Frailty is Mischaracterized in Spine Surgery Literature: A Systematic Review of Frailty Indices

Introduction: Frailty, marked by declines in weight, exhaustion, weakness, and physical activity, is a key predictor of postoperative outcomes in spine surgery. Previous frailty studies have primarily focused on a limited set of indices, such as the modified frailty index (mFI), neglecting other critical aspects of frailty. No comprehensive review has yet to characterize all frailty indices used in spine surgery. This systematic review addresses these gaps by assessing the prevalence of all frailty indices and their association with clinical outcomes in spine surgery. We hypothesize significant variation in frailty measures and propose that "frailty" is often misapplied in spine surgery literature.

Methods: This review adhered to PRISMA guidelines, with an extensive search of PubMed, Scopus, and Web of Science, identifying 34 relevant studies on frailty in elective spine surgery. Studies were included if they used a frailty index, were primary cohort studies, and focused on elective procedures. Data were collected on frailty indices, complications, and perioperative events. Outcomes like non-routine discharge, reoperation, readmission, and mortality were also recorded.

Results: The mFI was the most commonly used measure, with the mFI-11 employed in 38% of studies and the mFI-5 in 29%. The Hospital Frailty Risk Score appeared in 9%, while less frequently used indices included the Adult Spinal Deformity Frailty Index and FRAIL (6% each). Other indices, like the Fried Frailty Index and Canadian Study of Health and Aging Clinical Frailty Scale, were used in 3% of studies. Sarcopenia was the most assessed frailty-related term (12%). Frailty was treated as an independent variable in 94% of studies, and complications were reported in 85%. Medical and surgical complications were seen in 67% and 62% of studies, respectively, while non-routine discharge occurred in 47%, readmissions in 29%, and mortality in 26%.

Conclusion : While mFI is the most frequently used frailty measure in spine surgery literature, its comorbidity-based approach limits its ability to capture the multidimensional decline in physiological reserves that defines frailty. Future research should prioritize the use of more comprehensive frailty indices, such as the Fried Frailty Index and FRAIL scale, which incorporate functional assessments to better stratify patient risk for spine surgery.