Acute Shoulder Injuries

I. GENERAL PRINCIPLES

A. Anatomy. The shoulder is the most mobile joint in the body, allowing the hand and upper extremity a broad range of motion and function.The larger humeral head articulates with a relatively small glenoid, and this bony anatomy provides little constraint for the glenohumeral joint. It is this articulation that allows for the shoulder’s extreme range of motion. Static and dynamic stabilizers provide additional constraint. The labrum acts to increase the depth of the glenoid concavity and provide additional stability. The glenohumeral ligaments (superior, middle, and inferior) act to stabilize the joint in variable shoulder positions. The supraspinatus, infraspinatus, subscapularis, and teres minor, which make up the rotator cuff, act as important dynamic shoulder stabilizers and play a very important role in the mobility of the glenohumeral joint. The parascapular muscles are equally essential to normal shoulder function as these muscles function to position the scapula and glenoid appropriately in space. If the scapula is not stabilized by these muscles, the glenoid cannot act as a stable base with which the humeral head may articulate. It is the complexity of this joint that provides great mobility, although such extreme mobility may at times place the shoulder at increased risk for injury.

B. DifFerential diagnosis. The most common findings in acute shoulder injuries include glenohumeral dislocation, rotator cuff injury, and fractures. However, it remains essential to consider other possible etiologies in a patient presenting with acute shoulder pain including cervical disc disease (C5 nerve root), brachial neuritis, pleural irritation, tumors, and cardiac disease.

II. SHOULDER DISLOCATIONS

A. Classification. Shoulder instability is classified by the position of the humeral head with respect to the glenoid (anterior, inferior, posterior, or multidirectional). Shoulder dislocations typically include cases documented radiographically or those involving a formal manipulative reduction. Dislocations are further characterized by timing or chronicity (acute, recurrent, chronic), and by etiology (traumatic or atraumatic). Anterior dislocations are by far the most common. Patient age at the time of the first dislocation is a significant predictor of both accompanying injury and the patient’s risk of recurrent dislocation. The risk of recurrent dislocation has been shown to be inversely proportional to age; the classic article found that one-third of patients 20 years of age or younger at the time of the initial dislocation went on to require surgery for recurrent dislocation.¹

B. Anterior dislocations

Mechanism of injury. Anterior dislocations may occur in various mechanisms. Traumatic anterior dislocations classically result when the arm is forced into an abducted, externally rotated position at the extreme range of motion. In patients with multidirectional instability (MDI), ligamentous laxity, or multiple recurrent instability (especially including bone loss), an anterior dislocation may occur with little trauma in a broad range of shoulder positions.
Examination. A thorough examination of the shoulder is essential in the patient sustaining an acute shoulder injury. The appearance of the shoulder in the setting of an anterior dislocation is squared off with prominence of the posterolateral acromion and a hollow appearance of the posterior shoulder. The patient typically holds the arm in an adducted position, and attempts at range of motion of the shoulder that are extremely painful and mechanically limited. A thorough neurovascular examination of the upper extremity is essential before any reduction attempts are made because axillary nerve injuries are commonly seen in glenohumeral dislocations and must be documented before manipulation of the shoulder. One prospective study found that as many as 54% of patients with glenohumeral dislocations had an axillary nerve injury, and neurologic complications were more common in patients 50 years or older.²
Imaging. All patients with a suspected dislocation of the shoulder should have a complete series of shoulder X-rays. This should include an anteroposterior (AP), true AP in the plane of the scapula (Grashey view), a transscapular (“Y”) view, and an axillary view. The combination of these orthogonal views will not only clearly demonstrate the direction of the dislocation but also allow for the recognition of any associated fractures.
Initial treatment

a. Reduction without general anesthesia. Prompt reduction of the dislocation is important not only to relieve the patient’s pain but also to minimize the risk of associated neurologic injuries, as this risk increases in shoulders that remain dislocated over 12 hours.³ To achieve a gentle and pain-free reduction, muscle relaxation and pain relief are required. The patient may be provided IV pain medication and sedation, although an intraarticular lidocaine block is equally effective as well.⁴ For this block, 10 to 20 cc of 1% plain lidocaine is injected into the glenohumeral joint. Multiple methods of reduction can then be effective when applied correctly.

Prone reduction (Stimson technique). The patient is placed prone on the examination table or stretcher with the involved arm and shoulder hanging over the edge of the table. A 10-lb weight is suspended from the patient’s wrist or may be held in the patient’s hand. If good analgesia and relaxation are present, the shoulder may reduce in this position without further manipulation.
Reduction by traction. The patient is positioned supine and additional intravenous (IV) sedation is administered. An assistant provides countertraction while the physician grasps the forearm of the involved shoulder and gently pulls in a line of 30° of abduction and 20° to 30° of forward flexion. Countertraction may be effectively applied by placing a folded sheet around the thorax and applying linear traction in the opposite direction of the reduction force. Sustained traction for 5 minutes may be necessary. Vigorous and forceful attempts at reduction should be avoided. Firm, constant pressure is often effective in reducing the joint as long as the patient is adequately sedated.

b. Reduction under anesthesia. If the aforementioned methods fail or if a proximal humerus fracture (other than a tuberosity fracture) is present, a reduction under general anesthetic with complete muscle relaxation is indicated. The shoulder typically reduces easily with little risk of further damage to the glenohumeral joint or its surrounding structures.

5. Postreduction treatment. The length of immobilization has not been shown to have any effect on the incidence of redislocation.⁵ The shoulder should only be immobilized for 1 to 2 weeks as needed for pain control after a dislocation or subluxation episode. A range-of-motion and rotator cuff strengthening program is initiated early, avoiding the extremes of external rotation and abduction. Patients are allowed to return to sports and other activities when the shoulder has normal range of motion and strength.

6. Recurrent dislocations or subluxations.

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