Muscles and Tendons Action of Muscles
Action of Muscles
The movements of the knee are flexion, extension and rotation. Flexion is performed by the hamstrings and biceps femoris and to a lesser extent the gastrocnemius and popliteus.
Flexion is limited by the soft tissues at the back of the knee.
Extension is performed by the quadriceps and because of the shape of the articulation and ligament attachments, the femur rotates medially on the tibia in terminal extension, the screw home mechanism that locks the joint. This movement is purely passive as are other rotatory movements occurring during flexion/extension and is due to articular geometry and static stabilisers.
The exception is lateral rotation of the femur that proceeds flexion by unlocking the joint. This movement is performed by the popliteus muscle. The sartorius, gracilis and hamstrings are weak rotators of the knee but probably do not act as such primarily.
