Shoulder impingement is a common problem, and subacromial impingement is the most common type. This occurs when the tendons of the muscles surrounding the shoulder (rotator cuff) rub under the surface of the acromion bone.
Repetitive arm movements, especially above 90 degrees, can irritate the subacromial bursa, a fluid-filled sac, causing it to become inflamed and swollen (bursitis). Thickened ligaments and bone spurs may also narrow the space for the tendons to move, thus increasing the risk of impingement and bursitis, especially in those with prior injuries or above the age of 40 years.
