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The clavicle (collar bone) connects the upper limb to the trunk (Figs. 3.3 and 3.4). The shaft of the clavicle has a double curve in a horizontal plane. Its medial two thirds is convex anteriorly, and its sternal end is enlarged and triangular where it articulates with the manubrium of the sternum a...

The clavicle (collar bone) connects the upper limb to the trunk (Figs. 3.3 and 3.4). The shaft of the clavicle has a double curve in a horizontal plane. Its medial two thirds is convex anteriorly, and its sternal end is enlarged and triangular where it articulates with the manubrium of the sternum at the sternoclavicular (SC) joint. Its lateral third is flattened and concave anteriorly, and its acromial end is flat where it articulates with the acromion of the scapula at the acromioclavicular (AC) joint (Figs. 3.3B and 3.4). These curvatures increase the resilience of the clavicle and give it the appearance of an elongated capital S. The clavicle serves as a moveable, crane-like strut (rigid support) from which the scapula and free limb are ALGRAWANY suspended, keeping them away from the trunk so that the limb has maximum freedom of motion. The strut is movable and allows the scapula to move on the thoracic wall at the “scapulothoracic joint,” 1 increasing the range of motion of the limb. Fixing the strut in position, especially after its elevation, enables elevation of the ribs for deep inspiration. forms one of the bony boundaries of the cervico-axillary canal (passageway between the neck and arm), affording protection to the important neurovascular bundle supplying the upper limb transmits shocks (traumatic impacts) from the upper limb to the axial skeleton FIGURE 3.4. Right clavicle. Prominent features of the superior and inferior surfaces of the clavicle. The clavicle acts as a mobile strut (supporting brace) connecting the upper limb to the trunk; its length allows the limb to pivot around the trunk. The clavicle is subcutaneous and palpable throughout its length and is often used as a landmark for clinical procedures. Although it is designated as a long bone, the clavicle has no medullary (marrow) cavity. It consists of spongy (trabecular) bone with a shell of compact bone. The superior surface of the clavicle, lying just deep to the skin and platysma (G., flat plate) muscle in the subcutaneous tissue, is smooth. The inferior surface of the clavicle is rough because strong ligaments bind it to the 1st rib near its sternal end and suspend the scapula from its acromial end. The conoid tubercle, near the acromial end of the clavicle (Fig. 3.4), gives attachment to the conoid ligament, the medial part of the coracoclavicular ligament by which the remainder of the upper limb is passively suspended from the clavicle. Also, near the acromial end of the clavicle is the trapezoid line, to which the trapezoid ligament attaches; it is the lateral part of the coracoclavicular ligament. The subclavian groove (groove for the subclavius) in the medial third of the shaft of the clavicle is the site of attachment of the subclavius muscle. More medially is the impression for the costoclavicular ligament, a rough, often depressed, oval area that gives attachment to the ligament binding the 1st rib (L. costa) to the clavicle, limiting elevation of the shoulder. Scapula The scapula (shoulder blade) is a triangular flat bone that lies on the posterolateral aspect of the thorax, overlying the 2nd–7th ribs (see Fig. 4.1B). The convex posterior surface of the scapula is unevenly divided by a thick projecting ridge of bone, the spine of the scapula, into a small supraspinous fossa and a much larger infraspinous fossa (Fig. 3.5A). The concave costal surface of most of the scapula forms a large subscapular fossa. The broad bony surfaces of the three fossae provide attachments for fleshy muscles. The triangular body of the scapula is thin and translucent superior and inferior to the spine of the scapula, although its borders, especially the lateral one, are somewhat thicker. The spine continues laterally as the flat, expanded acromion (G. akros, point), which forms the subcutaneous point of the shoulder and articulates with the acromial end of the clavicle. The deltoid tubercle of the scapular spine is the prominence indicating the medial point of attachment of the deltoid. The spine and acromion serve as levers for the attached muscles, particularly the trapezius. FIGURE 3.5. Right scapula. A. Bony features of the costal and posterior surfaces of the scapula. B. Borders and angles of the scapula. C. Scapular suspension mechanism. The scapula is suspended from the clavicle by the coracoclavicular ligament, at which a balance is achieved among the weight of the scapula and its attached muscles plus the muscular activity medially, and the weight of the free limb laterally. D. Lateral aspect of scapula. Because the acromion is a lateral extension of the scapula, the AC joint is placed lateral to the mass of the scapula and its attached muscles (Fig. 3.5C). The glenohumeral (shoulder) joint on which these muscles operate is almost directly inferior to the AC joint; thus, the scapular mass is balanced with that of the free limb, and the suspending structure (coracoclavicular ligament) lies between the two masses. Superolaterally, the lateral surface of the scapula has a glenoid cavity (G., socket), which receives and articulates with the head of the humerus at the glenohumeral joint (Fig. 3.5A, C). The glenoid cavity is a shallow, concave, oval fossa (L. fossa ovalis), directed anterolaterally and slightly superiorly—that is considerably smaller than the ball (head of the humerus) for which it ALGRAWANY serves as a socket. The beak-like coracoid process (G. korak-odés, like a crow’s beak) is superior to the glenoid cavity and projects anterolaterally. This process also resembles in size, shape, and direction a bent finger pointing to the shoulder, the knuckle of which provides the inferior attachment for the passively supporting coracoclavicular ligament. The scapula has medial, lateral, and superior borders and superior, lateral, and inferior angles (Fig. 3.5B). When the scapular body is in the anatomical position, the thin medial border of the scapula runs parallel to and approximately 5 cm lateral to the spinous processes of the thoracic vertebrae; hence, it is often called the vertebral border (Fig. 3.5B). From the inferior angle, the lateral border of the scapula runs superolaterally toward the apex of the axilla; hence it is often called the axillary border. The lateral border is composed of a thick bar of bone that prevents buckling of this stress-bearing region of the scapula. The lateral border terminates in the truncated lateral angle of the scapula, the thickest part of the bone that bears the broadened head of the scapula (Fig. 3.5A, B). The glenoid cavity is the primary feature of the head. The shallow constriction between the head and body defines the neck of the scapula. The superior border of the scapula is marked near the junction of its medial two thirds and lateral third by the suprascapular notch, which is located where the superior border joins the base of the coracoid process. The superior border is the thinnest and shortest of the three borders. The scapula is capable of considerable movement on the thoracic wall at the physiological scapulothoracic joint, providing the base from which the upper limb operates. These movements, enabling the arm to move freely, are discussed later in this chapter with the muscles that move