Knee and Hip Osteoarthritis : When you suffer from osteoarthritis (OA), joints-most often the hands, knees, hips, and spine-become inflamed and painful. Simple everyday tasks can turn into nightmares. Go inside your body to view exactly how OA happens. See the human skeleton and the workings of your most complex joint-the knee joint. You'll watch as cartilage deteriorates, fissures, and starts to shred, leading to OA. Aging is the most common cause of OA. Other causes include athletic and overuse injuries, genetics, and obesity. See how you can break the cycle of pain and swelling with noninvasive treatments. If pain becomes so bad that life is no longer enjoyable, surgical replacement of the hip or knee may allow someone with OA to exercise and gain a new lease on life.