MR Imaging of Posterolateral Corner Injury of the Knee

Although injuries to lateral knee structures are less common than medial knee structures injuries but are important because they may be more disabling, frequently overlooked at clinical examination and also overlooked in interpretation of knee MRI studies due to association with cruciate ligaments and medial knee structures injuries which are more easily recognizable at MR images. The lateral knee stabilizers are composed of a complex arrangement of ligaments, tendons, and muscles. We can evaluate these structures by routine magnetic resonance (MR) imaging sequences performed in the sagittal, coronal, and axial planes. Anterolateral stabilization is provided by the capsule and iliotibial tract. Posterolateral stabilization is provided by the arcuate ligament complex, which comprises the lateral collateral ligament; biceps femoris tendon; popliteus muscle and tendon; popliteal meniscal and popliteal fibular ligaments; oblique popliteal, arcuate, and fabellofibular ligaments; and the lateral gastrocnemius muscle. Structures of the anterolateral quadrant are most frequently injured; posterolateral instability is considerably less common. Practically all tears of the lateral collateral ligament are associated with damage to posterolateral knee structures. Most injuries of the popliteus muscle and tendon are associated with damage to other knee structures. MR imaging can demonstrate these injuries. Familiarity with the musculotendinous anatomy of the knee will facilitate accurate diagnosis with MR imaging.