[Imaging of posterolateral rotational instability of the knee joint]

Posterolateral instability of the knee joint typically occurs with injuries to the posterolateral corner of the joint or with additional combined injuries involving the anterior and posterior cruciate ligaments. In addition to numerous, smaller anatomical structures, the most important are the lateral collateral ligament (LCL), the popliteus muscle with its tendon, and the popliteofibular ligament (PFL), which can usually be assessed using magnetic resonance imaging (MRI). On the contrary, small structures like the arcuate ligament and fabellofibular ligament cannot always be identified. However, they are also of lesser importance in the development of posterolateral rotational instability. Overlooked injuries to the posterolateral joint corner promote instability with the complication of inadequate ligament reconstruction and early onset posttraumatic osteoarthritis. Knowledge of MRI morphology of the anatomical structures involved, taking into account their biomechanical significance, is crucial to recognize and use the corresponding imaging findings.