As you get older, chances are good that you'll want to know what is osteoarthritis, or OA. OA is the most common form of arthritis, and it affects almost all of us as we get older. Cartilage, or the cushion on the end of your bones in a joint, wears away with time, trauma or overuse. Eventually bone rubs against bone, causing pain and stiffness. You can find more information here: .