Shoulder Dislocation
What is it: A traumatic shoulder dislocation occurs when the head of the humerus is displaced from the glenoid fossa. Anterior dislocations are most common and occur when the arm is forced into external rotation and abduction. Posterior dislocations can also occur, more commonly with a blow to the front of the shoulder or from a fall on the outstretched hand.
How does it present: Patients usually present after some type of shoulder trauma, and often report difficulty with moving their arm. Classically in anterior dislocation, the patient will hold their arm slightly abducted and externally rotated, in posterior dislocations, the arm will be held in internal rotation and adducted.
Common exam findings: During an acute dislocation, the shoulder anatomy may appear altered. In anterior dislocations, a bulge anteriorly may be noted. Conversely in posterior dislocations, there may be a flattening of the anterior shoulder and a posterior bulge. Range of motion is often limited in each of these acutely. In anterior dislocations, you should always check for injury to the axillary nerve, which innervated the skin over the deltoid. This should be assessed after relocation as well. If you see the patient after a reduction of a presumed shoulder dislocation, you may see a positive Apprehension and Relocation Test. You may also see laxity on the Load and Shift Test, or have a positive Sulcus Sign.
Tests and treatment: A clinical diagnosis can often be made immediately following the acute trauma, but x-rays should be used to confirm diagnosis and rule out other fractures. Reductions can be done immediately by appropriately trained professionals. Repeat x-rays should be used to confirm the reduction. X-rays sometimes show a Hill-Sach's lesion, which is a compression fracture of the posterior humeral head. The presence of a Hill-Sach's lesion may increase the risk of recurrent dislocation. In both anterior and posterior dislocations, treatment often includes slinging for comfort followed by progressive range of motion and strengthening. Surgical intervention may be indicated for those patients with recurring dislocation and sometimes even after the initial dislocation. With anterior dislocations, consider of MRI arthrogram testing after the first injury to evaluate for associated labral lesions and to identify patients at greater risk of re-dislocation. Patients identified as at risk for recurrent dislocation may benefit from surgical repair following the initial injury.