The knee joint is the largest joint in the human body. It is flexible and durable - after all, it depends on whether we will be able to move. Still, it is easy to damage. How is the knee joint built, how does it work, what diseases and injuries is it exposed to?
The knee jointis the most important joint in the human skeletal system. We need it for walking, running, climbing and cycling. So it is no wonder that it is the largest pond among its competitors. This makes it the most vulnerable and thus susceptible to numerous damage. Without it, the correct motor skills of the skeletal system are impossible.
Knee joint - structure
The knee joint connects the thigh with the shaving, so it is a femoral joint, the functions of which combine bending, extending and rotating. In the construction of the knee joint, we can distinguish the so-called articular surfaces. One of them is the articular head formed by the two convex condyles of the femur and the acetabulum consisting of the two condyles of the tibia and the patella.
The connection of these two articular surfaces is ensured by the patellar surface. The articular surfaces are covered with a thick cartilage from 3-4 mm, the greatest thickness is located on the kneecap articular surface and this is of key importance because thanks to this, the flexibility of the joint is increased and all shocks during walking and jumping are strongly reduced.
The knee joint also has strong protection in the form of ligaments - these are:
- sagittal collateral ligament
- tibial collateral ligament
- oblique popliteal ligament
- arcuate popliteal ligament
- anterior and posterior cruciate ligament
- transverse ligament
- posterior and anterior meniscal-femoral ligaments
- patellar ligament
- and numerous tendons
Thanks to these numerous safeguards, knee dislocations are rather rare.
Knee joint - mechanics
Mechanics of the knee joint is quite complex and we must come back to the previously discussed articular surfaces. So while we are standing on the acetabulum, the less curved, flatter, front parts of the femoral condyles are set up, so that when we stand the contact surface between the bonethe femoral and tibiae are the largest, the mass is transferred to the largest surface.
As you bend, more and more curved parts of the femoral condyles begin to contact the acetabulum of the tibia, the contact surfaces become smaller and the articular surfaces less fit.
Regarding therotational movement in the knee jointit can only be performed when the knee is bent as opposed to rotational movement in the elbow where moving the knee joint is independent of position of the bones in the elbow joint.
Such a complicated mechanics of movement in the knee joint requires further safeguards, this time concerning the acetabulum, which have movable restorations in the form of two sliding, crescent-shaped fibrocartilaginous rings, the so-called meniscus.
Meniscusincrease the articular surface of the tibia, they are connected with it by connective tissue strips. We distinguish:
- lateral meniscus (meniscus lateralis)
- medial meniscus (meniscus medialis)
The meniscus functionally divides the articular cavity into two floors. The upper floor between the meniscus and the femur allows for flexion and extension movements, the lower floor between the meniscus and the tibia for rotational movements.
During the movement of the knee joint, the menisci move on the acetabulum of the tibia, i.e. when straightened they move forward and when bent backwards. The path of such traffic is about 1 cm.
Lateral meniscushas a greater displacement thanmedial meniscus- it is of clinical significance because the damage is most often related to the medial, firmly attached meniscus and less movable, this is due to the sharp rotation of the tibia with the bent knee. In this case, removal of the menisci does not affect the movement impairment, but the straightening of the knee is disturbed, e.g. when walking uphill.
The mechanics of the knee joint would not be possible without supplying it with a bundle of muscles, e.g. the most important straightening muscle is the quadriceps muscle, its paralysis prevents the active straightening of the knee.
Among the most important flexion muscles:
- semimembraneous muscle
- semitendosus
- biceps muscle of the thigh
On the other hand, the muscles that enable rotational movements are the recurrent muscles:
- semimembraneous muscle
- semitendosus
- slender muscle
- tailor's muscle
- hamstring
and the inverters:
- biceps muscle of the thigh
- muscle tensioner of the broad fascia
Knee joint - diseases
Diseases related to the knee joint may have a different etiology. Among which we distinguish:
- infections
- autoimmune diseases
- urazy
- metabolic disorders
- degenerative changes
- cancer
The most common manifestations originating in the knee joint are degenerative changes, which are defined as the result of the action of biological and mechanical factors destabilizing the related processes of degradation and synthesis of articular cartilage and the subcartilage layer of bone.