John R. Gaughen, Jr., M.D.

October 26, 2005

Discussion

The pattern of bone contusions seen with MRI in patients with knee trauma can be a useful tool in evaluating for associated ligamentous and tendinous injuries. The pattern in the images presented, contusion in the posterior lateral tibial plateau and anterior lateral femoral condyle, should raise a high level of suspicion for an associated anterior cruciate ligament (ACL) tear. In the pivot-shift mechanism of knee injury, the femur is internally rotated, while the tibia is externally rotated with the foot planted and the leg in partial flexion. Injury to the ACL causes anterior instability, allowing the posterior lateral tibial plateau to impact upon the anterior lateral femoral condyle. On the plain films, this pattern of injury manifests as a prominent sulcus terminalis. Other patterns of bone contusion may also be seen with anterior cruciate ligament tears, depending on the mechanism of injury. Hyperextension injury may result in a tear of the ACL, with associated kissing contusions of the medial femoral condyle and medial tibial plateau. Pure valgus stress may also result in an ACL tear, with imaging findings often demonstrating a contusion on the lateral femoral condyle (from direct impact), as well as an ACL tear, medial collateral ligament avulsion, and medial meniscus tear. The constellation of ACL tear, MCL avulsion, and medial meniscus tear is known as O'Donohue's "unhappy" triad.

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