Anatomical basics, variations, and degenerative changes of the shoulder joint and shoulder girdle.

This paper summarizes the anatomical basics of the shoulder, their variations, and precise definitions, including differential diagnoses. It also describes the characteristic degenerative changes caused by aging. A typical variation (7-15%) is the os acromiale, which forms the triangular epiphysis of the scapular spine. This abnormality must be differentiated from a fracture of the acromion or a pseudarthrosis. Because ossification of the acromion is complete after age 25, the os acromiale should be diagnosed only after this age. The shape of the acromion is a further important feature. In a recent anatomical study, the following frequencies of the Bigliani-types of the acromial shape were anatomically determined - type 1 (flat), 10.2% and type 2 (curved), 89.8%. Type 3 (hooked) was not observed, which indicates that this type is probably a misinterpretation of the so-called acromial spur. Minor dehiscences and perforations in the infraspinate or supraspinate fossa should not be confused with malignant osteolyses. The scapula has three ligaments of its own, (1) the coracoacromial ligament and its osseous fixations form an osteofibrous arch above the shoulder joint, which plays a part in impingement syndrome; (2) the superior transverse scapular ligament or its ossified correlate arches the scapular incisure and can cause a typical compression syndrome of the suprascapular nerve; (3) the inferior transverse scapular ligament is of no great clinical importance. Two intraarticular structures (glenoid labrum and tendon of the long bicipital head) must be mentioned. The glenoid labrum consists of dense connective tissue and surrounds the margin of the glenoid cavity. Two areas exhibit specialized conditions, cranial at the supraglenoid tubercle an intimate relationship exists to the tendon of the long bicipital head and in about 55% of cases, the labrum is stretched over the glenoid rim at the ventral side. At the area of the biceps-tendon-labrum complex, so-called SLAP-lesions may occur and at the glenoid rim, where the labrum is often not fixed to the bony margin, avulsions of the labrum may occur. This well-established anatomical condition must not be mistaken for a manifest Bankart-lesion. The glenohumeral ligaments, which are located in the ventral articular capsule, have a stabilizing function for the ventral part of the glenoid labrum. The glenohumeral ligaments lift the articular lip where it crosses the glenoid notch. This 'labrum-lift effect' supports the stabilizing features of the articular lip and the glenohumeral ligaments. The rotator cuff is composed of the tendons of the teres minor, infraspinatus, supraspinatus, and subscapularis muscles. This cuff has a poorly vascularized area, due to mechanical conditions, about 1.5 cm from the major tubercle, which causes degenerative changes and eventually may lead to ruptures. Results of the impingement-syndrome and the osteoarthrotic changes of the shoulder and acromioclavicular joint are also presented and discussed. Finally, the coracoclavicular joint, which probably represents no congenital entity but appears due to a changed, lowered position of the shoulder girdle, is discussed. The paper also presents instructive figures of anatomical preparations that can be used to make more precise radiological and differential diagnoses. All preparations were done by the author and are part of a series of more than 300 preparations of the shoulder joint and girdle.