Does intrawound vancomycin powder reduce surgical site infection after posterior instrumented spinal surgery? A propensity score-matched analysis

Recent reports suggested that placing vancomycin powder into surgical wounds before closure can prevent surgical site infections (SSIs) in spinal surgery. The present study aimed to evaluate if intrawound vancomycin powder could prevent SSIs after spinal surgery with posterior instrumentation. This is a multicenter retrospective cohort study using propensity score matching. We reviewed all spinal surgeries performed with posterior instrumentation from July 2012 to December 2014 at 11 institutions among patients aged ≥15 years. The incidence of SSIs was compared between patients who received intrawound vancomycin powder (vancomycin group) and those who did not (control group). Demographic and operative data and microbiological findings of SSI cases were analyzed. After a preliminary whole-cohort analysis, we performed one-to-one propensity score matching to adjust for the differences between the two groups and then compared the incidence of SSIs between the matched groups. No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript. A total of 2,859 patients were included in the study. In the vancomycin and control groups (n=694 and n=2165, respectively), 12 (1.73%) and 21 (0.97%) patients developed SSIs, respectively, but the difference was not statistically significant (p=.10, chi-square test). During the propensity score-matched analysis, 507 pairs were analyzed. No significant change in the rate of SSIs was seen between the vancomycin and control groups (8 SSIs [1.58%] vs. 9 SSIs [1.78%], respectively; p=.81, chi-square test). Microbiological analysis revealed that 5 of 12 (42%) and 11 of 21 (52%) SSIs in the vancomycin and control groups, respectively, were caused by Staphylococcus (p=.72, Fisher exact test). Intrawound application of vancomycin powder was not associated with a significant decrease in the incidence of SSIs after posterior instrumented spinal surgeries in a propensity score-matched analysis. However, the rate of infections caused by Staphylococcus species was lower in the vancomycin group.