated with 28 mm heads. Hence, the improvement for the PA in 1999–2006 is not attributable to use of larger head sizes. As discussed below, improved surgical technique may contribute to the positive trend for PA. Lindgren et al. (2014) used the SHAR to study 42,233 patients undergoing primary THR for OA operated between 2002 and 2010 and found that the PA was associated with slightly better patient-reported outcomes compared with the DLA. Hence, we believe the possible difference in PROMs should be considered in the choice of THR approach in OA patients.

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To our knowledge there is no other study that has compared dislocation survival trends for the DLA and PA for such a long period of time. Our data from the SHAR showed statistically significant positive linear trends for both surgical approaches regarding the risk of being reoperated due to dislocation within 2 years after primary THR for OA in Sweden (Figure 5). This improvement over time was most apparent for the PA. Since its inception in 1979, Swedish orthopedic surgeons have been influenced by the reports of SHAR. Register findings discussed at internal meetings in the mid-2000s indicated an increased risk of revision for the PA and, as demonstrated here, the use of the DLA increased at the expense of the PA. Between 2001 and 2006, a large body of research, including clinical trials, meta-analyses, and literature reviews, suggested that improved surgical technique with soft tissue repair following the PA in primary THR would reduce the risk of dislocation (Masonis and Bourne 2002, Mahoney and Pellicci 2003, Soong et al. 2004, Suh et al. 2004, Kwon et al. 2006). However, Hailer et al. (2012) concluded that patients with femoral neck fracture or osteonecrosis of the femoral head were at higher risk of dislocation and raised the question as to whether patients belonging to risk groups should be operated using lateral approaches. Furthermore, in a study by Enocson et al. (2009) on 713 consecutive hips, the use of the anterolateral approach for THR in patients with femoral neck fractures was advocated. In the 2011 annual report, the SHAR reported specifically on the increased risk of revision due to dislocation for the PA compared with the DLA (Garellick et al. 2012). None of the surgical approaches were considered superior in adult patients undergoing THR for OA, which was consistent with the Cochrane review by Jolles and Bogoch (2006). However, the SHAR advocated the use of the DLA in patients with risk factors for dislocation (Garellick et al. 2012). These reports likely influenced surgeons’ awareness and provided evidence for improvements in the PA surgical technique. Strengths and limitations The SHAR has a high completeness on primary THR ranging from 98% to 99% and intentionally includes all reoperations and not only revisions. The SHAR has nationwide coverage, which makes the results generalizable. Hence, geographical differences are not likely to affect the results. The inclusion criteria contribute to a more homogeneous study population. The choice of surgical approach for the selected population has most likely been influenced by the local tradition at each hospital rather than patient-specific attributes, which in turn affect the risk of reoperation due to dislocation. The lack of data on BMI and ASA from 1999 to 2006 (given that the SHAR did not start the registration of those variables until 2008) means we were not able to adjust for these confounding factors. Another limitation pertains to the lack of information on the extent of soft tissue repair or the

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orientation of components. Furthermore, we did not include information on prosthesis type or surgeons’ experience. The SHAR does not capture information on closed reductions. It is unlikely, however, that dislocations can be treated non-surgically at higher success rates with one or the other approach. To what extent the recommendations from the SHAR’s Annual Reports may have caused a selection bias, with complex OA cases with higher anticipated dislocation risk having been operated through a DLA, is uncertain. The skewed accumulation of bigger head sizes and more cemented THRs in the PA group may have favored this surgical approach regarding dislocation survival; however, the accumulation of fewer women and older patients may have disfavored it. The differences between the groups are statistically significant but seemingly small and adjusted for in the statistical analyses. Conclusion In this nationwide observational study, we demonstrate that the historic increased risk of reoperation due to dislocation within 2 years for the PA compared with the DLA has declined substantially in contemporary Swedish THR practice. We believe enhanced surgical technique for the PA, increased awareness of the historically higher dislocation risk of PA, or possibly selection bias may explain this finding. The PA was associated with lower risk of reoperation due to all causes in 2007–2014 compared with the DLA. These findings warrant further research.

OR and MM conceived and designed the study. DO and SN performed statistical analysis. OS drafted the manuscript. All authors interpreted the results, contributed to the discussion, and reviewed the manuscript. Acta thanks Stephan M Röhrl for help with peer review of this study.

Berry D J, von Knoch M, Schleck C D, Harmsen W S. Effect of femoral head diameter and operative approach on risk of dislocation after primary total hip arthroplasty. J Bone Joint Surg Am 2005; 87(11): 2456-63. Byström S, Espehaug B, Furnes O, Havelin L I. Femoral head size is a risk factor for total hip luxation: a study of 42,987 primary hip arthroplasties from the Norwegian Arthroplasty Register. Acta Orthop Scand 2003; 74(5): 514-24. Demos H A, Rorabeck C H, Bourne R B, MacDonald S J, McCalden R W. Instability in primary total hip arthroplasty with the direct lateral approach. Clin Orthop Relat Res 2001; (393): 168-80. Enocson A, Hedbeck C J, Tidermark J, Pettersson H, Ponzer S, Lapidus L J. Dislocation of total hip replacement in patients with fractures of the femoral neck. Acta Orthop 2009; 80(2): 184-9. Fessy M H, Putman S, Viste A, Isida R, Ramdane N, Ferreira A, et al. What are the risk factors for dislocation in primary total hip arthroplasty? A multicenter case-control study of 128 unstable and 438 stable hips. Orthop Traumatol Surg Res 2017; 103(5): 663-8. Garellick G, Kärrholm J, Rogmark C, Rolfson O, Herberts P. The Swedish Hip Arthroplasty Register, Annual Report 2011; 2012.

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Gausden E B, Parhar H S, Popper J E, Sculco P K, Rush B N M. Risk factors for early dislocation following primary elective total hip arthroplasty. J Arthroplasty 2018; 33(5): 1567-71. Hailer N P, Weiss R J, Stark A, Kärrholm J. The risk of revision due to dislocation after total hip arthroplasty depends on surgical approach, femoral head size, sex, and primary diagnosis: an analysis of 78,098 operations in the Swedish Hip Arthroplasty Register. Acta Orthop 2012; 83(5): 442-8. Jolles B M, Bogoch E R. Posterior versus lateral surgical approach for total hip arthroplasty in adults with osteoarthritis. Cochrane Database of Systematic Reviews 2006; (3) CD003828. Kim Y S, Kwon S Y, Sun D H, Han S K, Maloney W J. Modified posterior approach to total hip arthroplasty to enhance joint stability. Clin Orthop Relat Res 2008; 466(2): 294-9. Kwon M S, Kuskowski M, Mulhall K J, Macaulay W, Brown T E, Saleh K J. Does surgical approach affect total hip arthroplasty dislocation rates? Clin Orthop Relat Res 2006; 447: 34-8. Kärrholm J, Lindahl H, Malchau H, Mohaddes M, Nemes S, Rogmark C, et al. The Swedish Hip Arthroplasty Register, Annual Report 2016; 2017. Lindgren V, Garellick G, Kärrholm J, Wretenberg P. The type of surgical approach influences the risk of revision in total hip arthroplasty: a study from the Swedish Hip Arthroplasty Register of 90,662 total hip replacements with 3 different cemented prostheses. Acta Orthop 2012; 83(6): 55965. Lindgren J V, Wretenberg P, Kärrholm J, Garellick G, Rolfson O. Patientreported outcome is influenced by surgical approach in total hip replacement: a study of the Swedish Hip Arthroplasty Register including 42,233 patients. Bone Joint J 2014; 96-b(5): 590-6. Mahoney C R, Pellicci P M. Complications in primary total hip arthroplasty: avoidance and management of dislocations. Instructional Course Lectures 2003; 52: 247-55. Masonis J L, Bourne R B. Surgical approach, abductor function, and total hip arthroplasty dislocation. Clin Orthop Relat Res 2002; (405): 46-53.

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Acta Orthopaedica 2019; 90 (3): 220–225

Body mass index is associated with risk of reoperation and revision after primary total hip arthroplasty: a study of the Swedish Hip Arthroplasty Register including 83,146 patients Arkan S SAYED-NOOR 1, Sebastian MUKKA 1, Maziar MOHADDES 2,3, Johan KÄRRHOLM 2,3, and Ola ROLFSON 2,3 1 Department 3 Department

of Surgical and Perioperative Sciences, Umeå University, Umeå; 2 Swedish Hip Arthroplasty Register, Centre of Registers, Gothenburg; of Orthopaedics, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden Correspondence: arkansam@yahoo.com Submitted 2018-11-05. Accepted 2019-02-01.

Background and purpose — The prevalence of obesity is on the rise, becoming a worldwide epidemic. The main purpose of this register-based observational study was to investigate whether different BMI classes are associated with increased risk of reoperation within 2 years, risk of revision within 5 years, and the risk of dying within 90 days after primary total hip arthroplasty (THA). We hypothesized that increasing BMI would increase these risks. Patients and methods — We analyzed a cohort of 83,146 patients who had undergone an elective THA for primary osteoarthritis between 2008 and 2015 from the Swedish Hip Arthroplasty Register (SHAR). BMI was classified according to the World Health Organization (WHO) into 6 classes: < 18.5 as underweight, 18.5–24.9 as normal weight, 25–29.9 as overweight, 30–34.9 as class I obesity, 35–39.9 as class II obesity, and ≥ 40 as class III obesity. Results — Both unadjusted and adjusted parameter estimates showed increasing risk of reoperation at 2 years and revision at 5 years with each overweight and obesity class, mainly due to increased risk of infection. Uncemented and reversed hybrid fixations and surgical approaches other than the posterior were all associated with increased risk. Obesity class III (≥ 40), male sex, and increasing ASA class were associated with increased 90-day mortality. Interpretation — Increasing BMI was associated with 2-year reoperation and 5-year revision risks after primary THA where obese patients have a higher risk than overweight or normal weight patients. As infection seems to be the main cause, customizing preoperative optimization and prophylactic measures for obese patients may help reduce risk.

The prevalence of obesity is on the rise, becoming a worldwide epidemic. Currently, more than two-thirds of Americans are classified as obese (Yang and Colditz 2015). In obese patients, total hip arthroplasty (THA) can be challenging because the extensive adipose tissue can compromise optimal surgical technique, prolong operative time, and increase intraoperative bleeding and risk for postoperative complications (Bowditch and Villar 1999, Liu et al. 2015, Wooten and Curtin 2016, Krauss et al. 2018). The effect of BMI on functional outcome, quality of life, and complication rate following THA has been investigated in a number of studies (Vincent et al. 2012, Liu et al. 2015, Haynes et al. 2017, Barrett et al. 2018). As BMI increases, the functional improvement and quality of life after THA may deteriorate. Based on this presumed increased risk, the American Association of Hip and Knee Surgeons Workgroup released a statement recommending that arthroplasty operations in patients with a BMI > 40 be delayed, especially in the setting of other comorbid conditions (Workgroup of the American Association of Hip and Knee Surgeons Evidence Based Committee 2013). However, only a limited number of studies reporting perioperative complications have been based on population-based cohorts (Murgatroyd et al. 2014, Ward et al. 2015, Husted et al. 2016, Wagner et al. 2016, Jung et al. 2017, Werner et al. 2017, Zusmanovich et al. 2018, DeMik et al. 2018, Jeschke et al. 2018). The main purpose of this register-based cohort study was to investigate whether under- or overweight, separated into BMI classes, is associated with increased risk of reoperation within 2 years, risk of revision within 5 years, and the risk of dying within 90 days after primary total hip arthroplasty. We hypothesized that increasing BMI would negatively influence the reoperation, revision, and mortality risks.

© 2019 The Author(s). Published by Taylor & Francis on behalf of the Nordic Orthopedic Federation. This is an Open Access article distributed under the terms of the Creative Commons Attribution-Non-Commercial License (https://creativecommons.org/licenses/by/4.0) DOI 10.1080/17453674.2019.1594015

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All THR 2008–2015 n = 127,663

Patients and methods Study design and setting The Swedish Hip Arthroplasty Register (SHAR) was launched in 1979 to prospectively monitor THAs performed in Sweden and to evaluate the performance of implants, fixation methods, and surgical techniques. The register covers all publicly and privately funded hospitals performing THA. The completeness of registration for primary THAs is between 97% and 99%. A unique patient identifier, the personal identity number, provides information on date of birth and sex. For each operation, participating hospitals record variables such as implant article number, type of fixation, and surgical approach. In 2008, information on American Association of Anesthesiologists’ physical status classification (ASA), weight, and height were added to the routine data collection. We followed the STROBE guidelines (von Elm et al. 2014). Patient selection Patients included in this observational study met the following criteria: primary osteoarthritis (International Classification of Diseases [ICD] M16.0 and M16.1) operated with THA between January 1, 2008 and December 31, 2015 using traditional (not resurfacing) implants with uncemented, cemented, hybrid, or reversed hybrid fixation. In patients with bilateral THA during the study period, we included only records concerning the first THA. Patients with missing documentation regarding BMI or ASA class were excluded. BMI was classified according to the World Health Organization (WHO) into 6 classes: < 18.5 as underweight, 18.5–24.9 as normal weight, 25–29.9 as overweight, 30–34.9 as class I obesity, 35.0–39.9 as class II obesity, and ≥ 40 as class III obesity. Outcome measures Reoperation is defined as any kind of subsequent open surgical procedure related to the inserted arthroplasty, no matter whether the arthroplasty, or any of its parts, is replaced, extracted, or left untouched. Revision is defined as a subsequent procedure where at least 1 part of the prosthesis is exchanged, added to, or extracted. All revisions are also classified as reoperations, but not all reoperations are revisions. The outcome measures of this study include: 1. Reoperations within the first 2 years from the index THA procedure, including all types of open surgical procedures to the hip and for any reason; 2. Revisions within the first 5 years from the index THA procedure. For first-time procedures, a revision in the SHAR is defined as exchange or removal of one or more implant component(s); 3. 90-day mortality. The mortality data are obtained by crossmatching data from SHAR with the Swedish Population Register, governed by the Swedish Tax Office.

Excluded (n = 44,517): – second hip, 14,853 – resurfacing, 1,010 – not OA, 23,140 – ASA and/or BMI missing, 5,514 Study group n = 83,146

Figure 1. Flowchart of patients through the study.

Causes of reoperation and revision were categorized into loosening/osteolysis, dislocation, infection, and other. Confounders A priori, we decided to include the age, sex, ASA class, fixation method, and surgical approach as confounders. These variables have previously demonstrated association with both exposure and outcome and are not considered to be in the causal pathway between potential risk factors and outcome. Statistics Survival estimates (with 95% confidence intervals [CI]) for not being reoperated within 2 years, not revised within 5 years, and being alive within 90 days were calculated using Kaplan–Meier survival analysis. The assumption of proportionality was checked graphically. Simple and multiple Cox regression analyses were applied to calculate unadjusted and adjusted hazard ratios (HR). We adjusted for age, sex, ASA class, fixation method, and surgical approach at primary surgery. R version 3.4.4 (https://www.r-project.org) was used to perform all analyses. Ethics, funding, and potential conflicts of interests The study was conducted in accordance with the ethical principles of the Helsinki Declaration and was approved by the Regional Ethical Review Board in Gothenburg, Sweden (decision 271-14). There was no external funding for the project and no competing interest to declare.

Results 127,663 primary THAs, registered in SHAR between January 1, 2008 and December 31, 2015 were primarily included. After exclusion of resurfacing arthroplasties, second hip THA, patients with secondary OA, and those with missing data, 83,146 patients (mean age 69 years, 57% females) remained for analysis (Figure 1, Table 1). The majority of patients were normal weight or overweight. Age at operation decreased and the ASA class increased with increasing

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Table 1. Demography per BMI class Factor Underweight

Normal weight Overweight

Class I obesity

Class II obesity

Class III obesity

All patients

Number of patients 579 ( 25,718 ( 36,301 ( 15,751 ( 3,939 ( 858 ( 83,146 ( Age, mean (SD) 73 (11) 70 (10) 69 (10) 67 (9) 65 (9) 64 (9) 69 (10) Female sex, n (%) 516 (89) 16,721 (65) 18,360 (51) 8,568 (54) 2,455 (62) 590 (69) 47,210 (57) ASA, n (%) I 125 (22) 7,998 (31) 9,147 (25) 2,499 (16) 272 (6.9) 54 (6) 20,095 (24) II 330 (57) 14,519 (56) 22,356 (62) 10,120 (64) 2,224 (57) 391 (46) 49,940 (60) III 116 (20) 3,120 (12) 4,675 (13) 3,067 (19) 1,416 (36) 398 (46) 12,792 (15) IV/V 8 (1) 81 (0.3) 123 (0.3) 65 (0.4) 27 (1) 15 (2) 319 (0.4) Fixation, n (%) All cemented 464 (80) 18,146 (71) 24,342 (67) 10,359 (66) 2,532 (64) 539 (63) 56,382 (68) All uncemented 46 (8) 3,839 (15) 6,342 (17) 2,890 (18) 775 (20) 186 (22) 14,078 (17) Hybrid 16 (3) 562 (2) 676 (2) 281 (2) 65 (2) 20 (2) 1,620 (2) Reversed hybrids 53 (9) 3,171 (12) 4,941 (14) 2,221 (14) 567 (14) 113 (13) 11,066 (13) Surgical approach, n (%) Posterior 273 (47) 13,044 (51) 19,049 (53) 8,496 (54) 2,119 (54) 477 (56) 43,458 (52) Direct lateral 253 (44) 10,859 (42) 15,046 (41) 6,435 (41) 1,643 (42) 353 (41) 34,589 (42) Other 53 (9) 1,813 (7) 2,205 (6) 818 (5) 177 (5) 28 (3) 5,094 (6)

Figure 2. Kaplan–Meier 2-year reoperation estimates by BMI class (including CIs).

Figure 3. Kaplan–Meier 5-year implant survival estimates by BMI class (including CIs). For color codes, see Figure 2.

weight and obesity class. The dominating fixation technique was cemented and a posterior approach was used in nearly half of the operations. Table 2 (see Supplementary data) presents survival estimates at 2 years for reoperation, 5 years for revision, and 90 days for mortality among the 6 BMI classes. Risk of reoperation within 2 years The probability of reoperation increased in overweight and obesity classes I–III (Figure 2). Both unadjusted and adjusted parameter estimates showed increasing risk of reoperation at 2 years with each overweight and obesity class, mainly due to increased risk of infection, whereas the HR for underweight was similar to the reference category normal weight (Tables 2 and 3, see Supplementary data). The 2-year risk of reopera-

Figure 4. Kaplan–Meier 90-day mortality estimates by BMI class. For color codes, see Figure 2.

tion was higher in men and increased with higher ASA class. Uncemented fixation and reversed hybrid fixations, and other surgical approaches than the posterior were all associated with increased risk. Risk of revision within 5 years The probability of not being revised was lower in BMI overweight and obesity classes I–III (Figure 3). Both unadjusted and adjusted parameter estimates showed increasing risk of revision at 5 years with each overweight and obesity class, mainly due to increased risk of infection, while the HR for underweight was similar to the reference category normal weight (Tables 2 and 3, see Supplementary data). The 5-year risk of revision was higher in men and increased with higher ASA class. Uncemented fixation and reversed hybrid fixa-

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tions, and other surgical approaches than the posterior were all associated with increased risk. 90-day mortality Underweight and obesity class III were associated with higher mortality compared with the other BMI classes (Figure 4). However, HRs for BMI classes were not statistically significantly higher compared with normal weight (Table 3, see Supplementary data). In the multiple regression model, only obesity class III (≥ 40), male sex, and increasing ASA class were associated with increased risk.

Discussion The impact of bodyweight on the occurrence and progression of hip OA as well as on the early and late results of THA has been in focus during the last 2 decades. Several studies have shown that overweight may be associated with hip OA symptoms, motivating THA at early ages (Harms et al. 2007, Changulani et al. 2008, Gandhi et al. 2010). Furthermore, increased BMI has been linked to higher risks for perioperative complications such as bleeding, infection, and dislocation, even though there is still a debate over the validity of some of these results (Vincent et al. 2012, Liu et al. 2015, Haynes et al. 2017, Barrett et al. 2018). The concept of obesity paradox, i.e., the favourable and protective effect of obesity on some aspects of the outcome of THA, has been raised (Shaparin et al. 2016, Zhang et al. 2018). By definition, obesity class I and II would yield an ASA class of II or above and obesity class III would yield ASA class III or above. Although there was a clear pattern with higher ASA class for the obesity levels, not all patients were classified as per the definition. This highlights the interrater variation in assessment of ASA class and possible local traditions among anesthesiologists in how the ASA classification system is applied (Sankar et al. 2014). Nevertheless, we believe this also reflects the result of an overall assessment of perioperative risk factors where some otherwise healthy obese patients are classified lower than as defined by the classification system. In our study, patients with class III obesity were younger. This concurs with other studies (Harms et al. 2007, Changulani et al. 2008, Gandhi et al. 2010). Changulani et al. (2008) studied the relationship between obesity and age among 1,025 THA patients and found that the morbidly obese were 10 years younger on average than those with a normal BMI. In their systematic review, Haynes et al. (2017) also found that obesity was associated with younger age at time of primary THA. These findings agree with a review of registry data from the Mayo Clinic (Singh and Lewallen 2014), which showed a decrease in the mean age of patients undergoing primary THA by 0.7 years. This was inversely associated with an increase of 1.6 in the BMI of primary THA patients over the same study

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period (1993–2005). A possible explanation for this association might be the increased pain sensitivity, high-level forces/ wear on the joint surface, and the lower physical activity in morbidly obese patients. We found an association of BMI class with increasing risk of reoperation within 2 years and revision within 5 years, mainly due to increased risk of infection (Table 2). This concurs with a recent report using German nationwide billing data for inpatient hospital treatment covering more than 130,000 THAs. In this report, Jeschke et al. (2018) found increased overall postoperative complication and 1-year revision rates with higher BMI class. Similar to our results, they found that 90-day mortality increased only in class III obesity patients. Other studies have demonstrated increased postoperative infection and dislocation rates both after primary and revision THA with increasing BMI (Vincent et al. 2012, Pulos et al. 2014, Houdek et al. 2015, Liu et al. 2015, Haynes et al. 2017, Barrett et al. 2018, Kennedy et al. 2018). Contrary to the above-mentioned results, some reports showed comparable postoperative complication rates across BMI classes (Davis et al. 2011, McCalden et al. 2011, Watts et al. 2016). This divergence requires further attention and analysis. Increased BMI is associated or has a causal relationship with medical comorbidities such as diabetes mellitus, and cardiovascular disorders, as well as antibiotic resistance. Moreover, THA in obese patients may be more surgically demanding as the voluminous deep adipose tissue, weak fatty-infiltrated periarticular soft-tissue envelope, and obscured anatomical landmarks may result in suboptimal positioning of THA components, prolonged operative time, and wound problems (Elson et al. 2013, Hanly et al. 2016). Higher weight increases load and forces on THA components, which potentially increases the risk of wear and implant loosening. However, a sedentary lifestyle might counteract this risk for wear and aseptic loosening. The above-mentioned parameters may, at least partly, explain the negative impact of increased BMI on 2-year reoperation and 5-year revision outcomes. Interestingly, we found comparable risks for reoperation within 2 years and revision within 5 years due to mechanical complications (loosening and dislocation) among the BMI classes (Table 2, see Supplementary data). Patients with increased BMI may also have some positive aspects such as adequate nutrition, careful preoperative preparation and surgical technique usually performed by more experienced surgeons, more active postoperative medical care, and physical rehabilitation and follow-up. These aspects can be protective to some extent, but apparently not for patients with a very high BMI such as class III obesity. This study has some limitations. SHAR does not capture all reoperations. The completeness of registrations of revisions is higher than that of other reoperations where components are not removed, exchanged, or added. Also, there are missing data in the reporting of weight and height. There is no reason to suspect a systematic underreporting of BMI or reop-

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erations based on BMI. However, the most common cause for a reoperation without revising implants is periprosthetic infection. Given that high BMI is a risk factor for infection, the underreporting may distribute differently between BMI classes. Hence, the higher risk of reoperation associated with increasing BMI class may be underestimated. Despite the comprehensive set of variables included in SHAR, parameters such as smoking, type of comorbidities, nutritional status, OA severity, surgical complexity, and surgeon experience were not available. Therefore, as with most register-based studies, residual confounding likely exists. Also, we did not correct for multiple testing; however, confounders were selected a priori and based on previous established relationships. The methods for measuring weight and height are heterogeneous and include estimates by health care professionals, patientreported values, and actual measurements at the preoperative assessment. Another limitation pertains to the use of BMI as a surrogate measure for excess fat although it does not distinguish between the distributions of fat, muscles, and bone mass. On average, women have greater amounts of total body fat than men with an equivalent BMI, while muscular highly trained athletes may have a high BMI because of increased muscle mass. Furthermore, there are numerous factors related to genetics, and the physical and social environment including comorbidities that will influence the body mass index. Thus, BMI could be viewed as a proxy for known and unknown factors related to the health status of the patient, but is as such attractive to use because it can be easily measured. Multiple comparisons among the BMI classes is another limitation. These limitations are counterbalanced by the strength of study: a nationwide large study group using a register with high completeness and validity. The inclusion of not only revisions as an endpoint but also any reoperation adds to the strength of the study. In summary, BMI classes were associated with reoperation and revision risks after primary THA, where morbidly obese patients have more than a doubled risk than obese or normal weight patients. As infection seems to be the main cause, customizing preoperative optimization and prophylactic measures for obese patients may help reduce risk. Furthermore, many clinical aspects could be addressed such as adequate antibiotic prophylaxis, e.g., weight-adjusted as well as the use of incisional vacuum-assisted closure in overweight patients. Although BMI is a well-established risk factor for complications following THA, this is the first study focusing on BMI and outcomes in a Swedish context. This will help inform surgeons and their patients on risks related to BMI classes. Supplementary data Tables 2–3 are available as supplementary data in the online version of this article, http://dx.doi.org/ 10.1080/17453674. 2019.1594015

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ASN and OR conceived the study and defined the analysis plan with input from all other co-authors. ASN, OR, and SM drafted the manuscript. All authors interpreted results and reviewed the manuscript. The authors would like to thank all orthopedic surgeons and administrative personnel at Swedish hospitals for their contribution of data and engagement in the register. They also thank registry coordinator Pär Werner who performed statistical analyses. Acta thanks Jeppe Lange and Mogens Laursen for help with peer review of this study.

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Krauss E S, Cronin M, Dengler N, Simonson B G, Altner K, Daly M, Segal A. Semin Thromb Hemost 2018 Dec 19. [Epub ahead of print]. Liu W, Wahafu T, Cheng M, Cheng T, Zhang Y, Zhang X. Review: The influence of obesity on primary total hip arthroplasty outcomes: a meta-analysis of prospective cohort studies. Orthop Traumatol Surg Res 2015; 101(3): 289-96. McCalden R W, Charron K D, MacDonald S J, Bourne R B, Naudie D D. Does morbid obesity affect the outcome of total hip replacement? An analysis of 3290 THRs. J Bone Joint Surg Br 2011; 93(3): 321-5. Murgatroyd S E, Frampton C M, Wright M S. The effect of body mass index on outcome in total hip arthroplasty: early analysis from the New Zealand Joint Registry. J Arthroplasty 2014; 29(10): 1884-8. Pulos N, McGraw M H, Courtney P M, Lee G C. Revision THA in obese patients is associated with high re-operation rates at short-term follow-up. J Arthroplasty 2014; 29(9 Suppl.): 209-13. Sankar A, Johnson SR, Beattie W S, Tait G, Wijeysundera D N. Reliability of the American Society of Anesthesiologists physical status scale in clinical practice. Br J Anaesth 2014; 113(3): 424-32. Shaparin N, Widyn J, Nair S, Kho I, Geller D, Delphin E. Does the obesity paradox apply to early postoperative complications after hip surgery? A retrospective chart review. J Clin Anesth 2016; 32: 84-91. Singh J A, Lewallen D G. Increasing obesity and comorbidity in patients undergoing primary total hip arthroplasty in the US: a 13-year study of time trends. BMC Musculoskelet Disord 2014; 15: 441. Vincent H K, Horodyski M, Gearen P, Vlasak R, Seay A N, Conrad B P, Vincent K R. Review: Obesity and long term functional outcomes following elective total hip replacement. J Orthop Surg Res 2012; 7: 16. von Elm E, Altman D G, Egger M, Pocock S J, Gøtzsche P C, Vandenbroucke J P; STROBE Initiative. The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) Statement: guidelines for reporting observational studies. Int J Surg 2014; 12(12): 1495-9.

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ASA class is associated with early revision and reoperation after total hip arthroplasty: an analysis of the Geneva and Swedish Hip Arthroplasty Registries Rory J FERGUSON 1, Alan J SILMAN 1, Christophe COMBESCURE 2, Erik BULOW 3, Daniel ODIN 3, Didier HANNOUCHE 4, Siôn GLYN-JONES 1, Ola ROLFSON 3, and Anne LÜBBEKE 1,4 1 Nuffield

Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, UK; 2 Division of Clinical Epidemiology, Geneva University Hospitals, Switzerland; 3 The Swedish Hip Arthroplasty Register and the Department of Orthopaedics, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Sweden; 4 Division of Orthopaedics and Trauma Surgery, Geneva University Hospitals, Switzerland Correspondence: rory.ferguson@ndorms.ox.ac.uk Submitted 2018-11-28. Accepted 2019-03-31.

Background and purpose — Data from several joint replacement registries suggest that the rate of early revision surgery after primary total hip arthroplasty (THA) is increasing. The ASA class, now widely recorded in arthroplasty registries, may predict early revision. We investigated the influence of ASA class on the risk of revision and other reoperation within 3 months and within 5 years of primary THA. Patients and methods — We used data from the Geneva and Swedish Hip Arthroplasty Registries, on primary elective THAs performed in 1996–2016 and 2008–2016, respectively. 5,319 and 122,241 THAs were included, respectively. Outcomes were all-cause revision and other reoperations evaluated using Kaplan–Meier survival and Cox regression analyses. Results — Within 3 months after surgery, higher ASA class was associated with greater risk of revision and other reoperation. 3-month cumulative incidences of revision by ASA class I, II, and III–IV respectively, were 0.6%, 0.7%, and 2.3% in Geneva and 0.5%, 0.8%, and 1.6% in Sweden. 3-month cumulative incidences of other reoperation were 0.4%, 0.7%, and 0.9% in Geneva and 0.2%, 0.4%, and 0.7% in Sweden. Adjusted hazard ratios (ASA III–IV vs. I) for revision within 3 months were 2.7 (95% CI 1.2–5.9) in Geneva and 3.3 (CI 2.6–4.0) in Sweden. Interpretation — Assessment of ASA class of patients prior to THA will facilitate risk stratification. Targeted riskreduction strategies may be appropriate during the very early postoperative period for patients identified as at higher risk. Systematically recording ASA class in arthroplasty registries will permit risk adjustment and facilitate comparison of revision rates internationally.

Data from several joint replacement registries suggest that the rate of early revision surgery after primary total hip arthroplasty (THA), widely defined as within 5 years of primary THA, is increasing (Thien et al. 2014, Cnudde et al. 2017). Recent data have shown that a high proportion of early revision surgeries are performed within 3 months (Swiss National Joint Registry 2018). Patients requiring such early revision surgery may share particular characteristics that put them at risk, such as preoperative health status. Evidence from the New Zealand Joint Registry suggests that poor preoperative health status, assessed by ASA class, places patients at increased risk of revision within 2 years of surgery (Hooper et al. 2012). However, there are few data on the influence of poor preoperative health status on very early revision, specifically within 3 months of primary THA. Understanding its influence on the rate of very early revision surgery would be beneficial for 3 reasons: 1st, enhanced preoperative risk stratification would support surgeons and patients; 2nd, riskreduction strategies could be identified and implemented for patients most at risk within 3 months postoperatively; and 3rd, risk adjustment would facilitate comparisons of outcomes between datasets. Other reoperations after primary THA include, but are not limited to, debridement of infection, osteosynthesis of periprosthetic fracture, and drainage of hematoma. Data on other reoperations are not widely collected by arthroplasty registries. Evidence on incidence and causative factors is limited (Ferguson et al. 2018). Many methods exist to measure preoperative health status. The ASA classification system is now the most widely collected system for measuring physical health status by arthroplasty registries worldwide (Lübbeke et al. 2018).

© 2019 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group, on behalf of the Nordic Orthopedic Federation. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits ­unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. DOI 10.1080/17453674.2019.1605785

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We investigated the influence of ASA class on the risk of revision and other reoperation within 3 months and within 5 years of primary THA. In cases of revision and other reoperation, we investigated the indication for surgery.

