The knee joint joins the thigh with the lower leg and consists of two articulations: one between the femur and tibia, and one between the femur and patella.[1] It is the largest joint in the human body and is very complicated.[2] The knee is a mobile trocho-ginglymus (a pivotal hinge joint),[3] which permits flexion and extension as well as a slight medial and lateral rotation. Since in humans the knee supports nearly the whole weight of the body, it is vulnerable to both acute injury and the development of osteoarthritis. It is often grouped into tibiofemoral and patellofemoral components.[4][5] (The fibular collateral ligament is often considered with tibiofemoral components.) The knee is a hinge type synovial joint, which is composed of three functional compartments: the femoropatellar articulation consists of the patella, or "kneecap", and the patellar groove on the front of the femur through which it slides; and the medial and lateral femorotibial articulations linking the femur, or thigh bone, with the tibia, the main bone of the lower leg.[7] The joint is bathed in synovial fluid which is contained inside the synovial membrane called the joint capsule. The posterolateral corner of the knee is an area that has recently been the subject of renewed scrutiny and research. The knee is one of the most important joints of our body. It plays an essential role in mo ement related to carrying the body weight in horizontal (running and walking) and vertical (jumps) directions. Upon birth, a baby will not have a conventional knee cap, but a growth formed of cartilage. In females this turns to a normal bone knee cap by the age of 3, in males the age of 5. The articular bodies of the femur are its lateral and medial condyles. These diverge slightly distally and posteriorly, with the lateral condyle being wider in front than at the back while the medial condyle is of more constant width.[8] The radius of the condyles' curvature in the sagittal plane becomes smaller toward the back. This diminishing radius produces a series of involute midpoints (i.e. located on a spiral). The resulting series of transverse axes permit the sliding and rolling motion in the flexing knee while ensuring the collateral ligaments are sufficiently lax to permit the rotation associated with the curvature of the medial condyle about a vertical axis.[9] The pair of tibial condyles are separated by the intercondylar eminence[8] composed of a lateral and a medial tubercle.[10] The patella is inserted into the thin anterior wall of the joint capsule.[8] On its posterior surface is a lateral and a medial articular surface,[9] both of which communicate with the patellar surface which unites the two femoral condyles on the anterior side of the bone's distal end.