The knee joint
The knee joint is a hinge joint, but it is not a true hinge joint because, as well as flexion and extension, it also allows slight medial and lateral rotation.
The condyles of the femur articulate with the proximal end of the tibia. The patella, attached to the quadriceps tendon, helps to provide a better angle of pull, and is a functional part of the knee joint. The fibula is not part of the knee joint and therefore the tibia bears all the weight. The weight-bearing function of the knee is considerable and it is important that the ankle, knee and hip are aligned properly to allow the line of stress to pass through the centre of the knee joint.
The strong ligaments surrounding the knee and the large muscle groups of the thigh help to maintain the most mechanically efficient position.
At the knee joint, flexion and extension are the main movements, which are caused by the quadriceps group of muscles. This group consists of four muscles – rectus femoris, vastus medialis, vastus intermedius and vastus lateralis – and is located on the anterior thigh.
The antagonist to the quadriceps group is the hamstrings group of muscles located on the posterior thigh. This group consists of three muscles – the biceps femoris, semitendinosus and semimembranosus – and are the prime movers of knee flexion, and also rotate the knee when it is semi-flexed.