Osteoarthritis. X-ray of a front view of the knee of a 73 year old man showing osteoarthritis, joint damage caused by wear. It has caused a lack of space between the femur (thigh bone, upper right) and the tibia (shin bone, lower right) due to erosion of the cartilage lining the joint. The fibula (lower centre) is also seen next to the tibia. This man also has rickets, in which the bones do not form properly during childhood due to a lack of vitamin D. Vitamin D helps the bones to absorb calcium, which is essential for correct growth. The legs are bowed outwards in rickets, seen by the curvature here. Osteoarthritis is treated with painkiller drugs and physiotherapy.