Prognostic Performance of mFI-5 and mFI-11 Frailty Indices in Elective Spine Surgery: A Systematic Review and Meta-Analysis

OBJECTIVE: Frailty is a known predictor of poor outcomes following spine surgery. While both mFI-11 and mFI-5 are used to assess frailty, no pooled analysis has independently evaluated their prognostic performance across multiple outcomes. This study examines how mFI-11 and mFI-5 stratify frailty and how consistently each index predicts postoperative outcomes in elective spine surgery. METHODS: A systematic literature search was conducted using PubMed, Scopus, and Web of Science databases to identify cohort studies reporting associations of mFI-11 or mFI-5 with postoperative outcomes in elective spine surgery. Meta-analyses using random-effects models calculated pooled odds ratios (ORs) and P-values for key outcomes including any adverse event, medical complication, surgical complication, mortality, reoperation, and non-routine discharge. RESULTS: A total of 22 studies were included in the meta-analysis. mFI-11 was associated with increased odds of medical complications (OR 2.09, P = 0.0014) and surgical complications (OR 2.03, P = 0.0390), but not reoperation (OR 0.95, P = 0.8822). These findings were inconsistently significant across sub-analyses comparing higher mFI-11 scores to mFI-11 = 0. mFI-5 predicted a broader range of outcomes, including any complication (OR 1.7, P < 0.0001), non-routine discharge (OR 3.29, P < 0.0001), and mortality (OR 2.29, P = 0.0133). These significant results persisted across sub-analyses comparing higher mFI-5 scores to mFI-5 = 0. mFI-5 showed more consistent associations with postoperative outcomes than mFI-11. CONCLUSIONS: MFI-5 demonstrates greater consistency in predicting adverse outcomes in elective spine surgery than mFI-11. mFI-5 may serve as a practical tool for frailty stratification in surgical patients. Further studies are needed to validate these results and optimize frailty assessment in spine surgery.