Shoulder Luxation: Understanding Anterior vs. Posterior Dislocations

What is the difference between anterior and posterior shoulder luxation?

Shoulder luxation, commonly known as a dislocation, occurs when the head of the humerus completely separates from the glenoid fossa of the scapula; the primary distinction between anterior and posterior types lies in the direction of the humeral head displacement relative to the glenoid, their respective mechanisms of injury, and their clinical presentations.

Understanding Shoulder Luxation (Dislocation)

The shoulder joint, or glenohumeral joint, is a highly mobile ball-and-socket joint, making it the most frequently dislocated major joint in the body. Its inherent mobility, while advantageous for function, comes at the cost of stability, relying heavily on a complex interplay of ligaments, the joint capsule, and surrounding musculature (primarily the rotator cuff) to maintain integrity. A "luxation" refers to a complete displacement of the joint surfaces, as opposed to a "subluxation," which is a partial or incomplete dislocation followed by spontaneous reduction.

Anterior Shoulder Luxation

Anterior shoulder luxation is by far the most common type, accounting for over 95% of all shoulder dislocations. In this scenario, the humeral head displaces forward and downward relative to the glenoid fossa.

• Mechanism of Injury:
  • Typically results from a combination of abduction, external rotation, and extension of the arm, often with an axial load.
  • Common scenarios include falling on an outstretched arm (FOOSH) with the arm in this position, direct impact to the posterior shoulder, or forceful overhead activities in sports (e.g., throwing, blocking in football, wrestling).
• Incidence:
  • Highly prevalent, particularly in young, active individuals.
  • Higher risk of recurrence, especially in those under 20 years old.
• Clinical Presentation:
  • Obvious deformity: The shoulder appears "squared off" or flattened anteriorly, with a prominent acromion.
  • Palpable humeral head: The humeral head may be felt anteriorly, often below the coracoid process.
  • Arm position: The arm is typically held in slight abduction and external rotation, with the patient reluctant or unable to move it.
  • Severe pain: Intense pain is immediate and often debilitating.
  • Nerve involvement: Potential for axillary nerve injury, leading to numbness over the lateral deltoid and weakness in deltoid or teres minor.
• Associated Injuries:
  • Bankart lesion: An injury to the anterior-inferior labrum of the glenoid.
  • Hill-Sachs lesion: A compression fracture on the posterior-superior aspect of the humeral head, caused by impact against the anterior glenoid rim during dislocation.
  • Rotator cuff tears (more common in older individuals).
  • Fractures of the greater tuberosity or glenoid rim.

Posterior Shoulder Luxation

Posterior shoulder luxation is significantly rarer, accounting for less than 5% of all shoulder dislocations. In this type, the humeral head displaces backward relative to the glenoid fossa. It is often missed on initial clinical examination and standard X-rays due to its less obvious presentation.

• Mechanism of Injury:
  • Typically results from a combination of adduction, internal rotation, and flexion of the arm, often with an axial load.
  • Common causes include:
    • Direct impact: A direct blow to the anterior shoulder.
    • Muscular contractions: Uncontrolled, violent muscle contractions such as those occurring during seizures, electrocution, or severe trauma.
    • Falling with the arm internally rotated and adducted.
• Incidence:
  • Infrequent, making diagnosis challenging as it's not always the first consideration.
  • Higher incidence of associated fractures than anterior dislocations.
• Clinical Presentation:
  • Less obvious deformity: The shoulder may appear flattened anteriorly, but the posterior prominence is often subtle.
  • Arm position: The arm is typically held in adduction and internal rotation, often "locked" in this position.
  • Limited external rotation: The most defining clinical sign is a marked and painful inability to externally rotate the arm.
  • Pain: Significant pain, though sometimes less acute than anterior dislocations.
• Associated Injuries:
  • Reverse Hill-Sachs lesion: A compression fracture on the anterior-medial aspect of the humeral head.
  • Posterior labral tears.
  • Fractures of the lesser tuberosity.

Key Differences Between Anterior and Posterior Luxation

Management and Rehabilitation Principles

Regardless of the direction, immediate medical attention is crucial for any suspected shoulder luxation.

• Acute Management:
  • Reduction: The primary goal is to safely and promptly reduce the dislocation (return the humeral head to the glenoid fossa). This is typically performed by a medical professional using specific maneuvers, often under sedation.
  • Immobilization: Following reduction, the shoulder is usually immobilized in a sling for a period to allow initial soft tissue healing and reduce pain.
• Rehabilitation:
  • Pain and Swelling Management: Initial focus on controlling inflammation.
  • Gradual Range of Motion (ROM): Carefully restoring pain-free movement without stressing the healing structures.
  • Strengthening: Progressive strengthening of the rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis) and scapular stabilizers (e.g., serratus anterior, rhomboids, trapezius). This is vital for dynamic stability.
  • Proprioception and Neuromuscular Control: Exercises to improve the joint's sense of position and movement, enhancing stability and preventing re-injury.
  • Return to Activity: A gradual, sport-specific or activity-specific progression is essential to minimize the risk of recurrence. Recurrence rates are significantly higher for anterior dislocations, especially in younger individuals.

When to Seek Medical Attention

Any suspected shoulder luxation requires immediate medical evaluation. Attempting to reduce a dislocation without medical training can cause further damage to nerves, blood vessels, or surrounding tissues. A healthcare professional will accurately diagnose the type of dislocation, rule out associated fractures or nerve damage, and perform a safe reduction, followed by appropriate rehabilitation planning.