Friday, December 6, 2013
Vancomycin Powder to Prevent Spine Surgery Infections—Less Effective Than We Thought?
Many recent studies have suggested that the addition of vancomycin powder to the surgical wound reduces the infection rate in posterior cervical, thoracic and lumbar instrumented fusions. All of these studies have been retrospective in nature, however, making it possible that other factors contributed to the observed decrease in infection rate. Despite the lack of high level evidence, the practice of placing vancomycin powder in the wound for instrumented posterior spine surgery has been widely adopted. In an effort to add some level 1 evidence to the literature, Dr. Rajasekaran and his colleagues from India performed an RCT comparing infection rates among spine surgery patients treated with standard perioperative antibiotics and those treated with standard perioperative antibiotics plus 1 g of vancomycin powder placed in the surgical wound. All spine surgery patients with at least 12 weeks of follow-up were enrolled in the study, including those having undergone instrumented and uninstrumented procedures anywhere from the occiput to the coccyx (n=907). It is unclear if patients undergoing anterior surgery were included. The overall infection rate was 1.6% and was the same for the two treatment groups. Subgroup analysis comparing the instrumented and uninstrumented cases separately revealed an infection rate of approximately 2% for the instrumented cohort and 1% for the uninstrumented cohort, with no differences between the treatment and control groups. No adverse events were attributed to the vancomycin.
Why did this study arrive at a markedly different conclusion than the previous studies addressing this question? There are many substantial differences between this and the earlier studies, all of which likely contributed to the inconsistent findings. The current study represents a Level 1 RCT, where the previous studies typically represented before-after study designs at risk for confounding by other changes that occur over time (i.e. changes in technique, patient mix, etc). This study included uninstrumented lumbar cases such as diskectomies and laminectomies, surgeries with relatively low infection rates where it is difficult to demonstrate an improvement. It is unclear if anterior cervical cases were included, but, if so, this would represent another low risk environment for infection. Additionally, this study had a very low infection rate in its instrumented cases even without the use of vancomycin powder (approximately 2%), so it was likely underpowered to detect even a 50% decrease in infection rate with only 300 instrumented patients in each group. Finally, the authors stated that they were careful to ensure that the vancomycin did not come in contact with the dura or bone graft, precautions that were generally not observed in prior studies. It is possible that the current authors’ technique did not allow for enough vancomycin to be present in the deeper tissues and was less effective in preventing infection. Given that this paper represents the first Level 1 study on this topic and had a negative result, should we abandon the use of vancomycin powder in spine surgery? The differences between this study and the earlier literature are significant, and this study is likely not the final word on this topic. There is at least fair evidence to suggest that vancomycin powder likely decreases the infection rate in high infection rate environments, namely posterior cervical, thoracic, and lumbar instrumented fusions. With no reported adverse effects related to the vancomycin powder, it seems reasonable to continue to use vancomycin powder in high risk cases, especially in cases where patient characteristics increase the risk of infection (i.e. obesity, diabetes, and trauma). In low risk situations like ACDF or uninstrumented posterior lumbar cases, there is scant evidence that the addition of vancomycin powder is helpful. This paper should fuel some debate on this topic and adds some evidence to suggest that vancomycin powder is probably not helpful in low infection rate environments, though it still seems prudent to consider its use in high risk situations.
Please read Dr. Rajasekaran’s paper on this topic in the December 1 issue. Does this paper change how you will use vancomycin powder in your practice? Let us know by leaving a comment on The Spine Blog.
Adam Pearson, MD, MS
Associate Web Editor