Abstract
Abstract Background Open patellar fractures are uncommon but clinically challenging injuries, and evidence regarding factors associated with postoperative surgical site infection (SSI) after surgery remains limited. Methods This multicenter retrospective cohort study included consecutive patients with open patellar fractures who underwent surgery at two level I trauma centers between 1 November 2013 and 31 January 2023. The primary outcome was postoperative SSI, analyzed as a binary outcome and defined according to Centers for Disease Control and Prevention criteria. Demographic, clinical, and admission laboratory variables available before surgery were collected. Univariable logistic regression estimated associations between candidate variables and SSI. The primary multivariable logistic regression model was prespecified to include ASA ≥ III, multiple fractures, and admission glucose based on clinical relevance, routine preoperative availability, and the limited number of SSI events. Complete-case analysis was used. Sensitivity analyses adjusted for high-energy injury, time from injury to surgery, and admission period. Supplementary receiver operating characteristic and bootstrap calibration analyses were performed only as internal descriptive assessments, not to establish a clinical prediction tool. Results A total of 373 patients were included, of whom 48 developed postoperative SSI (12.9%). In the primary multivariable model fitted in 355 complete cases, ASA ≥ III (OR 3.68, 95% CI 1.91–7.09; P < 0.001), multiple fractures (OR 4.06, 95% CI 1.36–12.15; P = 0.012), and admission glucose (per 1 mmol/L increase: OR 1.16, 95% CI 1.02–1.32; P = 0.029) were associated with postoperative SSI. In sensitivity analyses, ASA ≥ III and multiple fractures remained stable, whereas the glucose association was weaker and should be interpreted cautiously. Conclusions Postoperative SSI remained clinically relevant after surgery for open patellar fractures. ASA ≥ III and multiple fractures were the most consistent preoperative factors associated with increased odds of SSI, whereas admission glucose may represent an early metabolic or physiological stress marker rather than an isolated determinant of infection risk. These findings may help identify patients who warrant closer perioperative surveillance, but they should be interpreted as evidence on associated factors rather than as a validated clinical prediction model.