Comparison of the Risk Analysis Index and the modified 5-factor frailty index in predicting 30-day morbidity and mortality after spine surgery

OBJECTIVE Frailty’s role in preoperative risk assessment in spine surgery has increased in association with the increasing size of the aging population. However, previous frailty assessment tools have significant limitations. The aim of this study was to compare the predictive ability of the Risk Analysis Index (RAI) with the 5-factor modified frailty index (mFI-5) for postoperative spine surgery morbidity and mortality. METHODS Data were collected from the American College of Surgeons National Surgical Quality Improvement Program database for adults > 18 years who underwent spine surgery between 2015 and 2019. Multivariate modeling and receiver operating characteristic curve analysis, including area under the curve/C-statistic calculations, were performed to evaluate the comparative discriminative ability of RAI and mFI-5 on postoperative outcomes. RESULTS In a cohort of 292,225 spine surgery patients, multivariate modeling showed that increasing RAI scores, and not increasing mFI-5 scores, were independent predictors of increased postoperative mortality for the trauma, tumor, and infection subcohorts. In the overall spine cohort, both increasing RAI and increasing mFI-5 scores were associated with increased mortality, but C-statistics indicated that the RAI (C-statistic 0.802 95% CI 0.800–0.803, p < 0.0001, DeLong test) had superior discrimination compared with the mFI-5 (C-statistic 0.677 95% CI 0.675–0.679, p < 0.0001, DeLong test). In subgroup analyses, the RAI had superior discriminative ability to mFI-5 for mortality in the trauma and infection groups (p < 0.001 and p = 0.039, respectively). CONCLUSIONS The RAI demonstrates superior discrimination to the mFI-5 for predicting postoperative mortality and morbidity after spine surgery and the RAI maintains conceptual fidelity to the frailty phenotype. Patients with high RAI scores may benefit from knowing the possibility of increased surgical risk with potential spine surgery.