The knee joint is a relatively complex anatomical structure. In addition to a variety of ligaments to maintain stability and the presence of large muscle groups, internally, it is a classic example of a synovial joint. Both the femur and tibia are enclosed in a joint capsule lined with synovial tissue. Between the condyles of the femur and the condylar surface of the tibia are menisci, which serve as shock absorbers for the knee joint, located medially and laterally inside the joint. Between each muscle group are fluid-filled sacs called bursa and the presence of fat bodies named for their location which reduce friction and lend added protection to the joint capsule. During normal activity such as walking or running, and even for support while standing, the knee will function superbly. It can tolerate moderate stress without significant injury. However, the knee lacks support to withstand many types of injury, especially rotational forces such as those seen in many athletic activities. Knee injuries, even though minor, may require surgery, and if they involve the cartilage, may have delayed healing time due to a lack of blood supply to the cartilage.
The knee joint is the largest, most complex, and probably the most vulnerable joint in the body. The knee joint is a complex hinge joint and in addition to flexion and extension permits limited rolling, gliding, and rotational movement. It is formed by the femur superiorly on two rounded surfaces called condyles and inferiorly to the tibia, or the shinbone. On the outer aspects of both condyles are the epicondyles, which serve as sites for muscle and ligament attachment. In the space between the condyles is a depression called the intracondylar fossa, which is the site of attachment of the cruciate ligaments, the chief rotational stabilizing ligaments of the knee. On the superior aspect of the medial epicondyle of the femur is the adductor tubercle which serves as the site for muscle insertion to the adductor magnus muscle, one of three muscles that bring our legs in medially and helps to flex the thigh. The knee is held together by a complex ligamentous system and the site of muscle attachment for some of the most powerful muscles in the body.