Biomechanics of the rotator cuff: European perspective.

The rotator cuff has an important role in the stability and function of the glenohumeral joint. To understand the biomechanical proprieties of the rotator cuff, it is essential to understand the pathogenesis and effects of rotator cuff tears. The rotator cuff provides a stabilizing effect to the shoulder, because of compression of the humeral head against the glenoid cavity. The wide range of motion of the shoulder is allowed by the variety of rotational moments of the cuff muscles. Rotator cuff muscles action must be precisely coordinated to obtain the desired movement. Rotator cuff tendons are subjected to complex tension loads. The rotator cuff is also subjected to compressive loads. Upwardly directed humeral load squeezes the cuff between the humeral head and the coracoacromial arch. Extrinsic factors have always been considered among causes of cuff tears. However, evidence shows that acromial impingement is not the primary cause of rotator cuff tears. Tears of the rotator cuff change load distribution and determine a pattern that induces tear progression and extension. Progressive tears of the rotator cuff compromise glenohumeral stability and determine superior translation of the humeral head.