General information about the knee joint
The anatomical structure of the knee joint
The knee joint is the largest joint in the human body and represents the movable connection between the thigh (femur) and the lower leg (tibia). Three bones together with a complex capsule and ligament apparatus (collateral and cruciate ligaments) form the framework of the knee joint. These are:
- The thigh rolls (femoral condyles)
- The head of the tibia (tibial plateau)
- The kneecap (patella)
The figure above shows that the bones are in close contact with each other.
To ensure that pain-free and undisturbed mobility of the knee joint can also take place at the contact surfaces, the bones at the respective contact surfaces are covered with a very smooth, whitish cartilage layer, the so-called hyaline cartilage. Only through this layer is painless and undisturbed mobility of the knee joint possible. The hyaline cartilage is composed of cartilage cells and matrix tissue.
While adult cartilage cells have lost their ability to divide and thus heal, child cartilage cells can repair cartilage wounds by multiplying. The cartilage cells are embedded in the matrix tissue they produce themselves. This consists mainly of water and supporting tissue and gives the cartilage tissue both stability and elasticity.
In the knee joint itself, a distinction is made between the femoral condyle and the kneecap (femoropatellar joint) as well as the femoral condyle and the tibial head. The connection between the femoral condyle and the kneecap (patella) is the most heavily loaded part of the knee joint. When climbing stairs, for example, this joint is loaded with more than three times the body weight.
The most important tendon of the knee joint is the patellar tendon (patella tendon/patellar tendon), which runs from the kneecap at the front of the knee joint as a strong strand to the tibia (tibial tuberosity). The knee joint is encased by the knee joint capsule, the inner part of which is called the synovial membrane. It forms the synovial fluid that is important for the nutrition of the cartilage.
In adults, cartilage tissue is mainly nourished by diffusion (passive transport) from the synovial fluid, because cartilage tissue, unlike other tissues of the body (muscles, bone skin, etc. ), is not supplied with blood. The usual nutrition via the bloodstream therefore does not work.
Movements of the knee joint mix the synovial fluid and thus improve the absorption of nutrients by the cartilage cell (chondrocyte). The correct amount and composition of the synovial fluid is also crucial for the lubrication of the knee joint. It minimizes the friction of the corresponding cartilage surfaces during movement.
Hyaline cartilage has an extremely low frictional resistance, lower than all known artificial material pairings. Between the femoral condyle and the tibia there are two fibrocartilaginous discs (meniscus), which act as a buffer between the cartilage surfaces and are important for even pressure distribution in the knee joint under load. The cruciate ligaments run through the knee joint and connect the thigh with the lower leg.The main task of the cruciate ligaments is to ensure a stable knee joint and thus to enable a harmonious, low-friction movement sequence.
The two cruciate ligaments prevent the knee from shifting forward (anterior cruciate ligament) or backward (posterior cruciate ligament) under load. In their stabilizing effect, they are supported by the collateral ligaments (collateral ligaments), the knee joint capsule and the muscles that grip the knee. The knee-reclosing musculature makes up the function of the knee joint.
It is only through these muscles that movement becomes possible. They also support the passive joint stabilizers of the capsule-ligament apparatus. The extensor muscles of the knee joint (quadriceps muscles) on the front of the thigh are very strong.
The muscles are involuntarily activated when the knee joint is bent in order to avoid buckling when walking. The most important flexors of the knee joint are the ischiocrural muscles on the back of the thigh, which also have an active stabilizing effect on the knee joint. The ischiocrural muscles support the anterior cruciate ligament in particular, which is why their training is particularly important after a torn cruciate ligament.
