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© Dirk Biddle
Inserting a needle into a joint and aspirating, or removing, synovial fluid from it can provide a doctor with valuable information. Synovial fluid is the slippery fluid that fills a joint and acts as a lubricant, providing for smoother movement (also found in bursae, and tendon sheaths). Usually this procedure is done in the doctor's office. It generally causes no more pain than drawing blood. Nevertheless, ice or cold packs may be recommended to be applied to the joint for 24 to 36 hours after the test to reduce the swelling and joint pain.
In the laboratory, the fluid is initially analysed for colour and clarity. Abnormal joint fluid may look cloudy or abnormally thick. A microscopic examination of the fluid may reveal what is causing the inflammation, such as uric acid crystals, a sure sign of gout, or bacteria, a sign of infection. If uric acid crystals are found, proper medication may be prescribed. If an infection is found, the specific bacteria that are causing it can identified and the most effective antibiotic can be prescribed. An excess amount of normal synovial fluid can also be a sign of osteoarthritis.
In addition, aspiration can sometimes relieve the pain of a badly swollen joint. Sometimes also, if an infection is not present, a corticosteroid (usually cortisol) is injected through the needle to relieve inflammation. This helps reduce inflammation for up to three months in many cases and for months or years in a few instances. Corticosteroids are a group of drugs related to hydrocortisone, a natural hormone produced in the body. They are not the same as the steroids some athletes take. Corticosteroid are very helpful in reducing inflammation.
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