Clinical and Inflammatory Determinants of Postoperative Delirium After Hip Fracture Surgery: A Retrospective Cohort Study of 962 Patients

Background and Objectives: Postoperative delirium (POD) is a frequent neuropsychiatric complication following hip fracture surgery in older adults and is associated with prolonged hospitalization, functional decline, and increased mortality. Systemic inflammation is thought to play a central role in its pathogenesis, and the C-reactive protein CRP-to-albumin ratio (CAR) has emerged as a promising inflammatory biomarker. This study aimed to investigate the association between the preoperative CAR and POD and to identify clinical and perioperative factors independently associated with POD. Materials and Methods: This retrospective cohort study included 962 consecutive patients who underwent surgery for hip fractures between January 2022 and December 2025. Patients with femoral neck fractures underwent hemiarthroplasty, whereas those with intertrochanteric fractures were treated with proximal femoral nailing. Cases of postoperative delirium were evaluated following psychiatric consultation requested based on clinical suspicion by the orthopedic team, nursing staff or the patient’s caregiver; the definitive diagnosis was made by consultant psychiatrists according to the DSM-5 diagnostic criteria. Demographic characteristics, perioperative variables, and preoperative laboratory parameters were analyzed. Univariable and prespecified multivariable logistic regression analyses were performed to identify factors independently associated with POD. Model discrimination and calibration were assessed using receiver operating characteristic analysis, bootstrap internal validation, and the Hosmer–Lemeshow goodness-of-fit test. Results: Postoperative delirium developed in 112 of 962 patients (11.6%). Patients who developed POD had significantly higher preoperative CAR values than those without POD (0.76 vs. 0.33, p < 0.001). In the multivariable analysis, male sex (OR 1.567, 95% CI 1.007–2.438; p = 0.046), hemiarthroplasty (OR 1.931, 95% CI 1.213–3.075; p = 0.006), perioperative blood transfusion (OR 1.870, 95% CI 1.178–2.971; p = 0.008), general anesthesia (OR 1.829, 95% CI 1.093–3.061; p = 0.021), higher ASA physical status classification (OR 2.154, 95% CI 1.346–3.446; p = 0.001), longer time from hospital admission to surgery (OR 1.250 per 24 h increase, 95% CI 1.103–1.417; p < 0.001), and a higher log2-transformed CAR (OR 1.184 per doubling, 95% CI 1.037–1.352; p = 0.013) were independently associated with POD. The final model demonstrated acceptable discrimination (AUC 0.764; optimism-corrected AUC 0.744) and satisfactory calibration (Hosmer–Lemeshow p = 0.242). Conclusions: A higher preoperative C-reactive protein-to-albumin ratio was independently associated with postoperative delirium after hip fracture surgery, even after adjustment for established demographic and perioperative risk factors. Male sex, hemiarthroplasty, general anesthesia, higher ASA physical status classification, perioperative blood transfusion, and delayed surgery were also independently associated with POD. These findings suggest that CAR may be a low-cost and readily available inflammatory biomarker that could be used to develop a preoperative risk classification system for the development of postoperative delirium. However, since routine standardized delirium screening was not performed during the study, cases of hypoactive delirium in particular may not have been adequately identified. For this reason, the findings should be interpreted with caution. Prospective, multicenter studies incorporating standardized delirium screening methods are needed to validate these results and determine the additional predictive value of CAR beyond established clinical risk factors.