A Novel Composite Frailty Index for Predicting Postoperative Risk Following Femoral Neck Fracture Repair in Men Aged 18–65: Development and Validation

Purpose: Accurate preoperative risk stratification remains limited for younger adult men undergoing femoral neck fracture repair, particularly given the limitations of existing indices that assess physiologic, frailty, or acute condition domains in isolation. We aimed to develop and validate the Combined ASA–RAI–Preoperative Acute Severe Condition (CARP) score as a novel composite risk model to predict short-term postoperative outcomes in this population. Methods: Using ACS-NSQIP data from 2015–2021, we conducted a retrospective cohort study of 5,961 male patients aged 18–65 who underwent femoral neck fracture surgery. Risk was assessed using the Risk Analysis Index (RAI), modified Frailty Index-5 (mFI-5), Geriatric Nutritional Risk Index (GNRI), ASA classification, and Preoperative Acute Severe Condition (PACS) score. Multivariable logistic regression identified predictors of 30-day outcomes. The CARP score was derived from model coefficients and evaluated against individual indices using AUROC and bootstrap validation. Results: Thirty-day major complications occurred in 4.8% of patients, with mortality at 2.2% and non-home discharge at 45.8%. Multivariable analysis identified PACS (OR 1.79, p<0.001), ASA class (OR 1.44, p=0.011), and RAI (OR 1.04, p=0.009) as independent predictors of major complications. CARP significantly outperformed mFI-5, RAI, PACS, and ASA in predicting adverse outcomes (AUROC 0.713 vs. 0.623–0.661, all p<0.01). Conclusion: The CARP score provides superior risk stratification compared to traditional indices in younger male patients undergoing femoral neck fracture repair. Its integration of frailty, physiological, and acute condition factors enables more precise prediction of perioperative complications and discharge outcomes, supporting personalized surgical planning.