The Rotator cuff consists of the muscles 'Subscapularis', 'Supraspinatus' as well as 'Infraspinatus' and 'Teres Minor'. As long as the strengths of these muscles are well balanced without being impacted by external influences, the head of the humerus is centrally and sufficiently stabilized in the joint capsule. This ideal shoulder joint, however, does not exist due to ”disturbances from the outside”! Apart from the inside muscles of the rotator cuff, further outside muscles are fixed to the head of the humerus. As they are not uniformly distributed around the shoulder, their influence on the shoulder is very uneven in most cases. Hence the muscular balance of the rotator cuff is considerably disturbed, which results in a muscular imbalance with frequently far-reaching consequences!