MAGNETIC-RESONANCE-IMAGING (MRI) OF THE KNEE - A PATTERN APPROACH FOREVALUATING BONE-MARROW EDEMA

The applications of magnetic resonance imaging (MRI) have become numer ous for the assessment of disorders involving the knee. Once a techniq ue used nearly exclusively in the evaluation of internal derangement o f this joint, it now plays an important role in the diagnosis of proce sses that affect the bone marrow, including those that occur as a resu lt of trauma, infection, tumor, and rheumatogic disorders. Signal alte rations in the bone marrow frequently are present in association with these pathological processes. When the signal is of low intensity on T 1-weighted images and becomes heterogeneously increased in intensity o n T2-weighted images, it indicates the presence of edema in the bone m arrow. Two types of marrow edema are presented in this review: posttra umatic and reactive. In many situations, the area of altered signal in tensity is radiographically occult. The distribution of marrow edema o ften reflects the mechanism of injury in trauma and may correlate with additional injuries to the surrounding soft tissues. Reactive marrow edema occurs either in response to an inflammatory focus in the bone a nd/or joint or a neoplastic process in or adjacent to the bone.