Joint replacement surgery, which replaces a damaged or diseased joint with an artificial joint, has helped millions of people reduce chronic pain and restore mobility and independence. Knees and hips are the joints most frequently replaced via these procedures, with over a million Americans having one of these joints replaced every year, according the National Institutes of Health. So why do so many people need joint replacement? In many cases, arthritis is the answer to that question, as the disease causes joint damage and deterioration that can lead to chronic pain and significant disability, severely impacting quality of life.