Risk period for developing osteonecrosis of the femoral head in patients on steroid treatment

Patients who require long-term steroid use are at risk for the development of osteonecrosis. However, the risk period for developing osteonecrosis of the femoral head has not yet been defined. The authors attempted to determine the onset of osteonecrosis of the femoral head following steroid treatment. Medical record data of patients with steroid-related osteonecrosis of the femoral head from four university hospitals were reviewed. Information was collected regarding the duration and dose of steroid use for patients who were diagnosed at the early stage by magnetic resonance imaging (MRI) without positive findings on plain radiographs (Association Research Circulation Osseous stage I osteonecrosis). Twenty-two patients were diagnosed at Association Research Circulation Osseous stage I. There were eight male and 14 female patients ranging in age from 17 to 60 years (mean 33). The total dose of steroid, which was used until the time of detection of osteonecrosis by MRI, ranged from 1800 to 15 505 mg prednisolone or its equivalent (mean 5928 mg). The period from the start of steroid treatment to the diagnosis by MRI ranged from 1 month to 16 months (mean 5.3 months). Twenty-one of 22 patients were diagnosed within 12 months of the initiation of steroid treatment. The duration of steroid treatment within this period ranged from 1 month to 12 months (mean 4.5 months). There may be a risk period of 12 months for developing femoral head osteonecrosis in patients receiving long-term steroid treatment. Close observation and more aggressive screening are recommended within the first year of long-term steroid treatment to prevent advanced osteonecrosis of the femoral head.