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Removing fluid from a joint (joint aspiration) for laboratory testing can help a doctor diagnose the nature and severity of a patient's condition. Some types of conditions, such as tendonitis or bursitis, benefit from the injection of medications into the joint space. Joint injections or aspirations are usually done under local anesthesia in the doctor's office or in a hospital.
Joints that are commonly injected include the knee, shoulder, ankle, elbow and wrist, as well as small joints of the hands and feet. Hip joint injection may require the aid of an X-ray called fluoroscopy for guidance. Facet joints of the lumbar spine (low back area) may also be injected by experienced rheumatologists, orthopedists, anesthesiologists and radiologists.
Joint injections are given to treat inflammatory joint conditions, such as rheumatoid arthritis, psoriatic arthritis, gout and occasionally osteoarthritis. Most joint injections use anti-inflammatory drugs called corticosteroids (such as methylprednisolone or triamcinolone). Corticosteroids are frequently used for this procedure as they are anti-inflammatory agents that slow down the accumulation of cells responsible for producing inflammation within the joint space.
Although corticosteroids may also be successfully used in osteoarthritis, their mode of action is less clear. Hyaluronic acid (Hyalgan®, Synvisc®) is a viscous lubricating substance that may relieve the pain of osteoarthritis of the knee or other degenerative joint diseases.
Corticosteroids act locally and have few systemic side effects (such as a fever, rash or a disturbance of an internal organ). Common side effects include allergic reactions to the medicines injected into joints, to tape or to the betadine used to clean the skin. Infections are extremely rare. Another uncommon complication is post-injection flare - joint swelling and pain several hours after the corticosteroid injection - which occurs in about one out of 50 patients and usually goes away in several days.
It is not known if joint damage may be related to frequent corticosteroid injections. Generally, repeated injections into the same joint/site should be discouraged. Other complications, though rare, include a whitening of the skin, local thinning of the skin at the injection site and rupture of a tendon located in the path of the injection. The most common reasons for not doing a joint injection are having an infection in or around a joint or if someone has a serious allergy to one or more of the drugs that are injected into a joint.
Joint aspiration is usually performed as a diagnostic or therapeutic procedure. Laboratory analysis of the fluid taken from a joint may include:
- White and red blood cell counts
- Crystal analysis to confirm the presence of gout or pseudogout
- Cultures to determine if there is an infection inside the joint