Imaging of Athletic Injuries of Knee Ligaments and Menisci: Sports Imaging Series

■ MR criteria for unstable meniscal tears include a tear greater than 1 cm in length, presence of more than one morphologic tear pattern, high T2 signal intensity within the tear plane, and presence of a displaced meniscal fragment.
■ Acute anterior cruciate ligament (ACL) tears are one of the most common causes for an acute large hemarthrosis in the athletic population, and 41%–75% of acute knee injuries with a hemarthrosis have an ACL tear.
■ MR imaging assessment of chronic posterior cruciate ligament (PCL) injuries is less reliable than assessment of acute injury, as continuity of PCL fibers in chronic injuries can be mistaken for a partial tear or even a normal PCL, particularly if prior imaging or accurate clinical information is lacking.
■ Collectively, the posterolateral stabilizers act primarily as restraints to varus stress and external rotation of the knee; of these, the fibular collateral ligament, popliteofibular ligament, and popliteus tendon are considered the most important biomechanically and are the structures addressed in anatomic posterolateral reconstructions.
■ Features that affect decision making with regard to treatment of medial ligamentous injuries include grade of injury, involvement of the posteromedial corner or cruciates, presence of osseous avulsive injury, degree of ligament retraction, entrapment of the deep medial collateral ligament (MCL) within the medial joint, and presence of a Stener lesion of the MCL.