Osteoarthritis. Coloured X-ray of the knee of a 61 year old man, showing signs of osteoarthritis and the fixation staple (yellow) of a previous surgical procedure. In a healthy knee there would be a clear gap between the heads of the femur (thigh bone) and the tibia (shin bone). Osteoarthritis is a degenerative disease that leads to a loss of the protective cartilage, causing this gap to narrow. This results in pain and stiffness. The fixation staple is from a previous tibial osteotomy, a correctional procedure that involves removing a piece of the tibia to change the alignment of the shin and knee. This redistributes the weight to less worn areas of the knee, helping to relieve the pain.