Idiopathic necrosis of the femoral epiphyseal nucleus in rats.

To study the cause of osteonecrosis of the femoral head in spontaneously hypertensive rats, the site and mechanism of the occlusion of the blood vessels feeding the femoral head were investigated histologically and microangiographically. Tracing the blood vessels using serial sections revealed that the lateral epiphyseal vessels disappeared immediately before entry into the ossific nucleus. As the reparative process advanced, the blood vessels from the lateral side of the head entered the ossific nucleus again. To investigate the relationship between osteonecrosis and mechanical stress on the femoral head, some treatments to reduce mechanical stress were applied, and the frequency of the femoral head lesions, such as osteonecrosis, disturbed ossification, and abnormality of the growth plate, was compared among the groups of treatments for stress relief. The incidence of femoral head lesions was found to be directly proportional to the mechanical stress working on the area, as was evident from a decrease in the incidence of osteonecrosis as a result of reduction of mechanical stress. Thus, the obstruction of the vessels in the lateral part of the femoral head might result from the breakdown of cartilage caused by the mechanical stress on the femoral head.