Controversies in magnetic resonance imaging of the hip.

One of the first musculoskeletal areas to be imaged by magnetic resonance (MR) was the hip. Early on, and even today, the most frequent indication for imaging of the hip has been for the evaluation of osteonecrosis and related diseases. Despite the long history of MR imaging of osteonecrosis, there still exist many controversies. This article will look at three of these: (a) What is the best way of imaging early osteonecrosis? This question has proven to be particularly important in the evaluation of the posttraumatic patient. We provide some preliminary evidence that the use of gadolinium-enhanced MR imaging may be helpful. Specifically, gadolinium fails to enhance areas of early osteonecrosis while surrounding uninvolved areas do enhance. (b) How should the patient with "MR bone marrow edema of the hip" be evaluated and treated? If there is radiographic osteopenia, the assumption is that this represents transient osteoporosis (a self-limited disease) and no treatment is necessary. However, if no osteopenia is present, the diagnosis and treatment become more problematic. A decision-making algorithm is presented to help overcome this dilemma. (c) Is documented osteonecrosis of the hip ever reversible without surgical intervention? Work done with renal transplant patients suggests that the answer to this question is yes, but work reported from Europe casts some doubt on this conclusion.