Vertebral Columns Winter 2022

Benefits and Potential Drawbacks of Single-Position Anterior and Lateral Lumbar Interbody Fusion in the Lateral Decubitus Position Current State of Endoscopic Spine Surgery and Future Developments

Vertebral

COLUMNS International Society for the Advancement of Spine Surgery

Osteoporosis in Spine Surgery Impact of Obesity on Complications in Lumbar Spine Surgery Bone Marrow Aspirate Concentrate and Spinal Fusion Bone Graft and Bone Graft Substitute Options in Metastatic Spine Surgery

PLUS

BENEFITS OF

Transitioning Cases to an Ambulatory Surgical Center

WINTER 2022

INSIDE

Editor in Chief

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11 16 21 26 29

EDITORIAL

Kern Singh, MD

Benefits of Transitioning Cases to an Ambulatory Surgical Center

Editorial Board

CLINICAL PRACTICE

Brandon Hirsch, MD

Benefits and Potential Drawbacks of Single-Position Anterior and Lateral Lumbar Interbody Fusion in the Lateral Decubitus Position

Sravisht Iyer, MD Yu-Po Lee, MD Sheeraz Qureshi, MD, MBA

ENDOSCOPY Current State of Endoscopic Spine Surgery and Future Developments

BONE HEALTH Osteoporosis in Spine Surgery

Managing Editor Audrey Lusher Designer CavedwellerStudio.com

PATIENT OUTCOMES Impact of Obesity on Complications in Lumbar Spine Surgery

BIOLOGICS Bone Marrow Aspirate Concentrate and Spinal Fusion

BIOLOGICS Bone Graft and Bone Graft Substitute Options in Metastatic Spine Surgery

Become a member today https://www.isass.org/about/membership/

Winter 2022

Peter Derman, MD, MBA

Vertebral Columns

Vertebral Columns is published quarterly by the International Society for the Advancement of Spine Surgery. ©2022 ISASS. All rights reserved.

Opinions of authors and editors do not necessarily reflect positions taken by the Society.

This publication is available digitally at www.isass.org/news/vertebralcolumns-Winter-2022

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From the Department of Orthopaedic Surgery at Rush University Medical Center, Chicago, Illinois.

EDITORIAL

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Benefits of Transitioning Cases to an Ambulatory Surgical Center Hanna Pawlowski, BS

Over the past 2 decades, outpatient surgery has become more popular in spinal procedures due to its significant clinical and economic benefits. All parties involved benefit from cost savings, perseverance or enhancement of safety, greater patient satisfaction compared to its hospital inpatient counterparts,1 and increased physician autonomy. In 1995, 80% of surgeries were performed in hospitals on an inpatient basis, and more than 90% of outpatient surgeries were performed in hospital outpatient departments. 2 More recently, however, 64% of surgical procedures in 2015 were performed on an outpatient basis.2 In fact, more than 23 million surgical procedures are performed yearly at more than 5,300 outpatient ambulatory surgery centers (ASCs) in the United States.2 There is no doubt that healthcare costs continue to rise. In response to these financial pressures, insurance companies, patients, and physicians are seeking ways to optimize patient care without compromising the quality of care or increasing costs. One way to relieve these financial burdens is to perform surgeries in an ASC. Advances in surgical techniques, including minimally invasive surgery (MIS) approaches, have substantially contributed to the transition from inpatient hospital surgeries to outpatient surgeries in ASCs by optimizing perioperative and clinical outcomes.3–5 By performing a fewer variety of more specialized procedures, ASCs are able to standardize surgical workflow and instrumentation to increase efficiency, volume of cases, and productivity. Furthermore, costs that are typically encountered when patients are monitored postoperatively in hospitals are altogether avoided. Through specialization of care, multiple same cases scheduled on the same day, and consistent care teams, ASCs are able to rapidly decrease operative time and administrative costs.

Multiple studies have demonstrated real-world cost savings. Bekelis et al 6 reviewed data from 150,000 patients undergoing a laminectomy procedure and found that the median cost in a hospital was $24,000 but only $11,000 in an ASC. Moreover, Blue Cross Blue Shield demonstrated a savings of nearly $8,500 for a laminectomy procedure when performed in an ASC.7 A study by Erickson et al also reported savings of nearly $8,000 for anterior cervical discectomy and fusion (ACDF) procedures performed in an ASC when compared to the same procedures performed in hospitals.8 Accordingly, published data have demonstrated that

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Madhav R. Patel, BS

Kevin C. Jacob, BS

Nisheka N. Vanjani, BS

Michael C. Prabhu, BS

Kern Singh, MD

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Winter 2022

EDITORIAL

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Published data have demonstrated that the cost of a surgical procedure performed in an ASC is between 53% to 55% that of the same procedure performed in a hospital. the cost of a surgical procedure performed in an ASC is between 53% to 55% that of the same procedure performed in a hospital.9–11 Although ASC procedures are more efficient, surgeons must be careful to select the appropriate patients for the ASC environment.

Healthy individuals and surgical risk must be matched to the setting of surgery. Typically, patients who are appropriate for an ASC procedure have a body mass index of ≤30 kg/m2, an American Society of Anesthesiologists score of ≤2, no more than 2-level fusion procedures, and at-home support. Patients outside of this criteria must be carefully screened with clearance obtained from other physicians if necessary. When this criteria is followed, not only are the complication rates low,12 but patient satisfaction is improved.

Furthermore, by offering a tailored surgical arena that is free of hospital patients with more severe medical conditions or greater needs, patients receive specialized care, may be less likely to contract hospital acquired infection, and are discharged home the same day. In this way, patients may not only recover faster but also be more satisfied with the operative experience itself. We have published several articles demonstrating the safety and efficiency of various procedures—ACDF,13,14 cervical disc replacement,14 MIS transfo-

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raminal lumbar interbody fusion,15 lateral lumbar interbody fusion,15 and MIS lumbar decompression16 —which were all shown to demonstrate success in the outpatient setting. All the procedures had minimal or no postoperative complications, all patients were discharged the same day, and there were no reported hospital readmissions.

Aside from its economic and clinical advantages, physicians practicing in ASCs have the advantage of greater autonomy than hospitals. In general, physicians have the freedom to pick and choose what procedures they perform, which patients they treat, and the administrative processes used in their centers. As hospitals are required to offer emergency room services and provide a wide variety of procedures to everyone, including the uninsured, costs greatly increase and physicians have less say in decision-making processes. In an ASC setting, the hospitals carry less oversight and physicians have greater control of their own practice.

Accordingly, physicians may benefit from significantly increased revenue when they practice in ASCs. Over the years, physicians’ salaries have not only failed to keep up with inflation, they have decreased overall.17 As Medicare payments continue to decline and surgeons are forced to do more with fewer resources, physicians are seeking other forms of compensation. While private practice may seem like a suitable choice, the increase in overall healthcare costs and malpractice rates cannot be ignored. As hospitals acquire ASCs, physicians are able to maintain financial stability without their autonomy being consumed by large hospital networks.

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EDITORIAL

Entrepreneurial leadership among physicians in ASC facilities not only contributes to profit for physicians but also encourages them to be directly involved in making financial decisions regarding the allocation of the country’s limited healthcare expenditures.2 In partnering with physicians, hospitals keep physicians involved within the system for key clinical decisions who otherwise may not work with the hospital at all.

In conclusion, surgery in ASCs is becoming a more favorable option for hospitals,

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patients, and physicians. Hospitals may benefit from retaining physicians while a lso dec reasi ng t hei r ow n hea lt hc a re costs. Not only are patients paying less, but they are also more satisfied with their outcomes. Fu r t her more, ASCs present physicians an opportunit y for independence f rom la rge hea lt hca re s y stems, and physicians benefit financially while maintaining their autonomy. As such, ASCs present a rare win-win-win situation for all three parties involved. n

References 1. Sivaganesan A, Hirsch B, Phillips FM, McGirt MJ. Spine surgery in the ambulatory surgery center setting: Value-based advancement or safety liability? Neurosurgery. 2018;83(2):159–165. doi:10.1093/neuros/nyy057

7. How consumers are saving with the shift to outpatient care. Published February 24, 2016. Accessed January 28, 2022. https://www.bcbs.com/the-healthof-america/reports/how-consumersare-saving-the-shift-outpatient-care

13. Patel DV, Yoo JS, Haws BE, et al. Comparative analysis of anterior cervical discectomy and fusion in the inpatient versus outpatient surgical setting. J Neurosurg Spine. 2019;21:255–260. doi:10.3171/2019.1.SPINE181311

2. Badlani N. Ambulatory surgery center ownership models. J Spine Surg. 2019;5(Suppl 2):S195–S203. doi:10.21037/jss.2019.04.20

8. Erickson M, Fites BS, Thieken MT, McGee AW. Outpatient anterior cervical discectomy and fusion. Am J Orthop.

2007;36(8):429–432. https://www. ncbi.nlm.nih.gov/pubmed/17849028

14. Jenkins NW, Parrish JM, Nolte MT, et al. Multimodal analgesic management for cervical spine surgery in the ambulatory setting. Int J Spine Surg.

2021;15(2):219–227. doi:10.14444/8030

9. Healthcare Bluebook, HealthSmart.

Study: Commercial insurance cost savings in ambulatory surgery centers.

Accessed January 28, 2022. https:// www.ascassociation.org/advancingsurgicalcare/reducinghealthcarecosts/ costsavings/healthcarebluebookstudy

15. Parrish JM, Jenkins NW, Brundage TS, et al. Outpatient minimally invasive lumbar fusion using multimodal analgesic management in the ambulatory surgery setting. Int J Spine Surg.

2020;14(6):970–981. doi:10.14444/7146

3. Emami A, Faloon M, Issa K, et al. Minimally invasive transforaminal lumbar interbody fusion in the outpatient setting.

Orthopedics. 2016;39(6):e1218–e1222. doi:10.3928/01477447-20160721-04 4. Chin KR, Pencle FJR, Coombs AV, et al.

Lateral lumbar interbody fusion in ambulatory surgery centers: patient selection and outcome measures compared with an inhospital cohort. Spine. 2016;41(8):686– 692. doi:10.1097/BRS.0000000000001285 5. Patel PD, Canseco JA, Houlihan N, Gabay A, Grasso G, Vaccaro AR. Overview of minimally invasive spine surgery.

