The kneecap (patellar)
The kneecap, which is also called patellar, transfers the energy of the extensor muscles (quadriceps tendon) of the thigh onto the lower leg (patellar tendon). The kneecap slides like a kind of train of barges in a channel-shaped slide bearing of the thighbone. The sliding surfaces of the kneecap joint consist of joint cartilage, which reduces the load on the joint via its elasticity and which makes a frictionless function of the joint possible via its specific material. If these cartilage surfaces wear out, a cartilage damages will appear.