Prognosis of early stage avascular necrosis of the femoral head.

Seventy-two femoral heads in 63 patients in whom avascular necrosis of the femoral head was in the early stage were followed up prospectively for a mean period of 6 years 1 month. All of the necrotic lesions were confirmed by magnetic resonance imaging. At the time of final outcome, 46 (64%) of the 72 hips were symptomatic. Necrotic lesions greater than 2/3 of the weightbearing portion on T1 weighted central coronal images indicated a high risk of clinical deterioration. Fifty-nine of the 72 hips initially had necrotic lesions greater than 2/3 of the weightbearing portion, and 44 (75%) of these 59 hips were symptomatic at the final outcome. However, in the radiographic assessment of 15 (25%) asymptomatic hips, even when the necrotic lesions were greater than 2/3 of the weightbearing portion as shown by magnetic resonance imaging, the continuous absence of any radiographic abnormality indicated the possibility of a continuous asymptomatic stage for at least several years.