Characterization of a Femoral Segmental Nonunion Model in Laboratory Rats: Report of a Novel Surgical Technique

The literature is lacking conclusive results regarding the exact mechanism of maximizing the fracture healing stages with minimal traumatic side effects. This observation mandates the development of a novel surgical procedure using small animals as a model to study fracture healing in the presence of osteoinductive agents. Previously, stabilization of osteotomies in small animal models has mainly been accomplished using Kirschner wires, but the rat's tremendous ability to heal an osteotomy stabilized by this method has masked the effects of osteoinductive agents. Thus, this study proposes using a modified 20-hole, 1.5-mm stainless-steel plate to stabilize a 5-mm segmental defect. Thirty of 32 adult male rats were fully weight-bearing within 2 days and were followed over a 15-week period. Two animals showed evidence of fixation failure due to technical error, and the animals were humanely sacrificed. At the end of the study, the fractures were stable with significantly less bone formation evident when compared to controls (p <. 001). Therefore, this technique can effectively be used to evaluate compounds that will enhance bone formation and allows for stable fixation of the control with minimal callus formation or bony ingrowth. The goal of this article is to allow other investigators to reproduce this technique as well as outline the advantages and disadvantages of this novel plating technique versus the former Kirschner wire technique for the study of osteoinductive agents using small animals as a model.