All joints have synovial sacs, or bursa, for the lubrication of that joint. Bursitis is inflammation of the bursa -- a small sac containing fluid that lies between tendons and bones. A bursa allows a tendon to move smoothly over a bone by acting as an anti-friction device and shielding tendons from rubbing against bones. Bursae are found in the knee, elbow, shoulder and wrist. If the tendons become thickened and bumpy from excessive use, the bursa is subjected to increased friction and may become inflamed. The main symptom of bursitis is pain. In some cases, especially for shoulder bursitis, people may experience some restriction of movement. Bursitis of the elbow and knee joints is frequently caused by activities performed at work or sport. The pain of bursitis can disable the worker, and at the very least, its cure demands cessation of that activity.