Hyaluronic acid (HA) injection is used to treat knee pain caused by osteoarthritis (OA) in patients who have already been treated with pain relievers and other treatments that did not work well. HA is similar to a substance that occurs naturally in the joints and helps the knee joint move smoothly and moisturizes the skin. There is limited evidence that HA supplements may help ease osteoarthritis symptoms in some people. High molecular weight (HMW) hyaluronic acid (HA) is a treatment option for knee osteoarthritis (OA).