Transphyseal osseous bridges in experimental osteonecrosis of the femoral head of the rat - Histologic study of the bony bridges connecting the epiphyseal with the metaphyseal bony trabeculae through gaps in the physeal cartilage

In view of the lifelong persistence of the physis, the femoral head of rats may serve to model Perthes disease and slipped capital femoral epiphysis. To produce osteonecrosis. the blood supply of one femoral head of 133, 6-mo nth-old animals was severed by circumferentially incising the periosteum of the neck and cutting the ligamentum teres. The rats were killed 7 days to 90 days postoperatively. Associated with resorption of the necrotic bone an d marrow, remodeling of the epiphysis was characterized by an ingrowth of v ascularized fibrous tissue. formation of new bone and some cartilage, archi tectural deformation and flattening of the head. In 22 of 83 rats killed 30 days or more postoperatively, gaps in the continuity of the physeal cartil age were occupied by osseous bridges, connecting newly formed epiphyseal bo ny trabeculae with either the preexisting or newly formed metaphyseal osseo us trabeculae. This healing mode may follow ischemic death of physeal chond rocytes or be owing to another mechanism, e.g., release of mediatory substa nces of inflammation. These findings raise the possibility that fixation of the healing epiphysis of a child's previously necrotic femoral head to the metaphysis occurs by transphyseal osseous growth in cases in which the phy sis is involved in the necrotic process.