In medicine, a joint injection is a procedure used in the treatment of inflammatory joint conditions, such as rheumatoid arthritis, psoriatic arthritis, gout, tendonitis, bursitis and occasionally osteoarthritis. A hypodermic needle is injected into the affected joint where it delivers a dose of any one of many anti-inflammatory agents, the most common of which are corticosteroids. Hyaluronic acid, because of it's high viscosity, is sometimes used to replace bursa fluids.