Popliteus is a small muscle which is often described as the key of the knee joint. It unlocks the knee joint by rotating the femur at the beginning of knee flexion to allow full knee flexion to occur.
Origin: Lateral condyle of the femur
Insertion: Upper posterior surface of the tibia, above the soleal (popliteal) line
Actions: Knee flexion
Internal rotation of the knee when it is flexed
Innervation: Tibial nerve
Daily uses: Walking