The space between the acromion and rotator cuff is called the subacromial space and contains the subacromial bursa.
The bursa is lined by a synovial membrane creating a potential space reducing friction and allowing smooth gliding of the rotator cuff. Subacromial impingement represents a spectrum of pathology ranging from inflammation of the bursa to rotator cuff tendinopathy to full thickness tears and calcific tendinitis. Anatomical factors such as the shape of the acromion and thickened ligaments also play a role. Intrinsic degeneration of the rotator cuff tendons and inflammation of the subacromial bursal may also result in impingement. As with so many other shoulder conditions physical therapy, anti-inflammatory medication and cortisone injection are the first line of treatment. However, the value of cortisone has recently been questioned. Failure of conservative treatment is an indication for surgery. A subacromial decompression may be performed but the condition that causes impingement should also be addressed.