Shoulder bursitis refers to inflammation of one of the multiple bursae that reside about the shoulder. A layer or bursa material often referred to as a sac helps to minimize direct contact and friction as muscle and tendon come into close contact with bony structures. In the shoulder this most often involves the subacromial and subdeltoid bursae which can become inflamed as the space between the upper arm (humerus) and the corner of the shoulder blade (acromion) closes down with elevation and some rotation of the arm. Excessive contact between the subacromial bursa and the underlying rotator cuff tendon and the undersurface of the acromion is termed subacromial impingement. Patients will experience classic rotator cuff symptoms of upper arm pain particularly with lifting and rotating shoulder moves.
Two less common locations for bursitis involve the area between the humerus and a more anterior structure in the shoulder blade called the coracoid as well as an area between the shoulder blade and the ribs in the upper back. The latter is termed scapulothoracic bursitis and will lead to a greater degree of upper back pain on one side as opposed to upper arm pain.