bursitis

A bursa is a little pouch filled with fluid that sits between a tendon and a bone. When the fluid becomes infected by bacteria or irritated by too much movement, bursitis results. Throwing a baseball too many times at one session, for example, may inflame and irritate one of the bursae (notice the plural form) in the shoulder. Bursitis in another part of the body may be known by a traditional name such as "housemaid's knee", "soldier's heel", or "tennis elbow". Bursitis generally goes away after a few weeks of resting the affected area, and the pain can be treated with ice packs and aspirin.