Internal device decreases antibiotic's efficacy on experimental osteomyelitis

Purpose We have evaluated the effect of internal and external osteosynthesis devices on the efficacy of vancomycin treatment in a rabbit model of methicillin-resistant Staphylococcus aureus (MRSA)-induced post-traumatic osteomyelitis.Methods Double tibial osteotomies in female New Zealand rabbits were performed, inoculated with a MRSA strain, then fixed with an intramedullary rod. A debridement was performed 4 days later for each rabbit, and a bacterial count in pus was determined (B1). In the first group (G1), the osteosynthesis material was removed and replaced by a new sterile nail. In the second group (G2), the intramedullary rod was removed and then replaced by an external fixator. Immediately after surgery, G1 and G2 rabbits were treated with vancomycin (60 mg/kg twice a day). The animals were sacrificed at the end of a 5-day period, and a bacterial count in pus was performed again (B2).Results The difference of log 10 colony forming units per milliliter (CFU/ml) (B2−B1) was −1.2 ± 0.5 and −2.9 ± 1.1, respectively, for G1 and G2.Conclusion The efficacy of vancomycin treatment increased after removal of the internal osteosynthesis device.