Patients and methods We conducted a retrospective analysis of data from 2 arthroplasty registries. We performed a preliminary study in a hospital registry (Geneva Arthroplasty Registry, GAR), and compared the results with those from a national registry (Swedish Hip Arthroplasty Register, SHAR). GAR collects data on all THAs performed at Geneva University Hospitals, the only public hospital of the canton of Geneva, Switzerland serving a population of 500,000 inhabitants (Geneva Joint Arthroplasty Registry 2017). Completeness of recording THAs is > 99%. SHAR collects data on all THAs performed in Sweden, covering 80 clinics (Swedish Hip Arthroplasty Register 2016). Completeness of recording THAs in the registry is 98.3%. The completeness of capture of revision surgery following primary THAs recorded in the GAR was 100% in 2013–2016, based on revisions performed within Switzerland. It was not possible to directly calculate the completeness of capture of revision surgery prior to 2013 in GAR; however, loss to follow-up in GAR after 5 years was 6% during 1996–2012, hence we estimate the completeness of capture of revision surgery was ≥ 94%. In SHAR the completeness of capture of revision surgery was 93%, based on revisions performed within Sweden. Eligible procedures were elective primary THAs performed during the period that registries collected data on ASA class. This period was March 1996 through December 2016 for GAR and January 2008 through December 2016 for SHAR. THAs in patients with missing data on ASA class were excluded. Bilateral cases were included. 2 groups of cases were excluded: 1st, we excluded metal-on-metal THAs because they have a substantially higher revision rate than other bearings (Swedish Hip Arthroplasty Register 2016, Geneva Joint Arthroplasty Registry 2017, National Joint Registry 2017). Moreover, patients with lower ASA class received metal-onmetal prostheses more than other patients, meaning inclusion of such cases could have biased our results. 2nd, we excluded THAs for which the indication was trauma or malignancy. The ASA classification system classifies patients into 6 categories (classes I [normal health]–VI [brain death]). ASA classes V and VI are not appropriate to patients undergoing elective THA, leaving a range of ASA classes I–IV. We evaluated 2 outcomes: incidence of revision and of any other reoperation. Revision surgery was defined as any surgery that involved the addition, removal, or replacement of 1 or more components of the prosthetic hip. Other reoperation was defined as any surgery to the prosthetic hip that did not involve the addition, removal, or replacement of any

components of the prosthetic hip. Closed reduction of dislocation was not included as a reoperation. Indications for surgery were also extracted. Covariates were age at surgery, sex, BMI, and diagnosis (primary or secondary osteoarthritis [OA]). The GAR records revision, other reoperation, and mortality data continuously and actively follows patients up at 1, 5, 10, 15, and 20 years. The SHAR records revision and other reoperation data continuously. Mortality data are obtained from the Swedish Board of Health and Welfare. The end of followup was December 2016. Statistics Analyses were conducted independently for each registry. Baseline characteristics were described using frequencies, proportions, means, and standard deviations (SDs). The proportion of THAs in patients of ASA class IV (0.6% in GAR and 0.4% in SHAR) was too small for meaningful analysis on its own. Thus, ASA was categorized into 3 groups: class I, II, and III–IV. The cumulative mortality was assessed with Kaplan–Meier survival estimates. Cumulative incidence of revision and other reoperation by ASA class over 5-year follow-up after index THA was assessed using non-parametric models with death as competing event. As a sensitivity analysis, the survival analyses were re-run including only the 1st THA procedure in each patient. Cause-specific Cox proportional hazard models (presented as cause-specific hazard ratios [HRs] with 95% confidence intervals [CIs]) were used to assess the association between ASA class and risk of revision and other reoperation. Death was considered as a competing event. ASA class I was defined as the referent category. Details on the assumption of the models are presented in the Appendix (see Supplementary data). With the proposed models, the HRs for the associations were potentially different within 3 months following primary THA and after 3 months. Multivariable models with a pre-specified set of adjustment factors (age, sex, BMI, diagnosis) were conducted. Complete case analysis was used for adjusted models. Data were analyzed using SPSS Version 23 software (IBM Corp, Armonk, NY, USA) and R (R Foundation for Statistical Computing, Vienna, Austria) with alpha of 0.05 as the statistical threshold for significance (all tests were 2-sided). Ethics, funding, and potential conflicts of interests The registry data collection was approved by the Geneva University Hospital Institutional Review Board and the Gothenburg Regional Ethical Review Board. No funding was received for the study. The authors declare no potential conflicts of interest.

Results In GAR, 5,319 procedures in 4,501 patients were eligible for inclusion. In SHAR, 122,241 procedures in 106,522 patients were eligible for inclusion (Table 1). In both cohorts the pro-

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Table 1. Preoperative patient characteristics by ASA class GAR SHAR ASA I ASA II ASA III–IV Total ASA I ASA II ASA III–IV n = 481 n = 3,496 n = 1,342 n = 5,319 n = 29,280 n = 72,857 n = 20,104

Total n = 122,241

Women, n (%) 259 (54) 2,106 (60) 767 (57) 3,132 (59) 16,112 (55) 41,460 (59) 9,885 (53) 67,149 (57) Age (mean, SD) 60.1 (12.3) 68.8 (11.7) 76.1 (10.1) 69.9 (12.2) 62.5 (10.7) 69.2 (9.7) 72.9 (9.8) 68.2 (10.5) Age categories, n (%) < 55 150 (31) 393 (11) 42 (3.1) 585 (11) 6,325 (22) 5,152 (7.1) 863 (4.3) 12,340 (10) 55–64 127 (26) 667 (19) 109 (8.1) 903 (17) 9,679 (33) 15,756 (22) 2,701 (13) 28,136 (23) 65–74 152 (32) 1,226 (35) 357 (27) 1,735 (33) 9,766 (33) 29,660 (41) 6,999 (35) 46,425 (38) 75–84 49 (10) 1,024 (29) 550 (41) 1,623 (31) 3,225 (11) 19,423 (27) 7,648 (38) 30,296 (25) ≥ 85 3 (0.6) 186 (5.3) 284 (21) 473 (8.9) 285 (1.0) 2,866 (3.9) 1,893 (9.4) 5,044 (4.1) BMI (mean, SD) 24.8 (3.3) 26.8 (4.7) 27.3 (5.6) 26.8 (4.9) 26.1 (3.8) 27.4 (4.4) 28.7 (5.6) 27.3 (4.6) BMI categories, n (%) < 18.5 13 (2.7) 63 (1.8) 43 (3.3) 119 (2.3) 195 (0.6) 531 (0.7) 240 (1.2) 966 (0.8) 18.5–24 245 (51) 1,280 (37) 437 (33) 1,962 (37) 11,405 (38) 20,933 (29) 5,008 (26) 37,346 (31) 25–29 193 (40) 1,303 (38) 441 (33) 1,937 (37) 12,868 (43) 31,374 (44) 6,955 (36) 51,197 (43) 30–34 27 (5.6) 642 (19) 288 (22) 957 (18) 3476 (12) 14,512 (20) 4,520 (23) 22,508 (19) 35–39 2 (0.4) 156 (4.5) 85 (6.4) 243 (4.6) 416 (1.3) 3,234 (4.5) 2,115 (11) 5,765 (4.8) ≥ 40 0 (0.0) 26 (0.7) 27 (2.0) 53 (1.0) 66 (0.2) 529 (0.7) 629 (3.2) 1,224 (1.0) Missing data 1 26 21 48 854 1,744 637 3,235 Diagnosis, n (%) Primary OA 375 (78) 2,817 (81) 1,007 (75) 4,199 (79) 26,644 (91) 67,221 (92) 17,666 (88) 111,531 (92) Secondary OA 106 (22) 679 (19) 335 (25) 1,120 (21) 2,636 (9.0) 5,636 (7.7) 2,438 (12) 10,710 (8.8)   Table 2. Incidence of revision and other reoperation within 5 years of primary THA by ASA score

Total number (%)

Revision Cumulative incidence (CI) 3 months 5 years

Total number (%)

Other reoperation Cumulative incidence (CI) 3 months 5 years

Geneva All patients 126 (2.4) 1.1 (0.8–1.4) 2.6 (2.1–3.0) 95 (1.8) 0.7 (0.5–0.9) ASA I 10 (2.1) 0.6 (0.0–1.3) 2.3 (0.9–3.8) 9 (1.9) 0.4 (0.0–1.0) ASA II 73 (2.1) 0.7 (0.4–1.0) 2.3 (1.8–2.8) 58 (1.7) 0.7 (0.4–0.9) ASA III–IV 43 (3.2) 2.3 (1.5–3.1) 3.3 (2.3–4.3) 28 (2.1) 0.9 (0.0 –1.4) Sweden All patients 2,353 (1.9) 0.9 (0.8–0.9) 2.3 (2.2–2.4) 878 (0.7) 0.4 (0.4–0.4) ASA I 444 (1.5) 0.5 (0.4–0.6) 1.9 (1.7–2.1) 145 (0.5) 0.2 (0.2–0.3) ASA II 1,364 (1.9) 0.8 (0.7–0.9) 2.3 (2.2–2.4) 522 (0.7) 0.4 (0.3–0.4) ASA III–IV 545 (2.7) 1.6 (1.4–1.7) 3.3 (3.0–3.6) 211 (1.0) 0.7 (0.6–0.8)

portions of cases in obese patients (BMI ≥ 30), in those over 85 years of age, and in patients with secondary OA were highest in ASA classes III–IV. In GAR, 126 cases of revision were recorded within 5 years, with 59 (47% of total) within 3 months (Table 2). The incidence of death within 5 years was 12.8% (CI 11.8–13.8). In SHAR, 2,353 cases of revision were recorded within 5 years, with 1,030 (44% of total) within 3 months. The incidence of death within 5 years was 8.3% (CI 8.1–8.5). In both cohorts, the cumulative incidence of revision within 3 months and within 5 years was higher in ASA classes III–IV than in ASA class I (within 3 months, GAR: 2.3% versus 0.6%; SHAR: 1.6% versus 0.5%; within 5 years, GAR: 3.3% versus 2.3%; SHAR: 3.3% versus 1.9%). The cumulative incidence was lower for other reoperation than for revision in both cohorts.

1.9 (1.5–2.3) 2.0 (0.7–3.4) 1.8 (1.3–2.2) 2.2 (1.4–3.0) 0.8 (0.8–0.9) 0.6 (0.5–0.7) 0.8 (0.8–0.9) 1.2 (1.0–1.4)

There was a positive association between ASA class and the risk of revision within 5 years (GAR: p = 0.02 for the comparison between ASA class I or II versus III or IV; SHAR: p < 0.001 for the comparison among all ASA classes). Results were unchanged by including only the first procedure in each patient. An association between ASA class and risk of other reoperation within 5 years was detected only in SHAR (GAR: p = 0.6; SHAR: p < 0.001) (Figure). In GAR, ASA classes III–IV were associated with a higher risk of revision (Table 3). However, the association was restricted to within 3 months after primary THA (unadjusted HR: 3.4, CI 1.6–7.4). The association persisted after adjustment for differences in the preoperative baseline characteristics. The risk of revision was also higher in patients with a diagnosis of secondary OA and in obese patients.

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4

Cumulative revision rate (%) in GAR

Cumulative revision rate (%) in SHAR

Cumulative reoperation rate (%) in GAR

Cumulative reoperation rate (%) in SHAR

5

5

5

5

4

4

4

4

3

3

3

3

2

2

2

2

1

1

1

1

0

0

A

1

2

3

4

5

Years after index operation

0

0

B

1

2

3

4

5

Years after index operation

0

0

C

1

2

3

4

5

Years after index operation

0

0

D

1

2

3

4

5

Years after index operation

Cumulative incidence of revision in (A) GAR and (B) SHAR and cumulative incidence of other reoperation in (C) GAR and (D) SHAR by ASA class (95% CI shown in shading). The association with ASA class was statistically significant in SHAR (p < 0.001 for both revision and other reoperation). In GAR, the p-value was 0.07 for revision but the difference was statistically significant between ASA class III or IV and ASA class I or II (p = 0.02). No association with ASA class was detected in GAR for other reoperation (p = 0.6). Table 3. Associations with the risk of revision (time-invariant HR unless specified) Model

GAR cohort HR (CI)

SHAR cohort HR (CI)

Univariable model ASA I 1 (ref) 1 (ref) ASA II 1.0 (0.5–2.0) 1.6 (1.4–2.0) a,f 1.1 (0.9–1.3) b,f ASA III–IV 3.4 (1.6–7.4) a,c 3.2 (2.6–3.9) a,f 0.7 (0.3–1.7) b,c 1.3 (1.1–1.6) b,f Multivariable model ASA I 1 (ref) 1 (ref) ASA II 1.0 (0.5–1.9) 1.7 (1.4–2.1) a,g 1.2 (1.0–1.3) b,g ASA III–IV 2.7 (1.2–5.9) a,d 3.3 (2.6–4.0) a,g 0.7 (0.3–1.7) b,d 1.4 (1.1–1.6) b,g Sex Male 1 (ref) 1 (ref) Female 0.8 (0.6–1.1) 0.7 (0.6–0.7) Diagnosis Primary OA 1 (ref) 1 (ref) Secondary OA 2.4 (1.7–3.5) 1.4 (1.3–1.6) BMI < 35 1 (ref) 1 (ref) ≥ 35 3.7 (2.3–6.0) 2.6 (2.2–3.1) a,h 1.2 (1.0–1.5) b,h Age < 85 y 1 (ref) 1 (ref) ≥ 85 y 1.6 (0.8–3.3) a,e 1.9 (1.5–2.4) a,i 0.2 (0.1–1.7) b,e 0.6 (0.4–0.8) b,i a HR within the first 3 months. b HR after 3 months and within 5 years. c The change in HR within the first 3 months

and after was statistically significant (p < 0.001). d The change in HR within the first 3 months and after was statistically significant (p = 0.002). e A change in HR within the first 3 months and after was suspected (p = 0.07). f The change in HR within the first 3 months and after was statistically significant (ASA II: p < 0.001, ASA III–IV: p < 0.001). g The change in HR within the first 3 months and after was statistically significant (ASA II: p < 0.001, ASA III–IV: p < 0.001). h The change in HR within the first 3 months and after was statistically significant (p < 0.001). i The change in HR within the first 3 months and after was statistically significant (p < 0.001).

In SHAR, the association of ASA classes III–IV with revision within 3 months was confirmed (unadjusted HR: 3.2, CI 2.6–3.9). The association decreased after 3 months but remained statistically significant (unadjusted HR: 1.3, CI 1.1–1.6). In contrast to GAR, an association with ASA class II was also detected within 3 months (unadjusted HR: 1.6, CI 1.4–2.0). Adjustment for differences in the preoperative baseline characteristics did not importantly modify the associations. In contrast to GAR, sex and age were also associated with the risk of revision. Women had a lower risk of revision. Patients aged over 85 years had a higher risk within 3 months but a lower risk thereafter. The associations between the risk of revision and the diagnosis of both secondary OA and obesity were confirmed in SHAR. In GAR, ASA class was not associated with the risk of other reoperation (unadjusted HR ASA III–IV vs. ASA I: 1.2, CI 0.6–2.5) (Table 4, see Supplementary data). In SHAR, ASA class was associated with a greater risk of other reoperation within 3 months following primary THA than after 3 months and within 5 years (unadjusted HR ASA III–IV vs. ASA I within 3 months: 3.2, CI 2.3–4.3; after 3 months and within 5 years: 1.6, CI 1.2–2.1). The most frequent indications for revision in both cohorts were dislocation, infection, and periprosthetic fracture, and for other reoperation in both cohorts were infection, periprosthetic fracture, and hematoma (Table 5).

Discussion Our study had 3 important findings on outcomes within 3 months after primary THA. 1st, preoperative ASA classes III– IV compared with ASA class I were associated with a more than 3 times higher risk of very early revision. 2nd, preoperative ASA classes III–IV compared with ASA class I were associated with a more than 2 times higher risk of very early

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5

Table 5. Indications for revision and other reoperation within 3 months by ASA grade Geneva Sweden ASA I ASA II ASA III–IV Total ASA I ASA II ASA III–IV Total Factor n = 481 n = 3,496 n = 1,342 n = 5,319 n = 29,280 n = 72,857 n = 20,104 n = 122,241 Indications for revision, n (%) Dislocation 1 (0.2) 5 (0.1) 12 (0.9) 18 (0.3) 30 (0.1) 103 (0.1) 57 (0.3) 190 (0.2) Infection 1 (0.2) 8 (0.2) 7 (0.5) 16 (0.3) 81 (0.3) 356 (0.5) 195 (1) 632 (0.5) Periprosthetic fracture 0 6 (0.2) 7 (0.5) 13 (0.2) 24 (0.1) 80 (0.1) 42 (0.2) 146 (0.1) Aseptic loosening 0 4 (0.1) 3 (0.2) 7 (0.1) 8 (< 0.1) 21 (< 0.1) 8 (< 0.1) 37 (< 0.1) Implant malposition 0 1 (< 0.1) 1 (0.1) 2 (< 0.1) 3 (< 0.1) 8 (< 0.1) 3 (< 0.1) 14 (< 0.1) Other a 1 (0.2) 1 (< 0.1) 1 (0.1) 3 (0.1) 1 (< 0.1) 2 (< 0.1) 3 (< 0.1) 6 (< 0.1) Unknown 0 0 0 0 2 (< 0.1) 3 (< 0.1) 0 5 (< 0.1) Total 3 (0.6) 25 (0.7) 31 (2.3) 59 (1.1) 149 (0.5) 573 (0.8) 308 (1.5) 1,030 (0.8) Indications for reoperation, n (%) Infection 1 (0.2) 11 (0.3) 3 (0.2) 15 (0.3) 45 (0.2) 219 (0.3) 106 (0.5) 370 (0.3) Periprosthetic fracture 0 3 (0.1) 6 (0.4) 9 (0.2) 4 (< 0.1) 16 (< 0.1) 10 (< 0.1) 30 (< 0.1) Hematoma 1 (0.2) 4 (0.1) 1 (0.1) 6 (0.1) 1 (< 0.1) 9 (< 0.1) 8 (< 0.1) 18 (< 0.1) Abductor avulsion 0 2 (0.1) 1 (0.1) 3 (0.1) 1 (< 0.1) 1 (< 0.1) 0 2 (< 0.1) Dislocation 0 0 0 0 3 (< 0.1) 8 (< 0.1) 1 (< 0.1) 12 (< 0.1) Cement problem 0 0 0 0 1 (< 0.1) 3 (< 0.1) 2 (< 0.1) 6 (< 0.1) Other b 0 3 (0.1) 1 (0.1) 4 (0.1) 2 (< 0.1) 7 (< 0.1) 1 (< 0.1) 10 (< 0.1) Unknown 0 0 0 0 1 (< 0.1) 3 (< 0.1) 2 (< 0.1) 6 (< 0.1) Total 2 (0.4) 23 (0.7) 12 (0.9) 37 (0.7) 58 (0.2) 266 (0.4) 130 (0.6) 454 (0.4) a Other includes: infection suspected but not confirmed; hematoma; other material left in joint; nerve injury; delayed healing; b Other includes: infection suspected but not confirmed; pain; allergy to suture; other material left in joint; aseptic loosening.

other reoperation in SHAR. These risks were independent of age, sex, BMI, and diagnosis. 3rd, a substantial proportion of early revision and other reoperation procedures in patients with ASA classes III–IV were performed within 3 months of primary THA. We also found that beyond 3 months and within 5 years after primary THA patients with increased ASA class were not at increased risk of revision in GAR and were only at a slightly higher risk of revision in SHAR. This study has limitations. 1st, the ASA classification system has been criticized because of the subjective nature of the assessment, which has poor inter-observer correlation (Ranta et al. 1997, Mak et al. 2002). Despite this, as noted by Hooper et al. (2012), the ASA classification system has remained the most widely used anesthetic preoperative assessment and the most widely collected tool for measuring comorbidity by arthroplasty registries worldwide. We accept that there may be poor inter-observer reliability when determining between ASA class I and II, but we agree with Hooper et al. that the difference between ASA class I and III is so profound (a normal healthy patient compared with a patient with severe systemic disease) that we believe that the significance of our results, when comparing ASA class I with ASA classes III–IV, was unlikely to be affected by this potential error. 2nd, the ASA class in our data represents only a snapshot of the physical health status of each patient, taken immediately prior to primary THA. This is a general drawback of using ASA class because it is assessed only in the context of surgery. We do not know whether physical health status changed subsequent to THA, and if this had an influence on revision and other reoperation rates. With increasing follow-up, other health

pain.

changes might intervene that would attenuate the influence of a single baseline measure. However, we aimed to determine the influence of preoperative physical health status, to enable the identification of high-risk patients preoperatively, so the possibility of subsequent changes should not detract from our results. 3rd, our results were adjusted for age, sex, BMI, and diagnosis, but other factors may have had a confounding effect. Here, we elected to focus on patient factors that are routinely measured before THA, and so may be used when counselling patients considering THA. We did not adjust for surgical factors, such as surgical approach and implant fixation, which are known also to influence early revision and other reoperation rates (Jämsen et al. 2014, Meneghini et al. 2017). The reason for this decision is that each of these factors is chosen by the surgeon, and these choices may be influenced by ASA class, age, and BMI. Therefore, the inclusion of surgical factors in the models may lead to over-adjustment. We included both procedures in patients who had undergone bilateral THA. This is because the ASA class may change between the 2 operations. Indeed, a sensitivity analysis in GAR and SHAR including only the first procedure in each patient showed similar results to the analyses, including bilateral cases. Nevertheless, since ASA class is associated with outcome, the preoperative ASA class of the 2nd THA would influence the outcome of both the 1st and 2nd THAs. Thus, a degree of correlation in patients with bilateral THAs cannot be excluded. 4th, GAR is a small registry and we included cases since 1996. This might limit the applicability to modern patients;

6

however, we compared the results with results in the larger SHAR with recent data and the results were similar. Many studies have suggested that patients with poor overall physical health have a higher risk of early revision. A systematic review found 5 papers that reported greater preoperative comorbidity was associated with a higher risk of revision, with outcome ranging from 6 months to 8 years (Prokopetz et al. 2012). The Charlson Comorbidity Index was used as the measure of comorbidity in these papers. Whilst the Charlson score is widely validated, its limitation is that it simply considers the presence or absence of certain diseases and does not account for their severity. Furthermore, it requires more information than the ASA classification system to complete and is not routinely calculated before THA, or widely collected by registries. To our knowledge, 2 reports of arthroplasty registry data have investigated the influence of ASA class on early revision rate. Hooper et al. (2012) found an adjusted hazard ratio of 1.4 (CI 1.0–2.0) when comparing revision rates of patients with ASA class I versus III within 2 years postoperatively in the New Zealand Joint Registry. This agrees with our findings; however, the effect of increased ASA class on revision rate was less than in our study. This difference may be because Hooper et al. studied the longer period of 2 years postoperatively. Our data indicate that the effect of increased ASA class is highest within 3 months and decreases thereafter. The 2018 annual report of the Dutch Arthroplasty Registry reported graphically the revision rate after primary THA stratified by ASA class (Dutch Arthroplasty Register 2018). Although numerical data are not reported, the survival curve demonstrates a higher revision rate within 3 months of primary THA in ASA classes III– IV cases than ASA class I cases, similar to the trend observed in GAR and SHAR. Data on the rate of other reoperations are scarce and we could find no previous study that had investigated the influence of preoperative health status on other reoperation rate with which to compare our results. This likely reflects several factors. 1st, the previous lack of a formal definition of what constitutes reoperation after arthroplasty. 2nd, study of revisions has taken precedence because they are seen as a more serious complication. 3rd, very few arthroplasty registries collect data on other reoperations. Our study is the first to demonstrate that poor preoperative physical health status as measured with the ASA class is associated with increased risk of early other reoperation. We note the cumulative incidence of other reoperation was higher in GAR. Whilst there may be a real difference in other reoperation rate between the 2 registries, this observed difference alternatively may reflect greater completeness of capture of other reoperations in GAR. That a substantial proportion of early revision and other reoperation procedures, performed in patients with ASA classes III–IV, occurs within 3 months of primary THA is a clinically important finding. It identifies this period of 3 months as critical to efforts to reduce revision and other reop-

Acta Orthopaedica 2019; 90 (x): x–x

eration rates. Infection, periprosthetic fracture, and dislocation were the most frequent indications for very early revision and other reoperation. Strategies to reduce the risk of revision targeted to these complications during this very early postoperative period may be designed and implemented for patients with ASA classes III–IV most at risk, and are a key focus for future work. These may include preoperative, perioperative, and postoperative interventions. Such intensive strategies may be appropriate and acceptable in this cohort of patients over this time frame with regards to patient preference and resource constraints. In summary, our study has identified that within 3 months of primary elective THA patients with preoperative ASA classes III–IV have a higher risk of revision and other reoperation. The proposed benefits are improved patient counselling, targeted risk-reduction strategies, and improved risk adjustment between datasets. Supplementary data Table 4 and Appendix are available as supplementary data in the online version of this article, http://dx.doi.org/ 10.1080/ 17453674.2019.1605785

RJF, AJS, OR, and AL contributed to the conception and design of the study. RJF, CC, EB, and DO performed the statistical analyses. RJF, AJS, and AL drafted the manuscript. All authors critically revised the manuscript. The authors would like to thank all GAR and SHAR registry staff, and surgeons and patients who have contributed to the registries. Acta thanks Marianne Hansen Gillam and Liza N van Steenbergen for help with peer review of this study.

Cnudde P, Nemes S, Bülow E, Timperley J, Malchau H, Kärrholm J, Garellick G, Rolfson O. Trends in hip replacements between 1999 and 2012 in Sweden. J Orthop Res 2017; 36(1): 432-42. Dutch Arthroplasty Register. Landelijke Registratie Orthopedische Implantaten Annual Report 2018. Ferguson R J, Palmer A J, Taylor A, Porter M L, Malchau H, Glyn-Jones S. Hip replacement. Lancet 2018; 392(10158): 1662-71. Geneva Joint Arthroplasty Registry. Geneva Joint Arthroplasty Registry: Annual Report 2017. Available on request: christophe.barea@hcuge.ch. Hooper G J, Rothwell A G, Hooper N M, Frampton C. The relationship between the American Society of Anesthesiologists physical rating and outcome following total hip and knee arthroplasty: an analysis of the New Zealand Joint Registry. J Bone Joint Surg Am 2012; 94(12): 1065-70. Jämsen E, Eskelinen A, Peltola M, Mäkelä K. High early failure rate after cementless hip replacement in the octogenarian. Clin Orthop Relat Res 2014; 472(9): 2779-89. Lübbeke A, Silman A J, Barea C, Prieto-Alhambra D, Carr A J. Mapping existing hip and knee replacement registries in Europe. Health Policy (New York) 2018; 122(5): 548-57. Mak P H K, Campbell R C H, Irwin M G, American Society of Anesthesiologists. The ASA physical status classification: inter-observer consistency. American Society of Anesthesiologists. Anaesth Intensive Care 2002; 30(5): 633-40.

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Meneghini R M, Elston A S, Chen A F, Kheir M M, Fehring T K, Springer B D. Direct anterior approach: risk factor for early femoral failure of cementless total hip arthroplasty. J Bone Joint Surg 2017; 99(2): 99-105. National Joint Registry. National Joint Registry for England, Wales, Northern Ireland and the Isle of Man: 14th Annual Report 2017. Prokopetz J J, Losina E, Bliss R L, Wright J, Baron J A, Katz J N. Risk factors for revision of primary total hip arthroplasty: a systematic review. BMC Musculoskelet Disord 2012; 13: 251. Ranta S, Hynynen M, Tammisto T. A survey of the ASA physical status classification: significant variation in allocation among Finnish anaesthesiologists. Acta Anaesthesiol Scand 1997; 41(5): 629-32.

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Swedish Hip Arthroplasty Register. The Swedish Hip Arthroplasty Register: Annual Report 2016. Swiss National Joint Registry. Swiss National Joint Registry: Annual Report 2018. Thien T M, Chatziagorou G, Garellick G, Furnes O, Havelin L I, Mäkelä K, Overgaard S, Pedersen A, Eskelinen A, Pulkkinen P, Kärrholm J. Periprosthetic femoral fracture within two years after total hip replacement: analysis of 437,629 operations in the Nordic Arthroplasty Register Association database. J Bone Joint Surg Am 2014; 96(19): e167.

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Implant survival and patient-reported outcome following total hip arthroplasty in patients 30 years or younger: a matched cohort study of 1,008 patients in the Swedish Hip Arthroplasty Register Maziar MOHADDES 1,2, Emma NAUCLÉR 1, Johan KÄRRHOLM 1,2, Henrik MALCHAU 1,2, Daniel ODIN 1, and Ola ROLFSON 1,2 1 Swedish Hip Arthroplasty Register, Gothenburg, Sweden; 2 Department of Orthopaedics, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden Correspondence: maziar.mohaddes@gmail.com Submitted 2018-11-30. Accepted 2019-02-14.

Background and purpose — The outcome of total hip arthroplasty (THA) in younger patients is suggested to be inferior compared with the general THA population. There is a lack of studies with long-term follow up for very young patients. We report on implant survival and patient-reported outcome in patients aged 30 years or younger. Patients and methods — Data on THAs performed in Sweden between the years 2000 and 2016 were included. There were 504 patients 30 years or younger with complete demographic and surgical data (study group). A matched comparison group older than 30 years was identified. Implant survival was analyzed using the Kaplan–Meier method. Patient-reported outcome was analyzed in a subgroup of patients. Results — The 10-year and 15-year implant survivorship for the study group was 90% and 78%, respectively. The corresponding figures for the patients older than 30 years were 94% and 89%. The median preoperative EQ-5D index was lower in the study group; the improvement in EQ-5D index was similar between the study and the comparison groups. The preoperative EQ-VAS was lower and the improvement in EQ-VAS at 1 year was larger in the study group. Interpretation — The promising 10-year implant survival and 1-year improvement in patient-reported outcome suggests that THA is a feasible option in the patients 30 years or younger.

The outcome of total hip arthroplasty (THA) in the younger population is suggested to be inferior compared to the THA general population (AOANJRR 2018, Bayliss et al. 2017, Kärrholm et al. 2018, NJR 2018). For example, the lifetime risk of having a revision following THA for patients aged 50 to 54 years at primary surgery is reported to be 17% and 30% for females and males respectively (Bayliss et al. 2017). In a systematic review, Walker et al. (2016) in a meta-analysis on patients aged 30 years or younger found a revision rate of 5% with a mean follow-up of 8 years. They highlighted lack of register studies with long-term follow-up for the very young patients. The sparse long-term reports and a belief in inferior outcomes in younger patients might create difficulties for surgeons and patients when deciding whether THA is a feasible option. We analyzed long-term implant survival and patientreported outcomes at 1 year in patients aged 30 years or younger, registered in the Swedish Hip Arthroplasty Register. A propensity-score-matched group of patients older than 30 years were included for comparison.

Patients and methods The Swedish Hip Arthroplasty Register (SHAR) is a national register with full coverage. In the annual report for 2017, the register reported a completeness of 98% for primary THAs. (Kärrholm et al. 2018). We identified all primary THAs in individual patients aged 30 years or younger, operated on between January 2000 and

© 2019 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group, on behalf of the Nordic Orthopedic Federation. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits ­unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. DOI 10.1080/17453674.2019.1599776

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Primary THA in SHAR 2000–2016 n = 208,316

≤ 30 years old n = 687 Excluded diagnoses (n = 75): – tumor, 14 – fracture/trauma, 56 – other, 5 Excluded due to other reasons a n = 108 ≤ 30 years old included in the study n = 504

> 30 years old n = 207,629 Excluded diagnoses (n = 28,496): – tumor 1,351 – fracture/trauma, 26,959 – other, 184

Ethics, funding, and potential conflicts of interest This study is a part of a larger research project which has been reviewed and approved by the Regional Ethical Review Board in Gothenburg (2014-04-09, 271-14). The study was not financed by any external funding. The authors declare no conflicts of interest.

Excluded due to other reasons a n = 9,272 > 30 years old included in the study n = 169,861

Results

The average age of the patients in the study and the comparison group at the time of priFigure 1. Patient selection. Numbers given in this figure are patients having a THA. In mary surgery was 25 (SD 4) years and 54 a bilaterally operated cases only the first hip was included. Excluded: metal-on-metal (SD 13) years respectively. articulation, femoral head size > 36 mm or data missing on fixation, femoral head size or articulation. 60% were women in both groups (Table 1). Inflammatory joint disease and osteoDecember 2016 as reported to the SHAR. In patients operated arthritis (OA) following childhood disease were the most bilaterally only the first hip operated was included. Surgeries common indications for surgery. Uncemented fixation was performed due to a fracture (n = 56), tumor (n = 14), or with most common, followed by reversed hybrids in both study and unspecific diagnosis (n = 5) were excluded. Further, all sur- comparison group (Table 1). The average follow-up was 8 (SD geries performed with a metal-on-metal hip replacement and 5) years in both groups. The average time from primary THA those with missing data on fixation, femoral head size, and articulation (n = 108) were excluded. The study group con- Table 1. Demographic and surgical data. Numbers are given as n sisted of 504 patients 30 years or younger. During the same (%) unless otherwise stated period, 207,629 surgeries performed in patients older than 30 years had been reported to the register (Figure 1). For comparDemographics ≤ 30 years > 30 years and surgical data (n = 504) (n = 504) ison a propensity-score-matched group older than 30 years (n = 504) was included. Patient-reported outcomes were reported Women 300 (60) 300 (60) to SHAR on a national basis from 2008. The end of the study Age, mean (SD) 25 (4) 54 (13) Diagnosis was defined as March 23, 2018 (the date when the data reposiPrimary OA 50 (10) 49 (10) tory was created), revision or death, whichever occurred first. Inflammatory arthritis 119 (24) 123 (24) Primary outcome was implant survival at 15 years. SecondOA following childhood disease 120 (24) 119 (24) Avascular necrosis 73 (15) 73 (15) ary outcomes were implant survival at 10 years and patientOther 142 (28) 140 (28) reported outcomes pre- and at 1 year postoperatively. Statistics Normally distributed data are reported as mean (SD). Nonnormally distributed data are presented with median (IQR). The propensity score matching was done using sex, diagnosis, implant fixation, articulation, year of operation, and femoral head size. A 1:1 nearest-neighbor matching using logistic regression was applied to estimate the propensity scores. Non-parametric testing was performed to compare the patientreported outcomes. Statistical significance was set at p < 0.05. Unadjusted Kaplan–Meier survival analysis was performed to analyze implant survival with revision, defined as exchange or removal of parts or all of the implant. Survival data are presented as percentage and 95% confidence interval (CI). In the study group (30 years or younger) a univariable Cox regression analysis was performed to study the influence of fixation, articulation, and femoral head size on risk of revision.

Year of operation 2000–2004 133 (26) 144 (29) 2005–2009 115 (23) 109 (22) 2010–2014 170 (34) 167 (33) 2015–2016 86 (17) 84 (17) Fixation Cemented 75 (15) 76 (15) Hybrid 35 (7) 36 (7) Reversed hybrid 80 (16) 73 (15) Uncemented 314 (62) 319 (63) Articulation Ceramic on ceramic 131 (26) 141 (28) Ceramic on polyethylene 22 (4) 22 (4) Ceramic on polyethylene (x-linked) 6 (1) 5 (1) Metal on polyethylene 291 (58) 285 (57) Metal on polyethylene (x-linked) 54 (11) 51 (10) Femoral head size < 28 mm 62 (12) 54 (11) 28 mm 233 (46) 239 (47) 32 mm 161 (32) 168 (33) 36 mm 48 (10) 43 (9) Follow-up, mean (SD) 8 (5) 8 (5) OA = osteoarthritis, x-linked = highly cross-linked.

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Table 3. Patient-reported outcomes. Values are median (IQR) unless otherwise stated

EQ-5D-3L-index, n preoperative 1 year postoperative delta EQ-VAS, n preoperative 1 year postoperative delta

≤ 30 years 139 0.09 (–0.02 to 0.59) 0.70 (0.60 to 1.00) 0.51 (0.18 to 0.76) 153 44 (30 to 61] 80 (60 to 90) 29 (10 to 45)

> 30 years 198 0.16 (0.06 to 0.69) 0.80 (0.70 to 1.00) 0.36 (0.17 to 0.71) 219 50 (35 to 70) 80 (65 to 90) 20 (3 to 37)

p-value 0.003 0.04 0.1 0.006 0.3 0.02

Due to a migration from EQ-5D 3 level to EQ-5D 5 level, there was a discrepancy in the number of patients with valid EQ-5D-3L index and EQ-VAS.

