The shoulder joint is the most commonly dislocated of all joints.1-5 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 the Emergency Physicians (EPs).2
The human shoulder is remarkable for its degree of mobility. The same 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. Anterior shoulder dislocations are the most common and account for 95% of all shoulder dislocations.1-4 The overall incidence of shoulder dislocations is 17 per 100,000. There is a bimodal age distribution.1,4,6 It occurs most commonly in males from 20 to 30 years of age, typically related to athletics and trauma. The other large group is women from 60 to 80 years of age primarily due to falls.
ANATOMY AND PATHOPHYSIOLOGY
The shoulder or glenohumeral joint is a multiaxial ball-and-socket type of synovial joint that permits a wide range of motion. This range of motion is at the expense of stability.7 The shoulder has greater than 180° of motion in the sagittal and coronal planes and 180° of rotary movement.8 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 (i.e., supraspinatus, infraspinatus, teres minor, and subscapularis) that together form the rotator cuff. These muscles are torn and injured in shoulder dislocations, especially with posterior and inferior dislocations.9,10
The shoulder receives its blood supply from branches of the axillary artery (i.e., 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. The humeral head can be dislocated anteriorly 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 the most common and account for 95% of all dislocations (Figure 102-1). An anterior dislocation usually results from direct or indirect forces causing abduction, extension, and external rotation of the limb. Anterior dislocations are classified as subcoracoid, subglenoid, subclavicular, or intrathoracic based on the location of ...