Risk Stratification for Delirium After Hip Fracture Surgery: Comparing the Risk Analysis Index and mFI-5

Objectives: Postoperative delirium (POD) is a frequent complication following hip fracture surgery in older adults and contributes to increased morbidity and mortality. Frailty is a known predictor of adverse outcomes, but the optimal index for forecasting POD remains uncertain. This study compared the revised Risk Analysis Index (RAI-rev) and the five-item Modified Frailty Index (mFI-5) in predicting POD and short-term outcomes. Methods: Using the 2021 American College of Surgeons NSQIP database, 13,957 patients aged ≥ 75 years undergoing hip fracture surgery were identified. RAI-rev and mFI-5 scores were calculated, and frailty categories were analyzed against POD, 30-day mortality, extended length of stay (eLOS), non-home discharge (NHD), readmission, reoperation, and major complications. Multivariate logistic regression and receiver operating characteristic (ROC) analyses assessed associations and discriminative performance. Mediation analyses evaluated whether POD mediated frailty’s effects on adverse outcomes. Results: POD occurred in 3,200 patients (22.9%). Higher frailty categories were strongly associated with POD. RAI-rev demonstrated greater predictive accuracy (AUC 0.63) than mFI-5 (AUC 0.55; p < 0.001). POD independently increased the odds of 30-day mortality (OR 3.20), eLOS (OR 2.01), NHD (OR 2.23), and complications (OR 1.32). Mediation analyses showed POD partially mediated frailty’s impact on 30-day outcomes, with indirect effects for mortality (RIT 35.9%), eLOS (21.4%), readmission (15.1%), reoperation (24.5%), and complications (10.4%). Conclusion: The RAI-rev more accurately predicts POD and short-term adverse outcomes than mFI-5 in elderly hip fracture patients. POD significantly mediates frailty’s effect on surgical outcomes, underscoring the importance of frailty assessment and delirium prevention strategies.