World Neurosurg. 2020;142:43–56. doi:10.1016/j.wneu.2020.06.043 6. Bekelis K, Missios S, Kakoulides G, Rahmani R, Simmons N. Selection of patients for ambulatory lumbar discectomy: results from four US states. Spine J. 2014;14(9):1944–1950. doi:10.1016/j.spinee.2013.11.038

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10. The ASC cost differential. Accessed January 28, 2022. https://www.ascassociation.org/advancingsurgicalcare/ reducinghealthcarecosts/paymentdisparitiesbetweenascsandhopds 11. ASCs: A Positive Trend in Health Care.

Accessed January 27, 2022. https:// www.ascassociation.org/advancingsurgicalcare/aboutascs/industryoverview/apositivetrendinhealthcare 12. Cha EDK, Lynch CP, Hrynewycz NM, et al. Spine surgery complications in the ambulatory surgical center setting: systematic review [published online June 29, 2021]. Clin Spine Surg. doi:10.1097/BSD.0000000000001225

16. Patel DV, Yoo JS, Karmarkar SS, Lamoutte EH, Singh K. Minimally invasive lumbar decompression in an ambulatory surgery center. J Spine Surg. 2019;5(Suppl 2):S166-S173. doi:10.21037/jss.2019.04.05 17. Matthew R. Coffron MA, Zlatos C. Medicare physician payment on the decline: it’s not your imagination. The Bulletin. Published September 1, 2019. Accessed February 1, 2022. https://bulletin.facs.org/2019/09/ medicare-physician-payment-on-thedecline-its-not-your-imagination/

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From the Department of Orthopaedic Surgery at Rush University Medical Center, Chicago, Illinois.

CLINICAL PRACTICE

Benefits and Potential Drawbacks of Single-Position Anterior and Lateral Lumbar Interbody Fusion in the Lateral Decubitus Position Often it is true, in the field of spinal surgery, that innovations are conceived not in a dramatic reinvention, but rather in nuanced refinement of existing procedures in an effort to continually improve the patient experience. Such was the case with the development of minimally invasive tissue-sparing techniques for the transforaminal lumbar interbody fusion (TLIF) and lumbar decompression,1–4 and such is the case with the recently conceived single-position circumferential lumbar fusion surgery. 5 Degenerative conditions of the lumbar spine, after failure of response to conservative therapies, are often treated surgically with lumbar interbody fusion (LIF) procedures. Through the commonly used anterior (ALIF) and lateral (LLIF) techniques, the surgeon approaches the anterior spinal column in order to implant an interbody cage into the affected disc space.6 During ALIF procedures, the patient is placed in a supine position for implant insertion, whereas during LLIF procedures, the patient is treated in a lateral position. In pursuit of maximal lumbar spine stabilization, ALIF and LLIF procedures are often complemented by a subsequent posterior approach for percutaneous pedicle screw placement.

This approach has traditionally been accomplished by moving the patient intraoperatively from the supine (ALIF) or lateral (LLIF) position to a prone position. Recently, however, a single-position technique has been explored for these procedures, whereby the patient is placed in a lateral decubitus position and remains as such for both the implant insertion and posterior pedicle screw fixation. In the present article, we examine the current state of single-position circumferential lumbar fusion procedures and the advantages and disadvantages that may be present relative to the traditional dual-position procedures.

Dual-Position vs Single-Position The ALIF and LLIF techniques are well regarded for their proven ability to restore lumbar lordosis and proper disc height in degenerated lumbar segments.6,7 These procedures intuitively demonstrate an advantage over posterior approaches to

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Michael C. Prabhu, BS

Kevin C. Jacob, BS

Madhav R. Patel, BS

Nisheka N. Vanjani, BS

Hanna Pawlowski, BS

Kern Singh, MD

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CLINICAL PRACTICE

lumbar fusion, such as the posterior lumbar interbody fusion (PLIF) and TLIF, because their access route allows for an increased entry point to the anterior disc space and thereby enables the implantation of larger interbody cages that can better restore sagittal alignment and disc height.7 The addition of posterior percutaneous pedicle screw placement allows for a circumferential fusion and favorable three-column fixation, further stabilizing the vertebrae and reducing the risk of postoperative cage subsidence and non-union.8 Although this added step is advantageous by way of fusion facilitation, the traditional method of repositioning the patient between procedural steps limits these circumferential fusion procedures in their operative profiles.

The time requirement of repositioning a patient intraoperatively brings with it an undesirable extended period under anesthesia, which, particularly when used in the prone position, can contribute to complications of increased blood loss, postoperative infection, and postoperative ileus.7 Single-position circumferential fusion procedures aim to match the operative methodology and success of dual-position procedures with the patient in a lateral decubitus position throughout both stages of the operation, in hopes that the perioperative and safety profile of the operation may improve. This technique is still in its infancy, and as such it is not yet clear if it can in fact achieve the same operative effectiveness as dual-position techniques. However, early trials have shown promising results.

A recent systematic review and meta-analysis by Mills et al9 sought to evaluate the cur-

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rent state of single-position circumferential lumbar fusion surgery. In studies comparing lateral decubitus single-position ALIF/LLIF procedures with dual-position procedures, it was noted that single-position patients on average experienced reductions in operative time and blood loss, though the advantages of the single-position technique stopped there. No significant differences were noted in radiographic parameters or complications, suggesting that single-position circumferential fusion procedures can provide similar outcomes to their dual-position counterparts while adding the benefit of an improved perioperative profile.

In addition to perioperative benefits, Choi et al,10 in their study of 35 consecutive patients undergoing single-position LLIF with posterior pedicle screw fixation, demonstrated significant lordosis correction and improvements in visual analog scale measures of back and leg pain through 6-months following surgery. In conjunction with the observed clinical and radiographic improvement of their study cohort, they further proposed that the perioperative advantages of avoiding intraoperative repositioning may also lead to significant cost savings associated with single-position circumferential fusion.

A recently published study of notable power, in which Buckland et al7 evaluated the operative outcomes of 237 single-position and 153 dual-position ALIF/LLIF patients, provides particularly strong support for the maintenance of a single position for patients during circumferential fusion. In their analysis, single-position patients demonstrated significant advantages in operative time,

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CLINICAL PRACTICE

radiation dose, blood loss, length of hospital stay, development of postoperative ileus, and postoperative lumbar lordotic angle relative to their dual-position counterparts.

Of particular note in their findings was the dramatic reduction in operating room time, which averaged 306.59 minutes in dual-position procedures and 103.08 minutes in single-position procedures. The authors provide an insightful explanation for this impressive reduction, considering that the act of repositioning itself is not the only factor influencing OR time, but also prepping, draping, and reconnecting anesthesia lines and neuromonitoring technology.

Although single-position circumferential lumbar fusion procedures have demonstrated important perioperative advantages over dual-position techniques, there remain intuitive drawbacks to this concept. As the technique is still in its infancy, no evidence yet exists regarding the long-term clinical and radiographic outcomes of single-position patients. Until such data are reported, it will remain difficult to understand fully whether single-position procedures can match the efficacy of traditional dual-position techniques. Furthermore, new techniques always carry with them a significant learning curve that the surgeon must face, and this is no exception. During single-position ALIF, both the anterior and posterior approaches must be conducted with the patient in the lateral decubitus position, which may present a challenge to the surgeon.

The experience of Sellin et al11 with the single-position technique in obese patients led them to conclude overall that this inno-

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vation is a safe and effective evolution in the circumferential fusion procedure, but they noted that two pedicle screws were misplaced, both on the side of the patient closest to the bed. Although they deemed this complication a result of the patient being positioned too far from the edge of the bed, it presents a logical conundrum: does it simply make more sense to have the patient in a prone position for percutaneous pedicle screw insertion? Particularly in the case of the ALIF, it appears to be imperative that the anterior side of the patient be positioned as closely to the edge of the bed as possible, making it infeasible for the posterior side of the patient to also be positioned as closely as possible to its own edge of the bed. In addition, the systematic review by Mills et al9 found that although there were reductions in blood loss associated with single-position techniques, these reductions may not be clinically meaningful, further limiting the potential advantage of single-position circumferential fusion.

The likely response to these potential flaws in the single-position technique lies within another innovation: enhanced intraoperative navigation. Hiyama et al 12 recently wrote of their experience performing lateral decubitus single-position LLIF procedures using wearable smart glasses that provide an x-ray navigation image overlaid on the operative field so that the surgeon does not need to switch focus between the operative window and external imaging screens. Their preliminary assessment of 24 cases led this team of Japanese surgeons to conclude that these glasses are a safe and effective tool

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allowing for efficient navigation-assisted single-position LLIF without compromise given to traditional LLIF outcomes. Various modalities of extended reality have been explored in spine surgery13 and have proven to result in dramatically favorable accuracy rates regarding percutaneous pedicle screw placement. The incorporation of these tools into the single-position ALIF and LLIF techniques can enable the surgeon to pursue the single-position benefits of reduced operative and anesthesia time while giving no compromise to pedicle screw fixation accuracy.

Conclusion As surgeons continue to inventively refine procedures and strive toward ever-improved operative and clinical outcomes, it appears

that the future of spine surgery will reflect its past. Single-position circumferential ALIF and LLIF techniques look to improve upon traditional dual-position procedures by maintaining both the access window to the anterior disc space and posterior three-column pedicle screw fixation while eliminating the temporal burden of repositioning the patient between stages of the operation. As this procedure is investigated further, and perhaps additionally refined through modalities such as extended reality for enhanced visualization, long-term outcome data will show whether single-position circumferential lumbar fusion procedures can achieve the same operative success as traditional dual-position procedures with the added benefit of perioperative enrichment. n

References 1. Foley KT, Holly LT, Schwender JD. Minimally invasive lumbar fusion. Spine.

2003;28(15 Suppl):S26-S35.

2. Smith MM, Foley KT. Microendoscopic discectomy: Surgical technique and initial clinical results. Clin Neurol Neurosurg. 1997;99:S105. doi:10.1016/s0303-8467(97)81738-6 3. Foley KT, Lefkowitz MA. Advances in minimally invasive spine surgery.

Clin Neurosurg. 2002;49:499-517.

4. Hammad A, Wirries A, Ardeshiri A, Nikiforov O, Geiger F. Open versus minimally invasive TLIF: literature review and meta-analysis. J Orthop Surg Res. 2019;14(1):229.

