An externally fixed femoral fracture model for mice.

Transgenic and knockout mouse models can be used to help understand the molecular mechanisms of fracture repair. This study examines the feasibility of applying an external fixator to the mouse femur as one model for studying fracture repair. The external fixator consisted of two aluminum blocks connected by two rods. Four pins are used to connect the blocks to the bone. Mechanical characterization of the fixators was carried out prior to their use. Sixty-two wild type mice with bilateral femoral fractures were created using an open technique and fixed using the fixator. The progress of fracture healing was monitored radiologically before sacrifice and by mechanical testing and histology after sacrifice. Initially four mice died intraoperatively from excessive blood loss, the intraoperative mortality was subsequently reduced by subcutaneous saline infusion. The bone healed between 14 and 21 days after fracture and remodeled by 60 days. Both radiological and mechanical assessments showed a steady progression of bone healing. Histology demonstrated callus and endochondral bone formation. This study demonstrated that it is possible to create a mouse femoral fracture model stabilized by external fixation and will provide an additional model to the understanding of fracture healing in transgenic and knockout mice.