Bone bruises: their patterns and significance.

MR imaging is sensitive in the detection of occult stress and posttraumatic fractures in and around the knee joint. In some patients, the pain from these bony injuries can mimic that of meniscal tears. The abnormality of the bone may explain completely the patient's symptoms and obviate the need for any further work-up. The types of injuries detected by MRI include bone bruises, stress or insufficiency fractures, and osteochondral fractures. Bone bruises or contusions are characterized by a diffuse or localized pattern of low signal intensity on T1-weighted images without a defined fracture. Blood, edema, hyperemia, and perhaps microfracture of the trabeculae may all contribute to the marrow signal alterations. Anterior cruciate ligament injuries often are accompanied by a characteristic bone contusion pattern, such as hemorrhage or edema in the posterior aspect of the lateral tibial plateau, as well as the anterior aspect of the lateral femoral condyle.