The popliteus muscle is a small muscle located at the knee joint.
A general task of the popliteus muscle is to stabilize the dorsal knee region.
During the knee extension, the slight outward rotation (about 5º) of the tibia on the femur locks the knee joint (the so-called terminal rotation). The popliteus muscle is responsible for reversing this terminal rotation:
- In open kinetic chain (i.e. the foot is not on the ground), the tibia is free to move. Therefore, the popliteus muscle acts on its insertion, inwardly rotating the tibia on the femur.
- In closed kinetic chain (i.e. the foot is on the ground), the tibia cannot rotate. In this case, the popliteus muscle will act on its origin, outwardly rotating the femur on the tibia.
Furthermore the muscle pulls the lateral meniscus dorsally during the knee bend thus preventing its entrapment. Even though the popliteus muscle anatomically ranks among the flexors of the thigh musculature its ability to flex the knee is truly negligible.
The popliteus muscle may be injured in the scope of a rupture of the anterior cruciate ligament or damages involving the lateral meniscus. In contrast, an isolated damage of the muscle is rather rare.
Clinically the affected patients present with an unnatural outward rotation of the tibia when bending the knee. Additionally other general symptoms often occur such as muscle swelling, edema or bleeding.