What are the types of shoulder dislocations?

Types of Shoulder Dislocations

Shoulder dislocations are classified primarily by the direction of humeral head displacement relative to the glenoid, with anterior dislocations being the most common type, followed by posterior, inferior, and superior dislocations. 1

Anterior Shoulder Dislocations

Anterior dislocations account for the vast majority of all shoulder dislocations and can be further subdivided into:

• Subcoracoid: The humeral head is positioned beneath the coracoid process (most common subtype)
• Paraglenoid: A newly suggested subtype describing a portion of subcoracoid anterior dislocations 1
• Subglenoid: The humeral head is displaced below the glenoid
• Subclavicular: The humeral head is positioned beneath the clavicle
• Intrathoracic: The humeral head penetrates into the thoracic cavity (extremely rare)

Anterior dislocations typically occur from a fall on an outstretched hand or direct impact to the shoulder, often resulting in characteristic deformity and limited range of motion 1, 2.

Posterior Shoulder Dislocations

Posterior dislocations are much less common than anterior dislocations and can be challenging to diagnose. They typically occur from:

• Seizures
• Electric shock
• Fall on a flexed, adducted arm
• Direct posterior force to the anterior shoulder

Inferior Shoulder Dislocations (Luxatio Erecta)

Inferior dislocations, also known as luxatio erecta, are uncommon but have distinctive characteristics:

• The arm is typically locked in abduction
• The humeral head is displaced below the glenoid
• Often associated with higher rates of neurovascular injuries and humeral avulsion of glenohumeral ligaments 3
• Can be further classified as sub-coracoid and sub-glenoid inferior dislocations 4

Inferior dislocations often require specialized reduction techniques, such as the "two-step maneuver" which first converts the inferior dislocation to an anterior one before final reduction 4.

Superior Shoulder Dislocations

Superior dislocations are extremely rare and typically occur from:

• Severe trauma
• Often associated with fractures of the acromion or coracoid process

Clinical Implications

The type of dislocation significantly impacts:

1. Reduction technique selection: Different dislocations require specific reduction maneuvers
2. Associated injuries: Each type has characteristic patterns of soft tissue and bony injuries
3. Recurrence risk: Anterior dislocations have higher recurrence rates, especially in younger patients 2
4. Imaging requirements: Standard radiographs including anteroposterior views in internal and external rotation, and axillary or scapula-Y view are recommended for evaluating dislocations 5

Associated Injuries

Shoulder dislocations frequently involve additional injuries that affect treatment and prognosis:

• Bankart lesions: Detachment of the anteroinferior labrum (common in anterior dislocations)
• Hill-Sachs lesions: Compression fracture of the posterolateral humeral head (common in anterior dislocations)
• Combined defects: When both Bankart and Hill-Sachs lesions occur together, stability is significantly reduced compared to isolated defects 6
• Neurovascular injuries: More common with inferior dislocations 3

Diagnostic Considerations

Proper diagnosis requires:

• Thorough neurovascular examination
• Radiographic confirmation with multiple views
• Advanced imaging (MRI or CT) when associated injuries are suspected 5

It's important to note that many inferior dislocations may be misdiagnosed as other types of dislocations if the arm is no longer locked in abduction at the time of evaluation 3.