Association Between Preoperative Malnutrition Assessed by the Controlling Nutritional Status (CONUT) Score and Postoperative Delirium in Elderly Patients with Hip Fractures: A Retrospective Cohort Study.

BACKGROUND: Postoperative delirium (POD) is associated with impaired cognitive function, increased morbidity, and elevated mortality. Although preoperative nutritional impairment has been associated with POD, the specific association between the objective, laboratory-based Controlling Nutritional Status (CONUT) score and POD, including its dose-response pattern, remains insufficiently characterized in elderly patients with hip fractures. This study aimed to evaluate the association between preoperative CONUT score and POD in this population. METHODS: This retrospective cohort study included patients aged ≥ 65 years who underwent surgery for hip fracture at a university-affiliated hospital between January 2020 and December 2024. Preoperative nutritional status was assessed using the CONUT score, and POD was identified retrospectively from medical records with reference to the Confusion Assessment Method. Restricted cubic spline analysis was used to characterize the dose-response association between continuous CONUT score and POD, and multivariable logistic regression was performed as the primary adjusted analysis. Exploratory cutoff-based analyses included propensity score matching, conditional logistic regression, subgroup analyses, and sensitivity analyses. RESULTS: A total of 2030 patients were included, of whom 337 (16.6%) developed POD. Restricted cubic spline analysis showed a positive dose-response association between increasing CONUT score and POD. In the primary multivariable analysis, each 1-point increase in CONUT score was associated with higher odds of POD (adjusted OR, 1.08; 95% confidence interval [CI], 1.02-1.14; P = 0.009). In the exploratory categorical analysis, patients with a CONUT score ≥ 5 had higher odds of POD than those with lower scores after propensity score matching (OR, 1.63; 95% CI, 1.20-2.21; P = 0.002). No significant effect modification was observed across predefined subgroups, and sensitivity analyses yielded consistent findings. CONCLUSION: Higher preoperative CONUT scores were associated with greater odds of POD in elderly patients with hip fractures. The CONUT score may serve as a practical adjunctive marker for identifying patients with greater perioperative vulnerability to POD.