Contrast-enhanced fat saturation magnetic resonance imaging for studying the pathophysiology of osteonecrosis of the hips.

We imaged 75 hips in 40 patients using fat saturation technique before and after intravenous injection of contrast (0.1 mmol/kg gadolinium diethylene triamine penta-acetic acid, Gd-DTPA). Eighteen hips in 11 patients were determined to be osteonecrotic, either by pathologic or clinical examination. In the osteonecrotic hips, three distinct patterns of enhancement were found: (I) focal area outlined by brightly enhancing rim (7 hips); (II) diffuse enhancement in the femoral head and neck extending into the femoral shaft (3 hips); and (III) a combination of patterns I and II (8 hips). Our data support the hypothesis that early nontraumatic osteonecrosis is associated with hyperemia and/or an increase in capillary permeability rather than acute devascularization, and that diffuse marrow edema is the initial finding in early nontraumatic osteonecrosis.