Figure 2. Survival probability with implant revision as end-point. Age

0

≤ 30 > 30

504 504

Number at risk after index operation (years) 3 6 9 12 421 416

325 307

212 195

136 128

s15 66 70

Table 2. Reason for revision and type of revision performed Reason/type

≤ 30 years (n = 53)

Reason for revision, n Aseptic loosening 34 Dislocation 1 Fracture 0 Infection 6 Others 9 Type of revision, n Cup + stem exchange 9 Cup exchange 22 Extraction 6 Femoral head exchange 1 Liner ± head exchange 12 Stem exchange 3

> 30 years (n = 29) 14 3 1 7 3 4 13 3 1 5 3

to revision was 8 (SD 5) years in the study group and 6 (SD 5) years in the comparison group. The 15- and 10-year implant survivorship for patients aged 30 years or younger was 78% (CI 71–84) and 90% (CI 87–94) respectively. The corresponding figures for the comparison group were 89% (CI 84–93) and 94% (CI 91–97) (Figure 2). 53 out of 504 patients in the study group had been revised, and the most common reason for revision was aseptic loosening (n = 34). Corresponding figures were 29 and 14 in the comparison group (Table 2). Applying the Cox regression, the risk of revision in the study group was lower if uncemented fixation had been used (HR: 0.3, CI 0.2–0.7) when compared with cemented fixation. The limited number of events in different

strata with regards to articulation and head size did not allow for meaningful statistical analysis. Median (IQR) preoperative EQ-5D index was 0.09 (–0.02– 0.59) and 0.16 (0.06–0.69) in the study and the comparison group respectively (p = 0.003). The corresponding figures 1 year postoperatively were 0.7 (0.6–1.0) and 0.8 (0.7–1.0) (p = 0.04). In the study group the median preoperative EQ-VAS (44 [30–61]) was lower (p = 0.006). At 1 year, EQ-VAS was similar between the 2 groups (p = 0.3); the improvement in EQ-VAS (29 [10–45]) was larger (p = 0.02) in the study group (Table 3).

Discussion Our study represents a nationwide analysis of young patients operated with a total hip arthroplasty after the turn of the 21st century. We found acceptable long-term results with regards to implant survival. Patient-reported outcomes in the younger patients at 1 year following THA were satisfactory. Early reports on young patients operated with THA revealed a substantially higher risk of revision (Chandler et al. 1981, Dorr et al. 1983, Sarmiento et al. 1990) than comparable publications studying older patients. In 1990 Dorr et al. reported on 81 patients between 15 and 45 years of age operated with a THA. At an average follow up of 9 years 29 of the patients had been revised. Young age has since been considered a relative contraindication. Also, according to later data from national joint registries, the risk of revision is much higher in younger patients (Bayliss et al. 2017). In our study the implant survival was markedly higher than in the aforementioned studies. This could partly reflect the improvement in surgical techniques, tribology of the implants, and fixation technique (Barrack et al. 1992, Walker et al. 2016). These improvements could partly account for the higher implant survival being reported in recent single-center series (Makarewich et al. 2018, S ­ chreurs et al. 2018). Schreurs et al. (2018) analyzing 180 hips operated with a cemented hip replacement reported a 10-year implant survival of 87% (Schreurs et al. 2018). Makarewich et al. (2018) reported a 10-year implant survival of 89% in patients

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younger than 30 years. Due to concerns regarding generalizability when single-center studies are performed we decided to report on data from a national registry with high completeness. We found implant survival at 10 years consistent with recent reports. We are not certain whether differences in comorbidity, indications for surgery and number of previous surgeries are similar between our and previous studies. In our analysis the 15-year implant survival was 78%. Including metal-on-metal cases the 15- and 10-year implant survival were 76% and 89%. Thus there is still room for improvement for outcomes in the younger patients. To our knowledge there are no previous reports on patientreported outcomes in younger patients. Before operation both the EQ-5D index and EQ-VAS were lower in the younger group. This finding might reflect a reluctance by surgeons and perhaps also by patients to accept operation with a THA due to an expected high risk of future revisions. The corresponding values at 1-year post-surgery did not differ between the groups, hence the improvement was larger in the younger group. It could be argued that the large improvement and the comparable patient-reported outcomes at 1 year is a warrant for the success of THA with regards to risk of late re-operations (Eneqvist et al. 2018). There are several limitations to our study. First it could be argued that only the most skilled surgeons are operating on younger patients, making a comparison with a larger cohort of patients operated by all surgeons difficult. We do not have access to surgeon-specific data in the register, thus not allowing us to adjust for this supposed discrepancy. Although this limitation might benefit the implant survival in the younger group it should not have influenced the patient-reported outcomes (Jolbäck et al. 2018). Further, including data from national registries with high coverage and completeness will contribute to increased generalizability of our conclusions when compared with single-center series. Second, in our analysis more than half of the patients in the study group were operated with nonhighly cross-linked polyethylene (PE), mainly during the start of the study period. This could partly explain the less favorable implant survival at 15 years. It could be expected that the supposed long-term benefits of the highly cross-linked PE are more pronounced in the younger study group. If so, the results might be even better for these patients in the long term, but this hypothesis needs further investigation. Third, in performing an observational study there may be residual confounders such as case complexity and presence of previous surgical interventions that we could not account for. To what extent such factors might have influenced our results remains unknown. In summary we found acceptable implant survival in the long term in a cohort of 504 patients reported to the Swedish Hip Arthroplasty Register and promising patient-reported outcomes at 1 year. Our findings support the use of THA as a feasible option in young patients with severe symptoms at least in cases where no other joint-preserving surgery is expected to be successful.

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MM, HM, JK, and OR conceived and planned the study. DO and EN performed statistical analyses. MM drafted the manuscript with subsequent substantial inputs from all co-authors. All authors interpreted the findings. The authors would like to thank the orthopedic teams at the different centers in Sweden as well as the register coordinators at the Center of Registries, Västra Götaland for the high quality and integrity of the data being collected in the Swedish Hip Arthroplasty register.  Acta thanks Willem Schreurs and Claus Varnum for help with peer review of this study.

AOANJRR. Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR). Hip, Knee & Shoulder Arthroplasty: 2018 Annual Report. Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR). Hip, Knee & Shoulder Arthroplasty: 2018 Annual Report. https://aoanjrr.sahmri.com/documents/10180/576950/ Hip%2C%20Knee%20%26%20Shoulder%20Arthroplasty; 2018; 2018. Barrack R L, Mulroy R, Harris W H. Improved cementing techniques and femoral component loosening in young patients with hip arthroplasty: a 12-year radiographic review. Bone Joint J 1992; 74(3): 385-9. Bayliss L E, Culliford D, Monk A P, Glyn-Jones S, Prieto-Alhambra D, Judge A, et al. The effect of patient age at intervention on risk of implant revision after total replacement of the hip or knee: a population-based cohort study. Lancet 2017; 389(10077): 1424-30. Chandler H P, Reineck F, Wixson R, McCarthy J. Total hip replacement in patients younger than thirty years old: a five-year follow-up study. J Bone Joint Surg Am 1981; 63(9): 1426-34. Dorr L, Takei G, Conaty J. Total hip arthroplasties in patients less than fortyfive years old. J Bone Joint Surg Am 1983; 65(4): 474-9. Dorr L D, Luckett M, Conaty J P. Total hip arthroplasties in patients younger than 45 years. A nine- to ten-year follow-up study. Clin Orthop Relat Res 1990; (260): 215-19. Eneqvist T, Nemes S, Bülow E, Mohaddes M, Rolfson O. Can patientreported outcomes predict re-operations after total hip replacement? Int Orthop 2018; 42(2): 273-9. Jolbäck P, Rolfson O, Mohaddes M, Nemes S, Kärrholm J, Garellick G, et al. Does surgeon experience affect patient-reported outcomes 1 year after primary total hip arthroplasty? A register-based study of 6,713 cases in western Sweden. Acta Orthop 2018; 89(3): 265-71. Kärrholm J, Mohaddes M, Odin D, Vinblad J R, C, Rolfson O. The Swedish Hip Arthroplasty Register, Annual Report 2017. The Swedish Hip Arthroplasty Register, Annual Report 2017. https://registercentrum.blob.core. windows.net/shpr/r/-rsrapport-2017-S1xKMzsAwX.pdf; 2018; 2018. Makarewich C A, Christensen M, Anderson M B, Gililland J M, Pelt C E, Peters C L. Ten-year survivorship of primary total hip arthroplasty in patients 30 years of age or under: successful, but higher risk of revision. Bone Joint J 2018; 100(Suppl. 1): 50–. NJR. National Joint Registry for England, Wales, Northern Ireland and Isle of Man 15th Annual Report 2018. National Joint Registry for England, Wales, Northern Ireland and Isle of Man 15th Annual Report 2018. http://www. njrreports.org.uk/Portals/0/PDFdownloads/NJR%2015th%20Annual%20 Report%202018.pdf; 2018; 2018. Sarmiento A, Ebramzadeh E, Gogan W, McKellop H. Total hip arthroplasty with cement: a long-term radiographic analysis in patients who are older than fifty and younger than fifty years. J Bone Joint Surg Am 1990; 72(10): 1470-6. Schreurs B, Colo E, Schmitz M, Rijnen W, Gardeniers J. Total hip arthroplasty in patients under 30 years: a long-term report of 180 hips. Bone Joint J 2018; 100(Suppl. 1): 48–. Walker R P, Gee M, Wong F, Shah Z, George M, Bankes M J, et al. Functional outcomes of total hip arthroplasty in patients aged 30 years or less: a systematic review and meta-analysis. Hip Int 2016; 26(5): 424-31.

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Minor influence of patient education and physiotherapy interventions before total hip replacement on patient-reported outcomes: an observational study of 30,756 patients in the Swedish Hip Arthroplasty Register Christopher TORISHO 1, Maziar MOHADDES 1,2, Kristin GUSTAFSSON 3, and Ola ROLFSON 1,2 1 Department

of Orthopaedics, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg; 2 Swedish Hip Arthroplasty Register, Gothenburg; 3 Division of Physiotherapy, Department of Medical and Health Sciences, Linköping University, Linköping, Sweden Correspondence: christopher.torisho@vgregion.se Submitted 2018-11-30. Accepted 2019-03-08

Background and purpose — It is unclear whether physiotherapy interventions or patient education before total hip replacement (THR) is beneficial for patients postoperatively. Utilizing the Swedish Hip Arthroplasty Register (SHAR), we retrospectively studied the influence of preoperative selfreported exposure to physiotherapy and/or patient education on patient-reported outcomes 1 year after THR. Patients and methods — Data covering all THRs performed in Sweden for osteoarthritis, between the years 2012 and 2015, was obtained from SHAR. There were 30,756 patients with complete data. Multiple linear regression modelling was performed with 1-year postoperative PROMs (hip pain on a visual analogue scale [VAS], with the quality of life measures EQ-5D index and EQ VAS, and surgery satisfaction VAS) as dependent variables. Self-reported physiotherapy and patient education (yes or no) were used as independent variables. Results — Physiotherapy was associated with slightly less pain VAS (–0.7, 95% CI –1.1 to –0.3), better EQ-5D index (0.01, CI 0.00–0.01), EQ VAS (0.8, CI 0.4–1.2), and better satisfaction VAS (–0.7, CI –1.2 to –0.2). Patient education was associated with slightly better EQ-5D index (0.01, CI 0.00–0.01) and EQ VAS (0.7, CI 0.2–1.1). Interpretation — Even though we found statistically significant differences in favor of physiotherapy and patient education, the magnitude of those were too small and inconsistent to conclude a truly positive influence. Further research is needed with more specific and demarcated physiotherapy interventions.

Physiotherapy, in the form of supervised exercise, has been shown to reduce pain and improve function as assessed with patient-reported outcome measures (PROMs) for hip OA patients (Hernandez-Molina et al. 2008, Fransen et al. 2014), including later stages of the disease (Rooks et al. 2006, Villadsen et al. 2014). Self-management for knee and hip osteoarthritis improves pain (Chodosh et al. 2005) up to 21 months after intervention (Kroon et al. 2014), although both studies questioned the clinical relevance due to limited effect size. A recent meta-analysis including 13 RCTs reported a positive effect of preoperative exercise and patient education on postoperative pain for hip OA (Moyer et al. 2017). The meta-analysis found large differences in published studies with regard to interventions and minimal reporting on confounders. In Sweden, core treatment of OA is standardized in a national educational self-management programme for hip and knee OA patients, the Supported Osteoarthritis Self-Management Programme (SOASP) (Thorstensson et al. 2015). SOASP has the intent to increase quality of life during the course of the disease. Patients participating in the programme meet at group sessions and are taught about their disease, how to manage and cope with OA symptoms, and the rationale for exercising, by physiotherapists or occupational therapists. Participants are also offered individually adapted physical exercises, to be carried out in group training sessions or individually. The National Board of Health and Welfare of Sweden recommends non-surgical treatment options before listing OA patients for total joint replacement (Socialstyrelsen 2014). According to data from the Swedish Hip Arthroplasty Register 2015, the proportion of hip OA patients that have visited a physiotherapist (47–89%) or taken part in the SOASP (10–63%) prior

© 2019 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group, on behalf of the Nordic Orthopedic Federation. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits ­unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. DOI 10.1080/17453674.2019.1605669

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to THR, varies widely between different regions in Sweden (Kärrholm et al. 2016). We investigated the influence of self-reported exposure to physiotherapy and/or patient education before THR on patient-reported outcomes 1 year postoperatively. In addition we explored demographic differences in the patient groups receiving or not receiving physiotherapy and/or patient education.

Patients and methods This is an a posteriori study of observational routinely collected health data from the Swedish Hip Arthroplasty Register (SHAR) analyzing the influence of preoperative self-reported exposure to physiotherapy and/or patient education on patientreported outcomes 1 year after THR. The Swedish Hip Arthroplasty Register (SHAR) Data were obtained from the SHAR. This national joint registry has a coverage of all the hospitals performing hip replacements in the country and had a completeness of 98.3% of all total hip replacements performed in 2015 (Kärrholm et al. 2018). All data on primary THRs, including PROMs, are collected by the participating units, and entered into the register database using 2-factor authentication (Kärrholm et al. 2008). Patient-reported outcome measures in SHAR Since 2002, SHAR has gathered PROMs from THR patients. In conjunction with the preoperative visit, patients are asked to complete a short survey (paper and digital version available according to the unit’s preference) including the EuroQol 5 dimensions (EQ-5D), a hip pain visual analogue scale (pain VAS), and self-reported Charnley classification. At 1-year postoperative follow-up, the same pen-and-paper survey is sent by ordinary mail with the addition of a satisfaction item on a VAS. The SHAR PROMS program has been described in detail previously (Rolfson et al. 2011). EQ-5D measures health-related quality of life and consists of 2 parts. For the first part, we used the British value set to calculate the EQ-5D index, which ranges from –0.59 to 1.0, where 1.0 corresponds to perfect health and negative results to a state worse than death (Dolan and Roberts 2002). In the second part, the patient estimates his or her current health status on a 100-degree scale, where 0 corresponds to worst imaginable health and 100 to best imaginable health. With pain VAS, the patient estimates his or her current pain on a visual 100-degree scale, where 0 corresponds to no pain and 100 to worst imaginable pain. Satisfaction VAS measures patient satisfaction with the outcome of surgery on a visual 100-degree scale, where 0 corresponds to a completely satisfied patient and 100 to an unsatisfied patient.

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In 2012, 2 questions (yes/no) were added to the preoperative survey: (1) “Have you been to see a physiotherapist for your hip during the period of hip problems?” and (2) “Have you taken part in a so-called SOASP (may have been many years before the operation for a shorter period of time) during the period of hip problems.” The response rate in 2014 was 85% for preoperative PROMs and 90% for the 1-year follow-up postoperative PROMs (Garellick et al. 2015).   Patient selection Data retrieved from SHAR covered hip OA (ICD-10 codes M16*) patients who had undergone primary THR surgery (NOMESCO codes NFB29, 39, and 49) between 2012 and 2015, with the years covering all available data including physiotherapy, patient education, and 1-year postoperative PROMs. Data retrieval was done in March 2018 and included age, sex, surgery side, first or second surgery, BMI, ASA class, Charnley class, incision, fixation, patient education, and physiotherapy. In addition, all PROMs collected preoperatively and/or postoperatively (pain VAS, EQ-5D and EQ VAS, and postoperative satisfaction VAS) were included. We selected the surgeries where patients had their first primary THR, i.e., they had no previous hip replacement of their contralateral hip. Additional selection criteria were applied to exclude patients missing data (BMI, ASA class, incision, type of fixation, patient education, physiotherapy, preoperative and 1-year postoperative PROMs). Patients with extreme values (BMI < 15 and BMI > 50) were excluded since these were probably erroneously recorded. Statistics The software SPSS statistics version 25 (IBM Corp, Armonk, NY, USA) was used for all statistical analyses. The null hypothesis was rejected when p < 0.05. Continuous variables were compared by using paired t-test. Categorical variables were analyzed by conducting Pearson’s chi-square tests to check for statistical significance between the 2 groups. 95% confidence intervals (CI) were calculated when appropriate. Linear regression analysis The linear regression analyses were made by using a generalized linear model. A 95% confidence interval was used. The dependent variables used in the model were the postoperative PROMs: pain VAS, EQ-5D index, EQ VAS, and satisfaction VAS. The independent variables included were: age, sex, BMI, ASA class, Charnley class, incision, fixation, patient education, and physiotherapy. Also, for the preoperative pain VAS, EQ-5D index, and EQ VAS the corresponding preoperative variables were used as independent variables in the models. Non-respondent analysis 3 different non-respondent analyses were performed. First,

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All THR for OA 2012–2015 n = 54,167 Excluded (n = 23,411): – had second hip surgery, 13,537 — ”Missing 1” – missing preoperative PROMs and/or data on patient education and physiotherapy, 5,282 — ”Missing 2” – extreme BMI or missing data on BMI, ASA classification, surgical approach and/or fixation method, 1,203 – missing postoperative PROMs, 3,389 — ”Missing 3” Study group n = 30,756

Figure 1. The flowchart describes the selection of patients. As defined here, excluded patients form 3 groups: missing 1, missing 2, and missing 3, further investigated in the missing data/non-respondent analysis (see Appendix). Abbreviations: THR = total hip replacement, OA = osteoarthritis, BMI = body mass index, ASA = American Association of Anesthesiologists’ classification.

patients with missing data on preoperative PROMs, physiotherapy, and patient education were compared with the patients included in the current analysis (study group). Second, cases excluded due to patients having second hip surgery and, third, the group with missing postoperative PROMs were compared with the study group. The method used was ANOVA with post-hoc Tukey with continuous variables and Pearson’s chisquare test with categorical variables. Ethics, funding, and potential conflicts of interest This study is a part of a larger research project which has been reviewed and approved by the Regional Ethical Review Board in Gothenburg (2014-04-09, 271-14). The study was partly financed by grants from the Swedish state under the agreement between the Swedish government and the county councils, the ALF-agreement (ALFGBG–522591). The authors declare no conflicts of interest.

Results Demographics (Table 1) Of all the 54,167 cases obtained from SHAR, 30,756 (59%) met the selection criteria and were included in the regression analyses (Figure 1). Of these, 71% reported exposure to physiotherapy, patient education or both, prior to surgery. Among the study group, 68% reported exposure to physiotherapy and 27% reported exposure to patient education, prior to surgery. At baseline, patients exposed to PT/SOASP had a statistically significantly lower age, BMI, preoperative EQ-5D index, and preoperative EQ-VAS, but higher preoperative pain VAS when compared with patients not exposed, on average. The PT/ SOASP group also had a higher proportion of women, ASA I– II, and Charnley class A, and a lower proportion of cemented surgery.

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Table 1. Demographics Variable

Study group

Physiotherapy and/ or patient education No Yes

p-value a

Total numbers 30,756 9,040 21,716 Age b 68 (9.9) 70 (10) 68 (9.7) < 0.01 Female c 17,127 (56) 4,250 (47) 12,877 (59) < 0.01 BMI b 27.3 (4.3) 27.4 (4.4) 27.2 (4.3) < 0.01 ASA I–II c 26,315 (86) 7,356 (81) 18,959 (87) < 0.01 Charnley class c < 0.01 A 14,946 (49) 4,372 (49) 10,574 (49) B 4,125 (13) 1,129 (13) 2,996 (14) C 11,685 (38) 3,539 (39) 8,146 (38) Incision c 0.4 Posterior 16,316 (53) 4,743 (53) 11,573 (53) Lateral 14,205 (46) 4,227 (47) 9,978 (46) Other 235 (0.8) 70 (0.8) 165 (0.8) Fixation c < 0.01 Cemented 19,339 (63) 5,967 (66) 13,372 (62) Uncemented 6,165 (20) 1,673 (19) 4,492 (21) Other 5,252 (17) 1,400 (16) 3,852 (18) Pain VAS b 63.2 (15.3) 62.7 (16.3) 63.4 (14.9) < 0.01 EQ-5D index b 0.42 (0.3) 0.43 (0.3) 0.42 (0.3) < 0.01 EQ VAS b 57.9 (22.1) 59.0 (21.8) 57.5 (22.2) < 0.01   a A 2-column Pearson’s chi-square test was used on the categorical variables. An independent sample t-test was used on the continuous variables. b Continuous variables, presented with frequency (standard deviation). c Categorical variables, presented with frequency (percentage).

Linear regression analysis (Figures 2–5) Physiotherapy was associated with 0.7 units lower pain VAS (CI –0.3, –1.1), 0.01 units higher EQ-5D index (CI 0.00, 0.01), 0.8 units higher EQ VAS (CI 0.4, 1.2), and 0.7 units lower (= better) score on the satisfaction VAS (CI –1.2, –0.2) postoperatively. Self-reported patient education was associated with better EQ-5D index and EQ VAS. Patient education was associated with 0.006 units higher EQ-5D (0.01, CI 0.00, 0.01) and 0.7 units higher EQ VAS (0.7, CI 0.2, 1.1). Patient education did not influence pain VAS (–0.3, CI –0.7, 0.2) or satisfaction VAS (0.1, CI –0.4, 0.6) postoperatively. Non-respondent and missing data analysis Compared with the study group, patients excluded due to having THR on their second hip had on average higher age, higher BMI, and higher preoperative pain VAS. They also had a higher proportion of females, Charnley class A, and cemented fixation, but a lower proportion of ASA I–II. Compared with the study group, patients with missing data on preoperative PROMs, physiotherapy, or patient education had on average higher age. They also had a higher proportion of cemented fixation as well as a lower proportion of ASA I–II and posterior incision. As for patients missing postoperative PROMs, they had on average lower age, higher BMI, higher preoperative pain VAS, lower EQ-5D index, and lower EQ-VAS, compared with the study group (Table 2, see Supplementary data).

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1-year postoperative EQ-5D

1-year postoperative pain Variable

Variable

Coefficient (CI)

Age BMI Sex Men Women ASA class 1–2 3–4 Charnley class A B C Surgical approach Posterior Lateral Other Fixation Cemented Uncemented Other Preoperative pain VAS Physiotherapy No Yes Patient eduction No Yes

Age BMI Sex Men Women ASA class 1–2 3–4 Charnley class A B C Surgical approach Posterior Lateral Other Fixation Cemented Uncemented Other Preoperative EQ-5D Physiotherapy No Yes Patient eduction No Yes

0.1 (0.0 to 0.1) 0.2 (0.1 to 0.2) ref 0.8 (0.4 to 1.2) ref 2.3 (1.8 to 2.9) ref 3.4 (2.8 to 3.9) 5.2 (4.7 to 5.6) ref 2.3 (1.9 to 2.7) 1.6 (–0.6 to 3.8) ref –1.8 (–2.4 to –1.2) –0.7 (–1.3 to –0.2) 0.1 (0.1 to 0.1) ref –0.7 (–1.1 to –0.3) ref –0.3 (–0.7 to 0.2)

–5

–3

–1

1

3

1-year postoperative EQ VAS Age BMI Sex Men Women ASA class 1–2 3–4 Charnley class A B C Surgical approach Posterior Lateral Other Fixation Cemented Uncemented Other Preoperative EQ VAS Physiotherapy No Yes Patient eduction No Yes

–0.2 (–0.2 to –0.1) –0.3 (–0.4 to –0.3)

Age BMI Sex Men Women ASA class 1–2 3–4 Charnley class A B C Surgical approach Posterior Lateral Other Fixation Cemented Uncemented Other Physiotherapy No Yes Patient eduction No Yes

ref –1.3 (–1.7 to –0.9) ref –6.2 (–6.8 to –5.7) ref –4.5 (–5.1 to –3.9) –8.9 (–9.3 to –8.5) ref –2.0 (–2.3 to –1.6) –2.6 (–4.8 to –0.5) ref 1.2 (0.7 to 1.8) 0.9 (0.4 to 1.5) 0.2 (0.2 to 0.2) ref 0.8 (0.4 to 1.2) ref 0.7 (0.2 to 1.1)

–10

–8

–6

–4

–2

0

2

ref –0.057 (–0.064 to –0.050) ref –0.057 (–0.063 to –0.050) –0.11 (–0.11 to –0.10) ref –0.028 (–0.033 to –0.023) –0.013 (–0.041 to 0.015) ref 0.022 (0.014 to 0.029) 0.0093 (0.0022 to 0.016) 0.13 (0.12 to 0.14) ref 0.0061 (0.0006 to 0.012) ref 0.0060 (0.0003 to 0.012)

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Figure 4. Linear regression results with the dependent variable EQ VAS 1 year postoperatively.

Discussion In this study based on a national registry, patients visiting a physiotherapist at some point during the course of their disease had statistically significantly better 1-year postoperative PROMs. However, the positive influence was only on a par with or below the smallest factors the model was adjusted for, making the clinical relevance of the results uncertain. For patients with hip OA, physiotherapy in the form of supervised exercise has been shown to reduce pain and improve function (Hernandez-Molina et al. 2008, Fransen et al. 2014). A few authors have also reported beneficial preoperative effects of supervised exercise for patients awaiting surgery (Wallis et al. 2011, Gill et al. 2013). A recent meta-analysis by Moyer et al. (2017) evaluating postoperative effects after preoperative supervised exercise concluded that there were improvements for pain, function, and length of stay. One of the included studies (Rooks et al. 2006) did not show any positive postoperative effects on PROMs and another RCT found

0

–0.1

0.1

0.2

1-year postoperative satisfaction Variable

–12

ref –0.031 (–0.036 to –0.026)

Figure 3. Linear regression results with the dependent variable EQ-5D 1 year postoperatively.

Coefficient (CI)

–14

–0.0012 (–0.0015 to –0.0009) –0.0042 (–0.0047 to –0.0036)

–0.2

5

Figure 2. Linear regression results with the dependent variable pain VAS 1 year postoperatively. Variable

Coefficient (CI)

Coefficient (CI) 0.1 (0.1 to 0.2) 0.2 (0.1 to 0.2) ref 1.9 (1.5 to 2.4) ref 2.6 (2.0 to 3.2) ref 2.1 (1.4 to 2.8) 4.4 (3.9 to 4.8) ref 4.0 (3.6 to 4.4) 0.5 (–2.0 to 3.0) ref –2.2 (–2.9 to –1.6) –1.1 (–1.7 to –0.5) ref –0.7 (–1.2 to –0.2) ref 0.1 (–0.4 to 0.6)

–7

–5

–3

–1

1

3

5

Figure 5. Linear regression results with the dependent variable satisfaction 1 year postoperatively.

no effects lasting past 6 weeks postoperatively following total knee and hip arthroplasty (Villadsen et al. 2014). There is 1 small RCT with 21 participants that showed better postoperative PROMs for THR patients following preoperative supervised exercise (Ferrara et al. 2008). In that study, patients in the exercise group had a statistically significantly (0.97 points) lower pain VAS (scale 0–10) 3 months postoperatively compared with controls, though also had a non-significant lower pain VAS of 0.62 at baseline. Compared with our postoperative VAS difference of 0.69 (scale 0–100), their result was more than 10 times larger. Our study shows a statistically significant positive association with health-related quality of life as measured with EQ-5D and EQ VAS but not for pain and satisfaction in patients participating in preoperative patient education. There is a lack of larger RCTs (Wang et al. 2016) investigating the role of patient education during the course of the disease in postoperative outcomes. A few review articles (Ibrahim et al. 2013, McDonald et al. 2014, Aydin et al. 2015) have tried

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to analyze association between surgery-oriented preoperative patient education and postoperative outcomes with only 1 (Ibrahim et al. 2013) concluding that preoperative patient education resulted in better postoperative PROMs. The contradictory findings in the literature are partly reflected by our findings with a slight improvement in quality of life but no effect on pain or satisfaction in patients operated with THR following preoperative patient education. There are limitations in this study. First, the physiotherapy interventions were not defined. Some patients reporting they have visited a physiotherapist might have received only non-exercise-based treatment, which potentially may reduce the association we found between physiotherapy and postoperative PROMs. The recommended physiotherapy-based treatment by the Swedish National Board of Health Welfare is long-term exercise (Socialstyrelsen 2012). However, the patients might have visited their physiotherapist before those recommendations were published and/or before receiving other interventions. In addition, we are not aware of how quickly and to what degree those recommendations have been implemented in Sweden. Second, we do not know when the patients received their physiotherapy interventions, how regularly, to what intensity, or their compliance. This could affect our results. While there is a lack of validated evidence of preoperative exercise-based before joint replacement (Hoogeboom et al. 2012), the RCT in the field that has seen postoperative effects from preoperative physiotherapy has administered the interventions within a month from surgery and 5 times a week (Ferrara et al. 2008). The recruitment rate for physiotherapy within weeks before total joint replacement can be as low as 12% (Rooks et al. 2006) or 34% (Hoogeboom et al. 2010), with difficult transportation to the sessions a common complaint (Rooks et al. 2006, Hoogeboom et al. 2010). As 68% of the patients in our study group had answered “yes” to having been exposed to physiotherapy interventions, it is more likely that they have been exposed during earlier stages of the disease, with the intent of reducing OA symptoms. The third limitation is the lack of information regarding to what degree patients have taken part in rehabilitation following THR. Geographic areas that have a higher availability of physiotherapy and SOASP might also have different availability of postoperative rehabilitation, potentially affecting our results. The fourth limitation pertains to the demographic differences between the no PT/SOASP group and PT/SOASP group. 6 preoperative variables were favorable for the PT/ SOASP group according to the factors’ coefficients on our regression analysis: age, BMI, ASA I–II, Charnley class, incision, and fixation. 4 preoperative variables were favorable for the no PT/SOASP group: sex, preoperative pain VAS, EQ-5D index, and EQ VAS. Though all those factors are adjusted for in the linear regression model, there is still a risk of having the results derive from confounding factors not accounted for in

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the modelling. Finally, there is also always a risk, when excluding patients, that the results do not represent the reality. The 3 excluded groups had worse baseline variables compared with the analysis group, predicting worse postoperative PROMs. If the patients in the excluded groups had had complete data and had been included in the analysis group, we would probably have seen overall worse postoperative PROMs. How the factors in the linear regression models would have been affected is, however, hard to forecast. While much of the earlier focus has been on education and physiotherapy in close proximity to THR, our study indicates that interventions at some point during the course of OA have a positive influence on PROMs after surgery. Due to this study being observational, we cannot establish the causal relationships. Although earlier studies have not demonstrated lasting effects of physiotherapy post-THR, the influence observed in our study may be explained by increased compliance with supervised exercise after surgery. In OA patients without joint replacement, a previous systematic review article demonstrated the effect of supervised exercise lasting past 6 months with additional “booster” sessions with physiotherapists (Pisters et al. 2007). This could possibly be translatable for patients who have undergone THR. Further studies with more specific questions of supervised exercises before and after surgery could increase our understanding. Larger RCTs further exploring specific preoperative exercise interventions and their effect postoperatively are also needed. In summary, our study indicates that exposure to physiotherapy at some point during the course of OA has a small positive influence on 1-year postoperative PROMs after THR. Due to demographic differences, and uncertainties regarding the type of physiotherapy interventions and time frame, the clinical relevance of this small influence is uncertain. Therefore, the results should be interpreted with care. Further research is needed with more specific and demarcated physiotherapy interventions. Supplementary data Table 2 is available as supplementary data in the online version of this article, http://dx.doi.org 10.1080/17453674.2019. 1605669

The authors would like to thank all the surgeons and secretaries reporting to and coordinators maintaining the high quality and integrity of data being reported to the Swedish Hip Arthroplasty register. CT, OR, and MM conceived and planned the study. CT performed statistical analyses. CT drafted the manuscript with subsequent substantial inputs from all co-authors.   Acta thanks Allan Abbot and Siri Bjørgen Wintherfor help with peer review of this study.

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Aydin D, Klit J, Jacobsen S, Troelsen A, Husted H. No major effects of preoperative education in patients undergoing hip or knee replacement: a systematic review. Dan Med J 2015; 62(7). pii: A5106. Chodosh J, Morton S C, Mojica W, Maglione M, Suttorp M J, Hilton L, Rhodes S, Shekelle P. Meta-analysis: chronic disease self-management programs for older adults. Ann Intern Med 2005; 143(6): 427-38. Dolan P, Roberts J. Modelling valuations for EQ-5D health states: an alternative model using differences in valuations. Med Care 2002; 40(5): 442-6. Ferrara P E, Rabini A, Maggi L, Piazzini D B, Logroscino G, Magliocchetti G, Amabile E, Tancredi G, Aulisa A G, Padua L, Aprile I, Bertolini C. Effect of pre-operative physiotherapy in patients with end-stage osteoarthritis undergoing hip arthroplasty. Clin Rehabil 2008; 22(10-11): 977-86. doi: 10.1177/0269215508094714. Fransen M, McConnell S, Hernandez-Molina G, Reichenbach S. Exercise for osteoarthritis of the hip. Cochrane Database Syst Rev 2014(4): Cd007912. doi: 10.1002/14651858.CD007912.pub2. Garellick G, Kärrholm J, Lindahl H, Malchau H, Rogmark C, Rolfson O. The Swedish Hip Arthroplasty Register Annual Report 2014; 2015. doi: 10.18158/B1OyzZ00Z. Gill S D, McBurney H. Does exercise reduce pain and improve physical function before hip or knee replacement surgery? A systematic review and meta-analysis of randomized controlled trials. Arch Phys Med Rehabil 2013; 94(1): 164-76. doi: 10.1016/j.apmr.2012.08.211. Hernandez-Molina G, Reichenbach S, Zhang B, Lavalley M, Felson D T. Effect of therapeutic exercise for hip osteoarthritis pain: results of a metaanalysis. Arthritis Rheum 2008; 59(9): 1221-8. doi: 10.1002/art.24010. Hoogeboom T J, Dronkers J J, van den Ende C H, Oosting E, van Meeteren N L. Preoperative therapeutic exercise in frail elderly scheduled for total hip replacement: a randomized pilot trial. Clin Rehabil 2010; 24(10): 901-10. doi: 10.1177/0269215510371427. Hoogeboom T J, Oosting E, Vriezekolk J E, Veenhof C, Siemonsma P C, de Bie R A, van den Ende C H, van Meeteren NL. Therapeutic validity and effectiveness of preoperative exercise on functional recovery after joint replacement: a systematic review and meta-analysis. PLoS One 2012; 7(5): e38031. doi: 10.1371/journal.pone.0038031. Ibrahim M S, Twaij H, Giebaly D E, Nizam I, Haddad F S. Enhanced recovery in total hip replacement: a clinical review. Bone Joint J 2013; 95-b(12): 1587-94. doi: 10.1302/0301-620x.95b12.31303. Kroon F P, van der Burg L R, Buchbinder R, Osborne R H, Johnston R V, Pitt V. Self-management education programmes for osteoarthritis. Cochrane Database Syst Rev 2014(1): Cd008963. doi: 10.1002/14651858. CD008963.pub2. Kärrholm J, Garellick G, Rogmark C, Herberts P. The Swedish Hip Arthroplasty Register Annual Report 2007; 2008. doi: 10.18158/B1OyzZ00Z. Kärrholm J, Lindahl H, Malchau H, Mohaddes M, Nemes S, Rogmark C, Rolfson O. Swedish Hip Arthroplasty Register Annual Report 2016; 2018. doi: 10.18158/SJy6jKyrM.

