Bursitis is an inflammation of a bursa, which is a fluid-filled sac located near the bones around the joints and between muscle attachments at a joint. They cushion and lubricate the movement of tendons and muscle over bone. Bursitis is not arthritis; arthritis is a change within the joint and bursae are outside of the joint.
The joint most commonly affected with bursitis is the shoulder. Other joints that may develop bursitis include the elbow, the knee (this is also known as housemaid's knee), the hip, and the base of the big toe (part of what is called a bunion). Bursitis may be acute or chronic. The chronic form tends to come and go over cycles of weeks or months.
Bursitis can start in four different ways:
Trauma or injury: Ordinarily, a muscle-pull shouldn't affect a bursa. An injury that causes deep bruising, however, could provoke a brief inflammation of a bursa. This will often clear up without treatment.
Overuse: Many forms of bursitis have nicknames like "housemaid's knee," "miner's elbow," and even "tailor's bottom." Inflammation can result from repetitive strain placed on a joint, or continual pressure on the bursa itself (e.g., by kneeling).
Inflammatory arthritic disease: Conditions like rheumatoid arthritis and gout can lead to the release of inflammatory agents into the bursae. Also, calcium-based crystals can form in the sacs, causing friction and tearing.
Infection: Many common bacteria can infect the bursae.
The essential symptom of bursitis is pain that is localised near the joint, often accompanied by redness, tenderness, and swelling. The pain is likely to be worse when you make unaccustomed movements or strain the joint muscles. Many other diseases can cause joint pain, so it's important that you see a health care professional for a proper diagnosis. Very red, hot skin and extreme pain is often a sign of either crystal-induced arthritis or a bacterial infection.
Severe or long-lasting bursitis of the shoulder, for example, can lead to reduced movement or use of the joint and result in muscle atrophy (wasting). Permanent changes in the shape of the bursa, such as thickening or enlarging can occur and the surrounding tissues can become chronically inflamed.