The largest joint in your body if your knee joint. The knee is the lower joint connecting your lower and upper leg and supports nearly the entire weight of the human it belongs to, so it has to be pretty big to cope with various weights and body sizes. The knee is a complex piece of machinery and actually comprises two separate joints. The femoro-patellar joint, which consists of the patella or knee-cap to you and me, and the sesamoid bone, which sits within the tendon of the thigh muscle.
The joint is lubricated with a fluid which allows the knee to become flexible. In high sports such as wrestling, American football, competitive swimming and hockey, these can cause great stress to the knees and it is not uncommon for most sportsmen or women to tear one or more knee ligaments. Running, especially competitive running, can also cause a great deal of damage to the knee and cause on-going problems if it is not fixed.