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McDonald S, Page M J, Beringer K, Wasiak J, Sprowson A. Preoperative education for hip or knee replacement. Cochrane Database Syst Rev 2014(5): CD003526. doi: 10.1002/14651858.CD003526.pub3. Moyer R, Ikert K, Long K, Marsh J. The value of preoperative exercise and education for patients undergoing total hip and knee arthroplasty: a systematic review and meta-analysis. JBJS Rev 2017; 5(12): e2. doi: 10.2106/ jbjs.rvw.17.00015. Pisters M F, Veenhof C, van Meeteren N L, Ostelo R W, de Bakker D H, Schellevis F G, Dekker J. Long-term effectiveness of exercise therapy in patients with osteoarthritis of the hip or knee: a systematic review. Arthritis Rheum 2007; 57(7): 1245-53. doi: 10.1002/art.23009. Rolfson O, Karrholm J, Dahlberg L E, Garellick G. Patient-reported outcomes in the Swedish Hip Arthroplasty Register: results of a nationwide prospective observational study. J Bone Joint Surg Br 2011; 93(7): 867-75. doi: 10.1302/0301-620x.93b7.25737. Rooks D S, Huang J, Bierbaum B E, Bolus S A, Rubano J, Connolly C E, Alpert S, Iversen M D, Katz J N. Effect of preoperative exercise on measures of functional status in men and women undergoing total hip and knee arthroplasty. Arthritis Rheum 2006; 55(5): 700-8. doi: 10.1002/art.22223. Socialstyrelsen S. Nationella riktlinjer—Utvärdering—Vård vid rörelseorganens sjukdomar—Indikatorer och underlag för bedömning.: Socialstyrelsen; 2014. Socialstyrelsen S. Nationella riktlinjer för rörelseorganens sjukdomar 2012: osteoporos, artros, inflammatorisk ryggsjukdom och ankyloserande spondylit, psoriasisartrit och reumatoid artrit : stöd för styrning och ledning. Socialstyrelsen; 2012. Thorstensson C A, Garellick G, Rystedt H, Dahlberg L E. Better management of patients with osteoarthritis: development and nationwide implementation of an evidence-based supported osteoarthritis self-management programme. Musculoskeletal Care 2015; 13(2): 67-75. doi: 10.1002/msc.1085. Villadsen A, Overgaard S, Holsgaard-Larsen A, Christensen R, Roos E M. Postoperative effects of neuromuscular exercise prior to hip or knee arthroplasty: a randomised controlled trial. Ann Rheum Dis 2014; 73(6): 1130-7. doi: 10.1136/annrheumdis-2012-203135. Wallis J A, Taylor N F. Pre-operative interventions (non-surgical and nonpharmacological) for patients with hip or knee osteoarthritis awaiting joint replacement surgery: a systematic review and meta-analysis. Osteoarthritis Cartilage 2011; 19(12): 1381-95. doi: 10.1016/j.joca.2011.09.001. Wang L, Lee M, Zhang Z, Moodie J, Cheng D, Martin J. Does preoperative rehabilitation for patients planning to undergo joint replacement surgery improve outcomes? A systematic review and meta-analysis of randomised controlled trials. BMJ Open 2016; 6(2): e009857. doi: 10.1136/bmjopen-2015-009857.

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Patient-reported outcomes in hip resurfacing versus conventional total hip arthroplasty: a register-based matched cohort study of 726 patients Alexander OXBLOM 1, Håkan HEDLUND 1,2, Szilard NEMES 3,4, Harald BRISMAR 1, Li FELLÄNDER-TSAI 1, and Ola ROLFSON 3,4 1 Divison of Orthopaedics and Biotechnology, CLINTEC, Karolinska Institutet; 2 Visby Lasarett; 3 Swedish Hip Arthroplasty 4 Department of Orthopaedics, Institute of Clinical Sciences, Sahlgrenska Academy University of Gothenburg, Sweden

Register, Gothenburg;

Correspondence: alexander.oxblom@ki.se Submitted 2018-06-14. Accepted 2019-03-25.

Background and purpose — The theoretical mechanical advantages of metal-on-metal hip resurfacing (MoM-HR) compared with conventional total hip arthroplasty (THA) have been questioned. Studies including measures of patientreported function, physical activity, or health-related quality of life have been sparse. We compared patient-reported outcomes in MoM-HR patients with a matched group of patients with conventional THA at 7 years post-surgery. Patients and methods — Patients and patient data were retrieved from the Swedish Hip Arthroplasty Register. The case group, consisting of 363 patients with MoM-HR, was matched 1:1 with a control group, consisting of patients with a conventional THA. Patients were sent a postal patientreported outcome measures (PROM) questionnaire including the Hip Disability and Osteoarthritis Outcome Score (HOOS), EQ-5D, and VAS pain. We used multivariable linear regression analyses to investigate the influence of prosthesis type. Results — 569 patients (78%) returned the questionnaire with complete responses (299 MoM-HRs and 270 conventional THAs). MoM-HR was associated with better scores in HOOS function of daily living (4 percentage units) and HOOS function in sport and recreation (8 percentage units) subscales. Type of prosthesis did not influence HOOS quality of life, HOOS pain, HOOS symptoms, EQ-5D index, hip pain, or satisfaction as measured with visual analog scales. Interpretation — At mean 7 years post-surgery, patients with hip resurfacing had somewhat better self-reported hip function than patients with conventional THA. The largest difference between groups was seen in the presumed most demanding subscale, i.e., function in sport and recreation.

Hip arthroplasty in young and active patients is an orthopedic challenge. In 2011, the Finnish Arthroplasty Register (Mäkelä et al. 2011) reported a 15-year prosthesis survival rate of about 70% in patients younger than 55 years operated with conventional total hip arthroplasty (THA) compared with about 90% in patients older than 60 years in the combined Nordic Arthroplasty Registers (Havelin et al. 2009). Young patients have higher expectations following THA (Scott et al. 2012) and are more active, a patient-factor highly related to polyethylene wear (Schmalzried et al. 2000). They are also more prone to participate in high-impact sports following THA (Williams et al. 2012), which has been correlated with both increased wear (Ollivier et al. 2012) and higher revision rates (Flugsrud et al. 2007). Alternative surface bearings and prosthesis designs have therefore been developed to meet the demands of younger patients. Metal-on-metal hip resurfacing (MoM-HR) gained popularity in the mid-1990s due to advances in metallurgy and tribology, allowing manufacturing of thin acetabular cups accepting large-diameter components (Grigoris et al. 2006). It was believed that the wear-associated disadvantages seen with metal-on-polyethylene thereby could be solved. The method was expected to provide a sustainable arthroplasty for young and active patients with hip osteoarthritis (Amstutz and Le Duff 2012). Besides a bone-preserving surgical technique, MoM-HR was also claimed to restore hip mechanics with a better range of motion (Vail et al. 2006). However, there was a major setback when some MoM-HR implants and THAs with MoM articulations were reported to have unacceptably high failure rates (De Steiger et al. 2011, Smith et al. 2012). As a result, there was a dramatic decline in numbers of MoM-HR implanted worldwide and, in many countries, sur-

© 2019 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group, on behalf of the Nordic Orthopedic Federation. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits ­unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. DOI 10.1080/17453674.2019.1604343

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geons promptly stopped using the technique, due to perceived risks and the uncertainty regarding the long-term results of the implants (Cohen 2011). There are, though, some long-term follow-ups of certain brands of MoM-HR implants with acceptable implant survival in a selected group of patients (Matharu et al. 2013). It is evident that cautious patient selection is crucial, quite apart from implant design and surgical technique (Daniel et al. 2014). Reports on benefits of MoM-HR in terms of patient-reported function, physical activity, and health-related quality of life are sparse (Jiang et al. 2011). We compared patient-reported outcomes in patients operated with MoM-HR with a matched group of patients operated with conventional THA at mean 7 years post-surgery.

Patients and methods Patient selection This is an arthroplasty register-based matched cohort study. Patient data were retrieved from the Swedish Hip Arthroplasty Register. The case group, consisting of a consecutive group of all patients operated on with MoM-HR (all Birmingham Hip Resurfacing System, Smith & Nephew, Andover, Massachusetts, USA) at a single institution (Karolinska Huddinge) between the years 2002 and 2013, was matched 1:1 with a control group, consisting of patients with a conventional THA selected from the Register. In the case of bilateral MoM-HR (n = 105) or bilateral THA (n = 102) during the study period, we included data regarding the first operation. Patients deceased by December 2015 (n = 6) were excluded. The groups were matched by baseline characteristics: age, sex, surgical approach, year of surgery, and preoperative EQ-5D score when available. Outcome measures 726 patients (363 MoM-HRs, 363 conventional THAs) were selected for the study (Table 1). In December 2015, patients were invited to participate by mail and asked to complete a patient-reported outcome measures (PROM) questionnaire including the Hip Disability and Osteoarthritis Outcome Score (HOOS) (Nilsdotter et al. 2003), the EQ-5D (EuroQol Group 1990), hip pain measured with a visual analogue scale (VAS), and a VAS addressing satisfaction with the outcome of surgery. In addition to the postal questionnaire we used information from the Swedish Hip Arthroplasty Register covering surgical data, demography, data on subsequent reoperations and, when available, pre- and postoperative PROMs data including hip pain and the EQ-5D (Garellick et al. 2015). Statistics Subject-matter knowledge was used to identify and measure adjustment variables. The goal was to identify a sufficient set

Table 1. Patient demographics Characteristics

Case Control group group p-value

Number of patients 363 ( 363 ( Women, n (%) 90 (25) 86 (24) Age at primary operation, mean (SD) 52 (8.8) 51 (8.7) Year of surgery, mean (SD) 2008 (2.9) 2008 (2.9) Follow-up time, mean (SD) 7.3 (2.9) 7.3 (3.0) Distribution of diagnoses, n (%) Primary osteoarthritis 315 (87) 325 (90) Childhood hip disease 41 (11) 31 (8.5) Other hip joint disorders 7 (2.0) 7 (2.0) PROMs preoperatively, n 206 ( 363 ( VAS hip pain, mean (SD) 74 (16.4) 69 (18.4) EQ-5D index, mean (SD) 0.52 (0.29) 0.43 (0.32) Patients reoperated, n (%) 13 (3.6) 16 (4.4)

0.8 0.7 0.9 0.9 0.7

0.002 0.001 0.6

SD = standard deviation; PROMs = patient-reported outcome measures; VAS = visual analog scale; EQ-5D = EuroQol 5 dimensions.

for confounding adjustment for prosthesis type. This set was defined as a set of non-descendant variables for prosthesis type that block all backdoor paths. Confounder identification was based on Rubin’s 3 conditions (Robins 1999, Greenland et al. 1999). By matching we constructed a subset of the population in which the background has the same distribution in both the MoM-HR and the conventional THA groups. In observational studies, there is no guarantee that the treatment groups are conditionally exchangeable given the exposure only. Matching generally exploits the conditional exchangeability; however, matching cases and controls does not achieve unconditional exchangeability. Ignoring the matching variables in a cohort study can leave bias if there are additional confounders, even with adjustment for the additional confounders (Sjölander and Greenland 2013). Based on these 2 facts the final analysis included the variables used for matching. We identified age, sex, preoperative EQ-5D index, and time from surgery. Neither variable is on the path between the exposure and outcome and can block important backdoor paths (Figure 1, see Supplementary data). Using the Directed Acyclic Graph from Figure 1 and d-separation to infer associational statements (Textor et al. 2011) we could conclude that the minimal sufficient adjustment sets for estimating the direct effect and total effect is age, sex, and preoperative EQ-5D index. Time for surgery was included to reduce bias (Sjölander and Greenland 2013). We used multivariable linear regression analyses to investigate the influence of prosthesis type (MoM-HR versus conventional THA) adjusting for age, sex, preoperative EQ-5D index, and time from surgery. R (R Core Team 2017) and IBM SPSS Statistics version 25 (IBM Corp, Armonk, NY, USA) were used for statistical analyses. Missing covariate data were imputed using full-conditional specification (FCS) multiple imputation with the inclusion of the outcomes and matching variables (Seaman and Keogh 2015). The imputed data

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Table 3. Postoperative functional outcomes. Values are mean (SD) Variables HOOS index (%) Symptoms Pain ADL Sport/Rec QoL EQ-5D index VAS hip pain VAS satisfaction

Case Control group group p-value 85 (17) 90 (15) 90 (15) 77 (24) 77 (21) 0.90 (0.17) 11 (16) 13 (20)

83 (19) 87 (18) 84 (19) 68 (29) 74 (22) 0.87 (0.21) 12 (18) 12 (21)

0.09 0.01 < 0.001 < 0.001 0.07 0.2 0.4 0.7

SD = standard deviation; HOOS = Hip Disability and Osteoarthritis Outcome Score; ADL = Activity in Daily Living; Sport/Rec = Sport and Recreation; QoL = Quality of Life; EQ-5D = EuroQol 5 dimensions; VAS = Visual analog scale.

were used as input for regression analyses and estimates from each imputed dataset were combined into 1 overall estimate and associated variance, incorporating both the within and between imputation variability using Rubin’s rules (Marshall et al. 2009). Regression estimates (coefficients) were reported with 95% confidence intervals (CI). Observational studies are by nature subjected to unmeasured confounding. We postulate that the possible unblocked backdoor paths are weak. Confounding bias requires a strong confounder treatment and a strong confounder outcome association. Generally, baseline variables explain a low amount of variance of postoperative PROMs (Bengtsson et al. 2017, Nemes et al. 2018) and expectedly the residual confounding bias is low. Ethics, funding, and potential conflicts of interest The study was approved by the Regional Ethical Review Board in Gothenburg (Dnr 407-14). This research did not receive any specific grants from commercial funding agencies or bodies. The study was supported by public funding from the Swedish Hip Arthroplasty Register and research funds from Stockholm County Council. No competing interest declared.

Results 569 patients (78%) returned the questionnaire with complete responses. Mean follow-up time (F-U) was 7 years (IQR 2.2–13 years). The proportion of patients who had undergone any reoperation was similar between groups (Table 1). The preoperative demographics of the patients who did not answer the questionnaire did not demonstrate statistically significant difference from those who answered (Table 2, see Supplementary data). The case group had better unadjusted outcomes in all subscales of HOOS whereas EQ-5D index, VAS pain, and VAS satisfaction were equal between the groups (Table 3).

Figure 2. Graphic representation of postoperative PROMs after multivariable linear regression analyses. Bars represent 95% CI of the adjusted estimates (regression coefficients). For abbreviations, see Table 3.

Both the crude and adjusted estimates (Figure 2) showed that MoM-HR was associated with better scores in HOOS ADL (4.3, CI 1.8–6.9), and Sport/Rec (7.8, CI 3.8–12). We found no statistically significant association between type of prosthesis and remaining HOOS subscales, EQ-5D index, hip pain VAS, or satisfaction VAS.

Discussion Patients who underwent hip resurfacing reported better postoperative functional outcomes (HOOS subscales ADL and Sport/Rec) at mean 7 years post-surgery compared with a group of matched patients with conventional hip arthroplasty. We found no statistically significant differences in EQ-5D index, hip pain, or satisfaction. The largest difference between the groups was seen in the presumed most demanding subscale, i.e., function in sport and recreation. Our observation is in accordance with the study of Haddad et al. (2015), showing that hip resurfacing yields better results regarding return to sports compared with conventional THA. The results also conform to a retrospective study of 215 resurfacing arthroplasties (mean F-U 2 years) (Girard et al. 2013), which showed that 41 of the 50 patients who participated in high-impact activity before the operation and onset of pain, returned to high-impact activity whilst 48 patients returned to any kind of physical activity. Although the last-mentioned study did not include a control group, other studies have demonstrated that only up to 40% of high-activity patients return to sport activity after conventional THA (Del Piccolo et al. 2016, Schmidutz et al. 2012). When functional outcome scores were compared prospectively in 89 consecutively operated hips it was found that the resurfacing patients had greater improvement in Harris Hip scores, in UCLA activity score, and had a higher postoperative UCLA activity score than those operated with conventional THA (Fowble et al. 2009). On the other hand, the groups were not matched regarding overall health or preoperative functional outcome scores.

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Tan et al. (2015) found that functional outcome scores and activity level from short to long-term follow-up were timedependent. Among 100 patients with unilateral MoM-HR, they reported UCLA and SF-12 scores preoperatively, in the short term (mean F-U 2 years), and at a minimum of 10 years after the operation (mean F-U 12 years). They found no decrease in UCLA pain and walking scores between shortterm and long-term follow-up, but a decrease in function and activity scores. With this in mind, when evaluating functional outcomes after hip arthroplasty, the results do not seem to be dependent only on functional outcome validation instruments, age, and sex but also on the time of the follow-up. There are only a few previous studies comparing functional outcome scores between hip resurfacing and THA patients (Pollard et al. 2006, Mont et al. 2009, Costa et al. 2012). A retrospectively matched (sex, age, BMI, and activity level) study with a 7-year follow-up showed no difference in Oxford Hip Score but a higher level of activity as measured by UCLA score, and higher percentage (7% MoM-HR vs. 33% conventional THA) of patients participating in sports in the MoM-HR group (Pollard et al. 2006). Despite matching and medium– long follow-up, that study consisted of a rather small group of patients (53 MoM-HRs, 51 conventional THAs) making it difficult to draw certain conclusions. In another matched casecontrol study comprising 100 patients (50 MoM-HRs, 50 conventional THAs), the authors found no differences in mean Harris Hip Score (90 HR vs. 91 THA) or in patient satisfaction scores (9.2 HR vs. 8.8 THA) in short-term follow-up (Mont et al. 2009). As Harris Hip Score is limited to functional criteria, such a measure does not give an appropriate description of the patients’ functional outcome. In an assessor-blinded randomized controlled study (Costa et al. 2012) with 1:1 treatment allocation, hip function was similar between MoM-HR and THA at 12 months’ follow-up as measured with Harris Hip Score (88 MoM-HR vs. 82 THA) and Oxford Hip Score (40 MoM-HR vs. 38 THA). Furthermore, disability rating and activity level were similar in the first year after surgery. In that study, the long-term effects of HR were not studied. In the meantime, a 5-year F-U report is available that also shows similar hip function or health-related quality of life following a total hip arthroplasty vs. hip resurfacing (Costa et al. 2018). When analyzing the “Forgotten Joint” Score-12 (78 MoM-HR vs. 76 THA) between MoM-HR and conventional THA, it was concluded that the choice of implant should not be based solely on any expectation that either yields superior clinical outcomes compared with the other at short-term follow-up (Ortiz-Declet et al. 2017). Our study has some limitations. The collecting of PROMs did not reach nationwide coverage until 2008, which explains why preoperative data were not available for all of the patients (n = 157 had missing data preoperatively). However, missing preoperative EQ-5D data were successfully imputed and the EQ-5D scores were subsequently used for case-mix adjustment based on preoperative health status. Another limitation

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pertains to the lack of prospective HOOS data. Although groups were matched based on demography and baseline EQ-5D index, level of functioning in ADL and sports and recreation may have differed preoperatively. The occurrence of reoperations could be a potential source of bias albeit repeat surgeries were evenly distributed between the groups. Whilst conventional THA is performed in most orthopedic units in Sweden, hip resurfacing was only performed in a few specialist centers during the study period. Therefore, all patients operated with HR either actively searched for institutions performing resurfacing prosthesis or were referred from other orthopedic units. Patients operated with conventional THAs likely did not actively request a certain implant, suggesting a biased selection that cannot be adjusted for. Moreover, almost all HR surgeries were performed by 2 experienced surgeons following well-established principles of surgical innovation in contrast to the control group, which was selected from the registry not considering surgeon experience. It must be constantly emphasized that introduction of new devices should follow a systematic approach even if the theoretical basis or preclinical results are excellent. Recently, Reito et al. (2017) described the anti-stepwise introduction of metal-on-metal hip replacements. The strengths of our study include the careful 1:1 matching of the groups for the various demographic factors, surgical approach, time of surgery, and preoperative EQ-5D scores, which reduced many confounding factors. Our study also comprised a fairly large number of patients in the groups and with a satisfactory response rate. To our knowledge no study comparing functional outcome scores between MoM-HR and conventional THA has been undertaken with such a large number of patients followed for a comparable period of time. Although the type of hip prosthesis did not influence the level of satisfaction, postoperative pain relief, or quality of life, MoM-HR patients had better postoperative HOOS scores in the function of daily living and function in sports and recreation domains. Translating the adjusted regression estimates of these 2 HOOS subscales into effect sizes, the influence of MoM-HR was moderate (0.25 and 0.30, respectively). Furthermore, there was no statistically significant difference in reoperation rates using a Birmingham Hip Replacement (BHR) compared with a conventional implant in these 2 ageand sex-matched patient groups. As MoM-HR was developed to address the special demands of a younger and more active population, our results support the rationale for using the technique in this group of patients. Choice of hip arthroplasty for young and active patients with high expectations is still challenging, mostly due to higher risks of wear, dislocation, and need of revision surgery. In summary, by comparing MoM-HR with conventional THA in a matched study design (mean 7 years F-U) of a selected group of patients we have shown MoM-HR to yield better functional outcome scores in 2/5 HOOS subscales; all other outcome measures were similar. When a BHR implant is con-

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sidered, patients should be informed of the risk of developing of adverse reactions and uncertain long-term results. We highly recommend subsequent close follow-up for this matter. Supplementary data Figure 1 and Table 2 are available as supplementary data in the online version of this article, http://dx.doi.org/10.1080/ 17453674.2019.1604343

OR, HH, and LFT conceived and designed the study. OR and HH obtained ethical approval. OR and SN collected data. SN performed statistical analysis. AO drafted the manuscript. All authors interpreted the results and reviewed, edited, and approved the final version of the manuscript.   Acta thanks Nina Mathijssen and Marc Nijhof for help with peer review of this study.

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Evaluation of Forgotten Joint Score in total hip arthroplasty with Oxford Hip Score as reference standard Amanda LARSSON 1, Ola ROLFSON 1,2, and Johan KÄRRHOLM 1,2 1 Department

of Orthopaedics, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg; 2 The Swedish Hip Arthroplasty Register, Registercentrum, Västra Götaland, Gothenburg, Sweden Correspondence: amanda.em.larsson@gmail.com Submitted 2018-11-29. Accepted 2019-02-14.

Background and purpose — Total hip arthroplasty (THA) is performed mainly because of pain. To evaluate the result after surgery, different questionnaires measuring the patient-reported outcome regarding quality of life are used. Forgotten Joint Score (FJS), designed to chart postoperative symptoms, was developed to find subtle differences between patients who report that their operated hip is “very good” or “excellent.” We evaluated whether FJS provides additional information compared with the Oxford Hip Score (OHS) and ceiling and floor effects with use of these instruments. We also studied level of internal consistency for OHS and FJS, and the reproducibility of the FJS. Patients and methods — 111 patients who underwent unilateral primary THA in 2015 were included. The participants answered 2 questionnaires: Forgotten Joint Score and Oxford Hip Score. Floor and ceiling effects were recorded for each of the instruments and agreement between them. The FJS was studied with respect to reproducibility and level of internal consistency. Results — OHS ceiling effect (31%) was higher compared with FJS (21%), whereas the OHS seemed to provide a more nuanced picture of patients with an inferior clinical result. Floor effect for FJS was 3% and 0% for OHS. The degree of explanation was 68% between the 2 questionnaires (linear regression, r2 = 0.68). FJS items had a high internal consistency (Cronbach’s a = 0.93) and reproducibility (Pearson correlation = 0.87, ICC = 0.93); 92 patients answered on 2 distributions of the FJS questionnaires, 19 patients had identical answers. Interpretation — OHS had a larger ceiling effect than FJS, which could indicate that FJS is a more fine-tuned instrument to separate patients with good to excellent outcome after THA. The high internal consistency of FJS indicates that the items of the instrument consistently cover the construct of joint awareness.

The aim with total hip arthroplasty (THA) is to relieve pain, and improve joint mobility, physical ability, and quality of life. Since patients’ expectations on the postoperative pain and functional outcomes have changed over the past 20 years (Hamilton et al. 2017), it is of importance to apply validated methods to measure patient-reported outcomes (PROs) after surgery (Behrend et al. 2012). Questionnaires measuring PROs should preferably exhibit low ceiling and floor effects. Critical ceiling and floor effects are regarded to be present if 15% or more of the population reach the maximum or minimum score of a scale, respectively (Terwee et al. 2007). Ceiling and floor effects could make it difficult to study the development over time, since the true results and changes at follow up are concealed. The commonly used Oxford Hip Score (OHS) and the more recently developed Forgotten Joint Score (FJS) are 2 validated metrics for the evaluation of THA. OHS focuses on the preoperative status, while FJS primarily was designed to chart the symptoms postoperatively (Hamilton et al. 2016). Wylde et al. (2005) explored different weaknesses of the OHS questionnaire, e.g., that patients experienced that some questions did not have a clear meaning. The patients also commented on the difficulty of answering according to their “average pain” during the past 4 weeks, since their pain sometimes fluctuated based on current medication and level of physical activity. Some of the questions in OHS are so called “double-barreled questions,” meaning there is more than 1 claim in each question. This could result in difficulty in interpreting the answers, since some patients marked more than 1 of the possible answers for each question. In addition, the OHS has been criticized for exhibiting ceiling effects at postoperative follow-ups (Hamilton et al. 2016, 2017). The FJS was developed in 2012 as a reaction to the shortcomings of established measures following joint replacement and its use is growing.

© 2019 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group, on behalf of the Nordic Orthopedic Federation. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits ­unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. DOI 10.1080/17453674.2019.1599252

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Selected patients Unilateral THA performed 2015 n = 200 11 patients died and 10 were replaced Patients invited n = 199 Excluded (n = 88): – did not respond, 76 – incomplete answers, 12 Patients with complete answers n = 111 (56%) Did not respond to retest n = 14 Included in FJS test–retest n = 97

Figure 1. Participation.

The Swedish Hip Arthroplasty Register established a program collecting PROs in 2002 (Rolfson et al. 2011). The Registry direction is currently investigating new or alternative measures to include in the program. As both the newly developed FJS and the well-established OHS are tentative candidates, we sought to investigate these measures in a typical THA population. Hence, the objective of this study was to evaluate whether Forgotten Joint Score (FJS) provides more information compared with, or in addition to, Oxford Hip Score (OHS) regarding the clinical outcome after THA. Specifically, we aimed to compare ceiling and floor effects between OHS and FJS, to investigate the level of internal consistency for OHS and FJS, and to test the reproducibility of the FJS.

Table 1. Patient demographics: ASA classification and Charnley category in 200 patients (200 hips) primarily selected to be invited

All n = 200

Age < 65 Age ≥ 65 n = 99 n = 101

Male/female 100/100 50/49 50/51 Age, median 66 57 75 range 17–97 17–64 66–97 Diagnosis Primary osteoarthritis 135 66 69 Inflammatory joint disease 1 1 0 Fracture 36 10 26 Sequelae childhood hip disease 10 10 0 Femoral head necrosis 18 12 6 Charnley category a A 84 44 40 B 79 32 8 C 18 10 47 missing 19 13 6 ASA 1 49 39 10 2 118 49 69 3 30 9 21 4–5 0 0 0 missing 3 2 1 a Filled

in by patient 1 year after the index operation.

1 year after the primary index operation. 10 to 14 days after return of the questionnaire, the FJS was sent out once again to evaluate its reproducibility. Approximately 1 month after the first invitation to participate was sent out, patients who had not responded received a phone call reminder and an offer to receive a new set of questionnaires. If the patient declined participation or did not answer after 2 phone calls no further attempts to reach the patients were made. Numbers included were calculated based on an estimated response rate of 75%, i.e., 150 patients.

Study population (Figure 1) 200 patients who had undergone unilateral THA at the Department of Orthopaedics, Sahlgrenska University Hospital in Mölndal during 2015 were invited to participate. The population was selected from a consecutive series of THA with stratification for age and sex: half of the invited patients were over 65 years old and the other half were 65 years old or younger; half of the invited patients in each age group were females. All types of diagnoses (Table 1) and patients who previously had been operated on their opposite hip were included in the study. 1 of the 200 patients had been revised at the time when the questionnaires were sent out. This patient was also included.

Patient-reported outcome measures Oxford Hip Score The OHS, developed in 1996 (Dawson et al. 1996), is a patient-centered, 12 item-questionnaire with questions concerning pain and physical ability that the patient experienced during the past 4 weeks. The OHS originally used a scoring system ranging between 1 and 5 (worst–best). Since 2007, OHS items range from 0 to 4 where 4 is the best, which leads to a total score ranging from 0 to 48, where 48 equals the best outcome (Murray et al. 2007). When interpreting the answers and calculating the overall score of OHS, a maximum of 2 missing values are accepted. If the patient fills in more than 1 answer per question, the worst response should be used when calculating the total score (Nilsdotter and Bremander 2011).

Sample and logistics Invited patients were asked to complete 2 questionnaires, FJS and OHS, which were sent out by ordinary mail at the beginning of September 2017. Questionnaires were filled in at least

Forgotten Joint Score The Forgotten Joint Score (FJS) is a joint-specific questionnaire developed in 2012 (Behrend et al. 2012) with the aim to measure PRO of joint disorders (Hamilton et al. 2017). FJS is

Patients and methods

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designed to measure the ability of the patient Forgotten Joint Score Difference between FJS and OHS to “forget” about their problematic joint after 100 20 treatment. FJS is available in 3 versions: hip, knee, and shoulder. Studies imply that older 80 0 questionnaires do not provide quite as variegated a picture of the results, as they mostly 60 –20 differ between “good” and “bad.” Behrend y = –59.59 + 2.99x et al. (2012), however, states that since FJS –40 40 differ between “good,” “very good,” and “excellent” on a 5-grade Likert scale rang–60 20 ing from “never” to “mostly,” it could reduce –80 the risk of ceiling effects. As opposed to, for 0 example OHS, FJS is a questionnaire that 0 20 40 60 80 100 0 8 16 24 32 40 48 Mean of FJS and OHS Oxford Hip Score focus on the awareness, instead of the pain, of the affected joint (Hamilton et al. 2017). Figure 2. Linear regression analysis. The Figure 3. Bland–Altman limits of agreement. 4 missing values are regarded as acceptable degree of explanation between the 2 instruwhen the scores are summarized and trans- ments reached 0.68. formed to a scale ranging from 0 to 100, where a high value indicate that the patient tends to be less Board in Gothenburg (ref 607-17). OR and JK were financed aware of the affected joint when performing daily activities by grants from the Swedish state under the agreement between (Behrend et al. 2012). According to the official website of the Swedish government and the county councils, the ALF FJS (http://www.forgotten-joint-score.info/), the developers agreement (ALFGBG- 522591 and 721791, respectively). The have undertaken translation into several languages (includ- authors have no conflict of interest. ing Swedish) and subsequently linguistically validated the translated forms based on the Principles of Good Practice for the Translation and Cultural Adaption Process for PatientResults Reported Outcomes (PRO) Measures (Wild et al. 2005). Ceiling and floor effects of FJS and OHS Reasons for non-participation
 Of the 199 patients primarily invited, 111 (56%) answered Of those patients receiving a reminder phone call, 30 did not the questionnaires. Of these, 52% were female. The median answer. A further 16 patients accepted to participate in the age was 69 (19–100). Mean OHS was 42 (SD 9, median study, but did not, despite their positive answer, return any 45, IQR 40–48) and mean FJS was 64 (SD 32, median 71, questionnaires (Table 2, see Supplementary data). IQR 42–93). 68% to 94% chose option 1 (best) for each of the questions in the OHS questionnaire. The corresponding Ceiling and floor effect proportion for FJS ranged from 39% to 77%. The responses A critical ceiling or floor effect was regarded to be present on the FJS forms were more scattered among the different if 15% or more of the patients chose the best or worst pos- options, and all response options were chosen for all quessible answer when answering a specific question (Terwee et tions, which differs from OHS, where no patients chose al. 2007). Ceiling or floor effects at or above this level indicate option 5 (worst) on 3 questions (questions 2, 3, and 4. Tables limited content validity and reduced reliability. 3 and 4, see Supplementary data). The total ceiling effect for OHS was 31% and FJS 21%. The floor effect did not reach Statistics 15% for either questionnaire, but was slightly higher for FJS Cronbach’s a was used to measure the internal consistency (FJS 3%, OHS 0%). among the 7 questions that were assessed to measure the same health dimension in the 2 questionnaires. The relationship Level of internal consistency (Cronbach’s a) and between total OHS and FJS was assessed using simple linear agreement between questionnaires regression. The intraclass correlation coefficient (ICC) and 113 patients responded to the first distribution of FJS (CronPearson’s correlation were calculated to evaluate the repro- bach’s a = 0.97) and 111 patients answered the OHS (Cronducibility of the questionnaires. Statistical analyses were bach’s a = 0.93). In the linear regression analysis, the degree performed using IBM SPSS Statistics version 24 (IBM Corp, of explanation between the 2 instruments reached 68% (r2 = 0.68, Figure 2). The mean difference between FJS and OHS Armonk, NY, USA). was 22, i.e., FJS was mean 22 lower than OHS when conEthics, funding, and potential conflicts of interest verted to a 0–100 scale (Bland–Altman limits of agreement, The study was approved by the Regional Ethical Review Figure 3).

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Forgotten Joint Score reproducibility The Pearson correlation coefficient and the intraclass correlation (ICC) for the reproducibility of the FJS were 0.87 (95% CI 0.75–0.96) and 0.93 (95% CI 0.89–0.95).

