Osteoarthritis is the most common form of more than 100 kinds of arthritis. Osteoarthritis, also called degenerative joint disease or “wear and tear” arthritis, affects more than 20 million Americans, and is more common as we age. Osteoarthritis results when the protective cushion of cartilage covering the ends of the bones breaks down and wears away, causing irritation, stiffness and pain. Osteoarthritis can affect any joint, but is most common in the hands, spine and especially the large weight-bearing joints, such as the knees and hips.