5. Bodon G, Kiraly K, Baksa G, et al. Applied anatomy and surgical technique of the lateral single-position L5-S1 fusion. Clin Anat. 2021;34(5):774-784.

6. Mobbs RJ, Phan K, Malham G, Seex K, Rao PJ. Lumbar interbody fusion: techniques, indications and comparison of interbody fusion options including PLIF, TLIF, MI-TLIF, OLIF/ATP, LLIF and ALIF. J Spine Surg. 2015;1(1):2-18.

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7. Buckland AJ, Ashayeri K, Leon C, et al.

Single position circumferential fusion improves operative efficiency, reduces complications and length of stay compared with traditional circumferential fusion. Spine J. 2021;21(5):810-820.

8. Allain J, Dufour T. Anterior lumbar fusion techniques: ALIF, OLIF, DLIF, LLIF, IXLIF. Orthop Traumatol Surg Res. 2020;106(1S):S149-S157.

9. Mills ES, Treloar J, Idowu O, Shelby T, Alluri RK, Hah RJ. Single position lumbar fusion: a systematic review and meta-analysis [published online October 23, 2021]. Spine J. doi:10.1016/j.spinee.2021.10.012 10. Choi J, Rhee I, Sakar M, Park I, Maalouly J. Single position lateral lumbar interbody fusion and pedicle screw fixation: preliminary experience and perioperative results. Mini-invasive Surg. 2021;5;43. doi:10.20517/2574-1225.2021.73

11. Sellin JN, Mayer RR, Hoffman M, Ropper AE. Simultaneous lateral interbody fusion and pedicle screws (SLIPS) with CT-guided navigation. Clin Neurol Neurosurg. 2018;175:91-97.

12. Hiyama A, Katoh H, Sakai D, Watanabe M. A new technique that combines navigation-assisted lateral interbody fusion and percutaneous placement of pedicle screws in the lateral decubitus position with the surgeon using wearable smart glasses: a small case series and technical note.

World Neurosurg. 2021;146:232-239.

13. Morimoto T, Kobayashi T, Hirata H, et al. XR (Extended reality: virtual reality, augmented reality, mixed reality) technology in spine medicine: status quo and quo vadis. J Clin Med Res. 2022;11(2). doi:10.3390/jcm11020470

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From the Hospital for Special Surgery in New York, New York.

ENDOSCOPY

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Current State of Endoscopic Spine Surgery and Future Developments The origins of what is now known as endoscopic spine surgery can be traced back to 1973 when Parvis Kambin, MD, described a technique for percutaneous non-visualized indirect spinal canal decompression through a posterolateral approach.1,2 Kambin 3,4 and others, notably Hijikata, 5 Forst and Hausman, 6 Suezama,7 and Schreiber, 8 continued at early attempts of endoscopic surgery until 1990, when Kambin 9 introduced the triangular safe zone, also known as Kambin’s Triangle. 2,10 The borders of this triangle are the lateral edge of the thecal sac, the exiting root, and the superior endplate of the level below.

This transforaminal approach enabled significant advancement through several iterations, including percutaneous endoscopic lumbar discectomy, visualized endoscopic spine surgery using the inside-out approach with the Yeung system (as perfected by Anthony Yeung, MD), and the outside-in approach, which lands directly in the epidural space outside the disc.11-13

Current State of Lumbar Endoscopic Surgery Today, discectomy for symptomatic herniation remains the most prevalent and most well-studied application of endoscopic spine surgery.14 Other applications of this approach include foraminotomies and interbody fusions.

Although the transforaminal approach was the driving force behind the rise of endoscopic surgery, the newer interlaminar approach has further driven development. The interlaminar approach allows for the concurrent use of several instruments as well as direct access to the central canal and lateral recesses, allowing endoscopic surgery to treat a broader range of pathologies.15 Notably, the endoscopic interlaminar approach is particularly beneficial for direct decompression at the L5-S1 level, whereas the transforaminal approach has to overcome the anatomical constraints of the iliac crest at this level.

Spinal stenosis is one example of a pathology that has been successfully treated endoscopically since the advent of the interlaminar approach. Endoscopic central canal decompression may have a less steep learning curve as it is a more familiar approach for most spine surgeons. These endoscopic techniques have been performed using a uniportal approach or a unilat-

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Kasra Araghi, BS

Daniel Shinn, BS

Pratyush Shahi, MBBS, MS(Ortho)

Sheeraz Qureshi, MD, MBA

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ENDOSCOPY

eral biportal approach.16 Transforaminal endoscopic approaches lend themselves better to foraminotomies as the location of access is through the foramen.

Endoscopic lumbar interbody fusions are among the most recent developments due to advancements in available technology. In particular, a true endoscopic transforaminal lumbar interbody fusion (TLIF) performed using a uniportal approach without the use of a tubular retractor is now possible, as evidenced by the literature.17 When compared to tubular minimally invasive (MIS) TLIF, endoscope-assisted TLIF has been successfully performed under conscious sedation and has led to favorable outcomes such as decreased surgical time, blood loss, length of hospital stay, and expenditures.18-20 With the emergence of expandable interbody

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cages, it is now possible to achieve a larger and more stable interbody construct through a narrower and smaller endoscopic port. In addition, the progress of lateral interbody fusions has aided in the adoption of indirect spinal canal decompression (via interbody distraction) as an effective spinal canal decompression technique. As previously discussed, various expandable interbody cages can deliver such distraction forces t hrough an endoscopic approach. This obviates the need for direct decompression of the canal, as well as the additional time and potential difficulties that it entails.

Endoscopic lumbar interbody fusion also aims to provide a viable alternative to the more invasive lumbar interbody fusion surgeries, which are more likely to result in morbidity.17

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ENDOSCOPY

Despite the fact that current uses of endoscopic lumbar surgery have demonstrated outcomes comparable to traditional MIS, acceptance of this technology in the United States has been slow compared to Asian and European markets. 21 While the steep learning curve is the primary impediment to widespread adoption of endoscopic surgery in the US, it has also been hampered by improper US billing codes and a lack of industry involvement from major spine companies. 22,23

Current State of Cervical Endoscopic Surgery Full endoscopic cervical spine surgery is also an emerging technique with the same aims of endoscopic lumbar surgery: improve outcomes, decrease complications, a nd reduce overa l l cost. T he com mon pat hologies and pain generators of t he cer v ica l spine are disc herniat ion and stenosis. 2 4 W hen indicated, t radit ional approaches may involve anterior cervical discectomy and fusion (ACDF), posterior cervical foraminotomy, or posterior laminectomy w ith or w ithout fusion. Much li ke endoscopic su rger y of t he lu mba r spine, adoption of endoscopy in cervical spine surgeries focused on decompression rat her t han fusion. Moreover, t he fully endoscopic cer vical decompression approaches are divided into two categories: anterior full-endoscopic cervical discectomy (AFECD) and posterior full-endoscopic cervical discectomy (PFECD). 25,26 To determine the optimal endoscopic approach for single-level cer v ica l disc

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Full endoscopic cervical spine surgery is also an emerging technique with the same aims of endoscopic lumbar surgery: improve outcomes, decrease complications, and reduce overall cost. herniation, one retrospective cohort study of 84 patients compared clinical and radiographic outcomes bet ween pat ients who underwent either AFECD or PFECD. 27 The study results suggested a posterior approach may be better given a smaller volume of disc removed and smaller loss of disc height, though clinical outcomes did not differ significantly. An important caveat is that central herniations are more commonly treated with AFECD, whereas lateral herniations are more commonly treated with PFECD; therefore, this study only included paramedial herniations. 28,29 One randomized control trial with 175 total patients demonstrated that full-endoscopic posterior foraminotomy had non-inferior patient-reported outcomes and complication rates compared to traditional ACDF, and it can be a safe alternative for patients w ith lateral cer v ical disc herniations. 26 U lt imately, t he aut hors found not only comparable clinical outcomes but also reduced traumatization using endoscopy.

Ty pica l ly, poster ior cer v ica l decompression is achieved using the “keyhole” approach. One observational study by Liu et al described a technique with compara-

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ble clinical outcomes using a lamina-hole approach for posterior percutaneous endoscopic cervical discectomy in patients with a cervical disc herniation. 30 Clearly, there is still a need for further investigation on the optimal techniques for endoscopic cervical procedures. Full endoscopic cervical spine surgery has been adopted for treating mostly disc herniation, and specific approaches are actively being explored to optimize outcomes. Although only two general categories were discussed (anterior and posterior), the four common specific techniques are posterior cervical unilateral laminectomy and bilateral decompression, posterior cer v ica l foraminotomy,

anterior cervical discectomy, and anterior transcorporal discectomy. 31 Furthermore, endoscopy is not currently used for cervical fusion or cervical disc arthroplasty, but there may be potential to use endoscopy as an adjunct therapy to decompress adjacent levels. 32

Future Developments 1. Expansion of the scope: With the advancement in tools and instruments, endoscopy can be expected to be utilized for complex surgeries such as deformity correction and tumor resection. 33 Also, as the technology of expandable cages evolves, the complexity of performing

References 1. Kambin P, Gellman H. Percutaneous lateral discectomy of the lumbar spine a preliminary report. Clin Orthop Relat Res. 1983;174:127–132.

2. Telfeian AE, Veeravagu A, Oyelese AA, et al. A brief history of endoscopic spine surgery. Neurosurg Focus. 2016;40:E2.

3. Kambin P, Sampson S. Posterolateral percutaneous suction-excision of herniated lumbar intervertebral discs. Report of interim results. Clin Orthop Relat Res. 1986:37–43.

4. Kambin P, Brager MD. Percutaneous posterolateral discectomy.

Anatomy and mechanism. Clin Orthop Relat Res. 1987:145–154.

5. Hijikata S. Percutaneous discectomy: a new treatment method for lumbar disc herniation. J Tokyo Den-ryoku Hosp. 1975;5:39–44.

6. Forst R, Hausmann B. Nucleoscopy—a new examination technique. Arch Orthop Trauma Surg. 1983;101:219–221.

7. Suezawa Y, Jacob H. Percutaneous nucleotomy. Archives Orthop Traumatic Surg. 1986;105:287–295.

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8. Schreiber A, Suezawa Y, Leu H. Does percutaneous nucleotomy with discoscopy replace conventional discectomy?

Eight years of experience and results in treatment of herniated lumbar disc.

