Does Intrawound Application of Vancomycin Influence Bone Healing in Spinal Surgery?

Abstract

Introduction: Surgical site infection is a major complication of spinal deformity surgery. The application of lyophilized vancomycin into the wound is reported to significantly decrease infection rates. As concentrations applied can exceed the minimal bacterial inhibitory concentration for more than a thousand fold, an eventual inhibitory effect on eukaryotic cells might impair bone healing and increase the risk of non union. Methods: Primary osteoblast cell cultures were generated from bone tissue removed during routine spinal surgery in 5 patients. Bone samples were incubated in Dulbecco's Modified Eagle's Medium supplemented with 10 % fetal calf serum, 2 mM L-Glutamine, 0.05 mg/ml Ascorbic Acid and 50 μg/ml Gentamycin (Control Group). The test media were additionally supplemented with 3, 6 or 12 mg/ml Vancomycin. Cultures were inspected daily for signs of cell emigration. Emigrated cells were expanded in monolayer culture and cell proliferation, morphology and viability of cells cultured in control and Vancomycin-medium were analyzed. Results: Bone samples from all 5 patients showed emigration of osteoblasts after 3-6 days when cultured in control medium, but only 1 out of 5 samples was positive after Vancomycin supplementation independent from the concentration applied. Cell emigration occurred 48 h delayed compared to the corresponding control. 24 hours after antibiotic supplementation, cell counts were 6.2 × 104 in the control group, 4.8 × 104 after supplementation with 3 mg Vancomycin and 2 × 104 after the addition of 6 mg resp. 12 mg/ml Vancomycin (p<0.001). Average cell viability was 100% in the control group and after addition of 3 mg/ml Vancomycin, 97 % after supplementation with 6 mg and 84 % after supplementation with 12 mg Vancomycin (p<0.009). Vancomycin-supplementation led to morphological changes in a dose dependant manner: While control cells were polygonal with several pseudopodes and a tender cytoplasm seam, antibiotic supplementation led to a retraction of pseudopodia and a contraction of the nucleus. Discussion: Vancomycin application leads to a dose dependant inhibition of cell migration, cell proliferation and viability as well as severe morphological changes. As bone remodelling after fusion surgery requires the migration, proliferation and differentiation of osteoblasts at the fusion site, high dosages of intralesional Vancomycin might interfere with regenerative processes and increase the risk of non union.