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.