Hyaluronic acid injection therapy is used to treat osteoarthritis (OA) of the knee. HA is a natural substance injected into the joint of the knee to cushion, lubricate and help protect knee joints with OA. Prior to injection of HA, the physician will inject a local anesthetic. This type of intra-articular injection is used when conservative therapies alone are not providing adequate relief of pain from OA. HA injections are performed by a physician using ultrasonic guidance. HA injections are completed in a series of three injections into the knee, each 4-7 days apart.