Correlation between baseline femoral neck marrow status and the development of femoral head osteonecrosis in corticosteroid-treated patients: a longitudinal study by MR imaging.

OBJECTIVE: To test the hypothesis that the development of corticosteroid (CS)-associated femoral head osteonecrosis (ON) is influenced by baseline femoral neck marrow status. PATIENTS AND METHODS: The population consisted of 20 untreated patients with a newly diagnosed rheumatic disease in whom a standardized CS regimen was planned. Before CS treatment, baseline femoral neck marrow status was determined by magnetic resonance (MR) imaging on T1-weighted images (proportion of surface area of femoral neck and intertrochanteric area occupied by fatty marrow; index of marrow conversion [IMC]) and on a quantitative MR sequence (bulk T1 values of femoral head and neck). The presence of ON was assessed by coronal T1-weighted MR images of the hips at 6 and 12 months. RESULTS: None of the patients suffered from ON at baseline. Four patients (20%) developed bilateral femoral head ON at 6 months. The mean percentage of fat marrow in the femoral neck before treatment was significantly higher in ON-positive than in ON-negative patients (p=0.0025). The mean baseline femoral neck IMC value, which parallels the degree of red to yellow marrow conversion, was higher in ON-positive than in ON-negative patients (p=0.089). The mean baseline bulk T1 value of the femoral neck (but not of the femoral head), which inversely correlates with the amount of fat marrow, was significantly shorter in ON-positive than in ON-negative patients (p=0.0298). CONCLUSION: The development of CS-associated femoral head ON is correlated with a high fat content in the proximal femur before CS therapy