Bone contusion patterns of the knee at MR imaging: footprint of the mechanism of injury.

Bone marrow contusions are frequently identified at magnetic resonance imaging after an injury to the musculoskeletal system. These osseous injuries may result from a direct blow to the bone, from compressive forces of adjacent bones impacting one another, or from traction forces that occur during an avulsion injury. The distribution of bone marrow edema is like a footprint left behind at injury, providing valuable clues to the associated soft-tissue injuries. Five contusion patterns with associated soft-tissue injuries occur in the knee: pivot shift injury, dashboard injury, hyperextension injury, clip injury, and lateral patellar dislocation. The classic bone marrow edema pattern seen following the pivot shift injury involves the posterolateral tibial plateau and the midportion of the lateral femoral condyle. Edema occurs in the anterior aspect of the proximal tibia following the dashboard injury. Hyperextension results in the "kissing" contusion pattern involving the anterior aspect of the proximal tibia and distal femur. The clip injury results in a prominent area of edema involving the lateral femoral condyle and a smaller area of edema involving the medial femoral condyle. Finally, lateral patellar dislocation results in edema involving the inferomedial patella and anterior aspect of the lateral femoral condyle. In many instances, the mechanism of injury can be determined by studying the distribution of bone marrow edema, which then enables one to predict with accuracy the specific soft-tissue abnormalities that are likely to be present.