What is arthrocentesis?

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

When is it used?

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.

Examples of alternatives are:

• to have MRI (magnetic resonance imaging)

• to choose not to have treatment, recognizing the risks of your condition.

You should ask your doctor about these choices.

How do I prepare for arthrocentesis?

Follow any instructions the doctor gives you.

What happens during the procedure?

The doctor will clean the area around the joint and may give you a local anesthetic. He or she will insert a needle into the joint cavity and withdraw fluid. The doctor will put pressure on the place where the needle was inserted, and may put a bandage on it. He or she will send the fluid sample to a lab. The doctor may inject the joint with drugs that prevent inflammation, with or without pain medication.

What happens after the procedure?

• You can go home after the procedure.

• You may need to put ice on the joint 20 to 30 minutes every 3 or 4 hours until the pain goes away.

• You may need to put an elastic bandage on the joint.

• For pain you may take acetaminophen, aspirin, or medicine given to you by your doctor.

• You should avoid stressing the joint.

Ask your doctor what other steps you should take and when you should come back for a checkup.

What are the benefits of this procedure?

The procedure may help the doctor make a better diagnosis.

What are the risks associated with this procedure?

• A local anesthetic may not numb the area quite enough and you may feel some minor discomfort. Also, in rare cases, you may have an allergic reaction to the drug used in this type of anesthesia.

• More fluid may form in the joint.

• Infection or bleeding may occur.

You should ask your doctor how these risks apply to you.

When should I call the doctor?

Call the doctor immediately if:

• You have swelling.

• There is drainage from the puncture area.

• You develop a fever.

• You have pain that gets worse even though you are taking pain medicine.

• The area is red and warm.

Call the doctor during office hours if:

• You have questions about the procedure or its result.

• You want to make another appointment.