One out of every three adults has arthritis. There are two main types of arthritis: osteoarthritis and rheumatoid arthritis. Both involve painful inflammation of the joints. Osteoarthritis occurs when the cartilage between the joints breaks down. The knees, fingers, and the wrists are usually affected. Rheumatoid arthritis may impact joints as well as different areas of the body, such as circulation, lungs, and heart.