A Novel Model of Osteonecrosis in the Knee Joint

As the necrotic portions of the epiphysis in the current animal models are focal and the extent of necrosis also varies, these models are not suitable for treatment evaluation such as cell therapy. We will describe a new osteonecrosis model which shows total and constant necrosis of the epiphysis and can be for human treatment evaluation. Fifteen New Zealand white rabbits were used for making the osteonecrosis model. Their right knees were incised longitudinally using an anteromedial approach, and the femoral condyles were exposed. After dissecting the ligaments surrounding the distal femur, the metaphyseal-diaphyseal junction was cut using a saw, and the whole femoral condyle was isolated. After three liquid nitrogen treatments, the isolated femoral condyle was internally fixated to the femoral shaft using two or three k-wires. Radiographs were taken at four, 12, and 24 weeks postoperatively, and five rabbits were sacrificed at each time point. The necrotic regions with portions of the osteotomy areas were extracted, and the tissue sections were stained with hematoxylin-eosin and Masson's trichrome. The tissue reactions showed sluggish reparative processes in which granulation and fibrous tissue sluggishly penetrated necrotic tissue from the osteotomy sites. Viable osteocytes with well-stained nuclei were not present in necrotic areas at any stage. The distal femoral condyle of the rabbit is an appropriate model for demonstrating osteonecrosis. It is hoped that this model will facilitate future assessments of new, human treatment modalities.