Unfortunately, as we age, these muscles can have some wear and tear on them like other parts of your body. These muscles act to keep the shoulder joint centered and give you pain free motion. Unfortunately, they can be pathologic. The bursa sac sits between the shoulder blade and the rotator cuff muscles. As you raise your arm, that sac serves as a cushion to keep the rotator cuff muscles from rubbing under the under surface of your shoulder blade. This normally works great and allows you to reach over your head and do normal things away from your body without any pain. Unfortunately, if the rotator cuff muscles become inflamed, this also causes inflammation of the Bursa known as bursitis. The bursitis can be just as painful as a tear in your shoulder and can cause you difficulty with many things such as using your arm normally and even sleeping at night.