In order to predict the probability of collapse of a femoral head in
which there is avascular necrosis, we used magnetic resonance imaging to
evaluate sixty-six hips (fifty patients) in which avascular necrosis was in
the early stages and in which collapse of the head was not yet visible. The
hips were followed radiographically for an average of forty-nine months
(range, sixteen to eighty-four months), and with magnetic resonance imaging
for an average of forty-four months (range, twelve to seventy-three
months). Twenty-one (32 per cent) of the femoral heads had collapsed by
thirty-two months. Of the twenty-three femoral heads in which necrosis
involved at least one-fourth of the diameter of the head and encompassed at
least two-thirds of the major weight-bearing area, seventeen (74 per cent)
had collapsed by thirty-two months.