Anatomy of the knee joint

The knee joint is the second largest joint in the body after the hip joint. Three bones participate in the formation of the knee joint: the distal femur, the proximal tibia, and the patella.

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

On the anterior and lateral surfaces above the knee joint is the quadriceps femoris. The tendon of the quadriceps femoris is formed from four bundles of tendons of the corresponding muscles: the most superficial rectus femoris, located underneath it is the median vastus muscle, to which are attached the medial (on the right) and lateral (on the left) vastus muscles. Above the knee joint, all parts of the tendons of the quadriceps muscle form a common tendon, fixed to the base and lateral edges of the patella. Some of the fibers, following further along the anterior surface of the patella, reach the tuberosity of the tibia, forming the patellar ligament below the apex of the patella. Another part of the bundles follows in a 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 femur.

The medial collateral ligament originates from the medial condyle of the femur, fuses with the medial meniscus and attaches along the anterior surface of the tibia.

The fibers of the lateral collateral ligament originate from the lateral condyle of the femur, pass over the popliteal tendon, and attach to the head of the fibula, merging with the fibers of the biceps femoris tendons. On the lateral surface of the thigh is the broad fascia, which extends from the iliac crest and forms a tendon that attaches to the Herdiy tubercle on the lateral epicondyle of the tibia. Between the Herdiy tubercle of the tibia and the lateral condyle of the femur, the popliteal tendon is located in a notch. The gastrocnemius muscle consists of two muscle parts that originate from the posterosuperior parts of the femoral condyles.

The tendon of the medial head originates from the medial condyle of the femur. The tendon of the lateral head of the gastrocnemius is attached to the lateral condyle of the femur. The tendon of the semimembranosus is attached to the posteromedial surface of the proximal part of the tibia. The anterior cruciate ligament originates on the medial surface of the lateral condyle of the femur, ends in the anterior part of the intercondylar eminence and has its own synovial membrane.

The posterior cruciate ligament originates on the outer surface of the medial condyle of the femur and ends in the posterior part of the intercondylar eminence of the tibia.

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

Their outer edge is thickened and fused with the joint capsule. The inner edge is free, pointed and faces 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 condyles of the tibia, so the lateral meniscus resembles part of a circle, and the medial has a crescent shape.

The meniscus has two very important functions: the function of stabilizers and shock absorbers of the joint. The lateral meniscus takes 75% of the load on the lateral part of the joint, and the lateral meniscus takes 50% of the load on the corresponding part of the joint. In structure, the tissue of the meniscus is more similar to the composition of a tendon than to cartilage. The anterior and posterior horns of both menisci are attached to the tibia in the intercondylar zones by means of the menisco-tibial ligament. The medial meniscus has a tighter attachment to the joint capsule than the outer one. The medial 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 the medial collateral ligament. Behind, the posterior horn is attached to the posteromedial 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 lateral meniscus. The medial meniscus is attached to the tibia by the menisco-tibial or coronary ligaments; and posteromedially, through the capsular complex, it is attached to the very strong m.semimembranosus. This attachment helps the meniscus to move backwards when the knee joint is flexed.

Even minor injuries to the tendon fibers originating from the medial collateral ligament, posterior oblique ligament, and semimembranosus muscle lead to increased mobility of the posterior horn of the meniscus, and therefore to a delay in the posterior displacement of the meniscus during rapid flexion of the knee joint, especially in combination with rotation under load.

The lateral meniscus is spherical. It covers 2/3 of the underlying plateau of the tibia and has the same capsular attachments as the medial meniscus, except for a defect where the popliteal tendon passes through the body of the meniscus and attaches to the lateral condyle of the femur. It is due to this popliteal tendon channel that the lateral meniscus has greater mobility. This explains the fact that lateral meniscus tears are less common than lateral meniscus tears. Posterolaterally, the lateral meniscus attaches to the popliteal tendon. There are several synovial bursae in the knee joint, located along the course of the muscles and tendons. There are three main bursae, located in front of the patella. The largest is the suprapatellar bursa, located above the patella under the tendon of the quadriceps femoris. The suprapatellar bursa is the most superficial, located between the skin and the arcuate fascia and consists of transverse fibers that partially originate from the iliotibial tract and reach the patellar tendon. Between the fibers of the rectus femoris and the arcuate fascia is an intermediate layer that divides the joint space into two bags. Below the patella, behind the patellar ligament, is the deep infrapatellar bursa. In front of the patella is a small subcutaneous patellar bursa. Between the tendon of the semimembranosus muscle and the medial head of the gastrocnemius muscle there is also a small bursa that communicates with the joint cavity.

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