Development of a clinically relevant animal model for the talar osteonecrosis in sheep

There are a lot of reports and reviews about osteonecrosis of the talus (ONT), yet reports about the animal model of ONT to evaluate proper therapeutic approaches are rarely heard. In our study, a novel animal model was established. Pure ethanol was injected into the cancellous bone of sheep's talus. Macroscopic observation, X-ray, CT and histology were performed at two, four, 12 and 24 weeks postoperatively. It was revealed that the trabeculae of talar head began to change their structure after two weeks postoperatively compared to the normal talus. The ONT was obvious at the end of the fourth week, and their outstanding feature was the damage of trabeculae bone and formation of cavities. CT scans and pathological changes of the subjects all showed characteristics of the early stage of osteonecrosis, also the sections of the specimens confirmed necrosis of tali. By 12 weeks, the phenomenon of necrosis still existed but fibrous tissue proliferated prominently and bone reconstruction appeared in certain area. Most specimens (3/4) got late stage necrosis which presented as synarthrosis in X-ray and mass proliferation of fibrous tissue in histology at the end of 24 weeks. The novel animal model of ONT was successful, and it is inclined to deteriorate without any intervention. The study provides us a new way to evaluate various treatments on ONT in laboratory, which may eventually pave way to clinical applications.