The knee is a hinged joint, comprised of three bones and four main ligaments.  The basic design of the knee allows for flexion and extension.


The three bone structures of the knee are the femur (thigh bone), tibia (shin bone), and the patella (kneecap).  These structures are connected by four major ligaments; ligaments connect bones to other bones.  The ACL prevents forward movement (anterior translation) of the lower leg as well as stabilizes the knee from rotational stress of the tibia.  When rotational stress is applied when a cut or quick change in direction is performed, the ACL prevents anterior translation of the tibia, thus preventing tibial subluxation during the movement.
The shock absorbing structures between the femur and tibia are the medial and lateral meniscus.  The weight-bearing surfaces of the knee are covered by articular surface cartilage allowing the joint to move freely.  The menisci act as shock absorbers and work in conjunction with the articular cartilage to reduce stresses placed upon them with movement.
The four main ligaments of the knee are:

• Anterior Cruciate Ligament (ACL)
• Posterior Cruciate Ligament (PCL)
• Medial Collateral Ligament (MCL)
• Lateral Collateral Ligament (LCL)
These ligaments connect the femur to the tibia and provide the structural integrity to the knee.  There are other structures within the knee that are important for proper function such as the menisci, articular cartilage and the patella.