A comprehensive analysis of the triad of frailty, aging, and obesity in spine surgery: the risk analysis index predicted 30–day mortality with superior discrimination

[Display omitted] The United States has experienced substantial shifts in its population dynamics due to an aging population and increasing obesity rates. Nonetheless, there is limited data about the interplay between the triad of frailty, aging, and obesity. To investigate discriminative thresholds and independent associations of the Risk Analysis Index (RAI), Modified Frailty Index–5 (mFI–5), and greater patient age. An observational retrospective cohort study. We analyzed 49,754 spine surgery patients from the American College of Surgeons National Surgical Quality Improvement Program database from 2012 to 2020. A total of 30–day postoperative mortality. Using receiver operating characteristic (ROC) and multivariable (odds ratios [OR] and 95% confidence intervals [CI]) analyses, we compared the discriminative thresholds and independent associations of RAI, mFI–5, and greater patient age in elderly obese patients who underwent spine surgery. There were 49,754 spine surgery patients, with a median age of 71 years (IQR: 68–75), largely white (82.6%) and male (51.9%). The ROC analysis for 30–day postoperative mortality demonstrated superior discrimination for RAI (C–statistic 0.779, 95%CI 0.54–0.805) compared to mFI–5 (C–statistic 0.623, 95% CI 0.594–0.651) and greater patient age (C–statistic 0.627, 95% CI 0.598–0.656). Multivariable analyses revealed a dose–dependent association and a larger effect magnitude for RAI: frail patients OR: 19.52 (95% CI 18.29–20.82) and very frail patients OR: 65.81 (95% CI 62.32–69.50). A similar trend was observed in the interaction evaluating RAI–age–obesity (p