Progression and cessation of collapse in osteonecrosis of the femoral head.

Thirty-five patients (54 hips) with osteonecrosis of the femoral head without collapse or only with a crescent sign were followed up for at least 5 years to clarify the natural course of osteonecrosis. During the followup, 28 hips (52%) in 21 patients collapsed including nine hips in nine patients with small necrotic lesions occupying less than the medial (2/3) of the weightbearing area. Cessation of collapse then was observed in 15 (14 patients) of the 28 hips (54%), especially in eight of the nine hips (89%) with small necrotic lesions. Of the 15 hips in 14 patients with cessation of collapse, 11 hips (73%) in 11 patients had less than 2 mm collapse and 10 hips in nine patients became asymptomatic. The analysis indicated that collapse of the femoral head does not necessarily determine a poor prognosis, and even after collapse occurs, subsequent cessation of collapse can be expected in a certain percentage of hips. Hips with less than 2 mm collapse and necrotic lesions occupying less than the medial (2/3) of the weightbearing area have a high chance of cessation of collapse and improvement of symptoms with no surgical intervention.