“Due to the shape of the condyles and the menisci, and the location of ligaments of and muscles acting on the knee, the joint rotation axis is located medially in the knee joint. This also in part explains why the lateral condyle and meniscus are more mobile. Maximum extension of the knee is caused by these factors and the “screw home” mechanism of the cruciate ligaments. The popliteal muscle is connected with the lateral meniscus and the caput fibulae: it locks the knee joint in and unlocks the knee joint out of its maximum extension. Moreover, it plays an important role for proprioception in the knee joint and is known to cause posterolateral knee pain.
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from: http://www.anatomy-physiotherapy.com/…/94-test-your-knowled…