EUFLEXXA is an ultra-high purity hyaluronan, also called hyaluronic acid (HA) or sodium hyaluronate. HA is the natural substance found in the fluid that surrounds a healthy knee joint and helps cushion, lubricate, and protect the knee as you move throughout the day. EUFLEXXA is similar to the human HA found in healthy knee joints. When EUFLEXXA is injected into the knee joint, it works by replenishing the HA in the knee and restoring the synovial fluid's ability to cushion, lubricate, and protect the knee joint.