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the movable connection of the femur with the tibia of the crus and the kneecap, or patella, in man and most terrestrial vertebrates.
The principal movements in the knee joint are flexion and extension of the crus. In man, the knee joint is formed by the condyles of the femur, the superior articular surface of the tibia, and the articular surface of the patella. The intercondylar eminence is located between the external and internal condyles of the tibia. The curvature of the articular surfaces of the condyles of the femur does not correspond in radius to the curvature of the articular surface of the tibia. This noncorrespondence, or incongruence, is to some extent equalized by two crescent-shaped cartilaginous formations called the menisci, which are thickened along their peripheries. The flat inferior surfaces of the menisci face the superior articular surface of the tibia, and the concave superior surfaces face the condyles of the femur. The inner edges of the menisci are attached by thick ligaments to the intercondylar eminence; the thickened outer edges are fused with the inner synovial membrane of the bursa. Anteriorly, the menisci are joined to one another by the transverse ligament of the knee. Thus, the ends of the menisci are fixed. However, their bodies remain capable of shifting, which makes minor rotational movements possible when the knee is bent.
The principal ligaments of the knee joint are the cruciform, which cross each other from the external and internal condyles of the femur and attach to, in front of, and behind the intercondylar eminence. The bursa is fortified anteriorly by three broad bands, which are formed by ligamental fascicles of the quadriceps muscle of the femur. As though woven into the middle band is the patella, which covers the knee joint anteriorly. Laterally, the bursa is fortified by the internal, or medial, ligament of the tibia and the external, or lateral, ligament of the fibula. These ligaments prevent lateral movement and rotation of the crus when the extremity is extended. The posterior surface of the bursa is fortified by the tendons of the muscles of the crus and thigh, which are interwoven in it. The synovial membrane that covers the articular capsule internally lines the articulated surfaces and the cruciform ligaments, forming several pockets (involutions and bursae), of which the largest is located behind the tendons of the quadriceps muscle. These synovial bursae, which are located at the points of attachment of the muscles surrounding the joint, communicate with the cavity of the joint.
Blood is supplied to the knee joint by branches of the popliteal artery, which passes through the popliteal fossa, and by two return branches of the anterior tibial artery and the descending genicular artery (a branch of the femoral artery). Blood from the knee joint is collected by the great saphenous and deep femoral veins. The joint is innervated by branches of the lumbar and sacral plexuses.
M. A. KON