The popliteus muscle

The popliteus muscle is a small muscle that forms the floor of the popliteal fossa. It belongs to the deep posterior leg muscles, along with tibialis posterior, flexor digitorum longus and flexor hallucis longus.

The popliteus muscle extends over the posterior aspect of the knee joint. It originates from the femur and the posterior horn of the lateral meniscus, and inserts on the proximal tibia.
The popliteus muscle plays an important role in the gait cycle by initiating the flexion of the fully extended (“locked”) knee. Thus, the popliteus is referred to as the “key to unlock the knee”. In addition, the popliteus muscle is the main stabiliser of the posterior knee region.