In the knee joint the thigh bone (femur) moves together with the shin bone (tibia). The second bone in the lower leg, the fibula, is not part of the knee joint. The joint surfaces at the ends of the bones are covered with cartilage; this allows the bones to move smoothly and gently against each other. The joint surface of the femur, consisting of a medial and lateral condyle, is convex, whereas the joint surfaces of the tibia on the tibial head are slightly concave. The hollow spaces created at the edges are filled in by the menisci (i.e. the medial (inner) meniscus and lateral (outer) meniscus). The menisci are wedge-shaped pieces of cartilage with a “half moon” shape. By serving as “shock absorbers” in the knee, the menisci play a central role for movement and loading of the knee joint.

The third bone in the knee joint is the kneecap or patella. Together with a joint surface on the femur, the patella forms a joint within a joint. During each bending and extension of the knee joint, the patella glides upward or downward. The patella is fitted into the tendon of the femoral extensor muscle which is anchored on a projecting part of the tibia.

The ligaments ensure that the knee joint is guided firmly and exactly. There is a medial and lateral collateral ligament as well as two cruciate ligaments, the anterior cruciate ligament and the posterior ligament, inside the joint.

During knee joint movement, the ligaments – acting together with the muscles – guide and support the knee. Strong healthy muscles are an absolute must here.

Like all joints, the knee joint is enclosed in a joint capsule. The joint capsule consists of two parts: a taut joint capsule which protects the joint as a whole and a soft inner joint capsule (snyovia) which produces joint fluid (synovial fluid); the primary function of the synovial fluid is to nourish the cartilage and decrease friction.