Bursitis is inflammation of a bursa. A bursa is a thin, fluid filled sac that protects tendons, which are the tissues that connect muscles to bones. The bursa functions to reduce friction between tendons and the bones, allowing the tendon to glide smoothly over the bone.
Acute bursitis may be caused by trauma to the area, or over use of a joint. The repeated motion of a muscle-tendon unit causes friction in the bursa, causing inflammation and swelling with fluid. Chronic bursitis is usually caused by long term overuse; the bursa thickens and no longer functions well. Symptoms of bursitis include pain in the area of the bursa, swelling, redness, decreased motion and function of the affected limb.