Knee joint function

The knee is the largest joint in the human body and is considered the most complicated one. It is formed by the lower part of the femur, the tibial plateau and the knee cap. It enables hinge and rotating movements as the connection between the upper and lower leg. This means that we can not only bend the lower leg backward but also rotate the lower leg and foot towards the upper leg.

Particular challenges are presented for the knee joint function: it must be fairly flexible while walking and bending and, at the same time, it is supposed to offer humans great stability while standing up.

There are two menisci located between the upper and lower leg bones in each knee. One on the right and one on the left side. 

The knee cap is located on the anterior side of the knee. It is embedded in the tendon of the thigh muscles. The knee cap serves the transmission of force while extending the knee and protects the internal regions of the joint.

The knee joint is surrounded by a joint capsule. The capsule is lined internally by a mucous membrane which produces synovial fluid, also known as synovia. It must be present in sufficient quantity in the required consistency. Just like a bike chain which must always be well lubricated so that nothing squeaks.

Like most articulating joints, the opposing bone areas are covered by a layer of cartilage so that the desired knee joint function is fulfilled properly. This smooth, firm and elastic layer ensures that the knee moves easily and without friction. The major constituent of the cartilage is water and only a fifth is composed of collagen fibres.

Healthy cartilage is like a sponge: during compression, metabolic products are squeezed outward and, during relaxation, nutrients can go inward. The cartilage is  nourished in this way since it is not supplied by blood vessels.

Two intersecting ligaments are located in the centre of the knee joint: the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL). Both of these ligaments have significant importance for the stability of the joint. Furthermore, the medial and lateral ligaments of the knee are important for it to be precisely guided through the full range of motion of the knee.

Aside from that, adequately trained muscles are quite imperative for good knee joint function. They also ensure support and stability. Muscles which are too weak often lead to knee problems.