Popliteus is a triangularly shaped muscle situated deep in the popliteal fossa, below and lateral to the knee joint. It arises within the joint capsule from a tendinous attachment from the anterior aspect of the groove on the outer surface of the lateral condyle of the femur, below the lateral epicondyle and the attachment of the fibular collateral ligament. The tendon passes backwards, downwards and medially, crossing the line of the joint over the outer border of the lateral meniscus to which it is attached. This upper part, within the capsule of the knee joint, is enveloped in a double layer of synovial membrane until it leaves the capsule under the arcuate popliteal ligament, from which it has a fleshy origin. Continuing downwards and medially, popliteus attaches by fleshy fibres to a triangular area on the posterior surface of the tibia above the soleal line, and the fascia covering the muscle.
Popliteus is supplied by a branch from the tibial division of the sciatic nerve, root value L5, which enters the muscle on its anterior surface after winding around its inferolateral border. The skin covering the area is supplied mainly by S2.
Popliteus laterally rotates the femur on the tibia when the foot is on the ground, thus releasing the knee from its closepacked or locked position allowing the knee to flex. By exerting a backward pull on the lateral surface of the lateral condyle of the femur, the condyle is rotated laterally about a vertical axis running through it just medial to its centre. This allows the medial condyle of the femur to glide forward, releasing the ligaments and muscles involved in its closepacked position.
When strong flexion of the knee is required, popliteus comes into action, drawing the tibia backwards on the femoral condyles, and if the foot is off the ground, it will aid the medial hamstrings in medial rotation of the tibia.
Through its attachments to the lateral meniscus, it pulls the meniscus backwards during lateral rotation of the femur, preventing it from being trapped between the moving bones. This is believed by some authorities to be the reason for the lateral meniscus being damaged much less frequently than the medial.