Knee swelling, sometimes called an “effusion,” refers to swelling within the knee joint. An effusion can be caused by many different things, including injuries to the ligaments, cartilage, bones, or surrounding structures. Swelling can occur within the knee joint (effusion) or on the outside of the knee joint (bursitis), and can occur suddenly as a result of an injury or slowly as a result of overuse injuries.
The many causes of effusions include injuries such as tears of the anterior cruciate (ACL), posterior cruciate (PCL), and medial and lateral collateral (MCL, LCL) ligaments. Tearing of the meniscus (knee cartilage), fractures of the bones of the knee joint, or injuries to the cartilage lining the inside of the bones (articular cartilage) can also cause knee effusions. Bursitis, tendinitis, strains, and sprains are causes of swelling outside the knee joint. Forceful injuries, such as blows during contact sports or falls, can cause fluid or blood to build up within the knee. Broken bones, arthritis, gout, cysts, dislocated kneecaps, infections, tumors, and aging-related degeneration are other causes. Sudden turning, stopping, moving from side to side, and awkward landings can lead to knee stress or overuse.
Symptoms depend on the cause and they range from mild to severe swelling. Pain, tenderness, redness, fever, and chills can also occur. Knees can have bruises or become stiff so that walking is hard.
The health care provider makes a diagnosis from the medical history, physical examination, and additional tests as indicated. The health care provider will ask questions about the nature of the swelling, how quickly it occurred, and if there was an injury, how it happened. In addition, answering questions about what kind of exercises and activities have been performed, as well as previous injuries may be important. X-rays are often useful in evaluating knee swelling, and additional tests such as computed tomography (CT), magnetic resonance imaging (MRI), and arthrocentesis may help determine the cause of knee swelling. In arthrocentesis, the doctor puts a needle into the knee joint using sterile technique and removes fluid. This fluid is sent to a laboratory for study to determine what is causing the fluid to accumulate.
Treatment goals are to determine what is causing the swelling, decrease the swelling, and allow for return to activities as soon and safely as possible. Self care often works well, but any underlying conditions (such as rheumatoid arthritis or gout) must be treated. After injuries, the first 48 hours are most important. Use PRICE: protection, rest, ice, compression, and elevation. Resting and avoiding activities that may have started the problem (such as high-impact running, skiing, or playing tennis) are critical. Using ice packs, an elastic bandage around the knee, pillows under the knee, cane or crutches, and special stretching and strengthening exercises often help. Rehabilitative exercises to restore range of motion and strength are useful once a diagnosis is determined.
Nonsteroidal anti-inflammatory drugs (NSAIDs) (ibuprofen, naproxen) and acetaminophen may relieve pain. Other treatments depend on the underlying condition and can include orthotics, braces, other medications, and surgery if indicated. Arthrocentesis is a short-term treatment for alleviating pain due to swelling, but the swelling can recur, and this procedure can cause infection in the joint if not performed properly.
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