Arthrocentesis is joint aspiration, a procedure whereby a sterile needle with syringe are used to drain fluid from a joint. This is usually done as an office procedure or at the bedside in the hospital. Joint fluid is typically sent for examination to the lab to determine the cause of the joint swelling, such as infection, gout, and rheumatoid arthritis. Arthrocentesis can be helpful in relieving joint swelling and pain. Occasionally, cortisone medications are injected into the joint during the arthrocentesis in order to rapidly relieve joint inflammation and further reduce symptoms. However, the benefit us usually only temporary.