The shoulder joint is particularly susceptible to injuries because of its great mobility and inherent instability. The heavy reliance on soft tissue structures and balanced muscular control for stabilization through a large ROM places considerable demands on these structures, resulting in both acute and chronic injuries. Injury recognition is sometimes difficult because of the interplay of the muscles acting on the shoulder during functional activity.
Acute soft tissue injuries can result from direct trauma, movements forcing the joint beyond its normal range, and forceful muscle contraction during activity.
During sports such as football, wrestling, and soccer, direct contact with other players and the ground can result in contusions to superficial bony anatomy and the surrounding musculature. The clavicle, acromion, and lateral arm are bony structures with little soft tissue protection.
Contusion of the acromion is often referred to as a “shoulder pointer.” Blocker’s exostosis (also known as tackler’s exostosis or blocker’s spur), on the other hand, results from repetitive insult and irritation of the bone, causing excessive bone formation and at times a palpable spur on the anteriolateral surface of the humerus. Contusions to these isolated bony structures are rarely disabling, with signs and symptoms typically limited to localized swelling, pain, and point tenderness.
Contusions to the musculature can be more disabling, since hematoma formation and pain can severely limit muscular function as evidence by decreased range of motion and strength during your examination. A complication of biceps muscle contusion is myositis ossificans, or calcification within and around the biceps. Myositis ossificans can result from an unresolved hematoma in cases with large hematoma formation, repetitive insult, or continued use following the initial contusion. This calcification may be palpable as a firm mass in the belly of the biceps and can be confirmed with radiographs. Decreased range of motion in both flexion and extension may result. In most cases, this can be prevented with proper rest and treatment.
Sprains and Dislocation
Sprains involving the ligaments and capsule of the shoulder complex vary in frequency and severity, depending on the structure involved. Ligamentous and capsular disruption can result from both compressive and tractional forces that force the joint beyond its normal range of motion. Sprains of the glenohumeral and acromioclavicular (AC) joint occur more frequently than sternoclavicular (SC) joint sprains.
Glenohumeral Joint Sprains
In order to provide the mobility inherent in the glenohumeral joint, the joint’s capsule and ligaments are comparatively lax throughout most of glenohumeral motion. This means the capsule and ligaments are minimally involved in maintaining joint stability throughout most of the range, with tensioning and potential injury to these structures occurring at the extreme ranges of motion. As a result, mild to moderate (first- and second-degree) glenohumeral sprains are fairly uncommon. However, forces exerted at the end ranges of motion that are sufficient to tear the glenohumeral ligaments (third-degree sprain) can cause subluxation or dislocation of the humeral head because of its shallow articulation with the glenoid. While dislocations and subluxations are discussed later in this chapter, lesser degree glenohumeral sprains display signs and symptoms that include pain and apprehension near the end ranges of motion. Additionally, increased joint laxity may be observed with second degree injuries during glenohumeral instability (capsuloligament stress) tests in the direction of the applied force.
Acromioclavicular Joint Sprains
Within the shoulder complex, the acromioclavicular (AC) joint is the most commonly sprained or “separated” joint. Ligament injuries to this joint typically result from a fall or from direct contact to the point of the shoulder, driving the acromion caudally into the clavicle. Forces transmitted through the arm with a fall on an outstretched hand may also produce an AC sprain. First-degree sprains are characterized by localized pain, point tenderness, and swelling over the joint. The patient may complain of mild to moderate pain during shoulder motion, particularly with abduction above 120° and horizontal adduction. Second-degree injuries involve partial tearing of one or both of the AC and coracoclavicular ligaments. The patient will have increased complaints of pain, swelling, and disability with arm motion above horizontal. The distal end of the clavicle may or may not be elevated, depending on the extent of disruption of one or both of the associated ligaments (AC and coracoclavicular). If no obvious disruption is noted, shear and compression tests to the joint can be used to confirm the degree of instability. Third-degree injuries are characterized by complete disruption of the AC and coracoclavicular ligaments. The patient will complain of severe pain at the time of injury and demonstrate an unwillingness to raise the arm, typically protecting it at his side. Because you will note obvious swelling and elevation of the distal clavicle relative to the acromion (figure 12.5), no special tests are required to confirm a third-degree injury.
Sternoclavicular Joint Sprains
The SC joint is quite stable, and sprains are infrequent. SC joint injury involves disruption of both the SC and costoclavicular ligaments. Injury can result from an anteriorly directed force, or direct blow, but more commonly results from forces transmitted along the long axis of the clavicle. Signs and symptoms of SC sprains include localized pain, swelling, and point tenderness directly over the joint. Pain increases with forward rotation of the shoulders and horizontal adduction, which act to compress the joint. With a first-degree sprain there is minimal ligament tearing, with no laxity or joint displacement. Second-degree sprains involve partial tearing of both the SC and costoclavicular ligaments, resulting in increased joint laxity and some displacement of the proximal clavicle from the sternum.
Third-degree sprains are readily observed and are characterized by complete separation of the SC joint with complete rupture of both ligaments. In most cases, the proximal clavicle is displaced anteriorly and superiorly in relation to the sternum secondary to its bony joint contour at the articular surface. However, on occasion, an anteriorly directed force displaces the clavicle posteriorly. With posterior displacement, secondary injury to the trachea, esophagus, and vascular structures (subclavian artery and brachiocephalic vein) underlying the proximal end of the clavicle may occur, causing potentially life-threatening breathing and vascular complications (figure 12.6). Specific signs and symptoms to watch for in your on-site and acute examinations include difficulty breathing, vocal changes, difficulty swallowing, signs of vascular compromise in the upper extremity on the affected side (i.e., white or mottled skin coloration, reduced or absent distal pulses), and shock.