The "silent hip" of idiopathic ischemic necrosis of the femoral head in adults.

Of thirty-three patients with the asymptomatic (so-called silent) stage of idiopathic ischemic necrosis of the femoral head, eleven had serial roentgenograms available to review the progression of the disease during this stage. Pathological specimens obtained during bone-grafting of eleven femoral heads were available for histological study in another eleven patients. It was found that the duration of the asymptomatic period averaged 5.5 years (range, three to eight years). No evidence of spontaneous regression of the avascular change was found. Typical histological findings were: (1) early clogging of the marrow spaces by amorphous material in the necrotic zone, and (2) limited evidence of so-called crreping substitution (seams of new bone laid on old, dead bone trabeculae) during the early stages of idiopathic ischemic necrosis.