Chapter 2

### SHOULDER

The shoulder girdle consists of the clavicle, scapula, and humerus. It connects the upper extremity to the axial skeleton with only one true joint, the sternoclavicular joint. Between the scapula and the thorax, there is a muscular connection, allowing for extended mobility, compared to the limited mobility of the pelvic girdle. The joints of the shoulder girdle are the glenohumeral or shoulder joint, the acromioclavicular (AC) joint, and the sternoclavicular joint. The scapula is a complex bone and serves as a muscle attachment site. Seventeen muscles surround the scapula, supporting movement and stabilizing the shoulder. The scapula extends from the second to the seventh rib and has 30° anterior tilt. Scapular fractures (Figure 2-1) are relatively uncommon. They require high-energy and associated injuries, such as other fractures, pulmonary contusions, pneumothorax, neurovascular injuries, and spine injuries, which occur in 35–98% of patients.1,2

###### Figure 2-1.

Scapular neck fracture. There is a minimally displaced fracture of the scapular neck (arrow), with hairline extension into the scapular body. No extension to the glenoid surface is seen. Note that this patient is skeletally immature; the proximal humeral physis is patent.

Scapulothoracic dissociation (Figure 2-2) is a rare entity that consists of disruption of the scapulothoracic articulation. It is in essence an internal forequarter amputation. Vascular disruption (Figure 2-3) and brachial plexus injuries are usually present. Clinically, patients have massive soft tissue swelling, a pulseless upper extremity, and complete or partial neurologic deficits. Radiographically, there is lateral displacement of the scapula, AC separation, displaced clavicle fracture, or sternoclavicular disruption. These devastating injuries require violent traction and rotation, usually seen in motorcycle or motor vehicle accidents.3 There is a high mortality rate. Survivors with complete brachial plexus injuries suffer from flail upper extremity.

###### Figure 2-2.

Scapulothoracic dissociation. The medial scapula border is laterally displaced with respect to the rib cage (arrowheads). The acromioclavicular joint is disrupted (double-headed arrow).

###### Figure 2-3.

Angiogram, scapulothoracic dissociation. Same patient as in Figure 2-2. A catheter is placed in the brachiocephalic trunk. Contrast is opacifying the proximal aspect of the right subclavian artery with abrupt cutoff of the vessel, due to disruption (arrowhead).

The clavicle serves as a rigid support from which the scapula and arm are suspended. It keeps the upper limb away from the thorax so that the arm has maximum range of movement and transmits physical impacts from the upper limb to the axial skeleton. It also protects the neurovascular bundle and lung apices. Clavicle fractures are usually caused by a fall onto the affected shoulder. Eighty percent of fractures occur in the midshaft region (...

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