Diagnosis
It is often difficult to distinguish between pain caused by bursitis or that caused by a rotator cuff injury as both exhibit similar pain patterns in the front or side of the shoulder. Subacromial bursitis can be painful with resisted abduction due to the pinching of the bursa as the deltoid contracts. If the therapist performs a treatment direction test and gently applies joint traction or a caudal glide during abduction (MWM), the painful arc may reduce if the problem is bursitis or adhesive capsulitis (as this potentially increases the subacromial space).The following clinical tests, if positive, may indicate bursitis:

The patient actively abducts the arm and a painful arc occurs between 60° and 120°. This is due to the compression of the supraspinatus tendon or subacromial bursa between the anterior acromial arch and humeral head. When lowering from full abduction there is often a painful "catch" at midrange. If the patient can achieve adequate muscle relaxation, passive motion tends to be less painful. The patient performs an isometric flexion contraction against resistance of the therapist (Speed’s Test). When the therapist’s resistance is removed, a sudden jerking motion results and latent pain indicates a positive test for bursitis. Neer’s Sign: If pain occurs during forward elevation of the internally rotated arm above 90°.
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.