Preoperative Copper-to-Zinc Ratio and Postoperative Delirium After Hip Fracture Surgery: A Propensity Score-matched Cohort Study

Background: Postoperative delirium (POD) is frequent after hip fracture surgery, yet objective biomarkers that improve risk stratification beyond age, dementia, and frailty are limited. The serum copper-to-zinc (Cu/Zn) ratio reflects combined inflammatory and nutritional vulnerability, but its association with POD after hip fracture surgery is uncertain. Materials and Methods: We performed a single-center retrospective cohort study of 420 consecutive patients aged ≥65 years undergoing surgery for low-energy hip fracture. The preoperative Cu/Zn ratio, measured within 48 hours before surgery, was the exposure (prespecified high ratio >2.0). The primary outcome was POD within 7 postoperative days or before discharge. Secondary outcomes were numeric rating scale pain scores, 24-hour morphine-equivalent opioid consumption, and hospital length of stay (LOS). Results: In the matched cohort, POD occurred in 23/124 (18.5%) patients with low Cu/Zn ratios and 56/124 (45.2%) with high ratios (odds ratio [OR], 3.62; 95% confidence interval [CI], 2.04–6.42; P < .001). In the full cohort, high Cu/Zn remained associated with POD after adjustment (adjusted OR, 3.35; 95% CI, 2.00–5.59; P < .001). After matching, early postoperative pain and 24-hour opioid consumption were not significantly different, whereas LOS was modestly longer in the high Cu/Zn group (mean difference = 1.0 day). Conclusion: A high preoperative Cu/Zn ratio (>2.0) was independently associated with increased odds of POD and slightly longer hospital LOS after hip fracture surgery in older adults, with minimal impact on early pain-related outcomes.