Development and internal validation of a nomogram for predicting postoperative pneumonia within 7 days after hip fracture surgery in older adults: a retrospective cohort study

Background Postoperative pneumonia is one of the most common and serious complications following hip fracture surgery in older adults, substantially increasing morbidity, length of hospital stay, and mortality. Early identification of patients at high risk for postoperative pneumonia is essential for targeted preventive strategies. This study aimed to develop and internally validate a clinically applicable nomogram to predict the risk of pneumonia within 7 days after hip fracture surgery in elderly patients. Methods We conducted a single-center retrospective cohort study including consecutive patients aged ≥ 65 years who underwent surgical treatment for femoral neck or intertrochanteric fractures between January 2021 and December 2024. Patients with preoperative pneumonia were excluded. The primary outcome was postoperative pneumonia occurring within 7 days after surgery. Candidate predictors were prespecified based on clinical relevance and previous literature. A multivariable logistic regression model was developed, and internal validation was performed using bootstrap resampling (1000 iterations). Model performance was assessed using the concordance index (C-index), receiver operating characteristic (ROC) curve, calibration plots, and decision curve analysis (DCA). A nomogram was constructed to facilitate individualized risk prediction. Results A total of 760 patients were included in the final analysis, among whom 65 (8.6%) developed postoperative pneumonia within 7 days. Multivariable logistic regression identified age (OR 1.181, 95% CI 1.103–1.265, P  < 0.001), chronic pulmonary disease (OR 2.585, 95% CI 1.266–5.276, P  = 0.009), dementia (OR 3.138, 95% CI 1.445–6.812, P  = 0.004), minimum oxygen saturation within 24 hours (OR 0.795, 95% CI 0.694–0.910, P  < 0.001), serum albumin (OR 0.656, 95% CI 0.586–0.733, P  < 0.001), and log-transformed C-reactive protein (OR 4.729, 95% CI 2.308–9.686, P  < 0.001) as independent predictors. The nomogram demonstrated good discriminative ability, with an optimism-corrected C-index of 0.949. Calibration curves showed good agreement between predicted and observed risks. Decision curve analysis indicated that the nomogram provided a positive net clinical benefit across a wide range of threshold probabilities. Conclusions We developed and internally validated a nomogram for predicting postoperative pneumonia within 7 days after hip fracture surgery in older adults. This tool may assist clinicians in early risk stratification and implementation of targeted preventive interventions.