Coloured frontal computed tomography (CT) scan of the left knee of a 67 year old male patient. The narrowed spacing of the femorotibial joint and between the knee cap (patella) and thigh bone (femur) indicates advanced osteoarthritis. Osteoarthritis is a degenerative joint disease that results from the breakdown of joint cartilage and the underlying bone, resulting in joint swelling, pain and a decreased range of motion.