Definition and Overview
Joint aspiration or arthrocentesis is the process of drawing fluid from the joints for the diagnosis and treatment of a joint-related condition. It is slightly different from joint injections, which can be used to introduce medication into the joint.
Also known as articulation, the joint is part of the skeletal system where the bones meet. It is responsible for movement. It is composed of cartilage (a tissue on top of the bone in the joint that reduces bone friction during movement), ligament (a stretchable connective tissue that limits joint movement), and tendons (regulate joint movement). It also has synovial fluid in a membrane, which adds lubrication to the joint, as well as fluid in the bursa or the sac that offers cushion.
The fluid in the joints can help orthopedic specialists understand the cause of joint pain. Although the procedure can be carried out in all joints, it is more commonly performed in the knee joint.
Who should undergo and expected results
A doctor may recommend a joint aspiration if:
- There's consistent or worsening pain that may be affecting the joint
- The patient is believed to have arthritis, a broad term to indicate stiffness and inflammation of the joints.
- The doctor believes the pain is caused by gout, a joint problem characterized by the buildup of crystal deposits on the joint. These deposits form due to the high level of purines in the body.
- The possible reason for pain is an infection, which can lead to joint inflammation
- There's a growing tumor in or around the joints.
The collected sample should provide clinical information such as white blood cell count, the presence of bacteria that may be causing infection, or immune system anomalies. An example is rheumatoid arthritis, a condition wherein the body's immune system attacks the synovial membrane, causing inflammation, redness, and pain.
How the procedure works
The procedure is often conducted in a hospital setting, but it can be outpatient. Prior to the procedure, the doctor will discuss the specific details of the procedure to the patient. The patient will also be asked if he has allergic reactions to anesthetics.
During the actual process, the part of the body where the affected joint is located is exposed. The area is then cleansed with an antiseptic. A local anesthesia is then administered to minimize the discomfort and numb the pain. This means that the patient is awake throughout the entire procedure.
A sterile needle or syringe is slowly inserted into the joint area to collect fluid. It may take at least 30 minutes to complete depending on how much fluid needs to be collected. After that, the needle is gradually removed, and the injected site is dressed and bandaged. The sample is sent to the lab for analysis, and the results are delivered to the doctor, who will then discuss them with the patient.
Sometimes an ultrasound-guided aspiration is carried out, especially if the joints are small.
Possible risks and complications
In general, joint aspiration is a safe procedure with very minimal discomfort. The patient may feel some pressure at the injected site, but this should subside over time. There may also be bruising and minor bleeding. In rare instances, inflammation can occur especially if medications with cortisone are used.
El-Gabalawy HS. Synovial fluid analysis, synovial biopsy, and synovial pathology. In: Firestein GS, Budd RC, Gabriel SE, et al., eds. Kelly’s Textbook of Rheumatology. 9th ed. Philadelphia, Pa.: Elsevier Saunders; 2012:chap 53.
Parrillo SJ, Marrison DS, Panacek EA. Arthrocentesis. In: Roberts JR, Hedges JR, eds. Clinical Procedures in Emergency Medicine. 5th ed. Philadelphia, Pa.: Elsevier Saunders; 2009:chap 53.