Development of a bone nonunion in a noncritical segmental tibia defect model in sheep utilizing interlocking nail as an internal fixation system

BackgroundThe bone nonunion is an important complication of bone fracture repair. The existing models developed on small animal species prevent using osteosynthesis materials designed to be implanted in human bones. The goal of this study was to develop a nonunion process in a noncritical segmental tibial defect in sheep, a species analogous in size to humans.Materials and methodsThe animals were divided into two groups of four animals each. In Group 1 (experimental), the defect was created by surgically stripping the periosteum from the edges of a distal tibial osteotomy, keeping the edges 5 mm apart, and placing an incomplete O-shaped silicone ring in the gap. Group 2 (control) was intervened with a simple fracture at the distal end of the tibia. In both groups an interlocking nail was used as a fixation system. Over 8 wk after surgery, radiographs and histologic and histomorphometric analyses were performed.ResultsThe control group showed a typical bone repair process. In contrast, the experimental group showed a fracture line with rounded edges and a scarce callus formation. The bone callus showed reduced amount of bone formation and large content of fibrous tissue (P = 0.001).ConclusionsThese results indicate that our model developed an atrophic nonunion in sheep, a species having multiple similarities to humans, such as weight, size, bone structure, and bone remodeling process.