Pathological study of avascular necrosis of the femoral head in spontaneously hypertensive rat

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The femoral head lesions of male spontaneously hypertensive rats (SHRs), which occur naturally and resemble Perthes disease in man, were investigated radiographically and histologically. In the early phase of growth in SHRs, i.e., a period of 6 to 15 weeks after birth, the femur was shorter than that of control rats, and ossification in the epiphysis of the femoral head was considerably retarded. Osteonecrosis of the femoral head of SHRs appeared at the age of 9 weeks, and an abnormality of the cartilage in the epiphysis and metaphyseal growth plate and subsequent enchondral ossification were seen frequently. Furthermore, the cause of the vascular occlusion in osteonecrosis of the femoral head was investigated using serial sections. The lateral epiphyseal vessels, which supply the proximal femoral epiphysis, disappeared immediately before entry into the femoral heads. In fresh osteonecrosis, the pathway of the vessels between the margin of the articular cartilage and metaphyseal growth plate was replaced with granulation or scar tissue.We conclude that the vascular occlusion occurs in the layer of the epiphyseal cartilage where the lateral epiphyseal vessels penetrate, and that the abnormalities of the epiphyseal cartilage and metaphyseal growth plate might play a part in the occurrence of osteonecrosis.