Osteonecrosis in the rheumatoid femoral head.

OBJECTIVE

To define the prevalence and pathological spectrum of femoral head osteonecrosis in patients with rheumatoid arthritis (RA) and to correlate its presence with disease related clinical and therapeutic factors.

METHODS

A total of 545 primary total hip arthroplasties performed in 507 patients with RA were identified. A historical review of each patient's rheumatoid disease and treatment as well as pathological review of each femoral head specimen was performed.

RESULTS

Osteonecrosis was identified in 66 specimens (12.1%) in one of 2 discrete forms. Thirty-two specimens (5.9%) contained classic subchondral avascular necrosis. Thirty-four specimens (6.2%) contained osteonecrosis in association with degenerative changes (within regions of sclerotic and eburnated subchondral bone), but not classic avascular necrosis. Remaining femoral head specimens were characterized by inflammatory arthritis (431 specimens) or degenerative joint disease (48 specimens). Corticosteroid therapy was used in 81% of patients with avascular necrosis and 68% with degenerative osteonecrosis. This was significantly greater prevalence than in patients without osteonecrosis (33%). Average daily prednisone dosage was 8 mg and no association between dosage and the presence of osteonecrosis was identified. No correlation between pathological findings and clinical disease severity was identified. In 5 of 27 specimens showing classic avascular necrosis and 11 of 34 containing degenerative osteonecrosis, no steroid treatment had been administered.

CONCLUSION

Femoral head osteonecrosis is present in about 12% of patients with RA at hip arthroplasty, and occurs in 2 forms -- classic avascular necrosis and degenerative necrosis. Both forms are significantly associated with corticosteroid use. "Low dose" therapy does not protect patients against the development of osteonecrosis. Additionally, baseline prevalence of osteonecrosis of about 3% occurs in the absence of steroid use and may be related to the underlying inflammatory diseases. Despite its association with osteonecrosis the net effect of corticosteroid therapy on the natural history of rheumatoid hip disease remains unclear.