Bursitis

Bursitis is an inflammation of any of the roughly 150 bursae in the body - small sacs filled with synovial fluid that appear whenever a muscle, tendon, or other tissue meets a bone. When functioning normally, the bursae almost eliminate the friction between these moving parts of the body. However, when bursitis occurs, movement is painful and feels stiff and difficult. In addition, moving muscles and tendons over an inflamed bursa only worsens the condition.
Bursitis at Wikipedia
Category:Diseases