Clin Orthop Relat Res. 1989:35–42.

15. Simpson AK, Lightsey HMt, Xiong GX, et al. Spinal endoscopy: evidence, techniques, global trends, and future projections. Spine J. 2022;22:64–74.

9. Kambin P. Arthroscopic microdiskectomy. Mt Sinai J Med. 1991;58:159–164.

16. Goh KY, Hsu JC, Lee CY, et al. Uniportal endoscopic interlaminar decompression in lumbar spinal stenosis: a comprehensive review. Int J Spine Surg. 2021;15:S54–S64.

10. Kim M, Kim HS, Oh SW, et al. Evolution of spinal endoscopic surgery. Neurospine. 2019;16:6–14.

17. Brusko GD, Wang MY. Endoscopic lumbar interbody fusion. Neurosurg Clin N Am. 2020;31:17–24.

11. Mayer HM, Brock M. Percutaneous endoscopic lumbar discectomy (PELD).

Neurosurg Rev. 1993;16:115–120.

18. Wang MY, Grossman J. Endoscopic minimally invasive transforaminal interbody fusion without general anesthesia: initial clinical experience with 1-year follow-up. Neurosurg Focus. 2016;40:E13.

12. Yeung AT. Minimally invasive disc surgery with the Yeung endoscopic spine system (YESS). Surg Technol Int. 1999;8:267–277.

13. Schubert M, Hoogland T. Endoscopic transforaminal nucleotomy with foraminoplasty for lumbar disk herniation. Oper Orthop Traumatol. 2005;17:641–661.

14. Butler AJ, Alam M, Wiley K, et al. Endoscopic lumbar surgery: the state of the art in 2019. Neurospine. 2019;16:15–23.

19. Wang MY, Chang HK, Grossman J. Reduced acute care costs with the ERAS® minimally invasive transforaminal lumbar interbody fusion compared with conventional minimally invasive transforaminal lumbar interbody fusion.

Neurosurgery. 2018;83:827–834.

20. Wang MY, Chang P-Y, Grossman J. Development of an Enhanced Recovery After Surgery (ERAS) approach for lumbar spinal fusion. J Neurosurg Spine. 2017;26:411–418.

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interbody fusion surgeries endoscopically is likely to decline.

2. Endoscopic radiofrequency facet denervation: Ablation of the dorsal ramus causing facetogenic pain can be done under direct visualization with the help of an endoscope. Recent studies have demonst rated t hat t his is a safe and effective technique. 34 3. Merging of endoscopy with navigation and robotics: Combining these technologies can increase the comfort level of the surgeon, decrease radiation exposure, f latten the learning curve, and make the adoption of endoscopy more appealing. 35 With the recent rise in in-

21. Kim JS, Yeung A, Lokanath YK, et al. Is Asia truly a hotspot of contemporary minimally invasive and endoscopic spinal surgery? J Spine Surg. 2020;6:S224–S236.

22. Moon ASM, Rajaram Manoharan SR. Endoscopic spine surgery: current state of art and the future perspective. Asian Spine J. 2018;12:1–2.

23. Yoon JW, Wang MY. The evolution of minimally invasive spine surgery: JNSPG 75th anniversary invited review article.

J Neurosurg Spine. 2019;30:149–158.

24. Woods BI, Hilibrand AS. Cervical radiculopathy: epidemiology, etiology, diagnosis, and treatment. J Spinal Disord Tech. 2015;28:E251–E259.

25. Ahn Y, Lee SH, Chung SE, et al. Percutaneous endoscopic cervical discectomy for discogenic cervical headache due to soft disc herniation.

Neuroradiology. 2005;47:924–930.

26. Ruetten S, Komp M, Merk H, et al. Full-endoscopic cervical posterior foraminotomy for the operation of lateral disc herniations using 5.9-mm endoscopes: a prospective, randomized, controlled study. Spine (Phila Pa 1976). 2008;33:940–948.

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terest in endoscopic spine surgeries in North America, more innovations seem likely in the near future.

4. Teaching: One drawback of endoscopic spine surgery is the steep learning curve.

Incorporating it into t he curriculum of residency and fellowship programs can help in the wider adoption of this technology.

5. Management of dural tear: A lthough studies have shown that agents like fibrin glue, collagen sponge, and muscle or fat graft are effective in the management of dural tears in endoscopic spine surgery, 36 instruments should be developed to allow for suture repair of the tear. n

27. Yang JS, Chu L, Chen L, et al. Anterior or posterior approach of full-endoscopic cervical discectomy for cervical intervertebral disc herniation?

A comparative cohort study. Spine (Phila Pa 1976). 2014;39:1743–1750.

28. Ruetten S, Komp M, Merk H, et al. Full-endoscopic anterior decompression versus conventional anterior decompression and fusion in cervical disc herniations.

Int Orthop. 2009;33:1677–1682.

29. Kim CH, Chung CK, Kim HJ, et al. Early outcome of posterior cervical endoscopic discectomy: an alternative treatment choice for physically/socially active patients.

J Korean Med Sci. 2009;24:302–306.

30. Liu C, Liu K, Chu L, et al. Posterior percutaneous endoscopic cervical discectomy through lamina-hole approach for cervical intervertebral disc herniation.

Int J Neurosci. 2019;129:627–634.

31. Shen J, Shaaya E, Bae J, et al. Endoscopic spine surgery of the cervicothoracic spine: a review of current applications.

Int J Spine Surg. 2021;15:S93–S103.

32. Brown GS, Gibson JA. Early experience with cervical endoscopic spinal surgery (CESS): a potential adjunct to ACDF/ disc arthroplasty. Spine J. 2015;15:S74.

33. Moon ASM, Rajaram Manoharan SR. Endoscopic spine surgery: current state of art and the future perspective. Asian Spine J. 2018;12(1):1–2. doi:10.4184/asj.2018.12.1.1 34. Meloncelli S, Germani G, Urti I, et al.

Endoscopic radiofrequency facet joint treatment in patients with low back pain: technique and long-term results. A prospective cohort study. Ther Adv Musculoskelet Dis. 2020;12:1759720X20958979. doi:10.1177/1759720X20958979 35. Shin Y, Sunada H, Shiraishi Y, et al.

Navigation-assisted full-endoscopic spine surgery: a technical note.

J Spine Surg. 2020;6(2):513–520. doi:10.21037/jss-2019-fess-19 36. Müller SJ, Burkhardt BW, Oertel JM. Management of dural tears in endoscopic lumbar spinal surgery: a review of the literature. World Neurosurg. 2018;119:494– 499. doi:10.1016/j.wneu.2018.05.251

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From the Hospital for Special Surgery in New York, New York.

Osteoporosis in Spine Surgery Osteoporosis is an important public health problem that affects approximately 200 million people worldwide and at least 10 million people in the United States.1 The World Health Organization defines osteoporosis Junho Song, BS as a reduction in bone mineral densit y (BMD) of the femoral neck by 2.5 standard deviations relative to a reference population (T score ≤ −2.5). 2 Osteoporosis is very common among candidates for spine surgery. Wagner et al3 Sidhant Dalal, BS reported that 20% of all patients undergoing spine surgery had osteoporosis, as well as up to 50% of women older than 50 years.

Patients w ith osteoporosis have poor bone quality and compromised bone healing due to a Dimitra microarchitectural disruption Melissaridou, MD of trabecular and cortical bone.1 Increased bone stiffness and fragility often leads to poor implant anchoring and increases the risk for early and late postoperative complications. 2,4 Furthermore, osteoporosis is significantly asSravisht Iyer, MD sociated with higher readmission rates, longer length of hospitalization, and greater medical costs.5 Early diagnosis and a multidisciplinary approach are crucial. Spine surgery in osteoporotic patients is challenging, and further investigation will improve

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the quality of care for this population. In this review, we discuss the importance of bone health among spine patients, as well as the impact of osteoporosis and its medical treatments on postoperative outcomes.

Biomechanics of Osteoporosis Osteoporosis is characterized by a reduction in the apparent density of the trabecular bone; this reduction results in weakened compressive mechanical strength of the trabecular bone, which is related to the square of the apparent density.6 In the cancellous bone, severe osteoporosis significantly alters the strain energy distribution in vertebral bodies under compression.7 This reduction in compressive strength predisposes individuals to vertebral fractures.8 Beyond the vertebral body, osteoporosis also accentuates stress concentrations at the annulus fibrosus, articular facet, lamina, and pars interarticularis. 9 At the molecular level, osteoporosis disrupts the stability of the vertebral cells, which inhibits growth and interferes with the biologic process of fusion. This leads to poorer clinical outcomes following spinal procedures requiring fusion.10 In light of the considerable influence of osteoporosis on the biomechanics of the spine, it is critical to identify the presence of osteoporosis among patients being considered for spine surgery.

Preoperative Assessment of Bone Mineral Density Preparat ion for spine surger y involves

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the optimization of medical conditions to minimize complications. However, bone density is not as routinely assessed, with only approximately 40% of spine surgeons reporting that they evaluate BMD prior to fusion surgery.11 Osteoporosis is common among patients undergoing spine surgery but is often undiagnosed. Given that spine surgery typically involves bone removal, fixation, and the biologic process of fusion, preoperative consideration of osteoporosis is merited among both men and postmenopausal women older than 50 years.12 Other findings in the patient’s history may also necessitate a BMD evaluation. For example, a recent 2-cm change in height or historical 4-cm height loss should undergo dual-energy x-ray absorptiometry (DXA), as these height change findings have been shown to indicate osteoporosis in more than 80% of cases.13 In addition to DXA, the evaluation of BMD may involve other methods of measurement.

Data from computed tomography (CT) may also be used, as BMD Hounsfield unit (HU) measurement correlates strongly with BMD estimates via DEXA.14 Therefore, HU measurement provides a potential method of evaluating lumbar BMD without additional preoperative imaging. Widespread adoption of HU measurement for vertebral osteoporosis screening can reduce overall healthcare costs and resource utilization while still providing a precise method of preoperative evaluation.15 Additionally, the presence of degenerative spinal disease can influence lumbar spine BMD.16 Greater degrees of degenerative spinal disease correlate w ith increased

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lumbar spine BMD, which can lead to an underdiagnosis of osteoporosis within this patient population.17 Thus, for degenerative spine disease patients with risk factors for osteoporosis, the preoperative evaluation of BMD may occur in other locations, such as the proximal femur.18 Furthermore, HU measurements have been show n to be useful in detecting undiagnosed spinal osteoporosis in patients with degenerative lumbar disease.14,19

Impact of Osteoporosis on Surgical Outcomes Although surgical intervention with instrumentation for the osteoporotic spine is challenging due to the poor bone stock, it is sometimes a clinical necessity. Unsurprisingly, the biomechanical changes associated with osteoporosis of the spine have been linked to poorer surgical outcomes. Osteoporosis is a relative contraindication for the use of pedicle screws to achieve posterior fixation due to the heightened risk of failure at the bone-

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screw interface, leading to screw pullout.20 The damage resulting from such pullouts can also greatly complicate revision surgeries.