Discussion
 This pilot study emanated from the Swedish Hip Arthroplasty Register to explore and evaluate new instruments with potential use for specific or general purposes in the follow-up after THA. We found that the FJS had an acceptable and good reproducibility. It also had less of a ceiling effect when compared with the OHS. Because of these properties, the FJS could be considered for many purposes and especially in the evaluation of new implants claimed to provide improved patient satisfaction and/or clinical performance. Ceiling and floor effects of FJS and OHS Studies have shown that OHS has a risk for ceiling effects postoperatively (Hamilton et al. 2016, 2017), which also was found by us. These ceiling effects were greater for OHS for each of the 7 correlating questions as well as the overall ceiling effect, which further support our hypothesis that FJS is a more nuanced instrument when measuring the results after THA. According to Terwee et al. (2007), a ceiling effect is present if more than 15% of the participants score the “best” result, corresponding to the lowest possible score for OHS and FJS. In a study of patients operated with either total knee or total hip arthroplasty, Hamilton et al. (2016) found a ceiling effect in the latter group of 8% at 6 months, which increased to 10% at 1 year, i.e., well below this limit (Hamilton et al. 2016). In our study, the ceiling effect for the OHS and FJS were higher at 31% and 21% respectively. The reason for this is not known, but longer follow-up could have contributed. Neither of the 2 questionnaires reached 15% for floor effect, though 3% achieved the maximum score on FJS. Several patients achieved high total FJS values, which indicates high awareness of their hip joint in daily life. Thus, the FJS provides a better differentiation of hip-related symptoms in patients who are generally satisfied with their THA operation. So far, the majority of studies which have compared the FJS with other scoring systems, have found that the ceiling effect of FJS is smaller or about the same as the reference used. Matsumoto et al. (2015) compared FJS with the WOMAC and the Japanese Orthopaedic Association Hip Disease Evaluation Questionnaire (JHEQ) in 108 patients operated with THA about 2.5 years after the operation. A low ceiling effect was reported for the FJS (4%) and for the JHEQ (3%), (Matsumoto et al. 2015). Hamilton et al. (2016) suggested that FJS is more responsive to change than OHS based on findings of a more pronounced change in the FJS than for the OHS between the 6and 12-month follow-up. They also noticed that the measured

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ceiling effect was nearly doubled for OHS compared with FJS (21% and 10% respectively). In another study by Hamilton et al. (2017), they found a pronounced floor effect for FJS when used preoperatively. 22% of the THA patients achieved the lowest score. These number differs from OHS, where no floor effects were shown preoperatively. The ceiling effect, however, was approximately half for FJS 1 year postoperatively compared with OHS. Reproducibility and internal consistency To examine the reproducibility of FJS, a comparison was made between the answers of the 1st and 2nd distribution of FJS. Overall, patients chose the same response option for both questionnaires in the test–retest analysis. Fewer patients, however, answered on the second distribution of FJS (n = 92). 19 patients had identical answers on both FJS 1 and FJS 2 and the internal consistency was high (ICC = 0.93). Thomsen et al. (2016) found good reliability in test–retest of FJS total score (ICC = 0.91). When FJS was compared with the Oxford Knee Score (OKS), there was a high level of internal consistency (Cronbach’s a = 0.96). Behrend et al. (2012) also observed that FJS had high internal consistency (Cronbach’s a = 0.95). Both these studies and ours indicate that the items of FJS consistently measure the construct of joint awareness. Weaknesses of this study Our study was performed in a Swedish population. To what extent this circumstance has influenced our result is not known, but we think that the influence of differences in ethnicity between nations or groups is weak, at least in Europe. Since this was a cross-sectional study, change over time was not analyzed, which is a limitation of this study, as well as the fact that only primary THA patients were included. The response frequency was lower compared with the Register’s ordinary PROM routine (Rolfson 2016), which could be due to a number of extra questionnaires with stated research purpose outside normal routines. Another possible limitation of this study was that a moderately sized population was included. The calculated participation level was 75%, i.e., 150 respondents, and the actual participation level was 56%. 123 of the patients answered the FJS completely and 111 patients answered the OHS completely. The response frequency probably would have been higher if the study took place over a longer period and more attempts could have been made to reach the patients who did not answer. Despite the fact that the FJS had a lower ceiling effect than the OHS, 1 of 5 nevertheless reached the maximum score for all items included. This finding raises the question whether still more sensitive instruments should be used, especially in situations when implants used in surgical procedures supposed to address high-demand patients are operated. It could be that new instruments used to evaluate patients with femo-

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roacetabular impingement have still less ceiling effect in an arthroplasty population than the FJS (Thorborg et al. 2011, Griffin et al. 2012, Mohtadi et al. 2012). These questionnaires do, however, include items related to high-demand sport and work-related activities, these not being relevant for a majority of the population operated with total hip arthroplasty. Thus, these instruments might be less suitable to use in arthroplasty registers. Conclusion
 We found that FJS could be used as an alternative to OHS in primary THA. The answers on FJS are more scattered than on OHS, which could indicate that FJS provides a more variegated picture of the clinical results in this population. The ceiling effect of FJS was lower compared with that of OHS, which provides valuable information, not least in a field where new implants with proposed superior performance are continuously introduced and patient expectations in terms of the results tend to increase. On the other hand, FJS might, due to its floor effect, be less suitable to predict the need for future revision surgery. Further studies in the Swedish population of patients with THA are needed, preferably with a larger study population, to establish whether the Forgotten Joint Score is sensitive to change and if it could be included in the Swedish Hip Arthroplasty Register PROMs routine with maintained completeness. Supplementary data Tables 2–4 are available as supplementary data in the online version of this article, http://dx.doi.org/10.1080/17453674. 2019.1599252

JK conceived and planned the study. AL managed questionnaire logistics. AL and OR performed the statistical analyses. AL drafted the manuscript. All authors interpreted the results. Acta thanks Ove Furnes for help with peer review of this study.

Behrend H, Giesinger K, Giesinger J M, Kuster M S. The “Forgotten Joint” as the ultimate goal in joint arthroplasty: validation of a new patient-reported outcome measure. J Arthroplasty 2012; 27(3): 430-6.e1.

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Dawson J, Fitzpatrick R, Carr A, Murray D. Questionnaire on the perceptions of patients about total hip replacement. J Bone Joint Surg Br 1996; 78(2): 185-90. Griffin D R, Parsons N, Mohtadi N G, Safran M R. A short version of the International Hip Outcome Tool (iHOT-12) for use in routine clinical practice. Arthroscopy 2012; 28(5): 611-16; quiz 6-8. Hamilton D F, Giesinger J M, MacDonald D J, Simpson A H, Howie C R, Giesinger K. Responsiveness and ceiling effects of the Forgotten Joint Score-12 following total hip arthroplasty. Bone Joint Res 2016; 5(3): 87-91. Hamilton D F, Loth F L, Giesinger J M, Giesinger K, MacDonald D J, Patton J T, et al. Validation of the English language Forgotten Joint Score-12 as an outcome measure for total hip and knee arthroplasty in a British population. Bone Joint J 2017; 99-b(2): 218-24. Matsumoto M, Baba T, Homma Y, Kobayashi H, Ochi H, Yuasa T, et al. Validation study of the Forgotten Joint Score-12 as a universal patient-reported outcome measure. Eur J Orthop Surg Traumatol 2015; 25(7): 1141-5. Mohtadi N G, Griffin D R, Pedersen M E, Chan D, Safran M R, Parsons N, et al. The development and validation of a self-administered quality-of-life outcome measure for young, active patients with symptomatic hip disease: the International Hip Outcome Tool (iHOT-33). Arthroscopy 2012; 28(5): 595-605; quiz 6-10.e1. Murray D W, Fitzpatrick R, Rogers K, Pandit H, Beard D J, Carr AJ, et al. The use of the Oxford hip and knee scores. J Bone Joint Surg Br 2007; 89(8): 1010-4. Nilsdotter A, Bremander A. Measures of hip function and symptoms: Harris Hip Score (HHS), Hip Disability and Osteoarthritis Outcome Score (HOOS), Oxford Hip Score (OHS), Lequesne Index of Severity for Osteoarthritis of the Hip (LISOH), and American Academy of Orthopedic Surgeons (AAOS) Hip and Knee Questionnaire. Arthritis Care Res (Hoboken) 2011; 63(Suppl 11): S200-7. Rolfson O. Höftprotesregistret Årsrapport; 2016. Rolfson O, Kärrholm J, Dahlberg L, Garellick G. Patient-reported outcomes in the Swedish Hip Arthroplasty Register: results of a nationwide prospective observational study. J Bone Joint Surg Br 2011; 93(7): 867-75. Terwee C B, Bot S D M, de Boer M R, van der Windt D A W M, Knol D L, Dekker J, et al. Quality criteria were proposed for measurement properties of health status questionnaires. J Clin Epidemiol 2007; 60(1): 34-42. Thomsen M G, Latifi R, Kallemose T, Barfod K W, Husted H, Troelsen A. Good validity and reliability of the forgotten joint score in evaluating the outcome of total knee arthroplasty. Acta Orthop 2016; 87(3): 280-5. Thorborg K, Holmich P, Christensen R, Petersen J, Roos E M. The Copenhagen Hip and Groin Outcome Score (HAGOS): development and validation according to the COSMIN checklist. Br J Sports Med 2011; 45(6): 478-91. Wild D, Grove A, Martin M, Eremenco S, McElroy S, Verjee–Lorenz A, et al. Principles of good practice for the translation and cultural adaptation process for patient–reported outcomes (PRO) measures: report of the ISPOR Task Force for Translation and Cultural Adaptation. Value Health 2005; 8(2): 94-104. Wylde V, Learmonth I D, Cavendish V J. The Oxford hip score: the patient’s perspective. Health Qual Life Outcomes 2005; 3: 66.

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Increased early mortality and morbidity after total hip arthroplasty in patients with socioeconomic disadvantage: a report from the Swedish Hip Arthroplasty Register Rüdiger J WEISS 1,2, Johan KÄRRHOLM 2,3, Ola ROLFSON 2,3, and Nils P HAILER 2,4 1 Department of Molecular Medicine and Surgery, Section of Orthopaedics and Sports Medicine, Karolinska Institutet, Karolinska University Hospital, Stockholm; 2 Swedish Hip Arthroplasty Register, Gothenburg; 3 Department of Orthopaedics, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg; 4 Department of Surgical Sciences, Section of Orthopaedics, Uppsala University Hospital, Uppsala, Sweden Correspondence: rudiger.weiss@sll.se Submitted 2018-11-29. Accepted 2019-02-16.

Background and purpose — Socioeconomic status is associated with the outcome of major surgery. We investigated the association of socioeconomic status with the risk of early mortality and readmissions after primary total hip arthroplasty (THA). Patients and methods — We obtained information on income, education, immigration, and cohabiting status as well as comorbidities of 166,076 patients who underwent primary THA due to primary osteoarthritis (OA) from the Swedish Hip Arthroplasty Register, the Swedish National Inpatient Register and Statistics Sweden. Multivariable Cox regression models were fitted to estimate the adjusted risk of mortality or readmissions within 90 days after index surgery. Results — Compared with patients on a low income, the adjusted risk of 30-day mortality was considerably lower in patients on a high income (hazard ratio [HR] 0.5, 95% confidence interval [CI] 0.3–0.7) and in those on a medium income (HR 0.7, CI 0.6–0.9). Similar risk reductions were found for the endpoint 90-day mortality. Patients with a high income had a lower adjusted risk of readmission for cardiovascular reasons than those with a low income (HR 0.7, CI 0.6–0.9), as had those with a higher level of education (adjusted HR 0.7, CI 0.6–0.9). Patients with higher socioeconomic status had a lower degree of comorbidities than socioeconomically disadvantaged patients. However, adjusting for socioeconomic confounders in multivariable models only marginally influenced the predictive ability of the models, as expressed by their area under the curve. Interpretation — Income and level of education are strongly associated with early mortality and readmissions after primary THA, and both parameters are closely connected to health status. Since adjustment for socioeconomic confounders only marginally improved the predictive ability of multivariable regression models our findings indicate that comorbidities may under certain circumstances serve as an acceptable proxy measure of socioeconomic background.

Socioeconomic status is strongly associated with both access to and the outcome after major surgical interventions, including total joint replacements that represent one of the most common surgical interventions in developed countries (Kurtz et al. 2007, Hunt et al. 2013, Berstock et al. 2014, Katz et al. 2017). The relationship between health and socioeconomic status is complex since socially deprived total hip arthroplasty (THA) patients have greater comorbidity and a higher prevalence of smoking compared with more affluent patients (Jenkins et al. 2009, Clement et al. 2011). Even in a European healthcare system with less pronounced social inequality, socioeconomically disadvantaged individuals are less healthy (Padyab et al. 2013). It was therefore postulated almost 2 decades ago that “performance measures should be stratified by socioeconomic position…” (Fiscella et al. 2000), but such stratification is rarely presented in studies on short-term complications after THA surgery. Therefore we examined (1) how personal income, level of education, cohabiting, and immigration status affect early mortality and readmission rates after primary THA surgery due to OA, and (2) whether adjustment for such socioeconomic confounders substantially changes the attained risk estimates and the predictive ability of regression models. Early mortality was defined as 30- and 90-day mortality, and hospital readmissions were divided into those that occurred for cardiovascular disease, or for any reason.

Patients and methods Data sources We extracted all patients operated with a primary THA from the Swedish Hip Arthroplasty Register (SHAR) 1992–2012 but excluded patients operated for reasons other than primary OA of the hip (Figure 1, see Supplementary data). To avoid

© 2019 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group, on behalf of the Nordic Orthopedic Federation. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits ­unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. DOI 10.1080/17453674.2019.1598710

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dependency issues only the first operation was accounted for in patients with bilateral THA. National coverage of the SHAR is complete and completeness of registration has been found to be stable around 96–98% (SHAR 2015, Soderman et al. 2000). Age at index surgery was divided into 3 age groups (< 60, 60–75, and > 75 years). Socioeconomic factors including personal income and level of education were obtained from Statistics Sweden. Income was divided into low, middle, and high along tertiles, and level of education was divided into the categories low (9 years or less of school education), middle (high school level), and higher education (university level). Hospital type at the index operation was divided into university, county, and private hospitals. Immigration status was categorized as non-immigrant or immigrant (defined as a patient born outside of Sweden). Cohabiting status was categorized as living with a partner, irrespective of marital status, or living alone. Data on medical comorbidities, dates of death, and readmissions (for cardiovascular reasons or for any reason) were obtained from the Swedish National Inpatient Register (SNPR) where data on contacts with healthcare providers are recorded together with International Classification of Diseases (ICD)- and procedural codes (Ludvigsson et al. 2011). Categories of comorbidity were computed using the Charlson Comorbidity Index (CCI) (Charlson et al. 1987, de Groot et al. 2003) by analysing registered ICD codes from the year preceding the index procedure but excluding the inpatient period during which the index procedure was performed. Comorbidity was categorized into 3 levels: low (CCI 0), moderate (CCI 1 or 2), and high (CCI > 2) (Deyo et al. 1992, Quan et al. 2011). Patients who died or emigrated during follow-up were identified through the Total Population Register (Statistics Sweden). Outcomes Primary outcome was early mortality (30- and 90-day mortality), which was defined as death occurring within 30 or 90 days after the index procedure. Secondary endpoints were readmission due to cardiovascular reasons or for any reason within the first 90 days after the index procedure. Cardiovascular disease was defined as myocardial infarction, chronic heart failure, peripheral vascular disease, and/or cerebrovascular disease (Quan et al. 2011). Statistics Follow-up started on the day of surgery and ended on the day of death, emigration, or censorship at December 31, 2012, whichever came first. Continuous data were described using medians and ranges; observed and expected frequencies were analysed using the chi-square test. 95% confidence intervals (CI) were used to describe estimation uncertainty. Kaplan–Meier survival analysis was performed to estimate unadjusted survival. Cox proportional hazard models were fitted for each primary or secondary outcome at a time to

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Table 1. Description of the study population Factor

Number %

Total 166,076 Women 93,855 57 Men 72,221 43 Median age at index surgery (range) 70 (16–100) Median follow-up, years (range) 7 (0–22) Year of surgery 1992–1998 44,746 27 1999–2005 54,222 33 2006–2012 67,108 40 Income Low 57,397 35 Middle 55,151 33 High 53,528 32 Education Low 78,422 47 Middle 57,594 35 Higher 30,060 18 Cohabiting status Cohabiting 97,257 59 Non-cohabiting 68,819 41 Immigration status Non-immigrant 153,403 92 Immigrant 12,673 8 Charlson Comorbidity Index Low 139,197 84 Moderate 23,925 14 High 2,954 2 Hospital type County 125,801 76 Private 21,342 13 University 18,933 11 Implant fixation Cemented 136,554 82 Uncemented 13,233 8 Other a 16,289 10 Revision after index surgery No 157,698 95 Yes 8,378 5 a Hybrid,

reversed hybrid, and resurfacing.

calculate hazard ratios (HR) with CI, and confounders were subsequently included in multivariable regression models to calculate adjusted HR. The choice of covariates included in multivariable regression models was based on assessment of relevance and non-interference using directed acyclic graphs. The assumption of proportionality of hazards was investigated graphically and by calculating scaled Schoenfeld residuals. We used C-statistics to assess the area under the curve (AUC) and thus the ability of a given model to predict outcomes. The observation period was divided into 3 different time periods (1992–1998, 1999–2005 and 2006–2012) to investigate temporal trends in the demography, comorbidity, surgical technique, and mortality in the investigated cohort. The level of statistical significance was set at p < 0.05, but CIs were consistently used to assess estimation uncertainty. Characteristics of the study population We identified 166,076 patients (57% females) with primary

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Table 2. Hazard ratio (HR) for mortality up to 30 days after THA Crude Adjusted Factor % n HR (95% CI) p-value HR (95% CI) p-value Age < 60 years 0.1 16 Ref. Ref. 60–75 years 0.1 115 2.2 (1.3–3.7) 0.003 1.7 (1.0–2.8) > 75 years 0.5 264 9.3 (5.6–15.4) < 0.001 5.1 (3.1–8.6) Sex Female 0.2 176 Ref. Ref. Male 0.3 219 1.6 (1.3–2.0)) < 0.001 1.9 (1.5–2.4) Year of surgery 1992–1998 0.4 174 Ref. Ref. 1999–2005 0.2 123 0.6 (0.5–0.7) < 0.001 0.6 (0.5–0.8) 2006–2012 0.1 98 0.4 (0.3–0.5) < 0.001 0.3 (0.3–0.4) Income Low 0.4 213 Ref. Ref. Middle 0.2 127 0.6 (0.5–0.8) < 0.001 0.7 (0.6–0.9) High 0.1 55 0.3 (0.2–0.4) < 0.001 0.5 (0.3–0.7) Education Low 0.3 261 Ref. Ref. Middle 0.2 100 0.5 (0.4–0.7) < 0.001 0.9 (0.7–1.1) Higher 0.1 34 0.3 (0.2–0.5) < 0.001 0.8 (0.6–1.2) Cohabiting status Cohabiting 0.2 191 Ref Ref. Non-cohabiting 0.3 204 1.5 (1.2–1.8) < 0.001 1.4 (1.1–1.8) Immigration status Non-immigrant 0.2 374 Ref. Ref. Immigrant 0.2 21 0.7 (0.4–1.1) 0.1 0.8 (0.5–1.2) Charlson Comorbidity Index Low 0.1 193 Ref. Ref. Moderate 0.7 159 4.8 (3.9–5.9) < 0.001 4.4 (3.6–5.4) High 1.5 43 10.6 (7.6–14.7) < 0.001 9.9 (7.0–13.9) Hospital type County 0.3 314 Ref. Ref. Private 0.1 25 0.5 (0.3–0.7) < 0.001 0.9 (0.6–1.3 University 0.3 56 1.2 (0.9–1.6) 0.2 1.0 (0.8–1.4

0.05 < 0.001 < 0.001 0.001 < 0.001

Within the first 30 days after surgery 395 (0.2%) patients died, giving an unadjusted 30-day survival of 99.8% (CI 99.7–99.8). 709 (0.4%) patients died within 90 days, resulting in an unadjusted 90-day survival of 99.6% (CI 99.5–99.6). We identified 1,208 readmissions for cardiovascular reasons within 90 days (0.7% of the study population), and 27,197 (16% of the study population) were readmitted to hospital for any reason within this time frame.

0.4 0.4

Ethics, funding, and potential conflicts of interests Ethical approval was granted by the Regional Ethical Review Board in Gothenburg (approval number: 2013/360–13). No external funding was received. No competing interests were declared.

0.001

Results

0.006 < 0.001

Socioeconomic status and early postoperative mortality When compared with patients in the low< 0.001 income category, patients in the high< 0.001 income category had about half the risk of death within 30 days after THA surgery 0.5 (adjusted HR 0.5, CI 0.3–0.7), and patients 0.9 in the middle-income category also had a Number of events = 395; adjusted for age, sex, year of surgery, income, education, lower adjusted risk with an HR of 0.7 (CI cohabiting status, immigration status, Charlson Comorbidity Index and hospital type. 0.6–0.9; Table 2). 90-day mortality showed similar risk reductions for patients in the high- and middle-income categories when compared with those in the lowest income Table 3. Level of income and education divided by Charlson Comorcategory (Table 4, see Supplementary data). In contrast, the bidity Index. Values are frequency (%) level of education was not associated with statistically significant variation in the adjusted risk of 30- or 90-day mortal Charlson Comorbidity Index ity after surgery (Tables 2 and 4, see Supplementary data). Factor Low Moderate High Patients who were non-cohabiting had an increased risk of Income both 30- (adjusted HR 1.4, CI 1.1–1.8) and 90-day (adjusted Low 47,581 (83) 8,822 (15) 994 (2) HR 1.6, CI 1.4–1.9) mortality when compared with patients Middle 45,440 (82) 8,559 (16) 1,152 (2) living with a partner. High 46,176 (86) 6,544 (12) 808 (2) Level of education Low 64,849 (83) Middle 48,442 (84) Higher 25,906 (86)

12,098 (15) 8,119 (14) 3,708 (12)

1,475 (2) 1,033 (2) 446 (2)

OA operated with a THA at a median age at surgery of 70 years (16–100). About half of the patients had a low level of education (47%; Table 1). Patients with a higher level of education or high income had a slightly lower level of comorbidities (Table 3).

0.3

Readmissions within 90 days Patients in the high-income category had a lower risk of readmission for cardiovascular reasons than those in the lowincome category (adjusted HR 0.7, CI 0.6–0.9), and a similar risk reduction was found for patients with a higher level of education (adjusted HR 0.7, CI 0.6–0.9). Patients living without a partner had an increased adjusted risk of readmission (HR 1.2, CI 1.1–1.4) compared with those living with a partner. Immigrants had a slightly increased risk of readmission for cardiovascular reasons compared with non-immigrants,

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but this finding failed to reach the level of statistical significance (HR 1.2, CI 1.0–1.5, p = 0.09; Table 5, see Supplementary data). Patients with a high income (adjusted HR 0.9, CI 0.9–0.9) had a reduced risk for readmission for any reason, whereas patients living alone (adjusted HR 1.4, CI 1.3–1.4) and immigrants had an increased risk for readmission for any reason (adjusted HR 1.2, CI 1.1–1.2) (Table 6 and Figure 2, see Supplementary data). Access to healthcare and temporal changes in demography, comorbidity, and mortality The majority of the patients were operated in county hospitals (76%), followed by private hospitals (13%) and university hospitals (11%). A higher than expected proportion of patients with a high income (observed count n = 11,035, expected count n = 6,879; p < 0.001 derived from chi-square test) and of those with a higher level of education (observed count n = 6,692, expected count n = 3,863; p < 0.001) were operated upon in private hospitals. Patients operated in private hospitals had a lower adjusted risk of 90-day mortality (adjusted HR 0.7, CI 0.5–1.0; Table 4, see Supplementary data) when compared with patients in county hospitals. Patients operated during 1999–2005 had a lower risk of early death compared with those operated 1992–1998, and those who had THA surgery during the latest period of 2006–2012 had the lowest risk of all sub-cohorts (Tables 2 and 4, see Supplementary data). Impact of adjustment for socioeconomic factors on the predictive ability of multivariable models The regression model fitted for the endpoint 90-day mortality that included the covariates age, sex, comorbidity, income, and education had an AUC of 0.77 (CI 0.76–0.79), whereas the model without the covariates income and education had an AUC of 0.76 (CI 0.74–0.78). For the regression model fitted for the endpoint readmission for cardiovascular reasons within 90 days that included the covariates age, sex, comorbidity, income, and education we estimated an AUC of 0.74 (CI 0.73–0.76), and we attained a similar estimate of 0.73 (CI 0.72–0.75) for the model without the covariates income and education.

Discussion Main findings This study indicates that socioeconomic disadvantage is associated with an increased risk of both early postoperative mortality and early readmission after THA surgery. However, we also found that adjustment for socioeconomic status results in small changes in the attained risk estimates and only slightly improved C-statistics when modelling early mortality and readmissions after THA.

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Limitations and strengths Our study is subject to incompleteness of data registration and registration errors. Misclassification bias is another limitation since our estimates of comorbidity and causes for readmissions are entirely based upon ICD codes registered by healthcare providers. If there are changes or errors in the coding of diagnoses, these will translate into erroneous measures of comorbidity. For instance, the comorbidity of patients analyzed in this study seems to have progressed over time (Table 7 and Supplementary data), a finding that could be related to an actual increase in the proportion of patients suffering from a higher burden of comorbidities during the last decade. On the other hand, caregiver reimbursement based on the DRG system may also have triggered a more zealous way of coding comorbidities, a phenomenon described as “physician code creep” (Seiber 2007). We lack data on lifestyle-related confounders of our main outcome measures, such as body mass index, smoking, alcohol habits, and physical activity. Since these confounders may differ between socioeconomic strata they can profoundly influence the observed associations between socioeconomic variables and our outcome measures. Mutually adjusted effect estimates derived from multivariable regression models are presented in our analysis. It has to be noted that the presented risk estimates for specific confounders can either represent total-effect or direct-effect estimates, and effect estimates related to the primary exposure cannot be interpreted in the same way as effect estimates of secondary risk factors (Westreich and Greenland 2013). We attempted to limit the problems associated with the presence of effect mediators and colliders by devising directed acyclic graphs prior to regression analyses, but the interdependency of socioeconomic status and comorbidity is strong and our reported effect estimates of secondary risk factors must therefore be interpreted with caution. Strengths of our study includes the prospective data collection within 3 well-validated, population-based registers, creating high external validity. We chose to include only patients with primary OA of the hip as the reason for THA insertion, an import selection since some patients receiving THA for other reasons, such as those with a fracture of the femoral neck, are older and have a high burden of comorbidity, whereas those receiving a THA due to sequelae of childhood hip disorders are often younger and, possibly, fitter than those with OA. Taken together, by restricting our study population to patients with primary OA of the hip we avoided a large amount of residual confounding that would have been difficult to adjust for. The combined in-depth information on income, achieved level of education, and ethnicity is an additional valuable facet of our study, since this enables investigation of socioeconomic factors on a more profound level. Main findings related to previous literature The overall 30- and 90-day mortality was low in our study,

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which is in accordance with other studies analysing early mortality after primary THA surgery for OA (Aynardi et al. 2009, Berstock et al. 2014). In our study, lower socioeconomic status was associated with increased 90-day mortality, which is also in agreement with US studies on this topic, although the odds ratio in 1 of these studies was slightly higher than in ours (Mahomed et al. 2003, Clement et al. 2011), an effect that is possibly attributable to larger disparity in income and education in the United States compared with Sweden. It is described that socioeconomically deprived patients operated with a THA have greater comorbidity than more affluent patients, and deprived patients also have a higher prevalence of smoking, which has a profound impact on cardiovascular and respiratory comorbidity (Jenkins et al. 2009). Other studies indicate that patients with low incomes have a higher risk of acute adverse medical events after THA surgery (Agabiti et al. 2007). The association of lower socioeconomic status with higher mortality among hip fracture patients is known (Barone et al. 2009, Kristensen et al. 2017). Our finding of an association between early mortality after THA and non-cohabiting status is an expected finding when considering the fact that widowers have an increased mortality compared with married individuals, and that married persons have a longer life expectancy compared with unmarried persons (Hu and Goldman 1990, Shor et al. 2012). To have information on this parameter is a strength of our analysis; this facet of socioeconomic status is rarely reported in other studies. We found a readmission rate for any reason of 16% within 90 days after surgery, which can be compared with a prevalence of 30-day readmissions of 7% after hip replacements in a US study (Brooke et al. 2015). A study on the risk of death, readmissions to hospital, and wound infections after elective primary THA in United States Medicare patients supports our findings (Mahomed et al. 2003). THA patients in the higher socioeconomic strata were overrepresented in private hospitals. Some authors claim that wealthier patients have easier access to private sector care, which is associated with shorter waiting times (Agabiti et al. 2007), and this seems also to be true within the Swedish healthcare system. The ability of the adjusted regression models to predict their respective outcomes was investigated by assessing model C-statistics, a term used to describe the AUC. We found AUC that varied between 0.7 and 0.8, which indicates a relatively good predictive capacity when compared with an investigation of 3 different comorbidity measures to predict the incidence of reoperations within 2 years after primary THA surgery, where the maximal AUC was 0.5 (Gordon et al. 2013). However, when models without adjustment for socioeconomic background variables were re-fitted we attained similar AUC to the previously fitted models with adjustment for socioeconomic background.

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Conclusion Our findings support the notion that patients with socioeconomic disadvantage run a substantially higher risk of both early mortality and readmissions after THA surgery, even within the setting of a relatively egalitarian healthcare system. However, perhaps partly due to the fact that poor socioeconomic status is associated with a higher degree of comorbidities, adjusting for comorbidities may suffice in analyses where detailed information on socioeconomic background is lacking. Supplementary data Tables 4–7 and Figures 1–2 are available as supplementary data in the online version of this article, http://dx.doi.org/ 10.1080/17453674.2019.1598710

The authors would like to thank all Swedish orthopaedic surgeons and secretaries who contributed data. RJW and NPH: study design, database preparation, data analysis, manuscript drafting and editing. JK and OR: study design and final manuscript editing. Acta thanks Per Kjærsgaard-Andersen and Stephan Maximilian Röhrl for help with peer review of this study.

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Gordon M, Stark A, Skoldenberg O G, Karrholm J, Garellick G. The influence of comorbidity scores on re-operations following primary total hip replacement: comparison and validation of three comorbidity measures. Bone Joint J 2013; 95-B (9): 1184-91. Hu Y R, Goldman N. Mortality differentials by marital status: an international comparison. Demography 1990; 27 (2): 233-50. Hunt L P, Ben-Shlomo Y, Clark E M, Dieppe P, Judge A, MacGregor A J, Tobias J H, Vernon K, Blom A W, National Joint Registry for England W, Northern I. 90-day mortality after 409,096 total hip replacements for osteoarthritis, from the National Joint Registry for England and Wales: a retrospective analysis. Lancet 2013; 382 (9898): 1097-104. Jenkins P J, Perry P R, Yew Ng C, Ballantyne J A. Deprivation influences the functional outcome from total hip arthroplasty. The Surgeon: J Roy Coll Surg Edinburgh and Ireland 2009; 7 (6): 351-6. Katz J N, Winter A R, Hawker G. Measures of the appropriateness of elective orthopaedic joint and spine procedures. J Bone Joint Surg Am 2017; 99 (4): e15. Kristensen P K, Thillemann T M, Pedersen A B, Soballe K, Johnsen S P. Socioeconomic inequality in clinical outcome among hip fracture patients: a nationwide cohort study. Osteoporos Int 2017; 28 (4): 1233-43. Kurtz S, Ong K, Lau E, Mowat F, Halpern M. Projections of primary and revision hip and knee arthroplasty in the United States from 2005 to 2030. J Bone Joint Surg Am 2007; 89 (4): 780-5. Ludvigsson J F, Andersson E, Ekbom A, Feychting M, Kim J L, Reuterwall C, Heurgren M, Olausson P O. External review and validation of the Swedish national inpatient register. BMC Public Health 2011; 11: 450.

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Acta Orthopaedica 2019; 90 (1): 6–10

Early postoperative mortality similar between cemented and uncemented hip arthroplasty: a register study based on Finnish national data Elina EKMAN 1, Antton PALOMÄKI 1, Inari LAAKSONEN 1, Mikko PELTOLA 2, Unto HÄKKINEN 2, and Keijo MÄKELÄ 1 1 Department

of Orthopaedics and Traumatology, Turku University Hospital, Turku, Finland; 2 National Institute for Health and Welfare, Helsinki, Finland Correspondence: elina.ekman@tyks.fi ORCID: 0000-0003-1330-7418 Submitted 2018-06-05. Accepted 2018-11-18.

Background and purpose — Implant survival of cemented total hip arthroplasty (THA) in elderly patients is higher than that of uncemented THA. However, a higher mortality rate in patients undergoing cemented THA compared with uncemented or hybrid THA has been reported. We assessed whether cemented fixation increases peri- or early postoperative mortality compared with uncemented and hybrid THA. Patients and methods — Patients with osteoarthritis who received a primary THA in Finland between 1998 and 2013 were identified from the PERFECT database of the National Institute for Health and Welfare in Finland. Definitive data on fixation method and comorbidities were available for 62,221 THAs. Mortality adjusted for fixation method, sex, age group, and comorbidities among the cemented, uncemented, and hybrid THA was examined using logistic regression analysis. Reasons for cardiovascular death within 90 days since the index procedure were extracted from the national Causes of Death Statistics and assessed separately. Results — 1- to 2-day adjusted mortality after cemented THA was comparable to that of the uncemented THA group (OR 1.2; 95% CI 0.24–6.5). 3- to 10-day mortality in the cemented THA group was comparable to that in the uncemented THA group (OR 0.54; CI 0.26–1.1), and in the hybrid THA group (OR 0.64, CI 0.25–1.6). Pulmonary embolism or cardiovascular reasons as a cause of death were not overrepresented in the cemented THA group. Interpretation — Early peri- and postoperative mortality in the cemented THA group was similar compared with that of the hybrid and uncemented groups.

