Snapshot An 80-year-old woman presents to the emergency room with severe right shoulder pain and immobility. She fell down the steps outside her house and landed on her right side two hours prior to presentation. On exam, her right arm is abducted and externally rotated. She has decreased sensation to touch over the lateral aspect of her right shoulder. Radiographs demonstrate an anterior shoulder dislocation. Introduction Clinical definition complete anterior displacement of the humeral head out of the glenoid relevant definitions "dislocation" refers to complete displacement of the humeral head out of the glenoid "subluxation" refers to translation of the humeral head relative to the glenoid surface without frank dislocation Etiology Traumatic injury contact sports in younger patients falls in older patients Pathoanatomy normal glenohumeral anatomy humeral head articulates with the glenoid and is held there by several static and dynamic restraints static stabilizers glenohumeral ligaments anterior stability is conferred by 3 glenohumeral ligaments in addition to the subscapularis muscle superior glenohumeral ligament middle glenohumeral ligament inferior glenohumeral ligament glenoid labrum negative intraarticular pressure dynamic stabilizers rotator cuff muscles tendon of the long head of the biceps brachialis Associated conditions Bankart lesion fracture of the anterior inferior glenoid following impaction of the humeral head against the glenoid Hill-Sachs lesion compression chondral injury of the posterior superior humeral head following impaction against the glenoid axillary nerve injury transient neurapraxia present in 5% of shoulder dislocations may present with numbness or tingling over the lateral shoulder rotator cuff tear more likely in older patients Epidemiology Incidence one of the most common serious shoulder injuries 95% of shoulder dislocations are anterior 2-4% of shoulder dislocations are posterior < 1% of shoulder dislocations are inferior shoulder dislocations constitute approximately half of all joint dislocations Demographics bimodal gender distribution common in young males (20-30 years of age) with male-to-female ratio of 9:1 common in older females (60-80 years of age) with female-to-male ratio of 3:1 Presentation Symptoms pain deformity immobility feelings of instability Physical exam arm is abducted and externally rotated different from posterior dislocation in which the arm is held adducted and internally rotated "squaring" of the shoulder loss of rounded appearance (humeral head) and sharp prominence of the acromion ("squaring") axillary nerve neuropraxia reduced sensation over the lateral shoulder rotator cuff injury more common in elderly Imaging Radiographs indications radiographs are indicated in any patient in whom a shoulder dislocation is suspected anteroposterior (AP) and axillary lateral or scapular Y-views must be taken findings incongruence between the humeral head and glenoid the humeral head is displaced medially and overlies the glenoid anterior vs. posterior location of the humeral head can be best visualized on the axillary lateral or scapular Y view Differential Posterior shoulder dislocation distinguishing factors history is often related to seizure or electrical injury as opposed to blunt trauma arm is held adducted and internally rotated AP radiograph may demonstrate near congruence of the humeral head and glenoid scapular Y view radiograph will demonstrate posterior displacement of the humeral head relative to the glenoid Rotator cuff tear distinguishing factors arm will not be held in abduction and external rotation radiographs will demonstrate normal placement of the humeral head within the glenoid Treatment Nonoperative closed reduction followed by sling immobilization indication acute dislocations Operative surgical stabilization indication recurrent shoulder instability that has failed nonoperative management in young patients Complications Recurrence very common incidence estimates vary widely from 17-90% more common in younger patients (< 30 years of age) Axillary nerve injury Rotator cuff damage more common in older patients Prognosis Favorable prompt reduction Unfavorable recurrent dislocation rotator cuff tear old age shoulder hyperlaxity