Liu et al 21 assessed a cohort of 359 patients who underwent lumbar fusion surgery and found that low volumetric BMD on preoperative lumbar spine CT was a significant risk factor for postoperative complications, such as pseudoarthrosis, instrument failure, and adjacent fractures. Wang et al10 reported that after lumbar interbody fusion, osteoporosis of the fused vertebrae increased the risk of adjacent segment diseases, subsidence, cage failure, rod failure, and lumbar instability.

Several methods have been described to help opt im ize surg ica l outcomes in patients with osteoporosis, particularly with regards to improving screw fixation.

Cement augmentation of pedicle screws has been demonstrated as an effective means to significantly increase pullout strength.

Vertebroplasty has also been used to augment pedicle screws, with studies suggesting reductions in screw loosening, mechanical failure, and junctional segment fractures. 22 Since the cortex of the vertebral body is much stronger than cancellous bone, biocortical purchase of pedicle screws has also been used to improve fixation. However, the use of biocortical purchase also carries the risk of injury to anterior structures, such as the L5 nerve root, colon, iliac and middle sacral vessels, and sacral sympathetic trunk. 23 In addition, coating of pedicle screws with hydroxyapatite can improve screw-bone contact, bone ingrowth, and mineralization, providing the advantage of increased pullout strength and extraction

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torque in both healthy and osteoporotic vertebrae. 24,25 Finally, the utilization of robot assistance for pedicle screw insertion may be beneficial, as it is associated with improved radiologic and clinical outcomes in patients with osteoporosis compared to fluoroscopy-assisted technique. 26

Medical Management of Osteoporosis for Spine Surgery Given the potential impact of osteoporosis on surgical outcomes, it is critical to optimize bone health before surgery, which can ultimately improve outcomes and recovery after surgery.27 Traditionally, anti-absorptive treatments such as bisphosphonates have been considered first line for the medical management of osteoporosis. Anti-resorptive agents inhibit osteoclast function, thereby preserving BMD by diminishing resorption.28 Despite the broad acceptance of this therapy outside the realm of spine surgery, Buerba et al29 noted limited benefits of bisphosphonate on surgical outcomes after thoracolumbar fusion. Compared to the control group, the patients receiving bisphosphonates had no observable benefit regarding fusion rates and risk of screw pullout. 29 This lack of bisphosphonate influence on fusion outcomes was also observed in a similar study on posterior lumbar interbody fusion by Kang et al. 30 Conversely, some studies report the ability of bisphosphonates to improve the rate of fusion, shorten the time to fusion, and protect against vertebral fractures, further complicating the topic. 31,32 Despite the lack of clarity with regards to anti-absorptive treatment in surgery, a superior class of

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medications has the potential to address these doubts.

Anabolic agents, such as teriparatide (approved 2002) and abaloparatide (approved 2017), are relatively novel in the context of spine surgery. Anabolic agents directly stimulate osteoblasts with the intention of increasing bone mass/volume directly.28 In comparison to anti-resorptive agents, anabolic agents have consistently demonstrated superior results in treating osteoporosis, as well as in off-label applications such as spine fusion and arthroplasty. 33 Several retrospective studies showed that teriparatide greatly improved rate and time to fusion following surgery compared to placebo or bisphosphonates. 34,35 In a prospective RCT, Ebata et al36 demonstrated that among women undergoing single-level lumbar interbody fusion, those who received week ly teriparatide had superior rates of fusion (69.0% vs 35.1%) compared with the no-treatment group. Other potential benefits of teriparatide therapy for spinal fusion include greater pedicle screw insertional torque and reduced rates of implant failure, adjacent vertebral

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fractures, and arthrodesis. 37,38 Given these findings, anabolic agents should be recommended for patients with osteoporosis who require spine surgery, particularly for those undergoing fusion procedures.

Conclusion Spine surgery in the context of osteoporosis presents a nuanced challenge to physicians, and deliberate steps must be taken to tailor care from diagnosis to surgical intervention accordingly. Although there is a diverse range of ongoing investigations pertaining to the pathology and clinical course of osteoporosis, surgeons can strive to provide superior outcomes to this vulnerable population by staying abreast of the latest literature. Several surgical techniques and medical therapies have been proposed as methods to optimize postoperative outcomes for patients with osteoporosis, with some promising data to support their validity. Nevertheless, given the significant operative difficulty and impact on outcomes that osteoporosis poses, further research on ways to improve surgery of the osteoporotic spine is warranted. n References continued on page 20

References 1. Guzman JZ, Feldman ZM, McAnany S, et al. Osteoporosis in cervical spine surgery.

Spine (Phila Pa 1976). 2016;41:662–668.

2. Prost S, Pesenti S, Fuentes S, et al. Treatment of osteoporotic vertebral fractures. Orthop Traumatol Surg Res. 2021;107:102779.

3. Wagner SC, Formby PM, Helgeson MD, et al. Diagnosing the undiagnosed: osteoporosis in patients undergoing lumbar fusion. Spine (Phila Pa 1976). 2016;41:E1279–e1283.

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4. DeWald CJ, Stanley T. Instrumentation-related complications of multilevel fusions for adult spinal deformity patients over age 65: surgical considerations and treatment options in patients with poor bone quality. Spine (Phila Pa 1976). 2006;31:S144–S151.

5. Lee CK, Choi SK, An SB, et al. Influence of osteoporosis following spine surgery on reoperation, readmission, and economic costs: an 8-year nationwide population-based study in Korea. World Neurosurg. 2021;149:e360–e368.

6. Goldstein SA. The mechanical properties of trabecular bone: dependence on anatomic location and function.

J Biomech. 1987;20:1055–1061.

7. Lo CW, Chen SI, Chue CH, et al. Influences of osteoporosis and disc degeneration on lumbar spinal stability. J Chinese Instit Engin. 2003;26:757–769.

8. Yang J, Cosman F, Stone PW, et al.

Vertebral fracture assessment (VFA) for osteoporosis screening in US postmenopausal women: is it cost-effective?

Osteoporos Int. 2020;31:2321-35.

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References Continued 9. Lo CC, Tsai KJ, Zhong ZC, et al. Biomechanical differences of Coflex-F and pedicle screw fixation combined with TLIF or ALIF—a finite element study. Comput Methods Biomech Biomed Engin. 2011;14:947–956.

10. Wang QD, Guo LX. Biomechanical role of osteoporosis in the vibration characteristics of human spine after lumbar interbody fusion. Int J Numer Method Biomed Eng. 2020;36:e3402.

11. Dipaola CP, Bible JE, Biswas D, et al.

Survey of spine surgeons on attitudes regarding osteoporosis and osteomalacia screening and treatment for fractures, fusion surgery, and pseudoarthrosis. Spine J. 2009;9:537–544.

12. Anderson PA, Kadri A, Hare KJ, et al.

Preoperative bone health assessment and optimization in spine surgery.

Neurosurg Focus. 2020;49:E2.

13. Yu W, Chan K, Yu F. Abnormal bone quality versus low bone mineral density in adolescent idiopathic scoliosis: a case-control study with in vivo high-resolution peripheral quantitative computed tomography. Spine J. 2013;13:1493–1499.

14. Hocaoglu E, Inci E, Vural M. Could computed tomography Hounsfield unit values of lumbar vertebrae detect osteoporosis?

Curr Med Imaging. 2021;17:988–995.

15. Wang H, Zou D, Sun Z, et al. Hounsfield unit for assessing vertebral bone quality and asymmetrical vertebral degeneration in degenerative lumbar scoliosis. Spine (Phila Pa 1976). 2020;45:1559–1566.

16. Paiva LC, Filardi S, Pinto-Neto AM, et al. Impact of degenerative radiographic abnormalities and vertebral fractures on spinal bone density of women with osteoporosis. Sao Paulo Med J. 2002;120:9–12.

17. Muraki S, Yamamoto S, Ishibashi H, et al. Impact of degenerative spinal diseases on bone mineral density of the lumbar spine in elderly women.

Osteoporos Int. 2004;15:724–728.

18. Tenne M, McGuigan F, Besjakov J, et al. Degenerative changes at the lumbar spine—implications for bone mineral density measurement in elderly women.

Osteoporos Int. 2013;24:1419–1428.

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19. Zou D, Li W, Deng C, et al. The use of CT Hounsfield unit values to identify the undiagnosed spinal osteoporosis in patients with lumbar degenerative diseases. Eur Spine J. 2019;28:1758–1766.

30. Kang T, Park SY, Hong SH, et al. Bone union after spinal fusion surgery using local bone in long-term bisphosphonate users: a prospective comparative study. Arch Osteoporos. 2019;14:74.

20. Ponnusamy KE, Iyer S, Gupta G, et al.

Instrumentation of the osteoporotic spine: biomechanical and clinical considerations. Spine J. 2011;11:54–63.

31. Nagahama K, Kanayama M, Togawa D, et al. Does alendronate disturb the healing process of posterior lumbar interbody fusion? A prospective randomized trial.

J Neurosurg Spine. 2011;14:500–507.

21. Liu Y, Dash A, Krez A, et al. Low volumetric bone density is a risk factor for early complications after spine fusion surgery.

Osteoporos Int. 2020;31:647–654.

22. Sarzier JS, Evans AJ, Cahill DW. Increased pedicle screw pullout strength with vertebroplasty augmentation in osteoporotic spines. J Neurosurg Spine. 2002;96:309–312.

23. Ergur I, Akcali O, Kiray A, et al. Neurovascular risks of sacral screws with bicortical purchase: an anatomical study. Eur Spine J. 2007;16:1519–1523.

