Risk Factors for Positive Cultures in Presumed Aseptic Revision Spine Surgery

Study Design. Retrospective case-control study. Objective. To report culturing patterns and results in the setting of presumed aseptic revision spinal surgery. Summary of Background Data. The indications for obtaining cultures in revision spinal surgery remain unclear in the absence of a definitive diagnosis of infection. Culture results and risk factors for having positive cultures in this setting have not been previously studied. Methods. We retrospectively reviewed 595 consecutive revision spine surgeries performed by four senior spine surgeons between 2008 and 2013. Preoperative workup revealed the diagnosis of infection in 17 cases which were excluded from review. The remaining 578 presumed aseptic cases were included. Univariate and multivariate analyses were performed to identify variables associated with obtaining cultures and risk factors for positive cultures. Results. Cultures were obtained in 112 (19.4%) cases and were positive in 40.2%. Pseudarthrosis was the most common revision diagnosis when cultures were obtained (49.1%) and Propionibacterium acnes was the most common organism isolated from positive cultures (48.8%). Regarding culture results, multivariate analysis demonstrated that male sex (odds ratio [ OR] 1/4 3.4) and pseudarthrosis (OR = 4.1) were significantly associated with having positive cultures while fusion procedures (OR = 0.3) were negatively correlated, with area under the curve (AUC) 0.71. Conclusion. Unexpected positive cultures occurred commonly and P. acnes was the predominant isolated organism. Male sex, pseudarthrosis, and non-fusion cases predicted positive cultures. Considering these results, we recommend cultures be obtained in revision cases for pseudarthrosis, even in the setting of negative infectious work-up preoperatively.