The Humerus

The upper end of the humerus is composed of a head joined to the tuberosities through the medium of the anatomical neck. The head projects inwardly from the shaft at an angle of 120 degrees to it. The lesser tuberosity has inserted into it the subscapulars muscle; it presents forward. To its outer side and separating it from the greater tuberosity is the bicipital groove for the long tendon of the biceps muscle. To the outer side of the groove is the greater tuberosity with its three facets for the supraspinatus, infraspinatus, and teres minor muscles.

Fig. 233.   Anterior surface of upper end of humerus.

Fig. 233. - Anterior surface of upper end of humerus.

Fig. 234.   Outer surface of upper end of humerus.

Fig. 234. - Outer surface of upper end of humerus.

The greater tuberosity projects considerably beyond the acromion process and therefore forms the most prominent part of the shoulder. Immediately below the tuberosities is the surgical neck. It is described as being the portion between the tuberosities above and the insertions of the pectoralis major and latissimus dorsi muscles below. It is a common site for fractures. Half way down the shaft on its outer side is the rough deltoid eminence for the insertion of the deltoid muscle.

Sternoclavicular Joint

The ligaments uniting the inner end of the clavicle to the thorax at the upper end of the sternum are the interclavicular, which passes from one clavicle to the other across the top of the sternum, the anterior and posterior sternoclavicular, and the rhomboid or costoclavicular ligament which passes from the clavicle downward and forward to the first rib. This last one limits displacement in cases of luxation. There is a fibrocartilaginous disk between the clavicle and sternum, forming two distinct joint cavities. The line of the joint slopes downward and outward.

Acromioclavicular Joint

The outer end of the clavicle articulates with the acromion process by a joint whose surface inclines down and inward, thus favoring displacements of the clavicle upward. The ligaments joining them are called the superior and inferior acromioclavicular. In reality they are simply the thickened portions of the capsular ligament. This capsular ligament is ruptured in the not infrequent cases of luxation which occur here. Running from the under surface of the clavicle, a short distance from its outer end, to the coracoid process below, is the coracoclavicular ligament. It. is composed of two parts, an antero-external square ligament called the trapezoid, and a postero-internal conical one called the conoid.

Fig. 235.   Sternoclavicular joint and attachments of the inner end of the clavicle.

Fig. 235. - Sternoclavicular joint and attachments of the inner end of the clavicle.

The bone may be fractured just external to these ligaments, giving rise to a peculiar deformity to which attention will be called in describing the fractures of the clavicle.

From the coracoid process the coraco-acromial ligament runs outward and upward to the acromion process, the coracohumeral outward and downward to the neck of the humerus, and the costocoracoid ligament inward to the first rib at its cartilage.