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The shoulder joint is the most commonly dislocated of all joints.14 Shoulder dislocations were depicted in Egyptian murals as early as 3000 BC.1 Despite 5000 years of medical advancements, shoulder dislocations continue to be a major cause of Emergency Department (ED) visits. They account for more than 50% of all joint complications treated by Emergency Physicians (EPs).2

The human shoulder is remarkable for its degree of motion. The anatomic features that contribute to this mobility also contribute to its instability.3 The shallow glenohumeral joint allows the shoulder to be dislocated anteriorly, posteriorly, or inferiorly. The anterior shoulder dislocation is the most common and accounts for 95% of all shoulder dislocations.14 The overall incidence of shoulder dislocations is 17 per 100,000. There is a bimodal age distribution.1,4 It occurs in males from 20 to 30 years of age most commonly related to athletics and trauma. The other large group is women from 60 to 80 years of age, primarily due to falls.

The shoulder (glenohumeral) joint is a multiaxial ball-and-socket type of synovial joint that permits a wide range of motion. Unfortunately, the range of motion is at the expense of stability.5 The shoulder has greater than 180° of motion in both the sagittal and coronal planes as well as 180° of rotary movement.6 The spheroidal head of the humerus articulates with the shallow glenoid fossa of the scapula. The glenoid fossa accommodates roughly one-third of the humeral head. The bony landmarks surrounding the shoulder joint are the coracoid and acromion processes of the scapula. A loose, thin fibrous capsule encloses the glenohumeral joint. The muscular component of the shoulder is a fusion of four separate muscles (supraspinatus, infraspinatus, teres minor, and subscapularis) that together form the rotator cuff. These muscles have a tendency to be torn and injured in shoulder dislocations, especially posterior and inferior dislocations.7 The shoulder receives its blood supply from branches of the axillary artery (the anterior and posterior circumflex humeral arteries).

Innervation of the shoulder is from branches of the suprascapular, axillary, and lateral pectoral nerves. The axillary nerve lies at the level of the humeral neck. When it is dislocated anteriorly, the humeral head is displaced into the quadrangular space where it may compress and damage the axillary nerve. This can result in a neurapraxia, paralysis of the deltoid muscle, and/or a sensory loss to the skin over the shoulder.

Shoulder dislocations can occur anteriorly, posteriorly, or inferiorly depending on the mechanism of injury. Anterior shoulder dislocations are by far the most common and account for 95% of all dislocations. An anterior dislocation usually results from direct or indirect forces causing abduction, extension, and external rotation of the limb. Anterior dislocations are classified based on the location of the humeral head into subcoracoid, subglenoid, subclavicular, and intrathoracic. Subcoracoid dislocations account for 75% of all anterior ...

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