How is the knee joint structured?

Being the largest joint in the body the knee joint has important jobs to do: whenever we walk, run or sit our knee joint is active. It is subjected to substantial loads every day because after all it bears the whole weight of our body. As a moving link between the thigh and the lower leg it makes it possible to flex and stretch the leg and also allows slight rotation of the lower leg in relation to the thigh.

As a link between the thigh and the lower leg the knee joint comprises parts of two bone structures:

• the femoral condyle: curved (convex) lower end of the thigh;
• the tibial plateau: recessed (concave) plateau in the tibia

.When they are healthy the two parts of the joint are surrounded by a layer of joint cartilage which acts as a lubricant. The intra-articular space between the femoral condyle and the tibial plateau also contains the crescent-shaped menisci, which are made of cartilage. They alleviate pressure on the joint and thus protect the joint surfaces covered by cartilage.

The knee joint also includes the kneecap, which is a bone embedded in the knee extensor tendon. When the leg is stretched and flexed, the knee slides up or down and thus stabilises the knee joint at the front.

The fixed joint capsule forms an envelope around the knee joint to seal it off from the surrounding tissue. This capsule produces so-called synovial fluid which serves to ensure friction-free movement of the knee joint and also supplies the joint cartilage with essential nutrients.

The knee joint owes its stability to a complex set of ligaments:

on the inside and outside of the joint collateral ligaments provide stability whilst the interior of the joint is stabilised by the anterior and posterior cruciate ligaments. As a result the knee is an extremely stable joint, despite the high forces acting on it. In addition, it is surrounded by powerful muscles which enable the legs to be moved with great force.