False-colour X-ray of an arthritic knee joint, showing the erosion of cartilage on the tibia, the larger of the two bones in the lower leg, & the resulting narrowing of joint space. Arthritis is an inflammation in one or more joints, character- ised by swelling, warmth, redness of the overlying skin, & restriction of motion. It may be caused by many other diseases, including gout & tuberculosis. Osteoarthritis occurs in old age through overuse of a joint. Treatment consists of using anti- inflammatory drugs or steroids; reduction of pressure on the joint through losing weight or using a walking aid; and corrective or prosthetic surgery.