Intrawound antibiotic use and postoperative surgical site infection in instrumented spine surgery: a statewide registry analysis of 24,015 patients from the Spine Care Outcomes Assessment Program

OBJECTIVE The aim of this study was to evaluate the association between intrawound antibiotic use and postoperative surgical site infection (SSI) following instrumented spine surgery in a large statewide registry. METHODS The authors performed a retrospective cohort study using prospectively collected data from the Spine Care Outcomes Assessment Program (COAP) in Washington State. Adult patients undergoing instrumented cervical or lumbar spine surgery between July 2011 and January 2024 were included. Patients were stratified by intrawound antibiotic use at wound closure. The primary outcome was postoperative SSI. Univariate robust Poisson regression was used to estimate risk ratios (RRs). Multivariable robust Poisson regression was performed to identify independent predictors of SSI while adjusting for demographic, clinical, and operative variables. RESULTS Among 24,015 patients, 256 (1.1%) developed SSI. On univariate analysis, obesity (BMI ≥ 40), open surgical approach, lumbar procedures, diabetes, higher American Society of Anesthesiologists class, greater comorbidity burden, and higher Enhanced Recovery After Surgery score were associated with increased SSI risk, whereas higher serum albumin, minimally invasive surgery, and cervical procedures were associated with reduced risk. In multivariable analysis, open surgical approach (RR 4.94, 95% CI 2.26–10.79) and lumbar procedures (RR 2.33, 95% CI 1.45–3.75) were independently associated with increased SSI risk. Higher serum albumin was independently protective (RR 0.35, 95% CI 0.24–0.51). Intrawound antibiotic use was not associated with SSI on univariate analysis (RR 0.90, 95% CI 0.70–1.16) and was not an independent predictor after adjustment. CONCLUSIONS In this large statewide cohort of instrumented spine procedures, surgical approach, anatomical region, and preoperative nutritional status were the strongest independent predictors of SSI. Intrawound antibiotic use was not associated with reduced infection risk. These findings underscore the multifactorial nature of postoperative infection risk in spine surgery.