If a joint is painful, swollen, red, or has a limited range of motion, a doctor may recommend using a needle and syringe to remove fluid from the affected joint. Removing fluid can alleviate symptoms and help with diagnosis.
The medical term for any procedure that removes fluid, air, or other substance from an area of a person’s body is called aspiration.1 When a needle and syringe are used to aspirate fluid from a joint, it may be called arthrocentesis or joint aspiration. A similar procedure that involves aspirating fluid from a bursa is called bursal aspiration.
This article discusses the both joint and bursal aspirations, when they are recommended, what happens during these procedures, potential risks and recovery, and how the extracted fluid may be analyzed for diagnostic purposes.
Aspiration of a Joint (Arthrocentesis)
Arthritis, infection, and joint injuries are associated with joint inflammation and swelling. This swelling occurs when excess fluid collects in a joint capsule.
A joint capsule provides a semipermeable seal around a joint.
- The tough, resilient, outer layer of the joint capsule is made of fibrous, flexible tissues.
- The inner layer of the capsule is made of a delicate membrane, called synovial membrane or synovium.
- The synovial membrane produces a viscous, slippery fluid, called synovial fluid (joint fluid).
- The synovial fluid contained in the joint capsule lubricates the joint.
During arthrocentesis, a needle must pass through the joint capsule’s outer layer and inner membrane (arthro means joint, and centesis means to surgically puncture). Arthrocentesis is commonly performed on the knee but can be done on any joint, such as the hip, elbow, and the knuckle of the big toe (the first metatarsophalangeal joint).
Aspiration of a Bursa
Bursitis is the inflammation of a bursa. Inflammation can cause the bursa to fill with excess fluid and swell to many times its normal size.
A bursa is a tiny, slippery sac that normally contains just a drop or two of fluid. A healthy bursa facilitates a joint’s motion by providing a thin cushion and reducing friction between bone and soft tissue, such as skin or ligament tissue.
- The bursa sac is made of a synovial membrane (the same type of tissue that makes up the inner lining of a joint)
- The synovial membrane produces the fluid (synovial fluid) contained in the sac
During a bursal aspiration, a needle passes through the bursa’s synovium. Bursal aspiration is most commonly performed on bursae at the knees and elbows.
Read more: What Is a Bursa?
Reasons for Arthrocentesis or Bursal Aspiration
A physician will recommend removing excess fluid from a joint capsule or bursa for one or a combination of reasons: to get information needed to make a diagnosis, to relieve pressure and help alleviate pain and discomfort, or to prepare the joint or bursa for a therapeutic injection.
1. For diagnosis
A joint or bursa’s overall health can be reflected in the fluid it contains. The fluid collected during aspiration can be analyzed to help with diagnosis.
A physician may order fluid analysis if they suspect or want to rule out:
- An infection in the affected joint or bursa
- A joint disorder, such as gout, pseudogout, or rheumatoid arthritis
- Bleeding into the joint space caused by a traumatic injury
A doctor can perform a visual and physical analysis of the sample in the office. The sample may also be sent to a medical lab to be further analyzed for infectious materials and composition. Reports from the analysis, along with information from the patient exam, can help the physician make a diagnosis and set a course for treatment.
2. To reduce pain
People who have moderate to severe swelling may feel immediate pain relief after a joint’s or bursa’s fluid is aspirated. In addition to relieving painful pressure, aspiration may reduce joint stiffness and improve a joint’s range of motion.
If a diagnosis has already been established, a doctor may aspirate a painfully swollen joint solely to improve patient comfort. For example, if a patient has a swollen knee from osteoarthritis, and there are no signs of infection or other problems, a doctor might perform arthrocentesis and dispose of the fluid rather than sending it to a lab for analysis.
3. To prepare for a therapeutic injection
A doctor may perform arthrocentesis or bursal aspiration before administering a therapeutic injection, such as a cortisone, hyaluronic acid, or a platelet-rich plasma injection. In these cases, a diagnosis has already been made and the excess fluid may or may not be causing visible swelling and/or patient discomfort.
Removing excess fluid may increase the effectiveness of the injected material. Removing excess fluid also helps ensure that the addition of the injected medicine to the joint or bursa does not contribute to excess pressure and discomfort.
When Arthrocentesis or Bursal Aspiration Is Not Appropriate
Most people can undergo arthrocentesis or bursal aspiration. A doctor may decide not to perform a procedure if the patient has2:
- A skin infection or wound at the point of injection
- Certain bleeding disorders
- An acute fracture
- An infection of bone tissue (osteomyelitis)
Infections are a concern because the infectious bacteria may be spread as the needle passes through the skin and other tissues.
Physicians Who Perform Arthrocentesis and Bursal Aspiration
Orthopedic surgeons are doctors who specialize in musculoskeletal problems and can perform arthrocentesis and bursal aspirations. Trained rheumatologists, family doctors, internal medicine doctors, and emergency medicine doctors may also perform the procedure.
If the affected joint is an artificial joint, such as knee or hip replacement, an orthopedic surgeon who is familiar with the prosthetic anatomy should be consulted.2
In-office or hospital procedure
Many arthrocentesis and bursal aspiration procedures can be done in a doctor’s office. The procedure may be done in a hospital or surgical center if certain medical imaging tools or general anesthesia is required. For example:
- Real-time x rays (fluoroscopy) may be required to assist needle placement if a joint or bursa is particularly difficult to access with a needle.
- General anesthesia may be appropriate if the patient (such a small child) cannot remain still and relaxed while the needle is inserted into a joint or bursa.
The use of general anesthesia is rare.