The repair process in experimentally induced avascular necrosis of the femoral head in dogs.

Total necrosis of the femoral head was experimentally produced in dogs by freezing. The healing process was observed in a time sequence. There was a dense fibrous layer at the boundary between the necrotic bone mass and living bone tissue, in each dog which survived for 18 months after the surgery. The layers were similar to that commonly found in avascular necrosis of the femoral head in humans. Histological observation revealed that the establishment of the dense fibrous layer was the final result of three time dependent changes in biological potencies of granulation tissue, i.e., decreasing proliferating and differentiating potencies and increasing osteoclastic potency of mesenchymal cells within the granulation tissue.