Changes on magnetic resonance images after traumatic hip dislocation.

Fourteen patients with traumatic hip dislocation had serial magnetic resonance imaging and routine radiographic studies from the time of injury through 24 months after injury. One experienced radiologist interpreted all images prospectively for abnormalities suggesting osteonecrosis of the femoral head and posttraumatic arthritis. Eight hips demonstrated abnormal marrow signals on T1 and T2 weighted images within 6 weeks of injury. These changes progressed in 3 hips, and osteonecrosis was confirmed subsequently by plain radiography. The abnormal marrow signals in the remaining 5 hips proved to be transient, resolving on magnetic resonance images within 3 months in 4 of the 5 patients. Magnetic resonance imaging can be used with confidence for the early detection of osteonecrosis of the femoral head after traumatic hip dislocation or fracture-dislocation. The presence of acetabular or femoral shaft hardware did not preclude magnetic resonance imaging assessment of these patients when coronal, sagittal, and axial images were obtained. Magnetic resonance imaging was not reliable for assessing marrow changes within the first week after injury, nor was it helpful in predicting which patients were at risk for posttraumatic arthritis to develop. An algorithm is proposed for using magnetic resonance imaging in the early diagnosis of osteonecrosis of the femoral head after traumatic hip dislocation.