Intrawound Vancomycin Powder in Posterior Lumbar Fusion: In Vitro Osteoblast Effects and Clinical Outcomes in a Historical-Control Cohort

Study DesignRetrospective analysis.ObjectivesTo analyze the immediate post-operative effects on osteoblast activity, and long-term impact on bone healing, of intrawound vancomycin powder following posterior lumbar fusion (PLF).MethodsThis study had two phases: (1) an in vitro analysis of vancomycin effects on osteoblasts and (2) a retrospective chart review-spanning over a decade-analyzing outcomes of vancomycin use in PLF patients. Cellular metabolic and osteogenic activities were evaluated using well-established in vitro assays. The retrospective chart review included patients ages 18+ who underwent PLF (four levels or fewer) between January 2007-December 2015. Patients were divided into two groups: the pre-vancomycin group (PVG) and the vancomycin group (VG). Statistical analyses included descriptive and comparative analyses across groups.ResultsPhase One included 56 patients. Drain vancomycin concentrations peaked at POD 0, averaging 1253.67 ng/µL. Osteoblasts exposed to vancomycin concentrations of 1,250 ng/µL had significantly lower ALP activity compared to those exposed to 0, 245, 285, and 500 ng/µL (ps<0.05). Phase Two included 425 patients: 232 in the PVG and 193 in the VG. SSIs requiring debridement were observed in 3.02% of PVG patients compared to 2.07% of VG patients (p=0.761). There were no differences in pseudoarthrosis across cohorts (p=0.886), but lucency was more common in the VG (25.39%) than the PVG (11.64%; p<0.001).ConclusionsLocal drain concentrations of vancomycin decreased significantly across the postoperative period, suggesting its effects on osteoblasts are limited to the early inflammatory phase. In the long-term, intrawound vancomycin may not impact risk of SSI or pseudoarthrosis.