Anatomy of the knee joint

The knee joint is the second largest in the body after the hip joint. In the formation of the knee joint involved three bones: the distal femur, the proximal part of the lumbar bone and the patella.

Knowledge of anatomical and functional features of the knee joint is necessary for understanding the mechanism of injuries and diseases of the knee joint. For example, the ligaments are the main stabilizers in the knee joint. However, no less important is the soft tissue component, which includes mucous bags, fat bodies in the area of the pterygoid folds, menisci, and muscles that perform movements in the knee joint and stabilize it. Conditionally, all the stabilizers of the knee joint are divided into three groups: passive, relatively passive and active. Passive knee joint stabilizers include bones and the synovial joint capsule. To relatively passive - menisci, ligaments, fibrous capsule of the joint, to the active - the muscles and their tendons.

On the anterior and lateral surfaces above the knee joint is the quadriceps muscle of the thigh. The tendon of the quadriceps muscle of the thigh is formed from four bundles of tendons of the corresponding muscles: the most superficial rectus muscle of the thigh, the middle broad muscle located under it, to which the medial (right) and lateral (left) broad muscles adjoin. Above the knee joint, all parts of the tendons of the quadriceps muscle form a common tendon fixed to the base and lateral margins of the patella. Part of the fibers, following further on the front surface of the patella, reach the tuberosity of the lumbar bone, forming a patellar ligament beneath the apex of the patella. The other part of the bundles follows in the vertical direction along the sides of the patella, holding it and forming vertical supporting ligaments: medial and lateral, attached respectively to the medial and lateral condyles of the thigh.

The medial lateral ligament follows from the medial condyle of the femur, fuses with the medial meniscus and is attached to the anterior surface of the lumbar bone.

The fibers of the outer lateral ligament begin from the lateral condyle of the thigh, pass over the tendon of the popliteal muscle and attach to the fibula head, merging with the fibers of the tendons of the biceps femoris muscle. On the lateral surface of the thigh is a wide fascia that extends from the crest of the ilium and forms a tendon attached to the Girdian tubercle on the lateral epicondyle of the lumbar bone. Between the Gerdian tubercle of the lumbar bone and the lateral condyle of the femur, the tendon of the popliteal muscle is located in the notch. The gastrocnemius muscle consists of two muscle parts that originate from the posterior-upper sections of the condyles of the thigh.

The tendon of the medial head departs from the medial condyle of the thigh. The tendon of the external calf muscle is fixed to the lateral condyle of the hip. The tendon of the semimembranous muscle is attached to the posterior-medial surface of the proximal part of the lumbar bone. The anterior cruciate ligament originates on the inner surface of the external condyle of the femur, terminates in the anterior section of the intercondylar elevation and has its own synovial membrane.

The posterior cruciate ligament originates on the external surface of the inner condyle of the femur and terminates in the posterior section of the intercondylar elevation of the tibia.

Articulating articular surfaces of the lumbar bone do not correspond to the articular surfaces of the femur. The main element that maintains a uniform pressure distribution per unit area is the meniscus, which is a cartilaginous plate of triangular shape.

Their outer edge is thickened and fused with the joint capsule. The inner edge is free, pointed and inverted into the joint cavity. The upper surface of the meniscus is concave, the lower is flat. The outer edge of the meniscus almost repeats the configuration of the upper edge of the condylar cusp of the lobe, therefore the lateral meniscus resembles a part of the circumference, and the medial has a semilunar shape.

Meniscus performs two very important functions: the function of stabilizers and joint dampers. The external meniscus takes 75% of the load on the lateral part of the joint, and the inner meniscus takes 50% of the load on the corresponding joint department. The structure of the tissue of the meniscus corresponds more to the composition of the tendon, rather than the cartilage. The anterior and posterior horns of both menisci join the lumbar bone in the intercondylar zone via the meniscus-tibial ligament. The inner meniscus has a more tight attachment to the joint capsule than the outer one. The internal meniscus has a more rigid attachment to the capsular structures than the lateral meniscus. In the central part, the meniscus is attached to the capsule by means of a medial lateral ligament. Behind the posterior horn is attached to the posterior-medial capsular complex and has a particularly rigid attachment to the posterior oblique ligament. This attachment limits the mobility of the meniscus. It is less mobile than the outer meniscus. The internal meniscus is attached to the lobe of the pubescent bones by meniscus-typhoid or coronary ligaments; and posteriorly medially, through the capsular complex it is attached to a very strong m.semimembranosus. This attachment helps the meniscus to shift backward when bending the knee joint.

Even minor injuries of tendon fibers from the inner lateral ligament, posterior oblique ligament and semimembranous muscle lead to an increase in the mobility of the horn of the meniscus, and hence to the delay in the posterior bias of the meniscus with rapid bending of the knee joint, especially when combined with rotational loading.

The outer meniscus is spherical. It covers 2/3 of the underlying plateau of the sulcus and has the same capsular attachments as the inner meniscus, except for the defect, where the tendon of the popliteal muscle passes through the meniscus body and attaches to the outer condyle of the thigh. It is through this hamstring that the outer meniscus has greater mobility. This explains the fact that ruptures of the external meniscus are less common than internal. Anterior to lateral outer meniscus is attached to the tendon of the popliteal muscle. In the knee joint, there are several synovial bags lying along the muscles and tendons. There are three main bags located in front of the patella. The largest are the suprapatellar bag, located above the patella under the tendon of the quadriceps femoris muscle. The suprapatellar sac is the most superficial, located between the skin and the arch-shaped fascia and consists of transverse fibers, which partly originate from the orotibial tract and reach the tendon of the patella. Between the fibers of the rectus muscle of the thigh and the arcuate fascia is an intermediate layer that divides the joint space into two bags. Below the patella, behind the patellar ligament is a deep infra-patellar sac. Before the patella there is a small subcutaneous patella bag. Between the tendon of the semimembranous muscle and the medial head of the gastrocnemius muscle is also a small bag that has a connection with the joint cavity.

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