BONE DEFECT HEALING USING THE INDUCED MEMBRANE TECHNIQUE AFTER CHRONICALLY INFECTED NONUNION IN A NOVEL RABBIT MODEL

Abstract

In chronically infected fracture non-unions, treatment requires extensive debridement to remove necrotic and infected bone, often resulting in large defects requiring elaborate and prolonged bone reconstruction. One approach includes the induced membrane technique (IMT), although the differences in outcome between infected and non-infectious aetiologies remain unclear. Here we present a new rabbit humerus model for IMT secondary to infection, and, furthermore, we compare bone healing in rabbits with a chronically infected non-union compared to non-infected equivalents.A 5 mm defect was created in the humerus and filled with a polymethylmethacrylate (PMMA) spacer or left empty (n=6 per group). After 3 weeks, the PMMA spacer was replaced with a beta-tricalcium phosphate (chronOs, Synthes) scaffold, which was placed within the induced membrane and observed for a further 10 weeks. The same protocol was followed for the infected group, except that four week prior to treatment, the wound was inoculated with Staphylococcus aureus (4×106 CFU/animal) and the PMMA spacer was loaded with gentamicin, and systemic therapy was applied for 4 weeks prior to chronOs application.All the animals from the infected group were culture positive during the first revision surgery (mean 3×105 CFU/animal, n= 12), while at the second revision, after antibiotic therapy, all the animals were culture negative. The differences in bone healing between the non-infected and infected groups were evaluated by radiography and histology. The initially infected animals showed impaired bone healing at euthanasia, and some remnants of bacteria in histology. The non-infected animals reached bone bridging in both empty and chronOs conditions.We developed a preclinical in vivo model to investigate how bacterial infection influence bone healing in large defects with the future aim to explore new treatment concepts of infected non-union.