Posterior Instrumented Spinal Surgery Outcomes in the Elderly: A Comparison of the 5-Item and 11-Item Modified Frailty Indices.

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, = .047) and mFI-11 (OR 3.73, 95% CI 1.90-7.30, = .000). Both the mFI-5 and mFI-11 were statistically significant predictors of risk of all complications ( = .007 and = .003), surgical site infection ( = .011 and = .003) and 6-month mortality ( = .031 and = .000). Adjusted ROC curves determined statistically similar c-statistics for major complications (.68 vs .68, = .64), all complications (.66 vs .64, = .10), surgical site infection (.75 vs .75, = .76) and 6-month mortality (.83 vs .81, = .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.