Long-term observation of avascular necrosis of the femoral head in systemic lupus erythematosus: an MRI study.

Objectives To assess long-term prognosis of clinically silent, early-stage avascular necrosis of the femoral head (ANFH) in patients with systemic lupus erythematosus (SLE). Methods Twenty-four hips that showed ANFH by magnetic resonance imaging (MRI) in 13 patients with SLE were studied. All hips were radiographically normal and clinically asymptomatic. The percentage volume of necrotic bone was calculated at each study by dividing the sum of the necrotic areas by the sum of the femoral head areas from all MRI slices. Hips were also classified into three categories by the relation of the necrotic area to the weight bearing portion according to the system of the Japanese Investigation Committee for avascular necrosis of the femoral head, with modifications: Type A (medial lesions): 8 hips, Type B (central lesions): 4 hips, and Type C (lateral lesions): 12 hips. Patients were followed up with MRI for 12-95 (mean 51) months. Results Fifteen hips improved (more than 15% reduction in the volume of necrosis), 5 did not change and 4 worsened during the observation period. All hips with a volume of necrotic area less than 25% showed improvement. All but one Type A hip and one Type B hip improved, while the mean volume of necrosis did not change in Type C. The volume of the necrotic area was smaller in Type A & B than in Type C hips (p < 0.001). Conclusions Long-term prognosis of early-stage ANFH was favorable in patients with SLE when the necrotic area was small (less than 25%).