A person with shoulder bursitis has inflammation of a bursa near the shoulder joint. A bursa is a small sac that is filled with very slippery fluid. The bursa acts as a lubricating pad between a tendon and bone.

A common cause of shoulder bursitis is subacromial bursitis. This condition is caused by inflammation of the subacromial bursa, a bursa that is located below the acromion process.