An experimental canine model of osteonecrosis: characterization of the repair process.

Osteonecrosis of the femoral head was induced in dogs by a process of deep freezing, accompanied by stripping of the soft-tissue attachments from the femoral neck and intertrochanteric area, in an effort to develop an experimental model to study treatment modalities for avascular necrosis of the hip. Immediate uniform necrosis was created in a defined area. Thereafter, spontaneous healing originated mainly from the adjacent viable bone by migration of undifferentiated mesenchymal tissue into the necrotic bone, genesis of fibrosis, and, finally, formation of new bone. Osteogenesis occurred primarily through intramembranous ossification without a preexisting template. Quantitative measurements showed a difference in the rates of ingrowth and revascularization of the necrotic area during the fibrotic and osteogenic phases of the healing. The de novo osteogenesis was slower than the migration of fibrosis. These findings indicate that, without osteotomy, we can reproducibly create necrosis of bone in a defined area of the proximal femur and induce a reparative process that incompletely heals the defect. Although it does not fully simulate the human disorder of osteonecrosis, our experimental surgical model provides a basis for further laboratory investigation into the management of avascular necrosis of the femoral head.