The use of the psoas-to-lumbar vertebrae index and modified frailty index in predicting postoperative complications in degenerative spine surgery: can sarcopenia or frailty be underestimated?

Purpose: Degenerative spine disease (DSD) is increasingly prevalent due to aging populations, leading to higher surgical interventions and associated complications. This necessitates a comprehensive preoperative assessment, evaluating frailty through tools such as the modified Frailty Index 5 and modified Frailty Index 11 (mFI-5 and mFI-11). Despite the utility of mFI-5 and mFI-11 in predicting postoperative complications, these indices do not account for sarcopenia, a syndrome related to but distinct from frailty, which is associated with higher complication rates. This paper aims to retrospectively evaluate the influence of sarcopenia and frailty on postoperative adverse events in a cohort of patients who underwent posterior spine fusion for degenerative disease of the lumbar spine. Methods: A retrospective review of 286 patients who underwent posterior lumbar spine fusion for DSD was conducted. Frailty was measured using mFI-5 and mFI-11, while sarcopenia was assessed through Psoas to Lumbar Vertebral Index (PLVI) on magnetic resonance images. Primary outcomes included postoperative complications within 30 days. Statistical analysis involved univariate and multivariate models to determine the predictors of complications. Results: Higher frailty scores were significantly associated with increased postoperative complications (p <.05). However, sarcopenia showed no significant correlation with postoperative complications rates, except for pneumological complications (p =.031). Multivariate analysis confirmed frailty as a strong independent predictor of postoperative complications, while sarcopenia had limited impact. Conclusion: Frailty is a robust predictor of postoperative complications in DSD surgeries, while sarcopenia, appears to play a lesser role. The findings suggest that frailty alone provide a more comprehensive assessment of risk than sarcopenia.