Structure of the Knee Joint

Structure of the Knee Joint

The knee joint is the largest synovial joint, and is composed of 2 main biological systems: a bone and ligament system. The femur and tibia are connected by 2 condyloid joints. These 2 condyloid joints in the knee permit uniaxial movement in the knee. Although, condyloid joints are typically biaxial, the two in the knee joint combine to create one uniaxial joint. The patella is located in the front of the knee, and is used as a protective cover to the knee joint. Bursae are also protective to the knee joint. The bursae are the fluid sacs and synovial pockets that surround and sometimes communicate with the joint cavity. Thin-walled and filled with synovial fluid, they represent the weak point of the joint, but also produce enlargements to the joint space. They can be grouped into either communicating or non-communicating bursae. There are a total of 24 bursae in the knee joint.

There are 4 main ligaments in the knee, the medical collateral ligament, lateral collateral ligament, anterior cruciate ligament, and posterior cruciate ligament. Cruciate means cross, and collateral mean parallel. These terms indicate how they are positioned in the knee and with respect to other ligaments. The medial collateral ligament is located at the inside of the knee joint. It extends from the medial femoral epicondyle to the tibia. This ligament prevents excessive abduction of the knee. The lateral collateral ligament is located at the outside of the knee joint. It extends from the lateral femoral epicondyle to the head of the fibula. This ligament prevents excessive adduction of the knee. The anterior cruciate ligament extends posterolaterally from the tibia and inserts on the lateral femoral condyle. This ligament prevents excessive posterior movement of the femur on the tibia. The posterior cruciate ligament extends anteromedially from the tibia posterior to the medial femoral condyle. This ligament prevents excessive anterior movement of the femur on the tibia. These 4 ligaments are there to provide strength, structure, and to restrict specific movement.The knee is one of the most injured joints due to its complex ligament system. The MCL, ACL, and LCL are some of the injured ligaments in the knee. This is due to their placement in the knee joint, for example the ACL is positioned on the side of the knee, and is put under stress whenever a force is applied to the side of the knee. Partial or even complete tears of the posterior cruciate or the collateral ligaments can often heal with a prescribed rehabilitation programs. However, if more than one ligament is injured, surgery is often needed.

The knee is one of the most complex, if not the most complex joint in the body. This it due to its uniqueness; it's the largest, has the most ligaments, and has the most bursae. It's due to the knee's complexity that is has the most problems of all joints.