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

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.

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.

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.

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.