Osteoarthritis. Conceptual computer artwork of an arthritic ball and socket joint (foreground, centre) resulting from general wear and tear. Ball and socket joints are found in the human body in the shoulder and the hip. Arthritis is a degenerative disease that causes the loss of the protective cartilage between the joints. There are many types of arthritis. The most common are rheumatoid arthritis, in which the body's immune system attacks the joints' soft tissues, and osteoarthritis, which is caused by wear and tear. Both cause pain and stiffness. Treatment is with anti-inflammatory drugs and, in severe cases, surgical joint replacement.