Coloured computed tomography (CT) scans of the healthy left knee joint of a 30 year old man (left) and the arthritic left knee of a 67 year old male patient (right). At right 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.