24. Yildirim OS, Aksakal B, Hanyaloglu SC, et al. Hydroxyapatite dip coated and uncoated titanium poly-axial pedicle screws: an in vivo bovine model. Spine. 2006;31:E215–E220.

25. Nicoli Aldini N, Fini M, Giavaresi G, et al. Pedicular fixation in the osteoporotic spine: a pilot in vivo study on long‐term ovariectomized sheep. J Orthopaedic Res. 2002;20:1217–1224.

26. Feng S, Tian W, Sun Y, et al. Effect of robot-assisted surgery on lumbar pedicle screw internal fixation in patients with osteoporosis. World Neurosurg. 2019;125:e1057–e1062.

27. Anderson PA, Jeray KJ, Lane JM, et al.

Bone health optimization: beyond own the bone: AOA critical issues. J Bone Joint Surg Am. 2019;101:1413–1419.

28. Ensrud KE, Crandall CJ. Osteoporosis.

Ann Intern Med. 2017;167:Itc17–itc32.

29. Buerba RA, Sharma A, Ziino C, et al.

Bisphosphonate and teriparatide use in thoracolumbar spinal fusion: a systematic review and meta-analysis of comparative studies. Spine (Phila Pa 1976). 2018;43:E1014–e1023.

32. Liu WB, Zhao WT, Shen P, et al. The effects of bisphosphonates on osteoporotic patients after lumbar fusion: a meta-analysis. Drug Des Devel Ther. 2018;12:2233–2240.

33. Saag KG, Petersen J, Brandi ML, et al. Romosozumab or alendronate for fracture prevention in women with osteoporosis.

N Engl J Med. 2017;377:1417–1427.

34. Kaliya-Perumal AK, Lu ML, Luo CA, et al. Retrospective radiological outcome analysis following teriparatide use in elderly patients undergoing multilevel instrumented lumbar fusion surgery.

Medicine (Baltimore). 2017;96:e5996.

35. Ohtori S, Orita S, Yamauchi K, et al.

More than 6 months of teriparatide treatment was more effective for bone union than shorter treatment following lumbar posterolateral fusion surgery.

Asian Spine J. 2015;9:573–580.

36. Ebata S, Takahashi J, Hasegawa T, et al. Role of weekly teriparatide administration in osseous union enhancement within six months after posterior or transforaminal lumbar interbody fusion for osteoporosis-associated lumbar degenerative disorders: a multicenter, prospective randomized study. J Bone Joint Surg Am. 2017;99:365–372.

37. Seki S, Hirano N, Kawaguchi Y, et al.

Teriparatide versus low-dose bisphosphonates before and after surgery for adult spinal deformity in female Japanese patients with osteoporosis.

Eur Spine J. 2017;26:2121–2127.

38. Inoue G, Ueno M, Nakazawa T, et al. Teriparatide increases the insertional torque of pedicle screws during fusion surgery in patients with postmenopausal osteoporosis. J Neurosurg Spine. 2014;21:425–431.

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From The Core Institute in Mesa, Arizona.

PATIENT OUTCOMES

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Impact of Obesity on Complications in Lumbar Spine Surgery Obesity continues to be a major global public health problem, with a 2014 McKinsey Global Institute analysis estimating that more than 2 billion people worldwide are overweight or obese and the net estimated annual economic burden attributable to obesity is $2 trillion.1 The link between low back disorders and obesity has been well studied. 2,3 Multiple studies across patient populations have shown clear associations with both the severity and number of levels of lumbar disc degeneration. 4–6 Some debate ex ists as to whet her t his is t he result of increased biomechanical loading or a biochemical/metabolic phenomenon related to the inf luence of adipokines on disc health. 3 Patients with elevated body mass index have been show n to have a higher incidence of degenerative spondylolisthesis in large population health studies.7,8 Obesity is also associated with increased rates of epidural lipomatosis and is thought to be the most common cause of t his condit ion outside of exogenous steroid use. 9 In fact, studies have shown resolution of epidural lipomatosis w ith significant weight reduction, specifically in patients undergoing bariatric surgery.10 Given the prevalence of lumbar pathology in this population, many obese patients ultimately seek surgical treatment. Obesity often presents intraoperative challenges

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for t he su rgeon. Posit ion ing can be dif f icult, and caref ul attention must be paid to padd i ng super f ic i a l per ipher a l nerves to avoid injury.11 Obese patients undergoing traditionBrandon P. Hirsch, MD a l approaches to t he lumbar spine require larger incisions for exposure due to depth of the wound, leading to increased operative time and blood loss.12–15 T he ef fect of body mass i ndex (BMI) on complication rates during and after lumbar spine surgery has been well studied. 13,14,16,17 Surgical site infection is t he complication most consistently associated with elevated BMI. Lim et al performed a retrospective rev iew of the American Col lege of Su rgeons Nat iona l Su rg ica l Quality Improvement Program database including 3353 patients who under went single level lumbar fusion surgery between 2006 and 2011. They found a BMI >30 to be significantly associated with surgical site infection on multivariate logistical regression with an odds ratio (OR) of 1.6 (95% CI, 1.04–2.54).18 A meta-analysis of 24 studies performed in 2014 by Jiang et al reported similar findings, with an OR of 2.33 (95% CI, 1.94–2.79) for pat ients with BMI >30.16 Many theories exist on the mechanism by

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which obesity contributes to an increased risk of infection, including larger incision size, longer operative time, increased likelihood of fat necrosis, and higher overall wou nd tension. In a relat ively u n ique study, Mehta et al investigated whether the distribution of subcutaneous fat inf luences infect ion rates. 19 The aut hors respectively reviewed 465 patients who under went open posterolateral lumbar fusion and measured the thickness of the subcutaneous adipose layer on axial and midsagittal magnetic resonance images.

They found a statistically significant difference in the adipose layer thickness in patients who developed SSI compared to those who did not (30.2 vs 23.9 mm, p = 0.035). Patient BMI was actually not significantly different in patients who developed surgical site infections compared to those who did not (30.9 vs 28.9, p = 0.12). Interestingly, adipose layer thickness was not

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correlated with BMI. Gupta et al. further investigated this phenomenon by studying the Spine Adipose Index (SAI), the ratio of the distance from skin to fascia, and the distance from the skin to the L4 lamina on mid-sagittal T2 magnetic resonance images. 20 The aut hors evaluated 21 patients who under went posterior lumbar fusion complicated by deep infection and compared them to a propensity-matched cohort of 21 patients who did not develop a deep infection. The study demonstrated t hat patients who developed a deep infection had a significantly higher SAI than those who did not (0.48 vs. 0.41, p = 0.29). The authors also found that patient with an SAI >0.5 had twice the risk of deep infection when compared to those with an SAI ≤0.5. These studies suggest that the distribution of adipose tissue about the posterior lumbar spine may better predict infection risk than BMI alone.

Rates of durotomy appear to be higher in obese patients compared to non-obese patients. Burks et al analyzed nearly 300,000 patients from the PearlDiver database and included single, multilevel, and revision decompression as well as decompression and fusion cases. 21 The authors found that morbidly obese patients (BMI >40) had an OR of 1.54 (95% CI, 1.34–1.77, p < 0.0001) for durotomy compared to non-obese patients and that obese patients (BMI >30) had an OR of 1.33 (95% CI, 1.20–1.47, p < 0.0001) when compared to non-obese patients. A study of the European Spine Tango registry replicated these results showing an OR for durotomy of 2.12 (95% CI, 1.44–3.13, p <

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0.002) for patients with a BMI >35 and an OR of 1.40 (95% CI, 1.03-1.89, p < 0.002). 22 T h is i nc rease i n du rotomy rate l i kely relates to the difficulty in exposure and increased working distance to the spine encountered in obese patients.

I n genera l, a nter ior ret roper itonea l exposures to the lumbar spine are more c ha l leng i ng i n obese pat ient s. W h i le uncommon, injuries to vascular and/or visceral structures in the retroperitoneu m ca n be devastat ing complicat ions.

Surprisingly, several studies of anterior lu mba r i nterbod y f u sion (A L I F) have show n no sig nif icant dif ference in t he

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rates of cardiopulmonar y complications or of intraoperative bowel, ureteral, or vascular injur y. 23–25 One recent study by Sa faee et a l. did f ind a slig ht ly hig her overa l l complicat ion rate in obese patients undergoing ALIF. 26 However, this difference was the result of a higher rate of postoperat ive compl icat ions as opposed to intraoperative injury to adjacent structures. In this cohort of 268 patients, there was a higher rate of ileus (11.7% vs 7.2%, p = 0.02) and wound related complications (11.4% vs. 3.4%) in those patients with a BMI >30. Lumbar interbody fusion performed t hrough lateral and oblique

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approaches also does not appear to have sig nif icant ly increased risk of complication in the obese population. Rodgers et al investigated complication rates in 313 patients undergoing extreme lateral interbody fusion and found no significant difference in complication rate between obese and non-obese patients. 27 Xi et al analyzed 230 patients undergoing oblique lumbar interbody fusion and had similar findings. 28 While surgical time was longer in the obese cohort, there was no statistically significant increase in complications.

Over the past 2 decades, bariatric surgery has become a well-accepted, successful technique for weight loss. Patients who have a BMI >40 or who have a BMI >35 and complications related to obesit y can be considered as candidates for these procedures. 29 Patients tend to lose the majority of t heir weight during t he f irst 2 years after bariatric surgery. Typically, patients reduce their BMI by an average of 15 units and demonstrate improvements in diabetes and other metabolic syndrome–related comorbidities. 30 Jain et al evaluated several state inpatient databases to study the effects of bariatric surgery on complications following lumbar surgery. 31 Their analysis included 156,517 patients who underwent posterior lumbar fusion, of whom 590 had had prior bariatric surgery. These patients were compared to a severely obese (BMI >40) and a non-obese cohort (BMI <25).

Compared to the severely obese cohort, patients with prior bariatric surgery had lower rates of respirator y complications (OR 0.59, p = 0.019), urinary tract infections

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(OR 0.64, p = 0.031), acute renal failure (OR 0.39, p = 0.007), and infect ion (OR 0.65, p = 0.025). Patients who had undergone previous bariatric surgery still had significantly higher rates of infection (OR 2.70, p < 0.001), reoperation (OR 2.05, p = 0.045), and readmission (OR 1.89, p < 0.001) when compared to the non-obese cohort.

