Arthritis. Coloured gamma camera scan of a patient's knee joints, showing one of the joints affected by arthritis. At left, the hot spots" of the disease are coloured yellow. Arthritis is the inflammation of a joint characterized by pain, swelling and stiffness, and in severe cases joint deformity. Osteoarthritis is a degenerative form of the disease resulting from wear and tear, and most commonly affects elderly people. Rheumatoid arthritis is the most severe type of inflammatory joint disease. It is a disorder in which the immune system acts against the body, damaging body joints and surrounding tissues. The radioactive tracer Technetium-99m was used in this gamma scan."