Femoral head avascular necrosis: MR imaging with clinical-pathologic and radionuclide correlation.

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Abstract
A retrospective evaluation of magnetic resonance (MR) imaging for the detection of avascular necrosis (AVN) of the femoral head was performed in 49 patients (85 hips) with clinical suspicion of AVN. Positive findings at bone biopsy or evidence on plain radiographs was considered proof of AVN. Absence of clinical symptoms and of radiographic findings for a minimum of 18 months after MR imaging was considered evidence of the absence of AVN. All patients were studied with plain radiography and technetium-99m methylene diphosphonate bone scintigraphy. Five hips had negative MR images, positive findings at bone marrow biopsy, positive bone pressure measurement (BMP), and positive bone scans. A comparison between MR images and bone scans showed MR imaging to be superior, with a sensitivity of 88.8% (vs. 77.5%) and a specificity of 100% (vs. 75%). BMP was the most sensitive (92%) but least specific test (57%).