Knee joint. Coloured X-ray of the healthy knee joint of a 78 year old patient, seen from the side. The knee is the largest joint in the body. It is formed by the articulation of the femur (thigh bone, upper centre) with the tibia (shin bone, lower centre). The smaller fibula (right of tibia) is also seen. The kneecap (patella, far left) lies over the lower part of the femur.