According to the American College of Rheumatology, "Osteoarthritis is a joint disease that most often affects middle-age to elderly people. It is commonly referred to as OA or as "wear and tear" of the joints, but we now know that OA is a disease of the entire joint, involving the cartilage, joint lining, ligaments, and bone. Although it is more common in older people, it is not really accurate to say that the joints are just "wearing out.""