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Meniscus of the knee joint
Medical expert of the article
Articulating articular surfaces of the tibia do not correspond to those on the femoral. To maintain a uniform distribution of pressure per unit area in the appropriate range, and there are such anatomical entities as menisci. Meniscus of the knee joint is a semicircular connective tissue cord occupying the space between the tibia and the femur. The area of contact articulating surfaces in the joint is small, menisci significantly increase it. They are able to deform during movements, which allows the tibia to change the shape of the joint surface in full accordance with the change in the surface of the femur.
A careful study of the shape of the meniscus led anatomists to the conclusion that their sloping surface not only in the form of a barrier prevents the displacement of the tibia, but also contributes to the distribution of the vertical load on it but tangentially, that under extreme movements (jumping, running, etc.) significantly reduces the stress effect.
The knee joint meniscus is tightly attached to the tibia. When folded, they are displaced posteriorly. The mobility of the meniscus allows them to move in the anteroposterior direction independently of each other during internal and external rotation of the tibia. The medial meniscus of the knee joint has a more tight attachment to the capsule than the lateral one. In this regard, many authors note a higher incidence of ruptures of the internal meniscus. The most rigid it is attached to the place of retreat of the posterior oblique ligament. The knee joint meniscus is mainly avascular. Only their peripheral part is vascularized. The vascular zone of the meniscus feeds by alternating the compression and decompression of the cartilage of the meniscus during cyclic movements. This leaves the central part of the meniscus avascular and free from articulation, but it is this area that is predisposed to degenerative changes.
Half of the compression load on the knee joint. B is transmitted via the meniscus at extension and 85% respectively at 90 ° flexion in the joint. After its removal, the area of contact between the femur and the tibia is reduced by 50%. Even partial meniscectomy leads to a significant increase in pressure per unit area.
Types of meniscus of knee joint
The discoid knee joint meniscus is the most common form of the meniscus in the lateral section of the joint. Its frequency is from 2 to 15%. In this situation, the lateral meniscus covers almost the entire outer branch of the tibia. There are three types of this meniscus. The first two are full and incomplete - the usual variants of the structure. Peripheral attachment in these cases is standard. The third type is called the "Wrisberg ligament type", where the shortened Wrisberg ligament attaches the meniscus to the medial femoral condyle, thereby causing it to shift posteriorly with full extension in the joint. The first two types of meniscus are normal variants, although predispose to degenerative changes and ruptures, especially in the older age group. The third type - often makes itself felt in the early years of life, clinically it manifests as a "snapping" joint. There are some characteristic radiographic changes accompanying the discoid meniscus of the knee joint: flattening of the lateral condyle of the femur, widening of the outer part of the joint space, cup-like concavity of the lateral part of the tibia, high arrangement of the fibular head, flattening of the outer tubercle of the intercondylar elevation.