The shoulder is composed of the proximal humerus, clavicle, and scapula. The joints of the shoulder include the sternoclavicular, the acromioclavicular, and the glenohumeral. There is also an articulation between the scapula and the thorax. Figures 16–1, 16–2, and 16–3 provide the essential anatomy, both osseous and ligamentous, which must be understood to comprehend the disorders involving the shoulder. Superficial to the ligaments are the muscles that support the shoulder and provide for its global range of motion. The rotator cuff surrounds the glenohumeral joint and is composed of the teres minor, infraspinatus, and supraspinatus muscles (insert on the greater tuberosity) and the subscapularis muscle (inserts on the lesser tuberosity) (Fig. 16–4). Superficial to these muscles is the deltoid, which functions as an abductor of the shoulder.
The essential anatomy of the shoulder.
The ligaments around the shoulder.
The ligamentous attachments of the clavicle to the sternum medially and the acromion laterally.
The rotator cuff.
The clavicle is an oblong bone, the middle portion of which is tubular and the distal portion, flattened. It is anchored to the scapula by the acromioclavicular and the coracoclavicular ligaments. The sternoclavicular and the costoclavicular ligaments anchor the clavicle medially (see Fig. 16–3). The clavicle serves as points of attachment for both the sternocleidomastoid and the subclavius muscles. The ligaments and the muscles act in conjunction to anchor the clavicle and, thus, maintain the width of the shoulder and serve as the attachment point of the shoulder to the axial skeleton.
The scapula consists of the body, spine, glenoid, acromion, and coracoid process. The bone is covered with thick muscles over its entire body and spine. On the posterior surface, the supraspinatus muscle covers the fossa superior to the spine, whereas the infraspinatus muscle covers the fossa below the spine. The anterior surface of the scapula is separated from the rib cage by the subscapularis muscle. These muscles offer protection and support for the scapula. The scapula is connected to the axial skeleton only by way of the acromioclavicular joint. The remainder of the scapular support is from the thick investing musculature surrounding its surface.
When examining the shoulder, start by assessing neurovascular structures. Neurovascular injuries frequently accompany traumatic shoulder injuries. The structures in closest proximity to the shoulder include the brachial plexus, axillary nerve, and axillary artery (Fig. 16–5).
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