The knee joint essentially consists of three bone parts:
On the joint surface of the thighbone, there are two bony protrusions, which are referred to as condyles. The joint surface of the shinbone is referred to as the tibial plateau. When in a healthy condition, both joint surfaces are covered with a layer of joint cartilage, that acts as a kind of shock absorber. The synovial fluid acts as a lubricant and enables smooth movements of the bones and reduces friction.
The menisci sit between the thighbone and the shinbone. The two menisci, medial and lateral, are crescent-shaped and consist of fibrocartilage. They enable force to be better distributed in the knee, thus protecting the cartilage-covered joint surfaces.
The kneecap is embedded in the tendon structure which extends from the thighbone to the shinbone. When the leg is stretched and flexed, the kneecap slides up or down thus stabilising the knee joint at the front.
Role of the Joint Capsule
The knee joint is surrounded by a fixed articular capsule, which seals it off from the surrounding tissue. The articular capsule produces synovial fluid, which supplies the cartilage with nutrients and helps the knee joint to move free from friction.
Stability and Movement Thanks to Ligaments and Muscles
The knee joint is stabilised by a complex set of ligaments:
The collateral ligaments hold the joint in place on the inside and outside, while the cruciate ligaments stabilise the front and rear of the knee joint. This means the knee is a very stable joint despite being subject to considerable forces, whereby the powerful leg movements are supported by strong muscles.