The early postoperative mortality after total hip arthroplasty (THA) is low and has been decreasing over the last few years (Aynardi et al. 2009, McMinn et al. 2012, Lalmohamed et al. 2014). 2 recent publications have indicated that 90-day mortality after primary THA performed for any indication is 0.7% (Hunt et al. 2013, Garland et al. 2015). Improvements in surgical techniques and implants, the introduction of low molecular weight heparins in the 1980s, and operative room sterility have significantly reduced mortality risks (Nurmohamed et al. 1992, Harris 2009). On the other hand, the surgery is now being performed on older patients who often have multiple comorbidities, which increase adverse outcomes (Mahomed et al. 2003, Bozic et al. 2012). Cementing has been used for decades for THA implant fixation with good implant survival rates in long term followup (Morshed et al. 2007, Mäkelä et al. 2014a). However, cemented fixation is associated with potential perioperative morbidity in the form of bone cement implantation syndrome where fat and bone marrow cause emboli during cement pressurizing into the pulmonary arteries and may lead to intra- or early postoperative hypotension, and even death of the patient (Donaldson et al. 2009). Even though survival of cemented implants in the elderly population is higher than the survival of uncemented implants, the fear of bone cement implantation syndrome is one of the reasons for the increased use of uncemented implants (Junnila et al. 2016). The leading cause of death after THA is cardiovascular (Berstock et al. 2014). We studied whether early postoperative mortality of patients treated with uncemented THA differed from that of patients treated with cemented or hybrid THA based on data from the PERFECT database maintained by the National Institute for Health and Welfare in Finland. We also assessed bone cement implantation syndrome and early cardiovascular mortality in this same population.

© 2018 The Author(s). Published by Taylor & Francis on behalf of the Nordic Orthopedic Federation. This is an Open Access article distributed under the terms of the Creative Commons Attribution-Non-Commercial License (https://creativecommons.org/licenses/by/4.0) DOI 10.1080/17453674.2018.1558500

Acta Orthopaedica 2019; 90 (1): 6–10

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Table 1. Background characteristics of patients. Values are frequency (percentage) unless otherwise stated Background characteristics

Cemented Uncemented Hybrid THA THA THA

Number of patients 23,636 Mean age 73.7 Men 8,277 (35) Hypertension 11,104 (47) Ischemic heart disease 4,234 (20) Atrial fibrillation 1,868 (7.9) Heart insufficiency 1,284 (5.4) Diabetes 2,130 (9.0) COPD and asthma 2,422 (10) Cancer 1,833 (7.8) Depression 1,522 (6.4) Parkinson’s disease 283 (1.2) Dementia 281 (1.2) Uremia 30 (0.1) Mental disorders 659 (2.8)

38,477 64.9 18,747 (49) 15,771 (41) 4,135 (11) 2,082 (5.4) 797 (2.1) 3,715 (9.7) 3,973 (10) 2,575 (6.7) 2,688 (7.0) 381 (1.0) 212 (0.6) 61 (0.2) 978 (2.5)

11,802 66.5 5,636 (48) 4,725 (40) 1,466 (12) 676 (5.7) 431 (3.7) 964 (8.2) 1,059 (9.0) 724 (6.1) 704 (6.0) 111 (0.9) 98 (0.8) 19 (0.2) 284 (2.4)

These results have not been adjusted via propensity score weighting. THA = total hip arthroplasty.

Patients and methods Study population The study population was identified from the Finnish Hospital Discharge Register (FHDR) using the 10th revision of the International Classification of Diseases (ICD-10) diagnosis codes M16.0 to M16.9, and the Finnish version of NOMESCO Classification Procedural Codes NFB30 (uncemented THA), NFB40 (hybrid THA when only the femoral stem has been cemented), or NFB50 (cemented THA). During the study period from January 1, 1998 to December 31, 2013, 73,915 patients were treated with THA for primary or secondary OA in Finland. Definitive data on fixation method and comorbidities were available for 62,221 THAs, which formed the final study population. All public and private hospitals in Finland are obliged to report all surgical procedures to the Finnish National Institute of Health and Welfare. The present study was based on the PERFECT (PERFormance, Efficiency, and Costs of Treatment Episodes) hip replacement database, which uses data from numerous registries such as the Hospital Discharge Register (maintained by the Finnish National Institute of Health and Welfare), cause of death statistics maintained by Statistics Finland, the Social Insurance Institution’s drug prescription register and drug reimbursement register, and the Finnish Arthroplasty Register. Data on comorbidities, on the use of residential care, patient ID number, provider ID number(s), age, sex, residential area codes, diagnosis, operation codes, date of admission, operation, and the date of discharge or death, whichever came first, were extracted from the PERFECT database (Peltola et al. 2011) (Table 1). The validity of the individual registries mentioned above has been studied. The Finnish Hospital Discharge Register

data have been compared with external audit data in 32 studies (Sund 2012). The coverage and positive predictive values have been over 90% in those studies. The prescription database data have been found to be in high concordance with self-reported medication (Haukka et al. 2007). To assess bone cement implantation syndrome and cardiovascular reasons separately as a cause of death, mortality reported with the associated diagnostic codes (codes I21 acute myocardial infarction, I25 ischemic heart disease, I26 pulmonary embolism, I50 heart failure, and I63 stroke in the ICD-10 classification) within 90 days since the index procedure were extracted from the national Causes of Death Statistics. The validity of the Finnish mortality statistics is reliable (Lahti and Penttilä 2003, Pajunen et al. 2005). The primary outcome used in this study was total mortality and secondary outcome cardiovascular mortality and mortality associated with pulmonary embolism. The patients were followed up for 1 year postoperatively. Statistics Mortality among the cemented, uncemented, and hybrid groups was examined using logistic regression analysis. The analysis was repeated for 365 outcomes that each described the status of the patient (alive/dead) on a certain day after the operation. In order to reduce the effects of confounding in this observational study, differences in distributions of observed covariates between the groups were adjusted: fixation method, sex, age group (< 50, 50–59, 60–69, 70–79, ≥ 80), comorbidities (Table 1), and the year of operation. In the model, treatment assignment (cemented/uncemented/hybrid) was the dependent variable and all observed background variables (Table 1) were independent variables, as the aim was to balance all observed covariates between the groups. 95% confidence intervals (CI) were calculated for adjusted mortality. Ethics, funding, and potential conflicts of interest The ethics committee of the Finnish National Institute for Health and Welfare (THL) approved the study (Dnro THL/127/5.05.00/2015). This research received no specific grant from any funding agency. The authors declare no conflicts of interest.

Results The use of cemented THA decreased in Finland during the study period, whereas the use of uncemented THA increased (Figure 1). The adjusted overall mortality or mortality associated with cardiovascular reasons or pulmonary embolism were similar between cemented THA and uncemented or hybrid THA at any of the studied time points (Figure 2). There were 9 deaths during days 1 and 2 in the cemented THA group, 4 in the uncemented THA group, and 0 in the hybrid group (Table 2). The 1- and 2-day adjusted mortality in the cemented THA

Acta Orthopaedica 2019; 90 (1): 6–10

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Frequency

Relative and cumulative risk of death

5,000

5 Cemented Uncemented Hybrid

4,000

4

3,000

3

2,000

2

1,000

1

0

0 1998

2000

2002

2004

2006

Year

2008

2010

1

2012

92

183

273

365

Days after index operation

Figure 1. Annual numbers of cemented, uncemented, and hybrid THA in Finland during the study period.

Figure 2. Relative and cumulative risk of death in patients receiving a cemented THA compared with patients receiving an uncemented THA. No statistically significant difference in mortality was found.

Table 2. Patient mortality, raw data. Values are frequency (percentage)

Table 3. Postoperative mortality risk (OR (95% CI)) for cemented and hybrid THA compared with uncemented THA (reference)

Mortality 1–2 days 3–10 days 11–20 days 21–30 days

Cemented Uncemented Hybrid THA THA THA n = 23,636 n = 38,477 n = 11,802 9 (0.0) 45 (0.2) 35 (0.1) 22 (0.1)

4 (0.0) 23 (0.1) 14 (0.0) 4 (0.0)

0 (0.0) 6 (0.1) 6 (0.1) 3 (0.0)

30 days 111 (0.5) 45 (0.1) 15 (0.1) 90 days 228 (1.0) 93 (0.2) 29 (0.2) 180 days 389 (1.6) 155 (0.4) 52 (0.4) 365 days 712 (3.0) 254 (0.7) 115 (1.0)

group was the same as that in the uncemented THA group (OR = 1.2; CI 0.2–6.5) (Table 3). There were 45 deaths during the days 3 to 10 in the cemented THA group, 23 in the uncemented THA group, and 6 in the hybrid group (Table 2). The 3- to 10-day adjusted mortality in the cemented THA group was similar to that in the uncemented THA group (OR = 0.5; CI 0.3–1.1), and in the hybrid THA group (OR = 0.6, CI 0.3–1.6) (Table 3). Data on deaths and mortality for the follow-up periods 11 to 20 days, 21 to 30 days, 30 days, 90 days, and 365 days are presented in Tables 2 and 3. There were no deaths due to pulmonary embolism during days 1 and 2 in any of the groups (Table 4). There were 5 deaths during days 1 and 2 in the cemented THA group due to cardiovascular diseases, 4 in the uncemented THA group, and 0 in the hybrid group (Table 4). Data on cause of death for the follow-up periods 11 to 20 days, 21 to 30 days, 30 days, 90 days, and 365 days are presented in Table 4.

2 days 3–10 days 11–20 days 21–30 days

Cemented THA

Hybrid THA

1.2 (0.2–6.5) 0.5 (0.3–1.1) 0.7 (0.3–1.8) 2.8 (0.8–10.0)

0 (0.0–999.9) 0.6 (0.3–1.6) 0.9 (0.3–2.5) 1.9 (0.4–8.8)

30 days 0.8 (0.5–1.3) 0.8 (0.4–1.4) 90 days 0.8 (0.6–1.1) 0.7 (0.5–1.1) 365 days 1.2 (1.0–1.4) 1.2 (0.9–1.5) Table 4. Causes of death. Values are frequency (percentage) Cemented Uncemented Hybrid THA THA THA Cause of death n = 23,636 n = 38,477 n = 11,802 1–2 days Pulmonary embolism 0 0 0 Other cardiovascular 5 (0.02) 4 (0.01) 0 3–10 days Pulmonary embolism 1 (0.00) 2 (0.01) 0 All cardiovascular 11 (0.05) 19 (0.05) 4 (0.03) 11–20 days Pulmonary embolism 5 (0.02) 1 (0.00) 1 (0.01) All cardiovascular 15 (0.06) 9 (0.02) 5 (0.04) 21–30 days Pulmonary embolism 3 (0.01) 1 (0.00) 0 (0.00) All cardiovascular 8 (0.03) 3 (0.01) 2 (0.02) 90 days Pulmonary embolism 15 (0.06) 14 (0.04) 4 (0.03) All cardiovascular 76 (0.32) 60 (0.16) 22 (0.19) 365 days Pulmonary embolism 30 (0.13) 20 (0.05) 7 (0.06) All cardiovascular 208 (0.88) 127 (0.33) 62 (0.53) All cardiovascular: acute myocardial infarction, ischemic heart disease, pulmonary embolism, heart failure, stroke. Follow-up of the causes of death is to the end of 2013.

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Discussion Based on Finnish Registry data the adjusted early postoperative mortality after cemented THA compared with uncemented or hybrid THA was similar as regards death for any reason, death from pulmonary embolism, or death for cardiovascular reasons. However, using unadjusted data the proportion of perioperative deaths was higher in patients with cemented THA than in patients with uncemented or hybrid THA. Cementing is the gold standard for implant fixation, especially in elderly patients. In combined Nordic data, risk for revision has been both statistically and clinically significantly lower with cemented implants than with uncemented implants in patients aged 65 years or more (Mäkelä et al. 2014a, Varnum et al. 2015). Bone cement has been thought to strengthen bone from inside and therefore to decrease the risk for periprosthetic fracture, osteolysis, and loosening. Lower revision rates for cemented implants in elderly patients have been found in all major registries (Swedish Hip Arthroplasty Register 2013, AOANJRR 2016, NJR 2016). Even though superiority in implant survival of cemented THA in elderly patients, fear of bone cement implantation syndrome (BCIS) has led many surgeons towards using uncemented implant fixation (Dale et al. 2009, Fevang et al. 2010, Mäkelä et al. 2014b). BCIS is characterized by perioperative hypotension and hypoxia, and at worst cardiac arrest and death of the patient. The true incidence of cardiac arrest secondary to BCIS is unknown (Donaldson et al. 2009). In our study the 1- and 2-day adjusted mortality was similar in the cemented and uncemented THA groups. Thus, BCIS is seldom a cause of death in elective THA patients in Finland. Historically, cemented THA has been associated with greater than 3-fold higher intraoperative mortality (Coventry et al. 1974, Ereth et al. 1992, Parvizi et al. 1999), but at the end of the 1990’s a reduction in the intraoperative mortality rate has been reported (Parvizi et al. 1999) and the mortality has decreased even more during the twenty-first century (Hunt et al. 2013). A Swedish register study reported an increased adjusted risk of death during the first 14 days after surgery in patients who underwent cemented THA when compared with matched controls (HR of 1.3, 95% CI 1.11–1.44). This means 5 additional deaths per 10,000 observations. Such an increased risk of death was not found in patients with a cementless or hybrid THA. However, this risk in the cemented THA group disappeared during follow-up of 90-days (Garland et al. 2017). In our study the adjusted OR for mortality in the cemented THA group was not elevated during the first 20 postoperative days when compared with the uncemented THA group. Also, McMinn et al. (2012) reported a higher mortality rate in patients undergoing cemented THA compared with uncemented THA. However, this increase in mortality occurred gradually during 8 years after surgery and not early as would be expected if the increased mortality was caused by

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BCIS. We found similar adjusted mortality regarding the use of bone cement at any time point up to 365 days postoperatively. This is in line with a study by Parvizi et al. (2001) who found no increased risk of death with cemented THA 30 days postoperatively. In a recent systematic review the overall 30-day mortality was 0.30% and 90-day mortality was 0.65% following THA. The leading cause of death was ischemic heart disease (41% of deaths) followed by cerebrovascular accidents (23%), and pulmonary embolism (12%) (Berstock et al. 2014). In our material the unadjusted mortality at 30 and 90 days for the cemented THA group was 0.5% and 1.0%, and 0.1% and 0.2% for the hybrid and uncemented groups, respectively. These differences are mainly explained by patient selection, and after adjusting for the elderly and sicker population in the cemented group the mortality was similar between the cemented and uncemented groups. The leading cause of death was cardiovascular. Parvizi et al. (1999) studied intraoperative mortality during cemented THA and found an incidence of 0.03%, the leading cause of death being pulmonary embolism. In previous studies increasing age, male sex, worse ASA score (> 3), and higher number of comorbidities have been found to increase the risk of death after THA surgery (Bozic et al. 2012, Mahomed et al. 2003, Parvizi et al. 2001, Hunt et al. 2013). In our study we attempted to account for this by adjusting the treatment groups for sex, age, and comorbidities, whereafter early overall mortality between the groups was similar at any time point. Our study has several limitations. First, we have no information regarding perioperative resuscitations because of cardiac arrest due to BCIS. Second, data on revision surgeries of the study patients were not included. Thus, we do not know whether mortality is associated for example with multiple operations. Third, the number of deaths for cardiovascular accidents or pulmonary embolism in our study was fairly small. It is possible that in a larger population some smaller differences in the mortality could be detected. Nonetheless, our material consisted of over 60,000 THAs and therefore we believe that there is no difference in clinical importance. Further the PERFECT database does not include information on patients’ socioeconomic status, which is known to affect mortality after THA (Whitehouse et al. 2014, Garland et al. 2017). Therefore some amount of residual confounding cannot be ruled out. As we modeled the mortality difference between the groups using logistic regression analysis repeatedly (356 analyses) there is a possibility of overfitting as the statistical model may contain more parameters than can be justified by the data. This can mean that the results are based on an adaptation to random variation in the sample and therefore the conclusions of our sample could not be generalized to a greater population. In summary, adjusted perioperative and short-term mortality was similar between patients treated with cemented THA and patients treated with uncemented or hybrid THA. This

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pertained also when cardiovascular and pulmonary embolism mortality was studied separately. Based on our results and earlier literature, cemented THA is a safe option and should be the gold standard in the elderly patient population.

KM designed and coordinated the study. EE collected the data and drafted the manuscript. AP helped to draft the manuscript. MP and UH calculated the statistics. All authors contributed to the interpretation of the data and results and to the preparation of the manuscript. Acta thanks Ross W Crawford for help with peer review of this study

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Association between patient survival following reoperation after total hip replacement and the reason for reoperation: an analysis of 9,926 patients in the Swedish Hip Arthroplasty Register Peter CNUDDE 1,2,3, Erik BÜLOW 1,2, Szilard NEMES 2, Yosef TYSON 1,4, Maziar MOHADDES 1,2, and Ola ROLFSON 1,2 1 Swedish Hip Arthroplasty Register, Gothenburg, Sweden; 2 Department of Orthopaedics, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Sweden; 3 Department of Orthopaedics, Hywel Dda University Healthboard, Prince Philip Hospital, Llanelli, UK; 4 Section of Orthopaedic Surgery, Department of Surgical Sciences, Uppsala University Hospital, Uppsala, Sweden Correspondence: peter.cnudde@icloud.com Submitted 2018-11-19. Accepted 2019-02-12.

Background and purpose — The association between long-term patient survival and elective primary total hip replacement (THR) has been described extensively. The long-term survival following reoperation of THR is less well understood. We investigated the relative survival of patients undergoing reoperation following elective THR and explored an association between the indication for the reoperation and relative survival. Patients and methods — In this observational cohort study we selected the patients who received an elective primary THR and subsequent reoperations during 1999–2017 as recorded in the Swedish Hip Arthroplasty Register. The selected cohort was followed until the end of the study period, censoring or death. The indications for 1st- and eventual 2nd-time reoperations were analyzed and the relative survival ratio of the observed survival and the expected survival was determined. Results — There were 9,926 1st-time reoperations and of these 2,558 underwent further reoperations. At 5 years after the latest reoperation, relative survival following 1sttime reoperations was 0.94% (95% CI 0.93–0.96) and 0.90% (CI 0.87–0.92) following 2nd-time reoperations. At 5 years patients with a 1st-time reoperation for aseptic loosening had higher survival than expected; however, reoperations performed for periprosthetic fracture, dislocation, and infection had lower survival. Interpretation — The relative survival following 1stand 2nd-time reoperations in elective THR patients differs by reason for reoperation. The impact of reoperation on life expectancy is more obvious for infection/dislocation and periprosthetic fracture.

While the risk of dying and life expectancy following a primary THR has been studied extensively, patient survival after further surgical interventions is virtually unexplored (Jones et al. 2018, Yao et al. 2018). What happens to life expectancy if patients undergo reoperation and does the clinical indication for the reoperation influence life expectancy? So far, little is known about death following reoperation or revision after THR. The increasing age at the time of reoperation, the increased complexity of the surgery, and the timing of surgery might influence life expectancy. The relative survival method has been developed to provide better insights into the relation between a study population and a general population (Stare et al. 2005). The Swedish Hip Arthroplasty Register (SHAR), a reliable source of information on longitudinal outcome (Kärrholm 2010, Cnudde et al. 2016) combined with national aggregated data from Statistics Sweden provide a platform for this study, which investigates the relative survival of patients undergoing reoperation following elective THR and the influence of the indication for the reoperation on the relative survival. Additionally, it investigates time- and indication-dependent patterns for 1st- and 2nd-time reoperations.

Patients and methods Data sources For this study, we used prospectively collected data on all patients who underwent a 1st-time reoperation following elective THR in 1999–2017 as recorded in SHAR. Patients who had their primary THR before 1999 were excluded. All surgical- and patient-related variables could be accessed and

© 2019 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group, on behalf of the Nordic Orthopedic Federation. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits ­unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. DOI 10.1080/17453674.2019.1597062

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Table 1. Demographics of the study population. Values are mean years (SD) unless otherwise stated n Age at primary THR Time to 1st reoperation Time from 1st to 2nd reoperation Age at 1st reoperation Age at 2nd reoperation Women, n (%) Dead, n (%)

Aseptic Periprosthetic loosening Dislocation fracture

Infection

Other

Unknown

3,558 1,782 1,574 2,065 877 60 61 (11) 69 (11) 70 (11) 68 (12) 60 (13) 60 (16) 8.0 (4.4) 3.2 (4.0) 5.2 (4.4) 1.6 (3.1) 4.1 (4.0) 6.4 (5.3) 2.0 (2.6) 1.7 (2.9) 1.6 (2.4) 0.6 (1.5) 1.5 (2.2) 1.4 (3.1) 70 (11) 73 (11) 76 (12) 70 (11) 65 (12) 67 (16) 69 (11) 73 (11) 73 (13) 69 (11) 67 (13) 69 (14) 1,790 (50) 1,045 (59) 884 (56) 869 (42) 478 (55) 40 (57) 566 (16) 818 (46) 711 (45) 645 (31) 136 (16) 10 (14)

p-value < 0.001 for all comparisons.

analysed from the database. However, for this analysis we concentrated solely on age, sex, and indication for surgery at the time of primary THR and age at the time of and indications for further operations. A reoperation is defined as any further surgery to the hip regardless of whether implant components are exchanged, removed, added or not, whereas a revision is defined as a reoperation where implant components are exchanged, removed, and/or added. Cause for reoperation was categorized into aseptic loosening, dislocation, periprosthetic fracture, infection, and other causes. Closed reductions, aspirations and isolated tissue biopsies are not included in this definition. The selected cohort was followed until the end of the study period (December 31, 2017), censoring, or death. Statistics Continuous variables were summarized as means (SD), categorical variables as percentages. Subsequently, we summarized and illustrated survival with the help of relative survival curves with 95% confidence intervals (CI) (Pohar Perme et al. 2012). We used R version 3.5 for statistical analyses (R Core Team (2018), R: A language and environment for statistical computing, Vienna, Austria, https://www.R-project.org) with the “relsurv” package for statistical analysis and applied the Pohar Perme method for calculating the relative survival. Relative survival The relative survival was based on comparison of patients who underwent reoperation with aggregated data at national level from the general population (http://www.mortality.org). For any given time point onward, we estimated the relative survival ratio based on the observed survival in the patient group divided by the observed survival in general population matched on age, sex, and year of birth. The observed survival of the general population was extracted from publicly available mortality tables tabulated for birth year and sex. The formula has previously been published (Cnudde et al. 2018a). A relative survival of 1 indicates that the exposure of interest, here the reoperation or the condition causing it, does not affect the survival in any measurable way. It does not mean that all

patients survive. A relative survival of less than 1 indicates excess hazard for the patients, while values above 1 indicate better survival than expected. Ethics, funding, and potential conflicts of interests This study is part of a research project with the overall aim to perform a multidimensional longitudinal outcomes assessment following total hip replacement. Ethical review approval was obtained on April 7, 2014 from the Regional Ethical Review Board in Gothenburg, Sweden (entry number 271-14). The study was in part financed by grants from the Swedish state under the agreement between the Swedish government and the county councils, the ALF agreement (ALFGBG-522591). No competing interests declared.

Results Using the SHAR databases, 278,309 primary THRs were identified in the study period from January 1, 1999 to December 31, 2017. There were 9,926 1st-time reoperations, of which 7,581 were 1st-time revision procedures. Of these 2,558 underwent further reoperations, of which 1,541 were subsequent revisions. There were patients undergoing subsequent procedures (up to 19 recorded reoperations and 8 revisions). Patients’ demographics and indications for reoperations are presented in Table 1. Patients who underwent reoperation for infection and aseptic loosening were generally younger at the time of their surgery than patients undergoing the procedure for dislocation and periprosthetic fracture. The indications for reoperations varied according to sex, with more females undergoing reoperations for periprosthetic fractures and dislocations whereas more males had reoperations for infection. The median follow-up time was 8.4 years (0–18) from primary surgery. Patients undergoing 1st-time reoperation had a lower survival rate compared with the general population for the whole study period. The relative survival was 98% (CI 98–99) at 1 year, 94% (CI 93–96) at 5 years, 80% (CI 75–86) at 10 years, and 61% (CI 50–74) at 15 years. Relative survival was worse

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Indication for reoperation Aseptic loosening

Periprosthestic fracture

Other

Dislocation

primary to first reoperation first to second reoperation

Infection 0

1

2

3

4

5

6

7

8

Median years to reoperation

Figure 1. Relative survival after 1st-time reoperation per indication at the time of the reoperation (truncated at 10 years).

Figure 2. Relative survival (and confidence intervals) after the 2nd-time reoperation per indication at the time of the reoperation (truncated at 10 years).

for 2nd-time reoperations compared with 1st-time reoperations with 97% (CI 96–98) at 1 year, 90% (CI 87–92) at 5 years, 69% (CI 56–85) at 10 years, and 49% (CI 34–71) at 15 years. We stratified the relative survival per indication for reoperation (Figure 1). 1st-time reoperations for aseptic loosening had similar survival to the general population. In fact, the relative survival ratio implied a 4% increased survival compared with the general population at 5 years. Relative survival following reoperations performed for periprosthetic fracture was worse compared with aseptic loosening or other causes up to 15 years. Up to 5 years, relative survival following 1st-time reoperations for dislocation and infection was worse than for aseptic loosening and other causes (Table 2, see Supplementary data). The relative survival following a 2nd-time reoperation (Figure 2) was only marginally better if the reoperation was performed for aseptic loosening within the 1st year (Table 3, see Supplementary data). Further reoperations for infection, periprosthetic fracture, and dislocation had lower survival with the lowest survival in cases of re-reoperation for dislocation and periprosthetic fracture. The number of patients at risk is below 100 at 10 years in the group of the re-reoperations with the exception of infections and other (non-further specified) indications. There was a difference in time between primary THR and reoperation depending on the indication for the surgery (at the time of the reoperation), with a shorter time interval in the case of infection, dislocation, and periprosthetic fracture in the 1st postoperative year. A later and a more gradual increase in cases of loosening could be seen at later stages postoperatively. Further reoperations peaked very early after the 1st reintervention with the shortest interval when the 1st reoperation was performed for infection (Figure 3). We also studied the influence of the clinical diagnosis at the time of primary THR on further reoperations (Table 4, see

Figure 3. Median time between the primary THR and the 1st-time reoperation and between 1st- and 2ndtime reoperation for the different indications.

Supplementary data). Aseptic loosening was the most frequent indication at the time of reoperation when the primary THR was performed for almost all clinical indications except when a THR was performed as a result of trauma complications. Infections and dislocations frequently led to further infections for the same reasons (Table 5, see Supplementary data). Many treatment-resistant infections end up leading to an excision arthroplasty of the THR (classified as other procedure within the Tables and Figures).

Discussion We found that the survival following 1st- and 2nd-time repeat surgery in elective THR is influenced by the reason for the reoperation. Patients undergoing reoperations for aseptic loosening had a survival that is better compared with the survival of the general population up to 5 years following the reoperation. Reoperations for dislocation and periprosthetic fractures were associated with a worse survival compared with the survival of the general population, also visible in the case of a further reoperation. THR can fail for a variety of reasons in isolation or through a combination of factors. It is well known that the patientreported outcomes after revision are worse compared with those of a primary procedure (Lubbeke et al. 2007, Postler et al. 2017). It is also likely that activity levels, as well as a potential to return to work, is affected by the revision THR (Scott et al. 2018). Nevertheless, the crude indicators of success have been re-revision/reoperation and/or mortality following the surgical procedure. The risk of further reoperations after a reoperation has been alluded to in the annual reports of the SHAR (https://shpr.registercentrum.se) and a 20% risk of a subsequent reoperation has been described. In the majority of cases a 1st reoperation occurs early within the 1st couple of

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years with a shortening of time interval when further reoperations are needed. Mortality can be calculated in different ways and the effect of the procedure on life expectancy will be influenced by a multitude of factors. Short-term mortality has been described by Jones et al. (2018) based on a comparison of patients who underwent revision surgery and were compared with patients awaiting revision surgery. They found a higher mortality rate in patients who underwent revision surgery. This is likely attributed to the effect of the surgery. Yao et al. (2018) described long-term mortality following revision THR using the Mayo database and found a slightly higher mortality than in the general population. Our findings differ from the Mayo findings as we have an improved relative survival until 5 years postoperatively and from 5 years onward a survival that does not differ from the general population. The survival in patients reoperated for infections, periprosthetic fractures, and dislocations are, however, all worse than in the general population. The Mayo group combined aseptic loosening, bearing wear, and dislocation in a single group. Whilst we were not able to look at the influence of comorbidity, we did study the effect of further reoperations. Relative survival methods have been used to describe the cancer prognosis at population level. The overall relative survival 5 years after a 1st-time reoperation is comparable with the 5-year relative survival of melanomas (94% and 95%) in females in Australia and Sweden. Our 5-year relative survival after 2nd-time reoperation is slightly worse compared with the Australian and Swedish 5-year relative survival after diagnosis of breast cancer in women (91% and 92%). The overall 10-year relative survival for all cancers in Australia and Sweden is 61% and 69%. Our 10-year relative survival after reoperation is worse than the 10-year relative survival for breast cancer in Australia and Sweden (85% and 86%) and comparable to the relative survival after cervical cancer (70% and 76%) (https://ncci.canceraustralia.gov.au/outcomes/relative-survival-rate/10-year-relative-survival and https://www. cancerfonden.se/cancer-i-siffror). These comparisons illustrate the severity of suffering THR complications leading to reoperation. Despite the ongoing improvement in outcomes of THR, some issues remain. There is a gradual increase in patients undergoing reoperations for infection and dislocation (Cnudde et al. 2018b). These predominantly occur in the early postoperative stages and are associated with an increased mortality. There is also an accepted knowledge that revision THRs do worse than primary THRs (Espehaug et al. 1998, Lie et al. 2004). Therefore the right implant choice at the time of the primary procedure (Thien et al. 2014), management strategies at the time of the primary surgery, and subsequent surgeries will have to be developed and followed in an attempt to get the best outcomes and to avoid complications such as dislocation, infection, and periprosthetic fractures. Such complications not only put a burden on the patient but also have an impact on the

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scarce health care resources, and the question will have to be asked which departments and surgeons will be best placed to organise and provide the treatment and ensure the best possible outcomes. The risk of subsequent re-reoperations is quite prominent in the case of infection and dislocation, with further surgery for the same reasons being the most common indication if surgery takes place. This reiterates the complexity of this problem and the need to develop management pathways for the prevention and adequate treatment of infections and dislocations. Bigger head size and dual mobility cups have been advocated in the case of dislocation (Mohaddes et al. 2017). New pathways advocating a timely diagnosis, rigorous debridement, local delivery of antibiotics, and prolonged use of systemic antibiotics are now considered the mainstay of treatment protocols in the case of periprosthetic joint infections. Strengths and limitations This study is based on data from a validated national quality register with linkage to the administrative databases.We deliberately selected the period 1999–2017 as 1999 coincides with the year when more details of the implants used became available within the SHAR, and represents the time when increased use of more contemporary implants and head sizes was noticed, reflecting current practice. We acknowledge that selecting only reoperations following primary surgeries performed during this period does not reflect the actual proportion of different reasons for reoperations undertaken in Sweden; the distribution is skewed towards early and midterm complications. In our analysis there was no matching for comorbidity and socioeconomic status. A previous study of our research group has described the effect of both comorbidity and socioeconomic status on both mortality and revision after THR (Cnudde et al. 2018c). We are aware that the indication at the time of primary surgery probably influences the reason for subsequent revisions with those who have a THR for complications after trauma or acute fracture having a higher risk of dislocation, periprosthetic fracture, and infection (Cnudde et al. 2018c). Whether the risk of earlier death is linked to the reoperation per se or to the increased risk of reoperation in frail patients is something that will need further study. In summary the impact of reoperation on life expectancy is obvious for infection/dislocation and periprosthetic fracture. Treatment strategies should be developed to prevent these complications occurring and surgical pathways for the reoperations should be developed in order to improve outcomes for patients. Supplementary data Tables 2–5 are available as supplementary data in the online version of this article, http://dx.doi.org/ 10.1080/17453674. 2019.1597062

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PC, SN, and OR conceived and planned the study. EB and SN processed the data and performed the statistical analysis. PC prepared the 1st draft of the manuscript. All authors cooperated in the analysis and interpretation of the data and the writing of the manuscript. The authors would like to thank the orthopedic teams at the different centres in Sweden as well as the register coordinators at the Registercentrum Västra Götaland for their ongoing support with the data provision and collection. Acta thanks Ove Furnes and Per Kjærsgaard-Andersenfor help with peer review of this study.

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An international comparison of THA patients, implants, techniques, and survivorship in Sweden, Australia, and the United States Elizabeth W PAXTON 1,3, Guy CAFRI 1, Szilard NEMES 2,3, Michelle LORIMER 5, Johan KÄRRHOLM 2,3,4, Henrik MALCHAU 2,3,4, Stephen E GRAVES 5, Robert S NAMBA 6, and Ola ROLFSON 2,3,4 1 Department

of Clinical Analysis, Surgical Outcomes and Analysis, Southern California Permanente Medical Group, San Diego, CA, USA; 2 Swedish Hip Arthroplasty Register, Gothenburg, Sweden; 3 Department of Orthopaedics, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden; 4 Sahlgrenska University Hospital, Gothenburg, Sweden; 5 Australian Orthopaedic Association National Joint Replacement Registry, Adelaide, Australia; 6 Southern California Permanente Medical Group, Irvine, CA, USA Correspondence: Liz.w.paxton@kp.org Submitted 2018-08-13. Accepted 2018-12-18.

Background and purpose — International comparisons of total hip arthroplasty (THA) practices and outcomes provide an opportunity to enhance the quality of care worldwide. We compared THA patients, implants, techniques, and survivorship in Sweden, Australia, and the United States. Patients and methods — Primary THAs due to osteoarthritis were identified using Swedish (n = 159,695), Australian (n = 279,693), and US registries (n = 69,641) (2003– 2015). We compared patients, practices, and implant usage across the countries using descriptive statistics. We evaluated time to all-cause revision using Kaplan–Meier survival curves. We assessed differences in countries’ THA survival using chi-square tests of survival probabilities. Results — Sweden had fewer comorbidities than the United States and Australia. Cement fixation was used predominantly in Sweden and cementless in the United States and Australia. The direct anterior approach was used more frequently in the United States and Australia. Smaller head sizes (≤ 32 mm vs. ≥ 36 mm) were used more often in Sweden than the United States and Australia. Metal-onhighly cross-linked polyethylene was used more frequently in the United States and Australia than in Sweden. Sweden’s 5- (97.8%) and 10-year THA survival (95.8%) was higher than the United States’ (5-year: 97.0%; 10-year: 95.2%) and Australia (5-year: 96.3%; 10-year: 93.5%). Interpretation — Patient characteristics, surgical techniques, and implants differed across the 3 countries, emphasizing the need to adjust for demographics, surgical techniques, and implants and the need for global standardized definitions to compare THA survivorship internationally.

