Acta Orthopaedica 2018; 89 (6): 603–609 607 Table 3. Multivariable logistic regressions for preoperative risk factors for MI within 90 days of surgery Variable Model 1 OR (95% CI) p-value Model 2 OR (95% CI) p-value Model 3 OR (95% CI) p-value Model 4 OR (95% CI) p-value Age < 0.001 < 0.001 < 0.001 < 0.001 < 50 NA NA NA NA 50–60 0.13 (0.02–1.0) 0.05 0.12 (0.02–0.90) 0.04 0.13 (0.02–1.0) 0.05 0.14 (0.02–1.1) 0.06 61–65 0.14 (0.02–1.1) 0.06 0.13 (0.02–1.0) 0.05 0.14 (0.02–1.0) 0.06 0.14 (0.02–1.1) 0.06 66–70 1 Ref 1 Ref 1 Ref 1 Ref 71–75 0.78 (0.31–2.0) 0.6 0.81 (0.32–2.0) 0.6 0.81 (0.32–2.0) 0.6 0.78 (0.31–1.9) 0.6 76–80 1.2 (0.51–2.9) 0.7 1.3 (0.56–3.14) 0.5 1.3 (0.57–3.2) 0.5 1.2 (0.52–2.9) 0.6 81–85 2.2 (0.89–5.4) 0.09 2.5 (1.0–6.0) 0.05 2.5 (1.0–6.2) 0.04 2.3 (0.9–5.5) 0.07 > 85 5.0 (1.9–12.9) 0.001 5.9 (2.4–15.1) < 0.001 6.3 (2.5–16.0) < 0.001 5.5 (2.2–12.1) < 0.001 Male sex 2.3 (1.3–4.3) 0.005 2.5 (1.4–4.5) 0.002 2.5 (1.4–4.5) 0.002 2.3 (1.3–4.1) 0.006 Diabetes 0.003 0.002 0.006 0.006 Insulin-dependent 4.4 (1.7–11.5) 0.002 5.0 (1.9–12.9) 0.001 3.9 (1.5–10.2) 0.006 3.9 (1.5–10.1) 0.006 Non-Insulin-dependent 0.42 (0.10–1.7) 0.2 0.47 (0.11–1.9) 0.3 0.38 (0.09–1.6) 0.2 0.36 (0.09–1.5) 0.2 Cardiovascular disease 3.0 (1.7–5.4) < 0.001 – – – – 2.7 (1.4–4.9) 0.001 Anemia a 1.2 (0.62–2.2) 0.6 Hypercholesterolemia – – – – 2.2 (1.2–4.0) 0.01 1.8 (0.99–3.4) 0.06 Anticoagulant treatment b – – 1.7 (0.73–3.7) 0.2 – – – – For footnotes, see Table 2. days, 90-day readmission rate was 6.6% (CI 6.0–7.4%) and 30-day incidence of MI was 0.10% (CI 0.04–0.23%) and was similar compared with the entire cohort. When comparing the 2 subgroups, 30-day MI incidence was similar (p = 0.7). However, patients with multiple procedures had a lower proportion of LOS ≥ 5 days (p < 0.001) and readmissions within 90 days (p = 0.003). Discussion In this prospective cohort study on 24,862 consecutive unselected primary elective fast-track THA and TKAs we found a 30-day MI incidence of 0.12% with increased risk for age > 85, IDDM, cardiovascular disease, and hypercholesterolemia in multivariable analysis. Furthermore, perioperative anemia and intraoperative hypotension was frequent among patients with postoperative MI. Our MI incidence is lower than reported in studies on administrative databases reporting 30-day incidences of 0.25%– 0.9% (Singh et al. 2011, Lalmohamed et al. 2012, Belmont Jr et al. 2014, Pedersen et al. 2014, Thornqvist et al. 2014). A recent comparison of administrative data and the clinical NSQIP registry have shown a low specificity of ≈ 81% for both sources of data compared with chart review (Etzioni et al. 2018), potentially underestimating the true incidence. Nonetheless, we found an in-hospital incidence rate of only 0.05%, considerably lower than previous data from such administrative and clinical registries with comparable cohorts but variable follow-up (Pulido et al. 2008, Malviya et al. 2011, Pedersen et al. 2014, Bemenderfer et al. 2017, Urban et al. 2017). Although, the numbers we found are comparable to previous fast-track THA and TKA studies (Malviya et al. 2011, Khan et al. 2014), previous studies lack detailed information on potential risk factors and events preceding MI. Median time to MI ≤ 30 days was 4 (2–8) days and 11 (3–56) days for MI ≤ 90 days with increased cumulated incidence within the first 3 weeks. This is in concordance with previous data from the few THA- and TKA-specific studies, which report increased risk of MI within the first 2 weeks and up to 6 weeks for THA (Lalmohamed et al. 2012, Belmont Jr et al. 2014). When evaluating preoperative risk factors for MI ≤ 90 days, age > 85 years was found to be the most important risk factor for MI with OR of about 6. That increasing age is a risk factor for MI has been demonstrated in several studies (Belmont Jr et al. 2014, Menendez et al. 2015, Urban et al. 2017); however, we were unable to demonstrate any significant association between age and MI until age > 85 years. That IDDM, cardiovascular disease, and hypercholesterolemia were found to be associated with MI in our study is unsurprising as these are well-known risk factors (Mantilla et al. 2011, Belmont Jr et al. 2014, Menendez et al. 2015). However, that male sex was clearly associated with 90- but not 30-day MI has to our knowledge not been shown previously. A previous investigation on early thromboembolic events including some of the same patients as our study suggested postoperative anemia as a possible pathogenic mechanism (Jørgensen et al. 2016a). Preoperative anemia is well known to dispose to postoperative anemia and blood transfusions (Goodnough et al. 2011), including in fast-track THA and TKA (Jans et al. 2018). In our study, preoperative anemia was not associated with MI. However, 12 of the 48 patients with MI had preoperative and 27 had postoperative anemia. Although conflicting results on anemia as a risk factor for postoperative MI have been discussed previously (Mantilla et al. 2011, Menendez et al.

Acta Orthopaedica Vol. 89 Issue 6, December 2018