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Figure 2a. Posterolateral corner injury. (a) Sagittal spin-echo intermediate-weighted MR image (2,000/20) through the intercondylar notch shows a thickened posterior cruciate ligament (arrows) with intermediate signal intensity throughout, indicative of a torn posterior cruciate ligament. (b) Coronal fast spin-echo T2-weighted fat-suppressed MR image (3,000/70) reveals a torn medial collateral ligament (arrow). (c) Transverse fast spin-echo T2-weighted fat-suppressed MR image (3,000/70) at the level of the joint shows the posterior capsule (straight arrow) of the medial side of the joint, which is not evident on the lateral side. This indicates a torn arcuate ligament (which should be seen as a thickening of the lateral capsule at the joint line). In addition, the popliteus tendon (curved arrow) has high signal intensity within and a distended tendon sheath. (d) Transverse fast spin-echo T2-weighted MR image (3,000/70) several centimeters distal to the joint shows high signal intensity surrounding the popliteus muscle (arrow), indicative of injury. At surgery, the popliteus muscle was torn at the musculotendinous junction, and the posterior cruciate, medial collateral, and arcuate ligaments were torn.