What is it?

Arthrocentesis is a procedure in which the doctor takes a sample of the fluid in a joint out for testing.

What is the purpose?This procedure is used to find the cause of pain or swelling in a joint. Infection or gout, among other conditions, can cause fluid to form in joints, resulting in pain or swelling. Analysis of the fluid may help differentiate between types of arthritis with similar symptoms. Joint fluid can be tested for white cell count, crystals, protein, glucose, and cultured for infection. It may also be done as a treatment, draining excess fluid may lessen pain.
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 Is there any special preparation?There are usually no special pre-test instructions.How is it done?The doctor will examine the joint and find the best spot to enter the joint. The skin is cleaned with an antiseptic. The doctor will then numb the area, either with a cream or spray, or with an injection using a tiny needle. The aspirating needle is then inserted and guided into the joint space. The person under going the procedure may feel a “pop” as the needle enters the joint capsule. The excess fluid is drawn up into the syringe and the needle is removed. A bandaid is usually applied.What happens afterwards?There may be specific instructions given. Generally, the area should be iced as needed and the joint should be rested for several hours. What are the risks of this procedure?Infection and bleeding may occur. Any signs and symptoms of infection should be reported.

Does it hurt?There may be some pain felt during the procedure, though it shouldn’t be severe. Let the doctor know if you experience severe pain during the procedure.

Etc.Arthrocentesis may also be known as joint tap, synovial fluid analysis and joint aspiration. The entire procedure takes just a few minutes. For more information:

MedicineNet – Joint Aspiration
The Physician & Sports Medicine – Knee Aspiration

Yale University School of Medicine, Patient’s Guide to Medical Tests
Adult Health Advisor -Arthrocentesis, Copyright © Clinical Reference Systems 1999