Why do some people develop impingement and rotator cuff disease when others do not?

There are many factors that may predispose one person to impingement and rotator cuff problems. The most common is the shape and thickness of the acromion (the bone forming the roof of the shoulder). If the acromion has a bone spur on the front edge, it is more likely to impinge on the rotator cuff when the arm is elevated forward. Activities which involve forward elevation of the arm may put an individual at higher risk for rotator cuff injury. Sometimes the muscles of the shoulder may become imbalanced by injury or atrophy, and imbalance can cause the shoulder to move forward with certain activities which again may cause impingement.