A recent meta-analysis of this study and three others found similar results, with a lower overall rate of complications after thoracolumbar surgery in patients with a history of bariatric procedures compared to obese patients who had no such history. 32 In light of these data, spine surgeons t reat i ng pat ient s w it h morbid obesit y should consider consultation with a bariatric surgeon prior to undertaking elective lumbar surgery.

The impact of obesit y on complication rates after lumbar surgery have been well studied. Rates of wound infection, durotomy, and ot her medica l complicat ions are clearly higher in t he obese pat ient population. Some studies suggest that the thickness of the posterior lumbar adipose layer is a better predictor of complications i n poster ior lu mba r su rger y t ha n BMI a lone. Interest i ng ly, t he ex ist i ng data on anterior and lateral lumbar surger y does not suggest a signif icant ly higher rate of serious intraoperative complications in obese patients. Bariatric surger y appears to have a significant impact on compl icat ion rates fol low i ng t horacolumbar surger y and should be strongly considered for obese pat ients pr ior to elective spine surger y. n

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References 1. McKinsey Global Institute. Overcoming obesity: an initial economic analysis. www.mckinsey.com/ mgi. Accessed February 4, 2022.

2. Katsevman GA, Daffner SD, Brandmeir NJ, et al. Complexities of spine surgery in obese patient populations: a narrative review. Spine J. 2020;20:501–511.

3. Samartzis D, Karppinen J, Cheung JPY, et al. Disk degeneration and low back pain: are they fat-related conditions?

Global Spine J. 2013;3:133–144.

4. Steelman T, Lewandowski L, Helgeson M, et al. Population-based risk factors for the development of degenerative disk disease.

Clin Spine Surg. 2018;31:E409–E412.

5. Lee SY, Kim W, Lee S-U, et al. Relationship between obesity and lumbar spine degeneration: a cross-sectional study from the Fifth Korean National Health and Nutrition Examination Survey, 2010-2012.

Metab Syndr Relat Disord. 2019;17:60–66.

6. Cannata F, Vadalà G, Ambrosio L, et al.

Intervertebral disc degeneration: a focus on obesity and type 2 diabetes. Diabetes Metab Res Rev. 2020;36:e3224.

7. Yoshihara H. Pathomechanisms and predisposing factors for degenerative lumbar spondylolisthesis: a narrative review.

JBJS Rev. 2020;8:e20.00068-e20.00068.

8. Jacobsen S, Sonne-Holm S, Rovsing H, et al. Degenerative lumbar spondylolisthesis: an epidemiological perspective. Spine. 2007;32:120–125.

9. Walker PB, Sark C, Brennan G, et al. Spinal epidural lipomatosis: a comprehensive review. Orthop Rev. 2021;13:25571.

10. Mosch MHW, de Jong LD, Hazebroek EJ, et al. Lumbar epidural lipomatosis is increased in patients with morbid obesity and subsequently decreases after bariatric surgery.

World Neurosurg. 2022;158:e495-e500. doi:10.1016/j.wneu.2021.11.007 11. Patel N, Bagan B, Vadera S, et al.

Obesity and spine surgery: relation to perioperative complications. J Neurosurg Spine. 2007;6:291–297.

12. Cao J, Kong L, Meng F, et al. Impact of obesity on lumbar spinal surgery outcomes. J Clin Neurosci. 2016;28:1–6.

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13. Bono OJ, Poorman GW, Foster N, et al. Body mass index predicts risk of complications in lumbar spine surgery based on surgical invasiveness.

Spine J. 2018;18:1204–1210.

24. Lucas F, Emery E, Dudoit T, et al.

Influence of Obesity on access-related complications during anterior lumbar spine interbody fusion. World Neurosurg. 2016;92:229–233.

14. Buerba RA, Fu MC, Gruskay JA, et al.

Obese Class III patients at significantly greater risk of multiple complications after lumbar surgery: an analysis of 10,387 patients in the ACS NSQIP database. Spine J. 2014;14:2008–2018.

25. Phan K, Rogers P, Rao PJ, et al. Influence of obesity on complications, clinical outcome, and subsidence after anterior lumbar interbody fusion (ALIF): prospective observational study.

World Neurosurg. 2017;107:334–341.

15. Peng CWB, Bendo JA, Goldstein JA, et al. Perioperative outcomes of anterior lumbar surgery in obese versus non-obese patients. Spine J. 2009;9:715–720.

26. Safaee MM, Tenorio A, Osorio JA, et al.

The impact of obesity on perioperative complications in patients undergoing anterior lumbar interbody fusion. J Neurosurg Spine. 2020;33:332–341.

16. Jiang J, Teng Y, Fan Z, et al. Does obesity affect the surgical outcome and complication rates of spinal surgery? A meta-analysis. Clin Orthop Relat Res. 2014;472:968–975.

27. Rodgers WB, Cox CS, Gerber EJ. Early complications of extreme lateral interbody fusion in the obese. J Spinal Disord Techniques. 2010;23:393–397.

17. Jackson KL, Devine JG. The effects of obesity on spine surgery: a systematic review of the literature.

Global Spine J. 2016;6:394–400.

28. Xi Z, Burch S, Mummaneni PV, et al.

The effect of obesity on perioperative morbidity in oblique lumbar interbody fusion. J Neurogurg Spine. 2020;1–8.

18. Lim S, Edelstein AI, Patel AA, et al.

Risk factors for postoperative infections after single-level lumbar fusion surgery. Spine. 2018;43:215–222.

29. Mechanick JI, Youdim A, Jones DB, et al. Clinical practice guidelines for the perioperative nutritional, metabolic, and nonsurgical support of the bariatric surgery patient—2013 update: Cosponsored by American Association of Clinical Endocrinologists, The Obesity Society, and American Society for Metabolic & Bariatric Surgery. Obesity (Silver Spring). 2013;21:S1–S27.

19. Mehta AI, Babu R, Karikari IO, et al.

The distribution of body mass as a significant risk factor for lumbar spinal fusion postoperative infections. Spine. 2012;37:1652–1656.

20. Gupta VK, Zhou Y, Manson JF, et al.

Radiographic spine adipose index: an independent risk factor for deep surgical site infection after posterior instrumented lumbar fusion. Spine J. 2021;21:1711–1717.

21. Burks CA, Werner BC, Yang S, et al.

Obesity is associated with an increased rate of incidental durotomy in lumbar spine surgery. Spine. 2015;40:500–504.

22. Herren C, Sobottke R, Mannion AF, et al; Spine Tango Contributors. Incidental durotomy in decompression for lumbar spinal stenosis: incidence, risk factors and effect on outcomes in the Spine Tango registry. Eur Spine J. 2017;26:2483–2495. doi:10.1007/s00586-017-5197-1

30. Svane M, Madsbad S. Bariatric surgery— effects on obesity and related co-morbidities. Curr Diabetes Rev. 2014;10:208–214.

31. Jain D, Berven SH, Carter J, et al.

Bariatric surgery before elective posterior lumbar fusion is associated with reduced medical complications and infection. Spine J. 2018;18:1526–1532.

32. Alhammoud A, Dalal S, Sheha ED, et al.

The impact of prior bariatric surgery on outcomes after spine surgery: a systematic review and meta-analysis. Global Spine J. 2022;21925682211072492.

23. Peng CWB, Bendo JA, Goldstein JA, et al. Perioperative outcomes of anterior lumbar surgery in obese versus non-obese patients. Spine J. 2009;9:715–720.

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From the Mike O’Callaghan Military Medical Center, Nellis Air Force Base, in Nevada (Dr Shenoy) and the Texas Back Institute in Plano, Texas (Drs Derman and Satin).

Bone Marrow Aspirate Concentrate and Spinal Fusion The goal of spinal fusion surgery is to eliminate motion between spina l seg ments t hrough arthrodesis. This is achieved, in part, through the incorporation of autologous and/or allograft Kartik Shenoy, MD bone, which may be further augmented by orthobiologics. Bone marrow aspirate (BMA) concentrate (BMAC) is an orthobiologic whose potential has more recently been explored and popularized.

Delivering BMAC in an osteoconductive scaffold theoretically Peter B. Derman, MD, MBA gives it the three ideal fusion substrate properties of osteoinduction, osteoconduction, and osteogenesis.

BMAC for spine surgery is most commonly obtained from within the vertebral bodies via a transpedicular approach or percutaAlexander Satin, MD neously from the iliac crests. The aspirate is processed in a centrifuge and then can be applied to the chosen scaffold and placed in the fusion bed. Typical scaffolds that have been studied include crushed cancellous allograft, tricalcium phosphate, collagen, and demineralized bone matrix.1,2 The concentration process affects the type and number of cells. 3 Of particular interest are the mesenchymal stem cells (MSCs),

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which are multipotent and thus can differentiate into a variety of cell lineages, including bone. While MSCs represent only a small fraction (0.01%) of the harvested cells,4,5 the concentration process allows the surgeon to increase the percentage of MSCs. However, the ideal number of MSCs has yet to be determined. Furthermore, the process cannot be uniformly applied to every patient as the cell number varies based on the harvest location, patient age, and bone quality.6,7 The clinical impact of concentrating bone marrow aspirate is not established. In a study

by Odri et al, BMAC produced six times the number of nucleated cells, 3.5 times the number of platelets, and 2.2 times the number of osteoprogenitor cells than BMA, yet there was no increased bone growth in posterolateral fusion. 8 This may be due to varying quantities of MSCs present in the concentrate. The gold standard for fusion still remains iliac crest autograft, and several lumbar fusion studies have compared iliac crest bone graft (ICBG) to BMA applied with different carriers.

Although the optimal concentration process has not been identified, clinical studies investigating BMA and BMAC have been performed. Interpretation of these studies is not only limited by the lack of standardization in the concentration process but also by variability in the study methodol-

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ogy. Surgical approach, technique, control groups, and scaffolds vary between studies and therefore cannot be directly compared.

