Rotator cuff tendonitis, also knows as “bursitis” or “impingement syndrome” occurs when the rotator cuff gets irritated on the undersurface of the acromion. The reason this begins in the first place is a source of some debate. Some people are born with a “hooked” acromion that will predispose them to this problem. Others have rotator cuff weakness that causes the humerus to ride up and pinch the cuff. This means that the bursa — a water-balloon type structure that acts as a cushion between the rotator cuff and acromion/humerus — gets inflamed.