Arthritic elbow. Coloured X-ray of an arthritic elbow joint prior to replacement with a prosthetic joint. The elbow joint is where the humerus (upper arm bone, top right) joins with the two lower arm bones, the ulna (bottom) and the radius (centre left). Arthritis is a degenerative disease that causes the loss of the protective cartilage between joints. In this case this has led to the calcification (hardening, white) of tissue in the joint. There are many types of arthritis. The two most common are rheumatoid arthritis, in which the body's immune system attacks the joint's soft tissues, and osteoarthritis, which is caused by wear and tear. Both cause pain and stiffness. Treatment is with anti-inflammatory drugs, or in severe cases surgical elbow replacement.