In a preliminary prospective, comparative study by Kitchel, 25 patients underwent one-level lumbar interbody and posterolateral fusion. Mineralized collagen bone graft substitute with BMA was used on one side of the posterolateral fusion and ICBG on the contralateral side, resulting in fusions in 80% and 84%, respectively. 9 Similarly, in a study by Niu et al, 43 patients were split into two experimental groups: Group 1 had local laminectomy bone plus BMA, and Group 2 had calcium sulfate pellets soaked in BMA.10 The fusion material was placed into one posterolateral fusion gutter and was compared to ICBG as the control in the contralateral gutter. Group 1 had a fusion

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rate of 85.7% vs 90.5% for ICBG (p = 0.56) whereas Group 2 had a fusion rate of 45.5% vs 90.9% for ICBG (p = 0.0016). This study highlights the aforementioned potential differences in the scaffold for BMA, as the calcium sulfate pellets in this study were inferior to ICBG. In a study by Neen et al, 50 patients undergoing lumbar fusion using a Type 1 collagen/ hydroxyapatite matrix soaked in BMA were evaluated and compared to a historical control using ICBG.11 At 2 years, fusion had occurred in 84% of patients in the BMA group compared to 94% in the ICBG group which did not represent a statistically significant difference. Similarly, in a study by Johnson, 25 patients undergoing lumbar fusion were treated with allograft plus BMAC in one posterolateral gutter and autologous ICBG on the

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contralateral side. Computed tomographic evaluation of the fusion demonstrated no significant difference in fusion between BMAC and ICBG.12 Ajiboye et al also demonstrated successful fusion using demineralized bone matrix enriched with BMAC in two retrospective studies: In the first, of 80 patients undergoing lumbar fusion, 81.3% (65/80) demonstrated radiographic evidence of solid posterolateral and interbody fusion.13 In the second study, 31 patients older than 65 years undergoing lumbar fusion with minimum 1-year follow-up demonstrated a fusion rate of 83.9% (26/31).14 These two studies are limited by their retrospective design and lack of a control group.

Hart et al performed a prospective, blinded, randomized controlled study with 80 lumbar fusion patients—40 patients received allograft chips and 40 received allograft chips with BMAC.15 At 2-year follow-up, fusion was demonstrated in 40% of patients with allograft chips alone compared to 80% of patients with allograft chips with BMAC (p = 0.003). This study is limited as it does not compare BMAC to the gold standard of ICBG. There is presently insufficient evidence to recommend for or against the use of BMA/ BMAC for lumbar fusion. Further studies are needed to identify the optimal scaffold and stem cell concentration if the true utility of BMA is to be established and associated costs are to be justified. n

References 1. Bravo D, Jazrawi L, Cardone DA, et al. Orthobiologics: a comprehensive review of the current evidence and use in orthopedic subspecialties. Bull Hosp Jt Dis (2013). 2018;76:223-231.

2. Stephan SR, Kanim LE, Bae HW. Stem Cells and Spinal Fusion. Int J Spine Surg. 2021;15:94-103.

3. Schafer R, DeBaun MR, Fleck E, et al. Quantitation of progenitor cell populations and growth factors after bone marrow aspirate concentration. J Transl Med. 2019;17:115.

4. Logeart-Avramoglou D, Anagnostou F, Bizios R, et al. Engineering bone: challenges and obstacles.

J Cell Mol Med. 2005;9:72-84.

5. Gan Y, Dai K, Zhang P, et al. The clinical use of enriched bone marrow stem cells combined with porous beta-tricalcium phosphate in posterior spinal fusion.

Biomaterials. 2008;29:3973-3982.

6. Hustedt JW, Jegede KA, Badrinath R, et al. Optimal aspiration volume of vertebral bone marrow for use in spinal fusion. Spine J. 2013;13:1217-1222.

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7. Ajiboye RM, Eckardt MA, Hamamoto JT, et al. Does age influence the efficacy of demineralized bone matrix enriched with concentrated bone marrow aspirate in lumbar fusions?

Clin Spine Surg. 2018;31:E30-E35.

8. Odri GA, Hami A, Pomero V, et al. Development of a per-operative procedure for concentrated bone marrow adjunction in postero-lateral lumbar fusion: radiological, biological and clinical assessment. Eur Spine J. 2012;21:2665-2672.

9. Kitchel SH. A preliminary comparative study of radiographic results using mineralized collagen and bone marrow aspirate versus autologous bone in the same patients undergoing posterior lumbar interbody fusion with instrumented posterolateral lumbar fusion. Spine J. 2006;6:405-411; discussion 11-2.

10. Niu CC, Tsai TT, Fu TS, et al. A comparison of posterolateral lumbar fusion comparing autograft, autogenous laminectomy bone with bone marrow aspirate, and calcium sulphate with bone marrow aspirate: a prospective randomized study. Spine (Phila Pa 1976). 2009;34:2715-2719.

11. Neen D, Noyes D, Shaw M, et al. Healos and bone marrow aspirate used for lumbar spine fusion: a case controlled study comparing healos with autograft. Spine (Phila Pa 1976). 2006;31:E636-E640.

12. Johnson RG. Bone marrow concentrate with allograft equivalent to autograft in lumbar fusions. Spine (Phila Pa 1976). 2014;39:695-700.

13. Ajiboye RM, Eckardt MA, Hamamoto JT, et al. Outcomes of demineralized bone matrix enriched with concentrated bone marrow aspirate in lumbar fusion. Int J Spine Surg. 2016;10:35.

14. Ajiboye RM, Hamamoto JT, Eckardt MA, et al. Clinical and radiographic outcomes of concentrated bone marrow aspirate with allograft and demineralized bone matrix for posterolateral and interbody lumbar fusion in elderly patients.

Eur Spine J. 2015;24:2567-2572.

15. Hart R, Komzak M, Okal F, et al. Allograft alone versus allograft with bone marrow concentrate for the healing of the instrumented posterolateral lumbar fusion. Spine J. 2014;14:1318-1324.

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From UCI Health in Orange County, California.

BIOLOGICS

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Bone Graft and Bone Graft Substitute Options in Metastatic Spine Surgery Metastatic disease of the spine is the most common initial presentation of bony metastasis affecting about 70% of patients with bone metastasis (Figures 1 through 4).1 Surgical management of symptomatic metastatic spinal lesions is particularly challenging because the operating surgeon must weigh multiple factors including type of tumor, location of the lesion, surgical approach, extent of metastatic disease, prognosis, and type of reconstruction. Multiple bone grafts and bone graft substitutes have been described to assist with vertebral column reconstruction and fusion in the setting of spinal metastatic disease. Presently, there is no consensus on what type of graft to use for reconstruction efforts in the setting of metastatic disease of the spine. This article presents a list of bone graft options and their corresponding benefits and drawbacks.

sponse. Its primary disadvantage lies in its high morbidity in cases in which surgery is often already palliative in nature.

Loca l autog ra f t, ha r vested from spinous processes, lamina, Yu-Po Lee, MD pedicles, and vertebral bodies, is commonly used to promote fusion in spine surgery. However, due to concern for microscopic extensions of tumor in these tissues, local autograft is typically not utilized in the setting of metastatic spine disease due to the theoretical risk of spreading tumor.

Figure 1.

Sagittal image of T6 metastatic tumor in a 57-year-old man with metastatic lung cancer.

Autograft (Local and Vascularized) Iliac crest autograft has long been the gold standard and remains the benchmark for comparison for other graft and graft substitute options. Iliac crest autograft is the most commonly used, likely due to its ease of access, surgeon familiarity with harvesting, and availability of significant bone stock.

Autograft has the benefit of providing osteogenic, osteoinductive, and osteoconductive properties with a limited immunogenic re-

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Allograft In a poll among multiple spine surgeons, structural bony allograf t was t he most frequently used type of graft in the setting of metastatic spine disease. 2 Structural allografts have the benefit of being readily available and avoiding donor site morbidity while providing an osteoconductive scaffold for fusion. Additionally, structural allografts have a significantly higher compressive load to failure than iliac crest autograft or rib autograft. 3,4 They are commonly used as the bone graft of choice to fill structural and expandable cages. Disadvantages of allografts include the theoretical risk of infection and transmission of communicable disease such as hepatitis B, hepatitis C, or HIV.

Figure 2. Axial image of T6 with cord compression.

Figure 3. Atlantoposterior radiograph of T3-7 decompression and instrumentation.

Polymethylmethacrylate In general, polymethylmethacrylate (PMMA) has been indicated for anterior spine reconstruction in patients who need immediate support but have both a poor forward prognosis and short life expectancy. Benefits of PMMA include widespread availability, affordability, immediate support, and the lack of any donor site morbidity. Disadvantages include a risk of thermal tissue damage due to the exothermic reaction during the polymerization reaction as well as risk of dislodgement. Additionally, PMMA is frequently used in combination with a metallic structural cage.

Cages There are various prefabricated structural and expandable cages that have been developed for anterior column reconstruction.

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These cages are most commonly made from titanium or carbon-fiber reinforced polyetheretherketone (PEEK). The major benefit of these cages is that they can provide immediate stable fixation while also allowing for cancellous bone graft to be placed within the cage. Expandable cages have become increasingly popular for use in anterior column reconstruction due to their ease of insertion and their ability to apply axial load following appropriate placement between adjacent vertebrae.

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tial use of any graft/graft substitute in the management of metastatic spine disease. As additional research is needed in this field to clearly delineate strong indications for use of each graft option, surgeons must carefully consider the benefits and drawbacks of each graft option before curating the optimal approach for their patient with metastatic spinal disease in need of spinal reconstruction. n Figure 4. Lateral radiograph of T3-7 decompression and instrumentation.

No Graft In some cases, surgeons have utilized instrumentation to stabilize the spine without any use of bone graft. This has been referred to as a palliative posterior instrumentation.

In cases where life expectancy is less than 6 months, palliative posterior instrumentation may be an option.

Conclusion Symptomatic metastatic spine disease requiring surgical intervention provides a complex challenge for the spine surgeon. There are multiple graft types and graft substitutes that have been described for use in these challenging cases. However, currently, there is very weak evidence supporting preferen-

References 1. Jacobs WB, Perrin RG. Evaluation and treatment of spinal metastases: an overview. Neurosurgical Focus. 2001;11(6):1–11.

2. Altaf F, Weber M, Dea N, et al. Evidence-based review and survey

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of expert opinion of reconstruction of metastatic spine tumors.

Spine. 2016;41(1):S254–S261.

3. Wittenberg R, Moeller J, Shea M, White 3rd A, Hayes W. Compressive strength of autologous and allogenous bone grafts

for thoracolumbar and cervical spine fusion. Spine. 1990;15(10):1073–1078.

4. Finkelstein JA, Chapman JR, Mirza S. Anterior cortical allograft in thoracolumbar fractures. Journal of Spinal Disorders. 1999;12(5):424–429.

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