Anatomy and Function
The knee is a complex joint made up of bones, muscles, tendons, ligaments, and cartilage. It may be described as a hinge joint, similar to the hinge on a door. The knee not only bends back and forth but also has a complex rotational component that occurs with flexion (bending) and extension (straightening).
Each knee has two crescent-shaped menisci, or cushion pads which are made of cartilage. The lateral meniscus lies at the outer side of the knee and the medial meniscus lies at the inner side of the knee. The strong but flexible menisci act as shock absorbers between the femur (upper thigh bone) and the tibia (shin bone), especially during weight bearing activities such as walking or climbing stairs. The menisci also stabilise and evenly distribute your body weight across the knee joint.
The Anterior Cruciate Ligament (ACL) is one of a pair of crucial or main ligaments that forms a cross in the centre of the knee joint. Both the ACL and the Posterior Cruciate Ligament (PCL) function to stabilise the knee from front to back. The ACL limits the forward movement of the tibia, and the PCL limits the backward movement of this bone. Additional ligaments provide stability to other movements at the joint, including angulation (left/right motion) and rotation. Without such stability, you may feel that your knee is simply giving out from under you.