The characterization of frailty in spine surgery: a systematic review of frailty indices

Purpose: Frailty is a key predictor of postoperative outcomes in spine surgery, yet its definition varies widely across studies. Most research relies on comorbidity-based indices like the modified frailty index (mFI), overlooking the multidimensional nature of frailty. The purpose of this systematic review is to identify the frailty indices in use, assess their prevalence, and evaluate their association with clinical outcomes. Methods: Following PRISMA guidelines, a comprehensive search of PubMed, Scopus, and Web of Science identified 34 relevant cohort studies on elective spine procedures using frailty indices. Data were collected on frailty measures, complications, and perioperative events, including non-routine discharge, reoperation, readmission, and mortality. Results: The mFI was the most used measure, with mFI-11 (38%) and mFI-5 (29%) being the most common. The Hospital Frailty Risk Score appeared in 9%, while the Adult Spinal Deformity Frailty Index and FRAIL were used in 6%. The Fried Frailty Index and Canadian Study of Health and Aging Clinical Frailty Scale were less frequent (3%). Sarcopenia was assessed in 12% of studies. Frailty was an independent variable in 94%, and complications were reported in 85%. Medical and surgical complications occurred in 67% and 62%, respectively; non-routine discharge in 47%, readmission in 29%, and mortality in 26%. Conclusion: While mFI-5 and mFI-11 are commonly used, their comorbidity-based approach limits frailty assessment. Future research should prioritize multidimensional indices like the Fried Frailty Index and FRAIL scale, which incorporate functional measures for better risk stratification in spine surgery.