Causes
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.