Overcoming the detrimental impact of volumetric muscle loss on segmental fracture healing via the induced membrane technique.

AIMS: Open fractures pose a substantial treatment challenge, with adjacent muscle loss being a major complication. The induced membrane (IM) technique has shown promise in treating complicated fractures. The aim of this study is to investigate the impact of adjacent muscle trauma on segmental fracture healing using recombinant human bone morphogenetic protein-2 (rhBMP-2) via the IM technique. METHODS: Skeletally mature male rats (n = 10 to 11 per group) underwent unilateral 3 mm segmental bone defects (SBD) of the tibial diaphysis or a composite tissue injury (CTI), which included a SBD along with volumetric muscle loss (VML). A polymethyl methacrylate (PMMA) spacer was formed within the SBD of each rat. After a four-week period, the PMMA spacer was removed, and the defect was treated with a rhBMP2-impregnated collagen sponge. Longitudinal micro-CT (µCT) imaging was conducted at baseline (Day 0) and at weeks 2, 4, 8, and 12 post-spacer removal to monitor fracture healing progress. At the 12-week postoperative mark, a comprehensive analysis was conducted, including endpoint µCT analysis, evaluation of neuromuscular function, tibia torsional testing, and histological examination. RESULTS: Longitudinal µCT scans revealed no differences in bone formation or bone mineral density (BMD) at any timepoint between the SBD and CTI groups. High-resolution µCT analysis at the endpoint also showed no variations in bone quality. Torsion testing confirmed that VML did not affect bone strength. Notably, CTI animals exhibited an irreversible reduction in muscle mass and neuromuscular function, which was not observed in the SBD group. CONCLUSION: Introducing the additional challenge of VML alongside SBD did not hinder the effectiveness of the induced membrane technique in healing a critical-sized defect.