[Anatomy of the shoulder joint]

The shoulder joint and its associated joints form one of the most complex joint systems of the human locomotor apparatus. Its large range of motion is made possible by the interplay of 5 joints: sternoclavicular-joint, acromioclavicular-joint, glenohumeral joint, thoracoscapular joint and subacromial joint. The rotator cuff works mostly as an active stabilizer of the shoulder joint. The supraspinatus muscle causes a compression of the humerus in the glenoid mainly, furthermore it effects synergistic the abduction with the delta muscle. On the basis of its lever-arm the supraspinatus works between 0 and 60 degrees abduction the most optimally. With failure of the supraspinatus, the deltoideus can almost completely take its function. The inferior glenohumeral ligament-complex is the main passive stabilizer. The blood supply of the humerus head is ensured mainly by the a. circumflexa anterior and its rami ascendents, by several small branches from the a. circumflexa posterior and over intraosseous anastomoses. The most important vessel of the cap is the intraosseous a. arcuata out of the ramus ascendens lateralis of the a. circumflexa anterior.