Magnetic resonance imaging in the early diagnosis of ischemic necrosis of the femoral head. Preliminary results.

Magnetic resonance imaging (MRI) was performed on the hips of 25 patients with suspected ischemic necrosis of the femoral head. Twenty-six femoral heads manifested MRI changes of ischemic necrosis: diminished bone marrow signal in a ringlike, focal, or diffuse pattern. Plain radiographs were normal in 13 of 26 MRI-positive hips; six were asymptomatic. MRI was more effective in detecting early cases than conventional 99mTc-diphosphonate or 99mTc-sulfur colloid (SC) bone scanning. There were no false-negative MRI examinations, but diphosphonate scans were negative in nine hips with normal radiography and abnormal MRI. Sulfur colloid scans were normal in only two hips with positive MRI, but SC scan results were often equivocal because isotope deficits were bilaterally symmetric. The results of this preliminary investigation imply that MRI has extraordinary sensitivity for the detection of early ischemic necrosis. Unlike radionuclide scanning, MRI shows the exact location and extent of femoral head necrosis. Because MRI is expensive, it should be used in a cost-effective manner. Therefore, MRI is best suited for the diagnosis of early cases where less expensive tests are negative or equivocal and as a precursor to more costly interventional procedures, such as core biopsy study or decompression.