Arthroplasty registries provide a mechanism for evaluating patient, surgical, and implant characteristics associated with revision surgery (Paxton et al. 2012, 2015, Khatod et al. 2014) and to identify clinical best practices for enhancing quality of care (Herberts and Malchau 1999, 2000, Graves 2010, Paxton et al, 2010, 2012). In addition, identification of variations between countries provides an opportunity to evaluate similarities and differences in practices and outcomes. Investigation of total hip arthroplasty (THA) variation between countries has been examined in Scandinavia (Havelin et al. 2011, Makela et al. 2014) but has been limited in other countries. However, with an increased focus on the need for worldwide evidence on THA implant performance, international collaborations have increased (Sedrakyan et al. 2011, 2014). Despite an increased focus on such collaborations, variations in US, Australian, and Swedish THA patients, practices, and outcomes have not been fully examined. Therefore, we investigated similarities and differences in patient characteristics, surgical techniques, implant selection, and implant survival rates in THA patients across the 3 countries to identify future areas of research based on the country comparisons.

Patients and methods Primary THAs due to osteoarthritis were identified using national and regional registries in Sweden (n = 159,695) (SHAR 2014), Australia (n = 279,693) (AOANJRR 2015), and the United States (Paxton et al. 2012) (n = 69,641) from 2003 to 2015. The capture rate of these registries exceeds 95% and loss to follow-up is less than 8% over the study period. Validation and quality control methods of these registries have been previously published (Soderman et al. 2000, Paxton et al. 2010, 2012, AOANJRR 2016). Bilateral procedures were included in the study. Hip resurfacing procedures were excluded.

© 2019 The Author(s). Published by Taylor & Francis on behalf of the Nordic Orthopedic Federation. This is an Open Access article distributed under the terms of the Creative Commons Attribution-Non-Commercial License (https://creativecommons.org/licenses/by/4.0) DOI 10.1080/17453674.2019.1574395

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Figure 1. THA implant bearing surfaces by country.

Patient characteristics (i.e., age, sex, BMI, ASA score), surgical techniques (i.e., surgical approach, type of cement fixation), implant types (i.e., bearing surface, femoral head size), and 5- and 10-year implant survival were reported from the registries. Sweden’s BMI and ASA were available from 2008 to 2015. Australia’s BMI was available only for 2015 and their ASA scores from 2012 to 2015. For the US cohort, BMI and ASA were available for the entire time period. Tables with aggregate-level data were shared across countries. Descriptive statistics were used to compare and contrast patients, practices, and implant usage. Kaplan–Meier survival curves were used to evaluate time to all-cause revision across the countries. Chi-square tests of survival probabilities were used to assess differences in THA survival probabilities between the countries at 5- and 10-year follow-up. 95% confidence intervals (CI) are also presented.

ever, Australia had a higher proportion of males than the US and Swedish cohorts. The US cohort was younger than both Australian and Swedish cohorts. Sweden had the lowest proportion of obese patients and lowest ASA scores of the 3 cohorts (Table 2, see Supplementary data).

Ethics, funding, and potential conflicts of interest Approval from the Institutional Review Board was obtained prior to the start of this study (#5488 approved on August 27, 2009) and from the Regional Ethical Review Board in Gothenburg (entry number 271-14 approved on April 7, 2014 with amendment T-609-17 approved on July 10, 2017). There is no funding. There are no conflicts of interest.

Implant characteristics While metal-on-highly cross-linked polyethylene (HXLPE) was used more frequently in the United States and Australia, metal-on-conventional bearing surface was used more often in Sweden, especially during the early part of the period studied. Ceramic-on-ceramic was used more frequently in Australia and rarely in Sweden. Ceramic-on-HXLPE was used more frequently in the US cohort (Table 4, see Supplementary data). In all countries, metal-on-metal bearing surfaces decreased, in Sweden from a few hundred to zero. In all 3 countries, the use of ceramic-on-HXLPE increased during the study period (Figure 1).

Results Incidence rates of primary THA The volume of primary THAs for OA increased each year in all 3 countries during the study period. The 2015 incidence rates of THA with an OA diagnosis were higher in Australia and Sweden then in the US cohort (Table 1, see Supplementary data). Patient characteristics THA sex was predominantly female in all 3 countries. How-

Surgical techniques Cement fixation was used predominantly in Sweden while cementless fixation was used more frequently in the United States and Australia. The percentage of hybrid fixation was higher in Australia than for the US cohort and in Sweden. The posterior approach was the main surgical approach for all countries. However, the direct anterior approach used in Australia and the United States was not adopted in Sweden during the study period (Tables 3 and 4, see Supplementary data).

Femoral head size Femoral head size use differed across countries with Sweden using smaller head sizes (i.e., ≤ 28 mm and 32 mm) whereas the US and Australian cohorts had a greater proportion of 36 mm and larger head sizes (Table 4). The use of 32 mm femoral head size became more prominent in Sweden during the study period (Figure 2).

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Figure 2. THA implant head size by country.

Hospital annual volume Hospital volume was similar across US and Swedish cohorts. However, Australia had a higher percentage of low volume facilities compared with the United States and Sweden (Table 5, see Supplementary data). Outcomes THA survival at 5 years was higher in Sweden (97.8%, CI 97.8–97.9) than the US (97.0%, CI 96.7–97.2), and Australian (96.3%, CI 96.2–96.4) cohorts. The US cohort had a higher 5-year THA survivorship than the Australian. THA survival at 10 years was higher in Sweden (95.8%, CI 95.6–95.9) than for the US cohort (95.2%, CI 94.7–95.6) and in Australia (93.5%, CI 93.4–93.7). The US cohort had a higher 10-year THA survivorship than Australia (Table 6, Figure 3, see Supplementary data). The most frequent reasons for revisions differed across the countries. Aseptic loosening was higher in Sweden along with infection (Figure 4, see Supplementary data). Instability was a more common reason for revision in the US cohort than in Sweden and Australia.

Discussion This study provides the first comprehensive assessment of US, Swedish, and Australian THA practice patterns and outcomes, and identifies variation between countries in patient characteristics, fixation, implant characteristics, and THA implant survival. Patient characteristics First, the study highlights variation in the incidence of primary THA for OA with Sweden and Australia having a higher annual incidence rate than the US cohort. Our findings are consistent with other reports of variation in international total hip incidence rates (Merx et al. 2003). Differences in incidence rates

may reflect the younger population in the US health system, an actual variation in diagnoses leading to THA, differences in diagnostic accuracy and indications for surgical treatment, varying access to care in the different healthcare systems, or possibly variation in population demand. Second, patient characteristics appear to differ across countries with Sweden reporting lower BMI and ASA scores than Australia and the United States. This finding is consistent with other studies that have indicated a higher BMI in the US population (ProCon.org 2011). Differences in ASA scores could reflect a healthier population in Sweden but could also represent variations in coding practices across the countries. In addition to differences in BMI and comorbidities, cohorts also differed in age distribution with the US group having a younger THA population. This may reflect differences in thresholds for operating on younger patients or varying access to care across the different healthcare systems. The differences in patient characteristics emphasize the need to adjust for this variation when examining THA outcomes across countries. Surgical techniques Although the posterior approach was used most frequently in all 3 countries, Sweden did not utilize the direct anterior approach. Several systematic reviews and registry studies suggest that the anterior approach is associated with lower dislocation and revision rates (Barrett et al. 2013, Higgins et al. 2015, Sheth et al. 2015, Miller et al. 2018a, b). However, these studies focused on short-term and functional outcomes without any certain conclusions concerning longer term revision rates. Despite differences in surgical approaches, Sweden had lower THA revision rates than the US cohort and Australia. Fixation and implant characteristics Another identified difference was type of THA fixation used in the different countries. While Sweden used cement fixation more frequently, US and Australian practices were predominantly cementless. Studies examining fixation seem to suggest

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an advantage for cement fixation, especially in older patients (SHAR 2009, Hailer et al. 2010, AOANJRR 2017, Phedy et al. 2017). Future studies comparing international variations should account for fixation types and implants to fully evaluate differences in THA implant survival. Type of THA bearing surface also differed across countries with Sweden adopting more metal-on-conventional polyethylene. Several large registry studies have identified a higher revision rate in metal-on-conventional bearing surface than metalon-HXLPE (AOANJRR 2013, Paxton et al. 2015). However, this difference may be prosthesis-dependent (Johanson et al. 2017). Sweden’s use of metal-on-conventional has decreased and the use of metal-on-HXLPE increased during the study period. Sweden also adopted less large head size metal-onmetal, which has been reported as having a higher risk of THA revision (AOANJRR 2008). The use of large head size metalon-metal decreased in both the United States and Australia. In all 3 countries, the use of ceramic-on-HXLPE bearing surface increased. While the Australian registry reports lower revision rates in ceramic-on-HXLPE compared with metal-onHXLPE, a recent US study indicated similar revision rates among these bearing surfaces but higher dislocation rates in ceramic versus metal femoral heads of < 32 mm, suggesting both head size and bearing surface material influence risk of revision (AOANJRR 2017, Cafri et al. 2017). Hospital volume Annual hospital volume also differed across countries. While hospital volumes were similar in Sweden and the US cohort, the Australian registry had a higher number of cases performed at low-volume hospitals. Lower hospital volume has been identified in relationship to higher complication rates and readmissions (Dy et al. 2014, Laucis et al. 2016, Sibley et al. 2017). Evaluating further the effects of hospital volume may identify potential areas of focus for quality improvement within healthcare systems. THA survival In evaluating THA survival, all 3 countries had 5- and 10-year THA implant survival estimates above 95%. 5- and 10-year implant survival was highest in Sweden and lowest in Australia. Differences in survival could possibly be related to different thresholds for revision THA surgery in those countries. Most likely, however, the difference THA survival is related to the degree of variation in implant selection between the countries. While Sweden and the US cohort used a limited number of implants during this timeframe, Australia had much greater variation in THA implant models. In Australia alone, over 2,000 cup and stem combinations were used. 78 different THA acetabular cups and stem model combinations have been used with 10-year follow-up and cumulative percentage revision rates ranging from 2% to 46%. Only 35% of these combinations had less than a 5% 10-year cumulative percentage revision (AOANJRR 2017). In comparison, Sweden’s 10-year

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THA survival ranged from 94.4% to 98.1% based on a more restricted use of cup/stem combinations. In Sweden, 6 stems and 15 cups accounted for over 90% of the implant usage (SHAR 2016). This suggests that implant selection plays a key role in THA survival. The comparison of specific implant performance in similar patients with similar techniques must be evaluated to understand the underlying source of this international variation in THA survival. In addition to differences in revision rates, the reasons for revision also differed across countries. Sweden had a higher percentage of aseptic loosening than the US and Australian cohorts, which could be related to the higher percentage of metal-on-conventional polyethylene use in Sweden during the study period. The US cohort had a higher percentage of pain as the revision diagnosis. Revision due to pain and aseptic loosening combined in the US group was comparable to aseptic loosening diagnosis in both Sweden and Australia, suggesting aseptic loosening maybe the underlying diagnosis of pain in the US cohort. Revision diagnosis of infection was higher in Sweden than in the other countries. The US cohort had a higher rate of revision due to instability despite the use of larger femoral head sizes and the direct anterior approach. This most likely reflects the predominant use of uncemented cups in the US cohort, which has been reported to have more instability than cemented cups (Conroy et al. 2008). Differences in revision diagnoses may be related to the different underlying mechanisms of failure related to different implant usage and indications but could also be related to variation in surgeon documentation and definitions across registries, again emphasizing the need for standardized, global revision definitions to conduct international comparisons of THA outcomes. This study has both strengths and limitations. The strengths of this study include the large registry data sets with highquality data and minimal loss to follow-up. In addition, registries provide real-world data with high generalizability/external validity. Limitations include the descriptive nature of the study, which has not been adjusted for confounders, the observational study design limiting causality, and the use of only one US integrated healthcare system. In addition, although countries differed in patient, implant, and surgical factors, the difference in THA survival may be interpreted as not being clinically relevant due to the small differences. However, this study emphasizes there are differences in THA survival overall and further research needs to be conducted to evaluate THA outcomes by specific types of prostheses while controlling for patient, surgical, and hospital factors. In summary, patient characteristics, surgical techniques, and implant selection differs across the 3 countries, emphasizing the need to address regional and national differences in demographics, surgical techniques, implants, and the need for global standardized definitions to compare results across existing registries and to develop international THA benchmarking standards.

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Supplementary data Tables 1–6 and Figures 3–4 are available as supplementary data in the online version of this article, http://dx.doi.org/ 10.1080/17453674.2019.1574395 EP: conception of study, interpretation of data and manuscript preparation. SN, JK, HM, SG, RS, OR: interpretation of data and manuscript preparation. ML, GC: statistical analyses, interpretation of data, and manuscript preparation. Acta thanks Antti Eskelinen and Sarunas Tarasevicius for help with peer review of this study.

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Makela K T, Matilainen M, Pulkkinen P, Fenstad A M, Havelin L I, Engesaeter L, Furnes O, Overgaard S, Pedersen A B, Karrholm J, Malchau H, Garellick G, Ranstam J, Eskelinen A. Countrywise results of total hip replacement: an analysis of 438,733 hips based on the Nordic Arthroplasty Register Association database. Acta Orthop 2014; 85(2): 107-16. Merx H, Dreinhofer K, Schrader P, Sturmer T, Puhl W, Gunther K P, Brenner H. International variation in hip replacement rates. Ann Rheum Dis 2003; 62(3): 222-6. Miller L E, Gondusky J S, Bhattacharyya S, Kamath A F, Boettner F, Wright J. Does surgical approach affect outcomes in total hip arthroplasty through 90 days of follow-up? A systematic review with meta-analysis. J Arthroplasty 2018a; 33(4): 1296-302. Miller L E, Gondusky J S, Kamath A F, Boettner F, Wright J, Bhattacharyya S. Influence of surgical approach on complication risk in primary total hip arthroplasty. Acta Orthop 2018b; 89(3): 289-94. Paxton E W, Inacio M C, Khatod M, Yue E J, Namba R S. Kaiser Permanente National Total Joint Replacement Registry: aligning operations with information technology. Clin Orthop Relat Res 2010; 468(10): 2646-63. Paxton E W, Inacio M C, Kiley M L. The Kaiser Permanente Implant Registries: effect on patient safety, quality improvement, cost effectiveness, and research opportunities. Perm J 2012; 16(2): 36-44. Paxton E W, Inacio M C, Khatod M, Yue E J, Funahashi T, Barber T. Risk calculators predict failures of knee and hip arthroplasties: findings from a large health maintenance organization. Clin Orthop Relat Res 2015; 473(12): 3965-73. Phedy P, Ismail H D, Hoo C, Djaja Y P. Total hip replacement: a meta-analysis to evaluate survival of cemented, cementless and hybrid implants. World J Orthop 2017; 8(2): 192-207. ProCon.org. US and global obesity levels: the fat chart. Santa Monica, CA; 2011. Sedrakyan A, Paxton E W, Phillips C, Namba R, Funahashi T, Barber T, Sculco T, Padgett D, Wright T, Marinac-Dabic D. The International Consortium of Orthopaedic Registries: overview and summary. J Bone Joint Surg Am 2011; 93(Suppl 3): 1-12. Sedrakyan A, Paxton E, Graves S, Love R, Marinac-Dabic D. National and international postmarket research and surveillance implementation: achievements of the International Consortium of Orthopaedic Registries initiative 2014. J Bone Joint Surg Am 2014; 96(Suppl): 1-6. SHAR. Swedish Hip Arthroplasty Register Annual Report 2009. https://shpr. registercentrum.se/shar-in-english/annual-reports-from-the-swedish-hiparthroplasty-register/p/rkeyyeElz. DOI: 10.18158/Hysl6bA0Z SHAR. Swedish Hip Arthroplasty Register Annual Report 2014. https://shpr. registercentrum.se/shar-in-english/annual-reports-from-the-swedish-hiparthroplasty-register/p/rkeyyeElz. DOI: 10.18158/B1OyzZ00Z SHAR. Swedish Hip Arthroplasty Register Annual Report 2016. https://shpr. registercentrum.se/shar-in-english/annual-reports-from-the-swedish-hiparthroplasty-register/p/rkeyyeElz. DOI: 10.18158/SJy6jKyrM Sheth D, Cafri G, Inacio M C, Paxton E W, Namba R S. Anterior and anterolateral approaches for THA are associated with lower dislocation risk without higher revision risk. Clin Orthop Relat Res 2015; 473(11): 3401-8. Sibley R A, Charubhumi V, Hutzler L H, Paoli A R, Bosco J A. Joint replacement volume positively correlates with improved hospital performance on Centers for Medicare and Medicaid Services quality metrics. J Arthroplasty 2017; 32(5): 1409-13. Soderman P, Malchau H, Herberts P, Johnell O. Are the findings in the Swedish National Total Hip Arthroplasty Register valid? A comparison between the Swedish National Total Hip Arthroplasty Register, the National Discharge Register, and the National Death Register. J Arthroplasty 2000; 15(7): 884-9.

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Varying but reduced use of postoperative mobilization restrictions after primary total hip arthroplasty in Nordic countries: a questionnaire-based study Kirill GROMOV 1,2, Anders TROELSEN 1, Maziar MOHADDES 3,4, Ola ROLFSON 3,4, Ove FURNES 5,6, Geir HALLAN 5,6, Antti ESKELINEN 7,8, Perttu NEUVONEN 7,8, and Henrik HUSTED 1 1 Department

of Orthopaedic Surgery, Copenhagen University Hospital Hvidovre, Denmark; 2 Danish Hip Arthroplasty Registry; 3 Department of Orthopaedics, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden; 4 Swedish Hip Arthroplasty Register; 5 The Norwegian Arthroplasty Register, Department of Orthopaedic Surgery, Haukeland University Hospital, Bergen, Norway; 6 Department of Clinical Medicine, University of Bergen, Norway; 7 Coxa Hospital for Joint Replacement, and Faculty of Medicine and Life Sciences, University of Tampere, Tampere, Finland; 8 Finnish Hip Arthroplasty Registry Correspondence: kirgromov@gmail.com Submitted 2018-11-07. Accepted 2019-01-03.

Background and purpose — Mobilization has traditionally been restricted following total hip arthroplasty (THA) in an attempt to reduce the risk of dislocation and muscle detachment. However, recent studies have questioned the effect and rationale underlying such restrictions. We investigated the use of postoperative restrictions and possible differences in mobilization protocols following primary THA in Denmark (DK), Finland (FIN), Norway (NO), and Sweden (SWE). Patients and methods — All hospitals performing primary THA in the participating countries were identified from the latest national THA registry report. A questionnaire containing questions regarding standard surgical procedure, use of restrictions, and postoperative mobilization protocol was distributed to all hospitals through national representatives for each arthroplasty registry. Results — 83% to 94% (n = 167) of the 199 hospitals performing THA in DK, FIN, NO, and SWE returned correctly filled out questionnaires. A posterolateral approach was used by 77% of the hospitals. 92% of the hospitals had a standardized mobilization protocol. 50%, 41%, 19%, and 38% of the hospitals in DK, FIN, NO, and SWE, respectively, did not have any postoperative restrictions. If utilized, restrictions were applied for a median of 6 weeks. Two-thirds of all hospitals have changed their mobilization protocol within the last 5 years—all but 2 to a less restrictive protocol. Interpretation — Use of postoperative restrictions following primary THA differs between the Nordic countries, with 19% to 50% allowing mobilization without any restrictions. There has been a strong tendency towards less restrictive mobilization over the last 5 years.

Dislocation following primary total hip arthroplasty (THA) has been reported to occur in 1–10% of patients (Meek et al. 2006, Patel et al. 2007, Kotwal et al. 2009, Jørgensen et al. 2014). Both surgery- and patient-related factors have been shown to affect the risk for dislocation, including surgical approach, implant position, implant type, implant fixation, femoral head size, age, sex, comorbidities, and cognitive function (Jolles et al. 2002, Byström et al. 2003, Brooks 2013, Seagrave et al. 2017a, 2017b, Miller et al. 2018, Tsikandylakis et al. 2018). Movement restrictions and other hip precautions following THA have commonly been practiced to prevent dislocation and muscle detachment (Husted et al. 2014)—especially if a lateral transgluteal approach has been used. However, recent studies have questioned this rationale, as liberal postoperative mobilization protocols have been demonstrated not to increase the risk for dislocation (Peak et al. 2005, Restrepo et al. 2011, Gromov et al. 2015, Allen et al. 2018). This was confirmed by a recent systematic review, which concluded that a more liberal lifestyle restriction and precaution protocol did not increase the dislocation rates after THA (van der Weegen et al. 2015). Despite increasing evidence that postoperative restrictions may be unnecessary, a recent study from the UK showed that 97% of physiotherapists and occupational therapists routinely prescribed hip precautions (Smith and Sackley 2016). Later, a national survey from the Netherlands found that restrictions were recommended to between 69% and 100% of patients following primary THA depending on the surgical approach used (Peters et al. 2017). Little is known about the use of postoperative restrictions in the Nordic countries. Such knowledge of the utilization of postoperative restrictions would make it easier to compare and interpret studies from the different Nordic countries. This

© 2019 The Author(s). Published by Taylor & Francis on behalf of the Nordic Orthopedic Federation. This is an Open Access article distributed under the terms of the Creative Commons Attribution-Non-Commercial License (https://creativecommons.org/licenses/by/4.0) DOI 10.1080/17453674.2019.1572291

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Table 1. Coverage (n/N) of hospitals and procedures Coverage hospitals Country n a N b (%) Denmark Finland Norway Sweden Total

24 29 27 33 42 58 74 79 167 199 (84)

Coverage procedures n c N d (%) 10,470 10,708 (98) 10,125 10,657 (95) 7,431 8,881 (83) 17,414 18,140 (96) 45,440 48,386 (94)

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number of hospitals performing primary THA that returned correctly filled out questionnaires. b number of hospitals performing primary THA countrywide. c number of primary THA performed annually in the hospitals that returned correctly filled out questionnaires. d number of primary THA performed annually countrywide.

would also facilitate the investigation of complications and functional outcome following THA. Finally, with increasing evidence on limited benefits with postoperative restrictions, updated national guidelines are needed to reduce inequity in postoperative care following primary THA. This questionnaire-based study investigated the use of postoperative restrictions and describes differences in mobilization protocols following primary THA in Denmark (DK), Finland (FIN), Norway (NO), and Sweden (SWE).

Patients and methods We identified all hospitals in DK, FIN, NO, and SWE performing primary THA from the respective national arthroplasty register’s most recent annual report. A survey with questions regarding standard surgical procedure, use of restrictions, and postoperative mobilization was designed according to guidelines presented by Sprague et al. (2009). Besides asking if the hospitals used any mobilization restrictions at all following primary THA, we also asked about specific restrictions employed and specific aids given to the patients as a part of the standard mobilization protocol (Kornuijt et al. 2016, Lee et al. 2017). Authors KG, AT, and HH drafted the questionnaire, whereafter all other authors were asked to review it. Subsequently, we revised the questionnaire according to comments to increase clarity and face validity. The questionnaire was designed in English and is presented in Supplementary data. The questionnaire was distributed to all identified hospitals through national representatives for each participating arthroplasty registry by email or regular mail. The questionnaire was sent to the head of the arthroplasty department, who was asked to fill out the questionnaire on behalf of the department. If the head of the arthroplasty department was not identified, the questionnaire was sent to the head of the orthopedic department. Approximately 1 month after sending out the questionnaire, a letter or email was sent out to all nonrespondents with a reminder to complete and return the ques-

Table 2. Demographics of hospitals that returned the correctly filled out questionnaire

DK FIN NO SWE Total n = 24 n = 27 n = 42 n = 74 n = 167

Approach used Direct anterior – 1 5 1 7 Anterolateral 1 9 8 36 54 Direct lateral – 1 8 19 28 Posterolateral 23 27 31 48 129 Articulation Neutral 9 17 23 59 108 Highwall 15 10 19 15 59 Dual mobility 1 - - - 1 Standard protocol Yes 24 22 39 69 154 No – 5 3 5 13 Full weight-bearing) Yes 23 27 40 74 164 No 1 – 2 – 3 Restrictions Yes 12 10 27 28 77 No 12 11 8 28 59 Depending – 6 7 18 31 Aids Yes 10 18 20 52 100 No 14 9 22 22 67 Restriction changed within 5 years Yes 17 19 25 51 112 No 7 8 17 23 55 Supervised physiotherapy Yes 11 14 26 51 102 No 1 5 2 6 14 Individual 12 8 14 17 51 DK = Denmark; NO = Norway; FIN = Finland; SWE = Sweden

tionnaire. Descriptive statistics were applied using IBM SPSS Statistics v25 (IBM Corp, Armonk, NY, USA). Ethics, funding, and potential conflict of interest. No approval from the National Ethics Committee was necessary as this was a non-interventional observational study. No funding was received for this work. The authors declare no conflict of interest.

Results 29, 33, 58, and 79 hospitals performing primary THA were identified in DK, FIN, NO, and SWE, respectively. 24/29, 27/33, 42/58, and 74/79 of the hospitals in DK, FIN, NO, and SWE, respectively, returned complete questionnaires giving a coverage of 84% (167/199). The hospitals responding to the questionnaire included 94% (45,440/48,386) of all primary THAs performed in Nordic countries in 2017 (Table 1). A posterolateral approach was the most common surgical approach in all countries. DK was the only country using elevated-rim acetabular components more frequently than neutral acetabular components (Table 2). 92% of the hospitals had a

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Table 3. Restrictions utilized depending on the approach Restrictions Yes No

Direct Antero- Direct Postero anterior lateral lateral lateral n = 7 n = 54 n = 28 n = 129 2 5

28 14 86 26 14 43

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Distribution of restrictions in hospitals that used restrictions (%) Do not bend the hip over 90° Do not cross your legs Do not internally rotate the hip Do not twist your upper body Do not roll or lie on the non-operated side Do not use a bathtub

standardized mobilization protocol and 98% allowed immediate full weight-bearing (Table 2). 12/24, 11/27, 8/42, and 28/74 of the hospitals in DK, FIN, NO, and SWE, respectively, did not have any postoperative restrictions. For 31 hospitals that used different restrictions depending on the approach, 28 used restrictions for a posterolateral approach, 11 used restrictions for an anterolateral approach and 7 used restrictions for a direct lateral approach. 98% of the hospitals allowed immediate full weight-bearing. For hospitals applying restrictions (n = 108), these were used for 2 weeks in 1%, for 4 weeks in 6%, for 6 weeks in 47%, and for a minimum of 12 weeks in 45% of the hospitals. Restrictions were used for a median of 6 weeks. As regards the approach used, 71% of the hospitals using a direct anterior approach did not use restrictions compared with 33% of hospitals using a posterolateral approach (Table 3). Avoiding bending the hip over 90 degrees and not crossing the legs were the most commonly employed restrictions (Figure 1). Aids (other than walking aids) were routinely used by 60% of the hospitals, with aids for putting on socks and an elevated toilet seat being the most common (Figure 2). 67% (112/167) of all hospitals had changed their mobilization protocol within the last 5 years—all but 2 to a less restrictive protocol.

Discussion In this questionnaire-based study, we found that one-third of all participating hospitals did not use any postoperative restrictions following primary THA, while one-fifth imposed restrictions depending on the surgical approach. Denmark was the most liberal country with half of the hospitals not using any restrictions while Norway was the most restrictive country with one-fifth of the hospitals not employing any restrictions. Very few previous studies have investigated the use of restrictions on a national level. Recently, Peters et al. (2017) performed a national survey investigating use of postoperative restrictions following primary THA in the Netherlands and found that restrictions were applied for between 69% and 100% of the patients depending on the surgical approach used. Based on our results, even the most conservative country in our study (NO) had a more liberal approach than the Netherlands. Our results also showed a more liberal approach compared with a survey from the UK, which found hip precautions to

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Figure 1. Restrictions used in hospitals that used restrictions. Distribution of aids in hospitals that used aids (%) Sock aid Elevated toilet seat Elevated chair Abduction pillow 0

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Figure 2. Aids used in hospitals that utilized aids on discharge.

be routinely prescribed by 97% of health professionals (physiotherapists and occupational therapists) participating in the study (Smith and Sackley 2016). The median use of restrictions for 6 weeks reported in our study is in agreement with Peters et al. (2017), and Smith and Sackley (2016). We found that restrictions were most frequently used with a posterolateral approach and least with a direct anterior approach. This conforms with the survey results by Peters et al. (2017) reporting a 100% restriction use with the posterolateral approach compared with 69% with the direct anterior approach. This difference is most likely explained by higher dislocation rates for a posterolateral approach compared with the direct anterior approach reported by some authors (Hailer et al. 2012, Zijlstra et al. 2017, Miller et al. 2018). An important finding in our study is a strong trend towards a less restrictive mobilization protocol in recent years: twothirds of hospitals had changed their mobilization protocol to a less restrictive one in the last 5 years. This is supported by the emerging evidence that removal of postoperative restrictions does not seem to lead to an increased risk for dislocation following primary THA (Peak et al. 2005, Restrepo et al. 2011, Gromov et al. 2015, van der Weegen et al. 2015, Kornuijt et al. 2016, Allen et al. 2018). Furthermore, a recent study showed that while most patients can remember all of the restrictions recommended at 8 weeks after surgery only one-fifth adhere to all restrictions, suggesting that even if restrictions are prescribed most patients do not adhere to them (Lee et al. 2017). To our knowledge only 2 studies have found a correlation between removal of restrictions and increased risk of dislocation. In a registry-based study, Jørgensen et al. (2014) found

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that departments that did not use restrictions had a higher dislocation rate compared with departments that applied restrictions. However, the study was not designed to analyze restrictions, and the difference in dislocation rate could potentially be explained by a number of factors other than the use of restrictions. Mikkelsen et al. (2014) found a statistically nonsignificant increase in the dislocation rate in patients who were mobilized without restrictions, while no difference was seen in patient-reported outcomes after 6 weeks. However, this study investigated only 365 patients and was not powered to investigate dislocations following THA. Conversely, several authors have suggested that a liberal mobilization protocol following primary THA may lead to earlier return to work and higher patient satisfaction (Peak et al. 2005, Barnsley et al. 2015, van der Weegen et al. 2015). Our study has several limitations. First, we asked about standard protocols in the participating hospitals; we do not know to what extent the individual surgeons adhered to these protocols. Second, while the response rate was excellent, 16% of the hospitals (accounting for 6% of annually performed THAs) did not respond, allowing for some degree of bias. There is, however, no obvious reason to think that the departments that did not reply systematically were less or more restrictive than the those that did so. Also, although we included a question regarding articulation size in our questionnaire, we did not investigate other factors that could influence the risk of dislocation such as the type of implant and fixation. These factors could affect the postoperative protocols (Kim et al. 2009, Seagrave et al. 2017a). In recent years there have been a trend towards increased use of larger femoral heads, as this has been suggested to reduce the risk for dislocation. A recent study from the Nordic Arthroplasty Registry Association found that the risk for revision due to dislocation was lower when comparing 32-mm heads to 28-mm heads, while no benefit with use of 36-mm heads over 32-mm heads was found (Tsikandylakis et al. 2018). We did not investigate the femoral head size used by the individual departments, and this could potentially affect the surgeons in regard to use of postoperative restrictions. Further, we did not investigate whether or not the use of restrictions differed depending on the diagnosis. While we have investigated the restrictions recommended by the hospitals, we do not know if the physiotherapists working with the patients after discharge adhered to those protocols. Finally, while we investigated the use of restrictions, we did not investigate the dislocation rates, patient-reported outcomes, or patient satisfaction in departments using restrictions or in those with a more liberal mobilization protocol. Thus, no conclusion can be drawn from this study on the potential association between the use of postoperative restrictions and dislocation rates following primary THA. In summary, we found that use of postoperative restrictions following primary THA differed between the Nordic countries with 19–50% allowing mobilization without any restrictions.

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There has been a strong tendency towards less restrictive mobilization over the last 5 years. Whether this trend has had any affect on the dislocation rates and whether the dislocation rates differ between the less and the more restrictive hospitals in Nordic countries is unknown. Supplementary data The questionnaire is available as supplementary data in the online version of this article, http://dx.doi.org/ 10.1080/ 17453674.2019.1572291 KG and HH planned the study. KG, AT, and HH designed the questionnaire and collected the data from DK. MM, OR, OF, GH, AE, and PT distributed and collected the questionnaires in the respective countries. KG analyzed the data and drafted the manuscript. All authors reviewed the manuscript. Acta thanks Anil Peters and Stephan Vehmeijerfor help with peer review of this study.

Allen F C, Skinner D L, Harrison J, Stafford G H. The effect of precautions on early dislocations post total hip arthroplasty: a retrospective cohort study. Hip Int 2018; 28(5): 485-90. Barnsley L, Barnsley L, Page R. Are hip precautions necessary post total hip arthroplasty? A systematic review. Geriatr Orthop Surg Rehabil 2015; 6(3): 230-5. Brooks P J. Dislocation following total hip replacement. Bone Joint J 2013; 95-B(11_Suppl_A): 67-9. Byström S, Espehaug B, Furnes O, Havelin L, Norwegian Arthroplasty Register. Femoral head size is a risk factor for total hip luxation: a study of 42,987 primary hip arthroplasties from the Norwegian Arthroplasty Register. Acta Orthop Scand 2003; 74(5): 514-24. Gromov K, Troelsen A, Otte K S, Orsnes T, Ladelund S, Husted H. Removal of restrictions following primary THA with posterolateral approach does not increase the risk of early dislocation. Acta Orthop 2015; 86(4): 463-8. Hailer N P, Weiss R J, Stark A, Kärrholm J. The risk of revision due to dislocation after total hip arthroplasty depends on surgical approach, femoral head size, sex, and primary diagnosis. Acta Orthop 2012; 83(5): 442-8. Husted H, Gromov K, Malchau H, Freiberg A, Gebuhr P, Troelsen A. Traditions and myths in hip and knee arthroplasty: a narrative review. Acta Orthop 2014; 85(6): 548-55. Jolles B M, Zangger P, Leyvraz P-F. Factors predisposing to dislocation after primary total hip arthroplasty: a multivariate analysis. J Arthroplasty 2002; 17(3): 282-8. Jørgensen C C, Kjaersgaard-Andersen P, Solgaard S, Kehlet H. Hip dislocations after 2,734 elective unilateral fast-track total hip arthroplasties: incidence, circumstances and predisposing factors. Arch Orthop Trauma Surg 2014; 134(11): 1615-22. Kim Y-H, Choi Y, Kim J-S. Influence of patient-, design-, and surgery-related factors on rate of dislocation after primary cementless total hip arthroplasty. J Arthroplasty 2009; 24(8): 1258-63. Kornuijt A, Das D, Sijbesma T, van der Weegen W. The rate of dislocation is not increased when minimal precautions are used after total hip arthroplasty using the posterolateral approach. Bone Joint J 2016; 98-B(5): 58994. Kotwal R S, Ganapathi M, John A, Maheson M, Jones S A. Outcome of treatment for dislocation after primary total hip replacement. J Bone Joint Surg Br 2009; 91-B(3): 321-6. Lee G R H, Berstock J R, Whitehouse M R, Blom A W. Recall and patient perceptions of hip precautions 6 weeks after total hip arthroplasty. Acta Orthop 2017; 88(5): 496-9.

