[Application of vancomycin powder on graft. Does the fusion of the rabbits spine is affected?].

Introduction: In vitro studies suggest that vancomycin is highly cytotoxic for osteoblasts. However, several clinical studies in vivo have not provided evidence or determined that effect on osteogenesis. The aim of this work was to investigate the effect of topical vancomycin on a lumbar arthrodesis model on New Zealand white rabbits.

Material And Methods: Double-blind randomized experimental study. Posterolateral spinal fusion was performed on 30 rabbits, divided into two groups, A: graft/placebo, B: graft/vancomycin. After sacrificing them, the bone callus was evaluated with axial tomography and classified into three groups: no fusion (0), partial/incomplete fusion (1) and fusion (2). The samples were also histologically analyzed. The associations between the presence of fusion (complete/incomplete) and the group tested were estimated using Poisson log-linear models with two covariates. Adherences to histologically obtained responses were studied using contingency tables and 2 tests. The significance level was set equal to 0.05.

Results: Treatment with vancomycin has 30% (0.30. CI 95%: 0.12-0.94) less chance compared to the placebo group, of presenting complete fusion. In other words, the vancomycin group has 2.3 times (CI 95%: 1.02-4.91) more likelyhood, compared to placebo, to have incomplete fusion.

Conclusion: The application of vancomycin powder mixed with graft reduces fusion rates by 30%, but at doses 5 times higher than those routinely used in arthrodesis by the authors medical team.