Individuals affected by subacromial bursitis commonly present with concomitant shoulder problems such as arthritis, rotator cuff tendinitis, rotator cuff tears, and cervical radiculopathy (pinched nerve in neck).Impingement may be brought on by sports activities, such as overhead throwing sports and swimming, or overhead work such as painting, carpentry, or plumbing. Activities that involve repetitive overhead activity, or directly in front, may cause shoulder pain. Direct upward pressure on the shoulder, such as leaning on an elbow, may increase pain. Pathophysiology
The literature on the pathophysiology of bursitis describes inflammation as the primary cause of symptoms. Inflammatory bursitis is usually the result of repetitive injury to the bursa. In the subacromial bursa, this generally occurs due to microtrauma to adjacent structures, particularly the supraspinatus tendon. The inflammatory process causes synovial cells to multiply, increasing collagen formation and fluid production within the bursa and reduction in the outside layer of lubrication.Less frequently observed causes of subacromial bursitis include hemorrhagic conditions, crystal deposition and infection.Many causes have been proposed in the medical literature for subacromial impingement syndrome. The bursa facilitates the motion of the rotator cuff beneath the arch, any disturbance of the relationship of the subacromial structures can lead to impingement. These factors can be broadly classified as intrinsic such as tendon degeneration, rotator cuff muscle weakness and overuse. Extrinsic factors include bone spurs from the acromion or AC joint, shoulder instability and neurologic problems arising outside of the shoulder.
This will identify impingement of the rotator cuff but is also sensitive for subacromial bursitis.Irritation or entrapment of the lower subscapular nerve, which innervates the subscapularis and teres major muscles, will produce muscle guarding at the shoulder that will restrict motion into external rotation, abduction, or flexion. The aforementioned tests will assist in diagnosing bursitis over other conditions. The diagnosis of impingement syndrome should be viewed with caution  in people who are less than forty years old, because such individuals may have subtle glenohumeral instability. Imaging
X-rays may help visualize bone spurs, acromial anatomy and arthritis. Further, calcification in the subacromial space and rotator cuff may be revealed. Osteoarthritis of the acromioclavicular (AC) joint may co-exist and is usually demonstrated on radiographs.MRI imagining can reveal fluid accumulation in the bursa and assess adjacent structures. In chronic cases caused by impingement tendinosis and tears in the rotator cuff may be revealed. At US, an abnormal bursa may show

fluid distension,
synovial proliferation, and/or
thickening of the bursal walls.In any case, the magnitude of pathological findings does not correlate with the magnitude of the symptoms. Special considerations
In patients with bursitis who have rheumatoid arthritis, short term improvements are not taken as a sign of resolution and may require long term treatment to ensure recurrence is minimized. Joint contracture of the shoulder has also been found to be at a higher incidence in type two diabetics, which may lead to frozen shoulder (Donatelli, 2004).