[Clinicoradiologic anatomy of the shoulder region]

Besides the skeletal elements, i.e., the clavicle, scapula and humerus, several muscles and soft tissues also participate in the construction of the human shoulder. These elements from and surround the shoulder girdle joints, which are the acromioclavicular and glenohumeral joint. Towards the trunk a connection is achieved by the sternoclavicular joint. Ossification of the clavicle, scapula and humerus begins within the 5th to 7th embryonic week. Around the age of 20 years ossification is completed. Parallel to this development and during adulthood, age-dependent changes take place in the composition and mixture of the bone marrow from red to yellow marrow. The shoulder girdle joints are constructed to permit a wide range of motion of the arm against the trunk. At the glenohumeral joint the spherical humeral head glides within the concave groove of the glenoid cavity. Stability is attained by the fibrocartilaginous glenoid labrum, which enlarges the articulating areas and the joint capsule with its strengthening ligaments. Variation of the joint capsule insertion, the glenoid labrum or the bony surfaces may predispose to luxation. Additional support to prevent luxation is obtained by the glenohumeral ligaments and the long biceps tendon. Active movement is provided by the superficial muscles and the rotator cuff muscles. Several bursae support free movement and decrease friction of the musculotendineous systems near the joint. Despite this complex construction several degenerative diseases can impair free movement of the human shoulder.