Variations in the architecture of the coraco-acromial arch can lead to a clinically symptomatic rotator cuff lesion. Differences in the shape and slope of the acromion, anterior acromial spurs and inferior protruding acromio-clavicular osteophytes decrease the volume of the subacromial space, leading to impingement. Recent anatomic, radiographic, biomechanic and stereophotogrammetric studies have confirmed these architectural variations and their effect on the contents of the subacromial space. Abnormal contact between the acromion and these soft tissues can result in pathological lesions. Surgical procedures should be aimed at increasing the space beneath the coraco-acromial arch to reduce wear on the rotator cuff.