There are 3 main bursae around the rotator cuff.
The subacromial bursa protects the supraspinatus tendon from the coracoid process and acromion.
The subcoracoid bursa lies between the coracoid process and the joint capsule.
The subdeltoid bursa lies under the deltoid muscle, cushioning it from the bones in the shoulder joint capsule.
Often the subdeltoid and subacromial bursa are connected around the rotator cuff. The subacromial bursa is the bursa in the shoulder that is most commonly affected by bursitis. It acts as a cushion to allow the supraspinatus tendon to slide smoothly over the neighboring soft tissue and bone. Due to its location and relationship to the acromion and supraspinatus, the subacromial bursa tends to be most at risk of being impinged or irritated.
Shoulder bursitis is often connected to impingement syndrome and rotator cuff tendonitis. For this reason, it is always wise to address and treat shoulder pain as soon as possible so that the problem doesn't get worse. A healthy subacromial bursa is usually about the size of a small plum, but can swell to the size of an orange when bursitis sets in. This is what creates the soft tissue damage or possible impingement in the shoulder joint.
The most common symptom is experiencing pain when lifting overhead. This is because the head of the humerus is compressing the swollen bursa against the glenohumeral joint and the underside of the acromion. If you have pain when lifting over head, however, it could indicate one or more soft tissue injuries in the shoulder.
Subacromial bursitis is very often diagnosed alongside other rotator cuff problems or impingement syndrome.