Two-Stage Fixation in a Rat Model of the Induced Membrane: A Novel Surgical Technique.

INTRODUCTION: In the context of high-energy trauma or ballistic injury, wound healing is often compromised by underlying structural damage such as bone loss, infection, or instability. The induced membrane technique (IMT), a two-stage approach for segmental bone defects, is frequently used in the management of chronic infected wounds. Although a change in osteosynthesis is routinely performed between stages in clinical settings, no preclinical animal model has reproduced this key surgical step. We present a novel surgical technique in rats combining a reinforced polymethylmethacrylate (PMMA) spacer with a Kirschner wire during the first stage, followed by plate osteosynthesis during the second stage. This represents the first reported animal model of IMT that integrates a staged change in fixation.

METHODS: Eleven Sprague Dawley rats underwent a 5-mm femoral bone defect creation stabilized with an intramedullary Kirschner wire and a PMMA spacer (stage one). Four weeks later, the spacer and wire were removed, and internal fixation was achieved using a locking plate system, after grafting the defect with cancellous bone (stage two). Clinical monitoring, radiographic imaging, and postmortem micro-CT analysis at 10 weeks post-second surgery assessed model feasibility and bone regeneration.

RESULTS: All animals survived and maintained satisfactory weight and clinical status throughout the protocol. The mean bone volume of the newly mineralized bone into the defect was 64.05 ± 36.62 mm3.

CONCLUSION: This is the first reproducible animal model of IMT incorporating a staged change in osteosynthesis, closely mimicking clinical management of chronic bone wounds. The technique offers a robust preclinical platform for studying the influence of fixation methods on membrane properties and bone healing. It is particularly relevant for translational research in wound-associated bone defects and infection control.