Antibiotic Duration After Debridement and Implant Retention for Early Postoperative Spinal Implant Infections: A Multicenter Cohort Study

BACKGROUND: Postoperative spinal implant infections (PSII) are a serious complication of instrumented spinal fusion. Although debridement with implant retention is standard for early infection, the optimal duration of antimicrobial therapy remains uncertain. METHODS: We conducted a multicenter retrospective cohort study across ten U.S. academic centers, including adults with early PSII (≤90 days after fusion surgery) from 2017 to 2021. We excluded patients who experienced treatment failure within 6 weeks of debridement. The primary outcome was treatment failure. Antibiotic therapy effect was analyzed as a time-varying exposure using adjusted Cox proportional hazards models. Secondary analyses included 12-week landmark and clone-censor-weighted models to compare durations ≤12 weeks versus >12 weeks. RESULTS: 116 patients out of 499 (23.2%) experienced treatment failure during a median follow-up of 3.2 years. Among patients who remain failure-free six weeks from debridement, being on antibiotics was not associated with treatment failure (adjusted hazard ratio [aHR] 0.71, 95% confidence interval [CI] 0.48-1.07; p = 0.10). In a 12-week landmark analysis limited to 359 patients who were not on indefinite suppressive antibiotic therapy, treatment durations >12 weeks did not significantly reduce the risk of failure (aHR 1.01, 95% CI 0.62-1.64; p = 0.99). Results were consistent in the clone-censor-weight sensitivity analysis (aHR 0.85, 95% CI 0.62-1.16; p = 0.30). CONCLUSIONS: Prolonged antibiotic therapy was not associated with improved outcomes in early PSII managed with debridement and implant retention. These results support shorter, individualized antibiotic courses in patients with adequate surgical source control.