A bursa is a small, fluid-filled sac that serves to reduce friction between a bone and the surrounding soft tissues such as skin, muscles, ligaments and tendons. There are 160 bursae in the body, with the major bursae located in the large shoulder, hip, elbow and knee joints. Bursitis is the inflammation of a bursa.
In baseball players, shoulder bursitis is common in the subacromial bursa between the rotator cuff tendons and the acromion, or shoulder blade. The subdeltoid bursa, located under the deltoid muscle (the rounded contour at the top of the shoulder), may also become inflamed, but it is less common. Shoulder bursitis can be caused by a trauma, but it is more often an overuse injury caused by repeated minor trauma, such as repetitively throwing a baseball. It is often associated with impingement or tendonitis of the rotator cuff tendons.
Typical recovery time
With rest, mild bursitis can be resolved in 2-3 weeks. Cortisone injections into the bursa sac may reduce inflammation. If the condition becomes chronic, however, the inflamed bursa sac may be surgically removed and, over time, a new one will form in its place. Recovery from surgery is typically 6-8 weeks.
In 2017, Mariners right-hander Felix Hernandez missed all of May and most of June with shoulder bursitis, then sat out the entire month of August and half of September with a recurrence of the injury. In June, Tigers right-hander Michael Fulmer struggled with bursitis for about three weeks, but a cortisone injection relieved his symptoms.