Joints are the connections between two or more bones. They help to make it possible for us to move our bodies. If a joint is swollen or inflamed due to an injury or disease, more fluid may build up inside it. The medical term for this is "joint effusion."

Joint aspiration involves using a thin hollow needle to take some of the fluid out of the joint. This procedure, also known as arthrocentesis, is one of the most common procedures used for muscle and bone problems. It is most often done at the knee or shoulder.

When is joint aspiration necessary?

If a joint is swollen, analyzing a sample of joint fluid (synovial fluid) can help to find the cause of swelling. Even the color can be used as a first indication of what is wrong: Fluid from a healthy joint is usually clear. The fluid inside an injured joint is often a bloody reddish color, and the fluid inside an inflamed joint is usually cloudy. The sample of fluid can be tested to find out whether, for instance, it contains bacteria or abnormally high levels of white blood cells.

Aspiration may also be used as a treatment, to reduce the pressure on the joint, for example. Then the doctor uses the syringe to remove the excess fluid. If needed, medication can be injected into the joint during joint aspiration.

A contrast medium is sometimes injected into the area between the bones (the joint space) to make it easier to see details when taking an x-ray.

What happens during the procedure?

Special preparation is usually not needed. The surrounding skin is carefully disinfected beforehand to keep germs from entering the joint. Sometimes the area is covered with a sterile cloth. The doctor wears sterile disposable gloves, and usually a surgical gown, a surgical mask and a cap. Sterilized disposable cannulas and syringes are unpacked right before use.

Joint aspiration typically feels a bit like having blood drawn. A local anesthetic is usually not needed, but a numbing gel or spray may be used. The doctor can use ultrasound to locate the position of very small or deep joints, and will then mark the right spot for inserting the needle on your skin. Ultrasound is sometimes used to monitor the entire procedure.

If necessary, the fluid that is removed is sent to the laboratory in a tube for analysis. A pressure bandage is often applied after the procedure. The joint itself usually needs to be kept still - how long will depend on the cause of the swelling and whether medication was injected during the aspiration. Afterwards it is important to watch carefully for signs of inflammation. If the joint or puncture site are red, swollen or start feeling very warm, you should inform your doctor immediately. Other warning signs include fever and worsening pain.

What are the associated risks?

The doctor should explain the procedure and associated risks in as much detail as possible before carrying out the joint aspiration.

There may be bleeding in the joint afterwards. Inflammation at the needle insertion site is also possible. If medication is injected as well, it may cause a feeling of pressure or a short burning sensation. The medication might have side effects such as allergic reactions too. Anti-inflammatory drugs can lead to facial redness, increased blood pressure, a racing heartbeat and flushing.

The greatest risk is that of an infection caused by germs that have managed to get in. This risk varies depending on what is done during the aspiration and which joint is involved. Diabetes or a weakened immune system increase the risk of infection.

Joint aspiration is not advisable if you have an inflammation, wound or skin condition near the site of needle insertion. This greatly increases the risk of infection.