LAUSR

STUDY DESIGN Retrospective Cohort. OBJECTIVES To validate the most concise risk stratification system to date, the 5-item modified frailty index (mFI-5), and compare its effectiveness with the established 11-item modified frailty index (mFI-11) in the elderly population undergoing posterior instrumented spine surgery. METHODS A single centre retrospective review of posterior instrumented spine surgeries in patients aged 65 years and older was conducted. The primary outcome was rate of post-operative major complications (Clavien-Dindo Classification ≥ 4). Secondary outcome measures included rate of all complications, 6-month mortality and surgical site infection. Multi-variate analysis was performed and adjusted receiver operating characteristic curves were generated and compared by DeLong's test. The indices were correlated with Spearman's rho. RESULTS 272 cases were identified. The risk of major complications was independently associated with both the mFI-5 (OR 1.89, 95% CI 1.01-3.55, P = .047) and mFI-11 (OR 3.73, 95% CI 1.90-7.30, P = .000). Both the mFI-5 and mFI-11 were statistically significant predictors of risk of all complications (P = .007 and P = .003), surgical site infection (P = .011 and P = .003) and 6-month mortality (P = .031 and P = .000). Adjusted ROC curves determined statistically similar c-statistics for major complications (.68 vs .68, P = .64), all complications (.66 vs .64, P = .10), surgical site infection (.75 vs .75, P = .76) and 6-month mortality (.83 vs .81, P = .21). The 2 indices correlated very well with a Spearman's rho of .944. CONCLUSIONS The mFI-5 and mFI-11 are equally effective predictors of postoperative morbidity and mortality in this population. The brevity of the mFI-5 is advantageous in facilitating its daily clinical use.