The knee is the largest and most complex joint in the body. The knee joins the thigh bone (femur) to the shin bone (tibia). The surface of the end of each bone is covered with smooth articular cartilage to allow easy movement between them. Between these bones, there are two crescent-shaped shock-absorbing pieces of cartilage called menisci that lie on the top surface of the tibia. The menisci allow the femur to move on the tibial surface without friction, preventing the bones from rubbing on each other.
The kneecap (patella) articulates with the cartilage of the femur.
Several ligaments (thick bands of tissue) connect these bones together. The four key ligaments of the knee are:
• Anterior cruciate ligament (ACL)
• Medial collateral ligament (MCL)
• Lateral collateral ligament (LCL)
• Posterior cruciate ligament (PCL)
The joint capsule is a thick ligamentous structure that surrounds the entire knee. Inside this capsule is a membrane known as the synovial membrane which produces synovial fluid which lubricates the knee joint and provides nourishment to the cartilage.