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Meek R M D, Allan D B, McPhillips G, Kerr L, Howie C R. Epidemiology of dislocation after total hip arthroplasty. Clin Orthop Relat Res 2006; 447: 9-18. Mikkelsen L R, Petersen M K, Søballe K, Mikkelsen S, Mechlenburg I. Does reduced movement restrictions and use of assistive devices affect rehabilitation outcome after total hip replacement? A non-randomized, controlled study. Eur J Phys Rehabil Med 2014; 50(4): 383-93. Miller L E, Gondusky J S, Kamath A F, Boettner F, Wright J, Bhattacharyya S. Influence of surgical approach on complication risk in primary total hip arthroplasty. Acta Orthop 2018; 89(3): 289-94. Patel P D, Potts A, Froimson M I. The dislocating hip arthroplasty: prevention and treatment. J Arthroplasty 2007; 22(4 Suppl 1): 86-90. Peak E L, Parvizi J, Ciminiello M, Purtill J J, Sharkey P F, Hozack W J, Rothman R H. The role of patient restrictions in reducing the prevalence of early dislocation following total hip arthroplasty: a randomized, prospective study. J Bone Joint Surg Am 2005; 87(2): 247-53. Peters A, Veldhuijzen A J H, Tijink M, Poolman R W, Huis In ’t Veld R M H A. Patient restrictions following total hip arthroplasty: a national survey. Acta Orthop Belg 2017; 83(1): 45-52. Restrepo C, Mortazavi S M J, Brothers J, Parvizi J, Rothman R H. Hip dislocation: are hip precautions necessary in anterior approaches? Clin Orthop Relat Res 2011; 469(2): 417-22.

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Seagrave K G, Troelsen A, Madsen B G, Husted H, Kallemose T, Gromov K. Can surgeons reduce the risk for dislocation after primary total hip arthroplasty performed using the posterolateral approach? J Arthroplasty 2017a; 32(10): 3141-6. Seagrave K G, Troelsen A, Malchau H, Husted H, Gromov K. Acetabular cup position and risk of dislocation in primary total hip arthroplasty: a systematic review of the literature. Acta Orthop 2017b; 88(1): 10-17. Smith T O, Sackley C M. UK survey of occupational therapists’ and physiotherapists’ experiences and attitudes towards hip replacement precautions and equipment. BMC Musculoskelet Disord 2016; 17(1): 228. Sprague S, Quigley L, Bhandari M. Survey design in orthopaedic surgery: getting surgeons to respond. J Bone Joint Surg Am 2009; 91(Suppl 3): 27-34. Tsikandylakis G, Kärrholm J, Hailer N P, Eskelinen A, Mäkelä K T, Hallan G, Furnes O N, Pedersen A B, Overgaard S, Mohaddes M. No increase in survival for 36-mm versus 32-mm femoral heads in metal-on-polyethylene THA. Clin Orthop Relat Res 2018; 476(12): 2367-78. van der Weegen W, Kornuijt A, Das D. Do lifestyle restrictions and precautions prevent dislocation after total hip arthroplasty? A systematic review and meta-analysis of the literature. Clin Rehabil 2015; 30(4): 329-39. Zijlstra W P, De Hartog B, Van Steenbergen L N, Scheurs B W, Nelissen R G H H. Effect of femoral head size and surgical approach on risk of revision for dislocation after total hip arthroplasty. Acta Orthop 2017; 88(4): 395-401.

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High annual surgeon volume reduces the risk of adverse events following primary total hip arthroplasty: a registry-based study of 12,100 cases in Western Sweden Per JOLBÄCK 1,2,3,5, Ola ROLFSON 1,3, Peter CNUDDE 1,3,4, Daniel ODIN 3, Henrik MALCHAU 1,3, Hans LINDAHL 1,2,3, and Maziar MOHADDES 1,3 1 Department

of Orthopaedics, Institute of Clinical Sciences, The Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden; 2 Department of Orthopaedics, Skaraborgs Hospital, Lidköping, Sweden; 3 Swedish Hip Arthroplasty Register, Gothenburg, Sweden; 4 Department of Orthopedics, Hywel Dda University Healthboard, Prince Philip Hospital, Bryngwynmawr, UK; 5 Research and Development Centre, Skaraborgs Hospital, Skövde, Sweden Correspondence: per.jolback@vgregion.se Submitted 2018-04-30. Accepted 2018-11-17.

Background and purpose — Most earlier publications investigating whether annual surgeon volume is associated with lower levels of adverse events (AE), reoperations, and mortality are based on patient cohorts from North America. There is also a lack of adjustment for important confounders in these studies. Therefore, we investigated whether higher annual surgeon volume is associated with a lower risk of adverse events and mortality within 90 days following primary total hip arthroplasty (THA). Patients and methods — We collected information on primary total hip arthroplasties (THA) performed between 2007 and 2016 from 10 hospitals in Western Sweden. These data were linked with the Swedish Hip Arthroplasty Register and a regional patient register. We used logistic regression (simple and multiple) adjusted for age, sex, comorbidities, BMI, fiation technique, diagnosis, surgical approach, time in practice as orthopedic specialist and annual volume. Annual surgeon volume was calculated as the number of primary THAs the operating surgeon had performed 365 days prior to the index THA. Results — 12,100 primary THAs, performed due to both primary and secondary osteoarthritis by 268 different surgeons, were identified. The median annual surgeon volume was 23 primary THAs (range 0–82) 365 days prior to the THA of interest and the mean risk of AE within 90 days was 7%. If the annual volume increased by 10 primary THAs in the simple logistic regression the risk of AE decreased by 10% and in the adjusted multiple regression the corresponding number was 8%. The mortality rate in the study was low (0.2%) and we could not find any association between 90-day mortality and annual surgeon volume. Interpretation — High annual surgical activity is associated with a reduced risk of adverse events within 90 days. Based on these findings healthcare providers should consider planning for increased surgeon volume.

In order to improve the outcomes after total hip arthroplasties (THA) and thereby reduce the burden of complications (Lawson et al. 2013), it is crucial to identify factors influencing adverse events (AE) associated with surgery. Earlier studies have shown that patient comorbidities, ASA classification, age, sex, BMI, and smoking increase the risk of complications and reoperations (Bozic et al. 2012, Lalmohamed et al. 2013, Arsoy et al. 2014, Duchman et al. 2015, Singh et al. 2015, Kallio et al. 2015, Bohl et al. 2016, Lubbeke et al. 2016). Procedure -related factors such as surgical approach, type of implant, fixation technique, and surgery time (Yasunaga et al. 2009, Lindgren et al. 2012) as well as hospital- and/or surgeon volume (Kreder et al. 1997, Solomon et al. 2002, Kaneko et al. 2014, Glassou et al. 2016, Kurtz et al. 2016, Laucis et al. 2016) are also suggested to influence outcomes after THA. The association between annual volume for both hospitals and individual surgeon and AE and reoperations have been discussed during the last decade, not only for primary THAs, but also in knee arthroplasty surgery (Kreder et al. 2003), vascular procedures (Pearce et al. 1999), general surgical procedures and gynecological interventions (Muilwijk et al. 2007). Few studies have investigated the relation between surgeon’s annual volume and outcomes (both medical and surgical complication, reoperations, mortality, and patient-reported outcomes) following primary THAs. Most of these studies report an association between a higher annual volume and fewer AE (Kreder et al. 1997, Lavernia and Guzman. 1995, Katz et al. 2001, 2003, Losina et al. 2004, Paterson et al. 2010, Camberlin et al. 2011, Ravi et al. 2014, Koltsov et al. 2018). All of these published reports are based on patient cohorts in North America with the exception of Camberlin et al. (2011) who studied a Belgian cohort of patients. There are, however, differences between countries with regards to training programs and level of surgeon activity. Second, there is a lack of publications adjusting for important confounders such as type of

© 2018 The Author(s). Published by Taylor & Francis on behalf of the Nordic Orthopedic Federation. This is an Open Access article distributed under the terms of the Creative Commons Attribution-Non-Commercial License (https://creativecommons.org/licenses/by/4.0) DOI 10.1080/17453674.2018.1554418

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exceeds 98% during the last 10 years (Kärrholm et al. 2016). Patient data, age, sex, height, weight, ICD-10 diagnoses, fixation technique, surgical approach, and type of implant are registered in the Excluded (n = 2,986): SHAR. – reason for surgery not OA in SHAR, 120 Vega, a regional patient register, was initiated – other incision than posterior or direct lateral in SHAR, 140 – data on operating surgeon not available in local medial in 2000. It is an aggregated database, containing records, 29 records concerning all healthcare contacts (both – no information on volume 365 days prior to index THA, 1,756 public and privately funded) for all residents in – missing data on BMI in SHAR, 941 the region. In 2006 this regional patient register contained records of about 12 million healthcare THAs included in the analysis n = 12,100 contacts for the population of approximately 1.3 Figure 1. Flow chart. million people. Vega provides information to fixation, surgical approach, and time as orthopedic specialist. the National Patient Register (NPR). The PIN is used as the We evaluated possible associations between the surgeon’s unique identifier for all entries in Vega. The regional patient annual volume and the risk of AE and mortality within 90 days register contains details on: depiction of the caregiver at the following primary THA. We used data from a national qual- point of contact such as, for example, level of hospital or elecity register as well as hospital administrative data in Western tive care, diagnoses, and interventions such as, for example, Sweden, the second largest region in Sweden.  type of surgery, and length of stay in the hospital. Annual surgeon volume was defined as the number of primary THAs the operating surgeon performed in the 365 days prior to the index THA of interest (Ravi et al. 2014). Annual Patients and methods hospital volume was calculated as annual surgeon volume but Patient selection based on number of primary THAs in the 365 days prior to the Inclusion criteria for the study were: a primary THA either index THAs. with a cemented, uncemented, or hybrid fixation technique in A direct acyclic graph was used to visualize and determine patients with index diagnosis osteoarthritis (OA) of the hip covariates of interest based on previous publications. The foldefined by the International Classification of Diseases (ICD)- lowing covariates were identified as confounders and included 10 codes M16.0–M16.7 or M16.9. All patients underwent sur- in the multiple logistic regression analysis: age, sex, BMI, gery using a posterior or a direct lateral approach. We selected comorbidities, years in practice as orthopedic specialist at the all surgeries performed in all hospitals managed by the county time of the index THA, fixation technique, diagnostic indicacouncil of Western Sweden between 2007 and 2016 reported tion for implantation, surgical approach, and annual hospital to the Swedish Hip Arthroplasty Register (SHAR) and the volume. Smoking was also identified as a confounder but was regional patient register, Vega (Figure 1). not included in the multiple logistic regression analysis due to lack of information on patient smoking habits over the whole Sources of data investigated period (i.e., SHAR has not collected information Hospital medical records, SHAR, and the regional patient reg- during the entire investigated period). ister were used as data sources. The linking between hospital The years in practice for each orthopedic specialist at the time medical records and SHAR was done using the 10-digit per- of the index THA was defined as the difference between date sonal identity number (PIN) (Ludvigsson et al. 2009), name for surgery and date of certification as orthopedic specialist. of the hospital, and date of surgery. The linked dataset, conThe Elixhauser comorbidity index (ECI) is a comprehensive taining information from hospital medical records and SHAR, set of 30 comorbidities associated with substantial increase in was subsequently forwarded to the regional patient register length of stay, hospital charges, and mortality (Elixhauser et to add all adverse events and the data were pseudonymized al. 1998, van Walraven et al. 2009). The ECI has been considreplacing the PIN with a unique identifier. For each operat- ered as a superior predictor for long-term outcomes (beyond ing surgeon involved, data on the year for license to practice 30 days) to the Charlson comorbidity index (Sharabiani et al. and/or specialist certificate in orthopedics were obtained from 2012). The period used for calculating ECI in this study was publicly available data at the Swedish National Board of 365 days prior to the index THA. Comorbidities present in the Health and Welfare’s register of licensed healthcare profes- 365 days prior to the index THA were used for calculating ECI. sionals (HOSP). The variable sources are detailed in Table 1, An AE was defined as a readmission for a predefined set see Supplementary data. of World Health Organization International Classification of The SHAR’s aim is to register all primary THAs and reop- Diseases (ICD) and the Nordic Medico-Statistical Committee erations performed in Sweden. The coverage has been 100% (NOMESCO) Classification of Surgical Procedures codes for over the last 25 years and the completeness of primary THAs interventions (Appendix, see Supplementary data). Death for Primary THAs performed 2007–2016 extracted from hospital medical records n = 15,086

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Figure 2. Distribution of the experience of the surgeon at the time of the index THA. Experience is computed as years between orthopedic specialist certification and surgery. Note: There are 2 THAs for year 39 and 1 for year 40, not visible in the graph.

Figure 3. Distribution of annual volume 365 days prior to the index THA.

any reason was also included in the definition of AE. The code list for AE has been elaborated by the Swedish Knee Arthroplasty Register (SKAR) in collaboration with the National Board of Health and Welfare to be used after knee replacements. Based on the same principles SHAR elaborated a code list adapted for elective hip replacements. The codes were classified into the following groups; A = surgical procedure codes that include reoperations of THA implants and other procedures that may represent a complication, DA = diagnostic codes that imply surgical complications, DB/DB 2 = diagnostic codes that cover hip-related diseases that may have been used for complications after THA surgery, DC = diagnostic codes covering cardiovascular events that may be related to the surgery, DM/DM 2 = diagnostic codes concerning other medical events not related to the THA surgery but that may be related to the surgery if they occur shortly afterwards. A, DA, BD, and BD 2 in the Appendix are surgical complications (i.e., hip-related complications) and DC, DM, and DM 2 medical complications (i.e., serious cardiovascular or medical complications).

determined limits (0, 10, 20, 30, 40, and 50) for annual surgeon volume in Table 4. A sensitivity analysis was performed according to guidelines in statistical analysis of arthroplasty data to evaluate the consequence of violating the assumption of independent observation (i.e., analysis when the second hip was excluded in patients with bilateral THAs) (Ranstam et al. 2011). Patients operated with simultaneous bilateral THAs were captured as 1 surgery in the study. As Ranstam et al. (2011) concluded based on a literature survey, there is little practical consequence of analyzing bilateral prostheses—at least with knee and hip data. We expect that the dependency structure of 2 hips from the same patients is stronger and of more consequence that the dependency structure of different patients having the same surgeon. THA surgery is a highly standardized procedure and as such we do not expect surgeon-related base risks and modelling approaches did not indicate such results. Our primary outcome was AE within 90 days following the index THA surgery and our secondary outcome was mortality within 90 days following the index THA surgery.

Statistics SPSS version 25 (IBM Corp, Armonk, NY, USA) and R version 3.2.3 (R Foundation for Statistical Computing, Vienna, Austria) was used for the statistical analysis. We used both simple and multiple logistic regression. Data from the regressions are presented with regression coefficient (β-coefficient), 95% confidence interval (CI), and p-value. P-value for statistical significance was set at < 0.05. A predictive model was created to analyze risk of AE and mortality. Predicted risk was calculated using a fitted simple logistic regression model. Prediction intervals (PI) were calculated to see the prediction strength with a 95% prediction interval. The predicted risk of AE within 90 days is presented unadjusted with arbitrarily

Ethics, funding, and potential conflicts of interests The study was approved by the Central Ethical Review Board in Stockholm (DNR Ö 9-2016). A research grant for the project was received from Skaraborgs Hospital research foundation. There is no conflict of interest.

Results 268 different surgeons performed the 12,100 operations of which 8% (989) were performed by orthopedic trainees. The median years in practice as an orthopedic specialist at the time of the index THA was 12 (0–40) (Figure 2). The median

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Table 2. Patient characteristica and surgical data Age, years, mean (SD) All Male Female Sex, n (%) Male Female BMI, mean (SD) Diagnostic indication for implantation, n (%) Primary OA Secondary OA Fixation technique, n (%) Cemented Uncemented Hybrid Reverse hybrid Surgical approach, n (%) Posterior incision in lateral position (Moore) Lateral position (Gammer)

Table 3. Elixhauser comorbidity index 365 days prior to the index THA 69 (11) 68 (11) 70 (10) 5,101 (42) 6,999 (58) 28 (5) 11,414 (94) 686 (6) 8,820 (68) 2,330 (19) 620 (5) 930 (8) 4,201 (35) 7,899 (65)

annual surgeon volume was 23 primary THAs (0–82) 365 days prior to the THA of interest (Figure 3). Mean age for all patients was 69 years (SD 11) and the proportion of females was 58%. Primary OA was the most common diagnosis (94%). Some 68% of the patients received a cemented THA followed by uncemented (Table 2); 45% of the patients had no comorbidities according to ECI 365 days preceding the index surgery (Table 3). Outcomes Readmissions for any cause within 90 days occurred in 1,019 patients (8%) and with the AE definition used (see Appendix) the rate decreased to 818 (7%). In all, 69% of all AE could be classed as surgical complications and 31% as medical complications. For AE within 90 days the simple logistic regression showed a statistically significant reduced risk with increasing annual surgeon volume (regression coefficient = 0.990, CI 0.986–0.995). The corresponding numbers in the multiple regression were: regression coefficient = 0.992, CI 0.987–0.998. According to the predictive model the risk of an AE decreased by more than 35% if the surgeon had performed 50 or more THAs compared with 0 THAs during the 365 days preceding the index surgery (Table 4). A total of 28 patients died within 90 days. The annual surgeon volume did not influence the risk of mortality in the simple regression (regression coefficient = 0.999, CI 0.974– 1.022) or the multiple regression (regression coefficient = 1.000, CI 0.978–1.031). The prediction interval for mortality could not be calculated due to the low mortality rate. The result of the sensitivity analysis is similar to the result including both hips. 1,093 surgeries were excluded and the sensitivity analysis contained 11,007 THAs. 70 patients were operated with simultaneous bilateral THAs. Data for the sensitivity analysis are not shown.

Elixhauser comorbidity index 0 1 2 3 4 5 6 7 8 9 10 11

Total

n (%)

5,474 (45) 3,254 (27) 1,789 (15) 890 (7) 409 (3) 171 (1) 70 27 11 3 0 2

Table 4. Predicted risk of AE within 90 days for annual surgeon volume of primary THAs Annual Mean 95% prediction surgeon risk interval volume (%) (%) 0 10 20 30 40 50

8 7–10 8 6–9 7 5–9 6 5–8 6 4–7 5 4–7

12,100 (100)

Discussion We found that higher caseloads of annual THAs were associated with decreased level of AE within 90 days after surgery. This finding is supported by previous publications (Lavernia and Guzman 1995, Kreder et al. 1997, Katz et al. 2001, Losina et al. 2004, Paterson et al. 2010, Camberlin et al. 2011, Ravi et al. 2014). Based on previous publications it is difficult to understand what the optimal annual surgeon volume is in order to achieve low levels of AE and reoperation. Furthermore, annual surgeon volume can vary over time and by calculating the annual surgeon volume as the number of primary THAs performed 365 days prior to the index surgery we were able to capture this variation. This method has been used by Ravi et al. (2014) in their study and might be a more correct estimation than using all THAs during a calendar year where all surgeries are attributed with the same volume regardless of whether the actual surgery being analyzed is the first or the last one during the measured year. 90-day mortality is rare following primary THA surgery in Sweden. The 0.2% mortality rate in our study is lower than the average mortality rates following primary THAs in 2 published systemic reviews (0.7% and 0.5%) (Singh et al. 2011, Berstock et al. 2014). Berstock et al. (2014) included 7 studies on mortality within 90 days in their systemic review and in these the mortality rates varies between 0.1% and 0.7%. Ravi et al. (2014) (not included in any of the systemic reviews) did not find any obvious relation between mortality within 90 days and surgeon volume despite higher mortality rates. An explanation of the lower mortality rates in our study compared with the systemic reviews might be that the Swedish THA patients are healthier than patients included in systemic reviews (i.e., a selection bias of patients undergoing THA surgery between countries and hospitals). Hence, mortality rates between dif-

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ferent studies might not be generalized depending on differences in the organization of healthcare and individual surgical practices. Our study has some limitations. We have not adjusted the multiple logistic regression for smoking, despite the knowledge of its negative influence on AE (Singh et al. 2015, Duchman et al. 2015). In our dataset, during the years 2013–2016, around 5% of patients were reported as smokers (information from the SHARs PROM program). Furthermore, data are missing on 17% included procedures, and finally the frequency of smoking is decreasing during the years 2013–2016. In spite of the fact that we have some information on smoking behavior in our study, we decided not to include smoking in the regression analysis because of the high amount of missing values. A second limitation is that only primary THAs performed within the region of Western Sweden were included. Some of the surgeons involved in the study might have had a temporary or partial employment, having performed primary THAs outside the investigated region. In Sweden there is no central dataset on surgeons, regarding their employment and activity. We presumed that the limited number of surgeons operating on cases outside the region of Western Sweden not would influence our conclusions. Finally, we share the same limitation as in all observational studies using administrative data. Both change of practice during the study period and local trends but also differences in registration might occur between the included hospitals. The regional patient register we used is not validated on its own but it provides data to the NPR. The Swedish National Inpatient Register (IPR) is part of the NPR. The IPR has been validated and contains 99% of all hospital discharges (Ludvigsson et al. 2011). In this study we used a definition of adverse events requiring hospital admission. Hence, we believe our data are robust and our conclusions are valid. One strength is that we could control for the surgeon’s experience (i.e., years as orthopedic specialist) at the time of the index surgery. The Swedish National Board of Health and Welfare register of licensed healthcare professionals has the exact date of certification for all doctors applying for licenses to practice and orthopedic specialist certification. We decided to include years in practice in the regression model. We have previously shown that surgeons with longer experience operate on patients with different diagnoses, patient characteristics, and using other implants compared with less experienced surgeons (Jolbäck et al. 2018). Years as a recognized specialist in orthopedics might also be considered as a proxy for surgical skills accumulated by the experience of previous procedures during the surgeon’s career. But, also, the knowledge gained and experience of preparing patients both physically and mentally prior to the surgery can be of importance. More experienced surgeons are likely to make more appropriate decisions regarding the indication for surgery, the operative details (technical aspects), and other perioperative factors that could result in an improved outcome. By including the years in practice at the time of the index surgery in the analysis we were

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able to adjust for the above confounders. Another strength of the study is that we have been able to adjust for both surgical approach and type of fixation. To our knowledge, this is the first publication analyzing the risk of adverse events and mortality based on annual surgeon volume, adjusting for important confounders such as type of fixation, surgical approach, and time as orthopedic specialist. Finally, we used an administrative database registering all healthcare including readmission to hospitals in the whole of Sweden for the inhabitants of Western Sweden. This means that the risk of not collecting all readmissions within 90 days following the index THA is near to non-existent. Analyzing 12,100 surgeries reported to the SHAR, we conclude that high annual surgical activity is associated with a reduced risk of AE within 90 days following primary THAs. Based on these findings, healthcare providers should consider planning for an increased surgeon volume. Supplementary data Table 1 and the Appendix are available as supplementary data in the online version of this article, http://dx.doi.org/ 10.1080/ 17453674.2018.1554418

PJ had the original idea for the study, processed the data, and prepared the first version of the manuscript. All authors took part in the planning of the study, analysis, and interpretation of the data, and in writing of the manuscript. All authors read and approved the final manuscript. Acta thanks Sarah Whitehouse for help with peer review of this study.

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Technical note

The development of an online implant manufacturer application: a knowledge-sharing platform for the Swedish Hip Arthroplasty Register Johanna VINBLAD 1,2, Daniel ODIN 1, Johan KÄRRHOLM 1,2, and Ola ROLFSON 1,2 1 The Swedish Hip Arthroplasty Register, Centre of Registers Västra Götaland; 2 Department of Orthopedics, Institute of Clinical Science, Sahlgrenska Academy, University of Gothenburg, Sweden Correspondence: johanna.vinblad@registercentrum.se Submitted 2018-11-09. Accepted 2019-03-23.

We describe the development of an application for assessing implant performance based on data in the Swedish Hip Arthroplasty Register (SHAR) designed for implant manufacturers.

Technique

outcome measures program preoperatively, and 1, 6, and 10 years after surgery. Patient-reported outcome measures are all maintained in the principal database. Lastly, the register contains a separate surgical environment database with hospitallevel aggregate information. For the development of the manufacturer application, we included variables related to diagnosis, component features, reason for surgery, and surgery outcome in terms of revisions. Patient-reported outcome measures and surgical environment variables were not included.

Data source SHAR (founded in 1979) is a national quality register covering all orthopedic units performing hip replacement surgery in Sweden. The completeness of registrations during the last 10 years varies between 97–98% for total hip replacements, Work process 95–97% for hemi-arthroplasties, and 91–95% for revision The project delivery model can be divided into 7 phases procedures when linking data to the Swedish national patient (Figure). Planning, development, and test were carried out in register (Kärrholm et al. 2018). The register currently covers iterative cycles to optimize product outcome. more than 360,000 hip procedures, 1,100,000 registered items and 6,100 unique components. AdminisIdea • Project leader assigned. trative staff at the units report surgi• Identification of key competences and stakeholders (registry directors, orthopedic surgeons, implant industry representatives, cal variables for primary procedures statiticians, and system developer). • Assembly of project team. and reoperations. Medical records • Identification of demands related to content, function, and output. copies covering admission, surgi• Defining scope. cal procedure, and discharge for all patients undergoing reoperations are Planning Development Test • Defining variables and • Short daily development • Internal tests and revision sent to the register for further extracnomenclature within the project. team meetings. of application. • Defining work packages. • Biweekly or monthly project • End-user tests. tion of data. 57 variables are col• Assessment of technical feasibility. team meetings. lected regarding the primary surgery and 99 variables for reoperations. Launch The register also retains a separate • Free trial period for implant manufactures. component database with variables describing attributes of the implant. Closure of development project The component database contains 141 variables. Additionally, the Initiation of continuous improvement project register comprises 54 variables collected through the patient-reported The project delivery model. Lorem ipsum

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© 2019 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group, on behalf of the Nordic Orthopedic Federation. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits ­unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. DOI 10.1080/17453674.2019.1608094

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Platform specification The design of the application is based on the IT platform new Stratum and scripts for the R free software environment (https://www.r-project.org/) for statistical computing and graphics. Stratum is a technical platform for describing, collecting, and presenting data from quality registers in healthcare developed by the Centre of Registers, Västra Götaland. The platform provides a register and its users with a range of features for continuous quality improvement and follow-up, including advanced form management, statistics engine (in R), and visualization support (user interface components from ExtJS, developed by Sencha [https://www.sencha.com/]). Validation process The validation was done in several steps. The back-end code, which was written in R, was reviewed by 2 statisticians. Repeated quality assurance tests were performed. Comparisons were carried out between raw data and R-script outcome as well as between outcome of the R-scripts and outcome in the interface. Finally, the interface was tested by several persons not involved in the development of the project to find inconsistencies. Access/login requirements User access to data is restricted. The application displays only data on implants for the specific company, which the user represents. An electronic personal identification system widely used in Sweden, Mobile BankID, is used to confirm identity and securely log in to the application. Restriction of data usage In order to access the application, a contract must be in place between the industry and the register. This agreement restricts the use of data. The analyses performed may be used within the company for internal use, for regulatory purposes, and for marketing purposes as reported to regulatory agencies. The SHAR charges an annual subscription fee for the service based on number of implants registered during the previous year in addition to a fixed basic rate.

Product description Using previous experience from industry collaboration in combination with discussions between industry and registry as well as in-house orthopedic expertise, key areas were identified. These were consolidated into 4 modules in the application: volume, revised implants, implant survival, and market share. The 4 modules will be further discussed below, and a summary of the choices and filters can be accessed in Tables 1–4, see Supplementary data. Volume Broken down by hospitals, the volume module displays

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number of implants registered based on catalogue number for a selected period. There are several data-filtering options available. Type of surgery is one of them, allowing for filtering with regards to primary or revision surgery. Other filtering opportunities are type of prosthesis and group of implant. The date range is variable between 1999 and current date with 28 days being the minimum number of days that you can choose (Table 1, see Supplementary data). Revisions per implant The 2nd module presents number of inserted and revised implants on article number level in Sweden. The filtering option “Type of surgery” allows the user to explore revisions after primary surgery and/or all re-revisions after revision surgery. Search criteria allow for selection of either total or hemi-arthroplasty as well as implant family as previously defined by the register. It is also possible to select type of revision; all 1st-time revisions, 1st stem revision, 1st cup revision, and 1st revision of other kind. For example, if 1st stem revision is selected, then any revision that is not a stem revision will be disregarded. In this module, there is also a possibility to focus on cause for revision. The returned revision data will be divided into revision occurring 0–90 days, 91 days to 2 years, and more than 2 years after the surgery. The date range may be set between any time point from 1999 to current date and the shortest date range is 1 year (Table 2, see Supplementary data). Implant survival The 3rd module displays Kaplan–Meier and cumulative incidence survival graphs for stems and/or cup families based on 1st revision after primary surgery. The survival graphs can be tailored for specific needs by choosing patient population based on diagnosis, type of prosthesis, type of revision, and cause for revision (Table 3, see Supplementary data). In this module, the stems and cups are grouped, since there are usually not a sufficient number of observations related to a specific article number (e.g., a specific cup design with a specific size) to perform a robust analysis. On the other hand, if a specific cup design is selected for analysis all article numbers included (e.g., sizes) can easily be extracted. It is possible to choose 1 or more implant families to be analyzed in 1 group. A specified group of company stems can be combined with a corresponding group of cups without restrictions. It is also possible to combine a specified group of stems with all company cups and vice versa and compare combinations of stems and cups from one’s own company with aggregated data on hip prostheses from all other suppliers. A number of revision outcomes can be defined such as all 1st-time revisions, 1st stem revision, 1st cup revision, and other types of 1st-time revisions. The Kaplan–Meier analyses provide estimates of the probability of a selected implant or implant group being revised at given time points. Competing risk-based cumulative incidence, on the other hand, will visu-

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alize the proportion of implants that have been revised and the proportion of patients who have died at given time points. The date range may be set between any time point from 1999 to current date and the shortest date range is 1 year. The primary surgeries performed in the chosen time interval are followed up until current date or until the number of hips at risk is below 50. In addition, 95% confidence intervals are visualized in the graphs. Market share The last module in the application addresses market share for a selected type of implant (i.e. cup, stem, head, liner, and distal plug) from the company. It is also possible to filter with regards to type of prosthesis (i.e., total or hemi arthroplasty) and fixation. In addition to market share, manufacturers may also access the total number of registered implants in Sweden as compared with all implants used for the specific company (Table 4, see Supplementary data). Outputs All aggregated results are presented in tables and graphs may be downloaded to excel.

Discussion The overall aim with quality registers is to sustain and improve healthcare for patients. The Swedish Hip Arthroplasty Register is working with a wide group of stakeholders in order to ensure delivery of high-quality healthcare. Strong collaboration between the registry and the industry is paramount. Early detection of implants with substandard performance is important for the industry, the healthcare system and patients. There are values in the form of saving patient suffering as well as a high economic value in detecting failing implants early on. Several ongoing international initiatives aim to monitor and assess implants survival, such as the Orthopaedic Data Evaluation Panel (ODEP, http://www.odep.org.uk/), Beyond Compliance (http://www.beyondcompliance.org.uk/), and Arthroplasty Watch (http://www.arthroplastywatch.com/). The consequences of using an evidence-based system for rating of implants in the UK are demonstrated by Ng Man Sun et al. (2013). That paper highlights that healthcare providers in the UK follow recommendations based on clinical evidence regarding choice of implants. The Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) has previously reported a method of detecting prostheses with a higher than expected rate of revision, so-called “outlier” prostheses (de Steiger et al. 2013). The coexistence of several robust systems for detecting failing implants should increase the likelihood of as early detection as possible.

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Limitations Early detection of failing implants or product development may require different statistical robustness of data. In some cases, one would wish to access data as early as possible to look at trends and for other activities, and the data must be solid and robust. When discussing this, patient data security is also an important factor. We have included time-range restrictions and minimal number of hips at risk to allow for any analysis in order to ensure patient confidentiality as well as data robustness. In any real-time search application it is important to keep in mind the register validation process. At the beginning of a new year the data going into the annual report for the previous year are validated in several steps to ensure high quality. During the year, administrative staff at the hospital carry out registrations. The time between surgery and registration will to a certain extent differ between hospitals, which means that there is an inherent uncertainty in analyses based on aggregated data collected during the last weeks. When the annual report has been published for a specific year, the data can be regarded as well validated up to this specific year. Until then the data available from the latest calendar year should be considered as preliminary data. When comparing data generated in the application one should consider that patient population characteristics, for example age, sex, and diagnosis, might differ between data sets and this could potentially influence the results. In conclusion, the sharing of data between register and manufacturer comes with a responsibility. The manufacturers must be aware of limitations and take the responsibility when presenting the data. There is a critical balance between early access to data with the intention to alert regarding failing implants, and delivering robust high-quality data. All relevant stakeholders must be aware of this and use the data appropriately. This is partly addressed in the contract as data can only be used for marketing purposes as reported to the regulatory agency. To summarize, a well-established collaboration between the registry and the industry is not only beneficial for industry but also for the register, the orthopedic profession and not least the patient. Poorly performing implants can indeed be identified without involvement of the industry, but we think that this application will increase their interest in this process. We hope that our newly developed application will stimulate a collaboration to find the true background behind substandard implant performance, which may or may not be related to the properties of the prosthesis or the implant part of interest itself. The registry will continue to build on the application and will continue with yearly meetings with the industry in order to share knowledge and develop the collaborations further. Supplementary data Tables 1–4 are available as supplementary data in the online version of this article, http://dx.doi.org/10.1080/17453674. 2019.1608094

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OR, JK, and JV conceived the project. DO developed scripts and performed testing of statistical methods. All authors were involved in the internal testing. JV and OR drafted the manuscript.   Acta thanks Geke Denissen and Stephen Ellis Graves for help with peer review of this study.

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de Steiger R N, Miller L N, Davidson D C, Ryan P, Graves S E. Joint registry approach for identification of outlier prostheses. Acta Orthop 2013; 84(4): 348-52. Kärrholm J, Mohaddes M, Odin D, Vinblad J, Rogmark C, Rolfson O. Svenska Höftprotesregistret, Årsrapport 2017. 2018. Ng Man Sun S, Gillott E, Bhamra J, Briggs T. Implant use for primary hip and knee arthroplasty: are we getting it right first time? J Arthroplasty 2013; 28(6): 908-12.

AC­TA OR­THO­PA­E­DI­CA

The Swedish Hip Arthroplasty Register 40-year anniversary

Ezine edition: The Swedish Hip Arthroplasty Register — 40-year anniversary

Cover illustration: Pontus Andersson, Pontus Art Production

Ezine edition, May 2019