Role of impairment of blood supply of the femoral head in the pathogenesis of idiopathic osteonecrosis.

To investigate the role of blood supply in the pathogenesis of idiopathic osteonecrosis of the femoral head, superselective angiography of the medial circumflex artery was performed. Sixteen hips with early stage osteonecrosis diagnosed by bone scintigraphy were studied, as were 22 contralateral normal hips (from unilateral cases) and 22 roentgenographically and scintigraphically normal hips in patients who had been administered corticosteroids. All hips demonstrated abnormal superior retinacular arteries in the extraosseous area, and small arteries penetrated 14 hips with early stage osteonecrosis. Abnormal findings were noted in 17 of 22 contralateral normal hips and in 20 of 22 normal hips with corticosteroid administration. Follow-up roentgenographic analysis showed that the hips with small arterial penetration most often developed osteonecrosis. There were two important findings: (1) The blood supply of the superior retinacular arteries from the extraosseous site was impaired. (2) Revascularization was observed not only in hips with early stage osteonecrosis but also in contralateral normal hips and normal hips with corticosteroid therapy. Osteonecrosis is not necessarily a consequence of a single episode of impairment of blood supply of the femoral head but that of a repetitive episode if interruption of revascularization.