Popliteus muscle assists in flexing the leg upon the thigh; when the leg is flexed, it will rotate the tibia inward. It is especially called into action at the beginning of the act of bending the knee, inasmuch as it produces the slight inward rotation of the tibia, which is essential in the early stage of this movement. When the knee is in full extension, the femur slightly medially rotates on the tibia to lock the knee joint in place. Popliteus is often referred to as the "Key" to unlocking the knee since it begins knee flexion by laterally rotating the femur
Douzhanopterus then the fourth, which is still about 80% the length of the second. Fused entirely to the sacrum is the pelvic girdle. The portion of the pelvic girdle in front of the femoral joint appears to consist of two unfused prepubes, which are longer than they are wide. The femur is slightly curved, and the femoral head and neck form an angle of about 150° with the shaft. On the lower leg, the relatively straight tibia is about 180% the length of the femur; the fibula, which is about 45% the length of the tibia, is fused to it at