Magnetic resonance imaging of osteonecrosis.

Because the available preliminary data strongly indicate that MRI is accurate in diagnosing osteonecrosis, MRI of the hips is recommended in patients suspected of having osteonecrosis, especially if other diagnostic studies are equivocal. MRI also may be useful in following patients who have strong risk factors for osteonecrosis, such as corticosteroid therapy, femoral neck fracture, traumatic femoral head dislocation (Fig. 13), slipped capital femoral epiphysis (Fig. 14), and congenital hip dislocation. In diseases such as systemic lupus erythematosus, both hips eventually may become involved in 50 to 80 per cent of cases. Therefore, the unaffected hip of patients with systemic lupus erythematosus and unilateral nontraumatic osteonecrosis of the hip should be monitored regularly with MRI. The hope is that early diagnosis and treatment of femoral head osteonecrosis will prevent the relentless progression to subchondral collapse and disabling arthropathy. MRI also may be useful in staging patients known to have osteonecrosis. The ability of MRI to image directly in multiple planes facilitates the determination of the volume and location of infarcted segments of bone. This information is important in planning any of the surgical procedures used relatively early in the disease, such as core decompression, rotational osteotomy, or bone graft. Moreover, MRI may prove helpful in evaluating the effectiveness of any therapeutic intervention.