Most people will experience shoulder pain at some point in their lives. There are many potential causes of shoulder pain, with one of the most common being shoulder bursitis. What is shoulder bursitis? A bursa is a fluid filled sac which functions to reduce friction between two surfaces in the body. Bursae are often located adjacent to tendons near large joints. In the shoulder, a bursa sits under the acromion (part of the shoulder-blade), giving rise to its name, 'sub-acromi