 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.