OBJECTIVE Surgical site infections (SSIs) are a major source of morbidity after spinal surgery. Several recent studies have described the finding that applying vancomycin powder to the surgical bed may reduce the incidence of SSI. However, applying vancomycin in high concentrations has been shown in vitro to inhibit osteoblast proliferation and to induce cell death. Vancomycin may have a deleterious effect on dural healing after repair of an intentional or unintentional durotomy. This study was therefore undertaken to assess the effect of different concentrations of vancomycin on a human dura mater cell culture. METHODS Human dura intended for disposal after decompressive craniectomy was harvested. Explant primary cultures and subcultures were subsequently performed. Cells were characterized through common staining and immunohistochemistry. A growth curve was performed to assess the effect of different concentrations of vancomycin (40, 400, and 4000 μg/ml) on cell count. The effect of vancomycin on cellular shape, intercellular arrangement, and viability was also evaluated. RESULTS All dural tissue samples successfully developed into fusiform cells, demonstrating pseudopod projections and spindle formation. The cells demonstrated vimentin positivity and also had typical features of fibroblasts. When applied to the cultures, the highest dose of vancomycin induced generalized cell death within 24 hours. The mean (± SD) cell counts for control, 40, 400, and 4000 μg/ml were 38.72 ± 15.93, 36.28 ± 22.87, 19.48 ± 6.53, and 4.07 ± 9.66, respectively (p < 0.0001, ANOVA). Compared with controls, vancomycin-exposed cells histologically demonstrated a smaller cytoplasm and decreased pseudopodia formation resulting in the inhibition of normal spindle intercellular arrangement. CONCLUSIONS When vancomycin powder is applied locally, dural cells are exposed to a concentration several times greater than when delivered systemically. In this in vitro model, vancomycin induced dural cell death, inhibited growth, and altered cellular morphology in a concentration-dependent fashion. Defining a safe vancomycin concentration that is both bactericidal and also does not inhibit normal dural healing is necessary.
Keywords: CI = confidence interval; CSF leakage; LV = lyophilized vancomycin; PBS = phosphate-buffered saline; SSI = surgical site infection; durotomy; spine surgery; surgical site infection; vancomycin.