Glenohumeral Dislocation, Posterior

A posterior glenohumeral dislocation occurs when the humeral head disarticulates from the glenoid and rests posteriorly to its normally seated position on the glenoid.

Glenohumeral instability is classified by:

Other names:

The shoulder is the most commonly dislocated joint in the human body. Glenohumeral instability affects 2% of the general population, ranging from mild subluxation to frank dislocation. Recurrent, unidirectional posterior subluxation is the most frequent form of posterior instability (1)[C].

Anterior dislocations are much more common than posterior dislocations.

Posterior shoulder dislocations account for only 2–5% of all traumatic shoulder dislocations. However, trauma is associated with ∼50% of all posterior dislocations.

A posterior shoulder dislocation is the most commonly missed shoulder pathology. ∼60–79% of these dislocations are not diagnosed at initial presentation, which may compromise the potential effectiveness of orthopedic intervention. Proximal and diaphyseal humeral fractures are often associated with posterior dislocation. Compared to anterior dislocations, posterior dislocations associated with vascular or neurologic compromise are unusual.

In the absence of trauma, posterior dislocations occur most often as a result of a seizure (contraction of the internal rotators) or electrical shock injury. Dislocation can occur when an axial load is applied to the upper extremity in the “at risk” position: forward flexion, adduction, and internal rotation.

Injury can occur in athletes with a fall upon a flexed elbow and adducted arm, or by a direct axial load to the humerus.

Extremely rare in pediatrics because force necessary to cause a dislocation will instead cause a proximal humerus fracture

History of seizure disorder

History of electric shock (2)[C]

History of posterior shoulder dislocation or instability

Disorders such as Charcot shoulder and Ehlers-Danlos syndrome have been well documented.

Congenital anomalies, such as scapular aplasia, increase the risk of dislocation.

Glenoid hypoplasia and excessive glenoid retroversion increase risk.

At-risk sports/positions for posterior instability and/or dislocation include offensive linemen with arms in blocking position, backhand stroke in racket sports, pull-through phase of swimming, and follow-through phase in golf or throwing motion (2)[C].

Mechanism of injury? Generally direct trauma to anterior aspect of shoulder.

Direction of applied force and position of the arm (the “at-risk” position)

Acute vs chronic in nature?

Overhead athletes may have insidious onset of weakness and pain, especially with muscle fatigue.

History of previous injury or pain in affected shoulder?

Previous or present description of pain, including location, intensity, and duration

Previous or present history of tingling, weakness, catching, locking

Any aggravating or alleviating factors?

Severe shoulder pain that increases with movement

Cardinal sign: An arm held in internal rotation and adduction with inability to externally rotate or abduct the arm

Mild flattening of the anterior shoulder with an anterior glenohumeral void and loss of normal deltoid contour may be present.

There may be prominence of the coracoid process and squaring-off of the anterior-lateral acromion.

The humeral head may be visible or palpable posteriorly.

Routine observation, gentle palpation, range of motion, and strength of the affected extremity should be performed.

Limitation with passive external rotation and abduction may be noted

It is of utmost importance to monitor the neurovascular status of the affected arm. Injury to the axillary vessels is rare but potentially catastrophic.

Examine axillary nerve function by testing active contraction of the deltoid as well as sensation over the lateral aspect of the shoulder.

Neurologic involvement is often in the form of a neurapraxia.

Evaluate for atrophy of posterior rotator cuff muscles as an indication of chronic posterior instability.

Assess for generalized ligamentous laxity.

Scapulothoracic mechanics and rhythm should be observed, if position not “fixed.”

Acute subluxation

Fractures (clavicle, scapula, and humerus)

Rotator cuff pathology (strain, partial or complete tear)

Adhesive capsulitis/frozen shoulder

Acromioclavicular joint pathology

Intra-articular pathology (labral, glenoid, or ligamentous)

Scapular winging/instability