What It Is
A joint aspiration (arthrocentesis) is a test that involves withdrawing (aspirating) a small sample of joint fluid from a joint using a needle and syringe.
Joints are located where two bones meet, allowing our bodies to move — the hips, knees, ankles, elbows, shoulders, knuckles, etc. Joints contain synovial fluid, which acts as a lubricant to help them move easily.
In a joint aspiration, a needle is carefully inserted into a joint to collect a sample of synovial fluid.
Why It's Done
Doctors perform joint aspiration and examine the synovial fluid to detect or rule out suspected diseases or conditions in a joint.
Joint aspirations are most often done to help in the diagnosis of arthritis (inflammation of a joint). Arthritis can cause redness, swelling, warmth, and pain in and around the joint, and difficulty moving the joint.
Most important, joint aspiration can help determine whether bacterial infection in the joint (also known as septic arthritis) has caused the inflammatory symptoms. Septic arthritis is a serious illness requiring prompt diagnosis and treatment.
Other noninfectious causes of arthritis that can occur in kids and teens include juvenile rheumatoid arthritis (JRA), systemic lupus erythematosus (SLE), and Lyme disease.
Joint aspiration not only is diagnostic but also can be therapeutic, helping to relieve pain and swelling caused by a buildup of joint fluid. Removing some of the fluid decreases pressure in the joint and improves joint movement.
After the procedure is explained to you, you'll be asked to sign an informed consent form — this states that you understand the procedure and its risks and give your permission for it to be performed.
The doctor doing the joint aspiration will know your child's medical history, but might ask additional questions, such as whether your child is allergic to any medicines or has any bleeding tendencies. You should tell the doctor about any antibiotics your child is taking or has taken recently, since this can affect the results.
Numbing cream may be placed on the skin over the joint about an hour before the procedure. In some cases, a patient receives sedation during the aspiration. This is commonly used with infants and young kids, especially for larger joints such as the hip. If sedation is used, your child will be asked to not eat any food or liquids at a certain point beforehand to allow the stomach to empty. Sedation medications are usually given through an IV line (intravenous tube) and help your child stay asleep during the entire test.
You might be able to stay in the room with your child during the procedure, or you can step outside to a waiting area.
A joint aspiration usually takes about 5-10 minutes. Your child may be asked to change into a cloth gown, depending on the joint to be aspirated, then will be positioned on an exam table and the joint and surrounding area will be cleaned with a special soap.
If your child is sedated, his or her vital signs (heart rate, blood pressure, temperature, and blood oxygen level) will be monitored during the procedure. Your child may have a cuff around the upper arm and a small fingertip clip to monitor blood pressure and blood oxygen level.
If your child is awake, a small amount of anesthetic medicine will be injected into the skin at the aspiration site to prevent pain. The doctor will carefully insert a needle into the joint, and will then withdraw a sample of fluid into a syringe.
Sometimes, imaging with an X-ray or ultrasound is required to guide the aspiration needle to ensure its accurate placement in the joint.
Once the fluid sample has been collected, it will be sent to a laboratory for analysis. A bandage will be placed over the aspiration site.
What to Expect
The effects of a joint aspiration on your child will vary according to the specific procedure.
If your child is awake, the injected anesthetic may sting a bit for a minute or two. If given a sedative, your child may need a few hours to rest after the procedure.
Getting the Results
A person with expertise in interpreting joint fluid samples will look for signs of infection or inflammation by analyzing the white blood cell count and glucose and protein levels. He or she will look for germs (such as bacteria or fungi) and any other abnormal cells. The information will then be given to your doctor, who will go over the results with you.
In an emergency, the results of a joint aspiration can be available quickly. Otherwise, they're usually ready in 1-2 days. In most cases, results can't be given directly to the patient or family at the time of the test.
If a bacterial infection is suspected, a culture is sent to a lab and the results are usually available in 48 hours. A doctor may start antibiotic treatment while waiting for the results of the culture, especially if the child looks ill. Treatment will be based on the most likely cause of the infection, but can be revised to be specific for the germ found when the culture is completed and the most effective treatment has been determined.
A joint aspiration is considered a safe procedure with minimal risks. Most of the time, there are no complications; rarely, infection or bleeding can occur.
Helping Your Child
You can help prepare your child for a joint aspiration by explaining that while the test might be uncomfortable, it shouldn't take long. If your child isn't sedated, the injected anesthetic may sting briefly, but the rest of the procedure shouldn't be painful.
Tell your child about the importance of lying still during the test, and explain that a nurse might hold him or her in place. Explain the procedure in simple language, including where on his or her body the aspiration will be performed. After the procedure, make sure your child rests and follow any other instructions the doctor gives you.
If You Have Questions
If you have questions about the joint aspiration, speak with your doctor. You also can talk to the doctor performing the procedure right before it's done.
Reviewed by: Steven Dowshen, MD
Date reviewed: February 2009