Shoulder dislocations are a fairly common injury in younger patients with shoulder injuries. Anterior dislocations are more common than posterior dislocations; the mechanism is typically forces that push the arm out and back. After an anterior dislocation, the patient’s arm is typically held in a guarded position by the other arm in about 15 degrees of abduction and mild external rotation. Posterior shoulder dislocations occur in approximately 5% of cases, with the typical mechanism either a direct blow, electric shock injury, or seizure that triggers intense muscle contractions.

Shoulder dislocation should be confirmed by radiograph prior to attempts at reduction except for patients with severe vascular compromise or recurrent dislocations with a trivial mechanism of injury. An anteroposterior radiographic view will usually demonstrate a shoulder dislocation. Ordering an axillary view will confirm if the dislocation is either posterior or anterior.

On imaging, anterior dislocations typically will show the humeral head inferior and medial to the expected location. Posterior dislocations will often show more subtle humeral head displacement typically associated with internal rotation, which causes a light bulb-like contour of the humeral head. The position of the dislocation should be confirmed by an axillary view radiograph if possible, but a scapular Y-view is an acceptable alternative when the patient has too much pain to lift the arm for the axillary view.


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The radiograph should also be examined for associated fractures.  Sometimes there are subtle dents in either the superior humeral head or the inferior glenoid rim; these are known as Bankart and reverse Bankart lesions, respectively.

Ordering a chest radiograph is appropriate if the shoulder radiograph is normal and the clinician wants to rule out referred pain from a diaphragmatic or rib injury. Bilateral acromioclavicular (AC) views, preferable holding weights, are appropriate when an AC separation is suspected but not clear on the initial films. Computed tomography (CT) of the abdomen is appropriate when referred pain from a splenic injury is suspected. In these cases, the patient would have low blood pressure, elevated pulse, abdominal tenderness, or normal range of motion in the shoulder without guarding.

There are many techniques to perform shoulder reduction in a patient with anterior dislocation [too many to cover here]. Most reductions can be managed successfully without procedural sedation, but patients should not eat or drink in case sedation or surgical reduction is required. With posterior dislocations, traction-counter-traction is the first choice for anatomic reduction.

After reduction, a repeat neurovascular exam and confirmation radiograph are standard. This is followed by placement in a sling or shoulder immobilizer and follow-up with an orthopedist. There has been a move to use a sling rather than an immobilizer because it keeps the arm in a more neutral position. 

Figure 2. Axillary view showing posterior shoulder dislocation. Credit: Brady Pregerson, MD.

Brady Pregerson, MD, is an emergency physician at Tri-City Medical Center in Oceanside, California and at Scripps Coastal Urgent Care in Oceanside, California.

Reference

Pregerson DB. Orthopedics: arms-shoulder. In: Emergency Medicine 1-Minute Consult Pocketbook. 5th ed. 2017;5:217. http://www.erpocketbooks.com/emergency_medicine_reference_books/quick-essentials-emergency-medicine/