<p>Osteoarthritis (OA) is the most common form of arthritis in the United States, affecting an estimated 21 million adults. OA begins with the breakdown of joint cartilage, resulting in pain and stiffness.  OA commonly affects the joints of the fingers, knees, hips, and spine. Other joints affected less frequently include the wrists, elbows, shoulders, and ankles. When OA is found in a less-frequently affected joint, there is usually a history of injury or unusual stress to that joint.</p>
