Knee Pain (Osteo Arthritis of the Knee):

Your knee is the largest joint in your body. When it's healthy, your knee joint moves easily and lets you walk, turn and squat without any pain. The network of bones, muscles, ligaments and other soft tissues in your knee all work together to keep your body stable and active.Knee joint pain can result from natural aging and breakdown of these bones and tissues. Pain can also come from overuse of the knee during high-impact activities and sports, or from acute injuries due to falls and missed footing. (Source http://www.orthovisc.com/knee-joint-pain)