The domain of the input material is Orthopedics and Musculoskeletal Trauma.

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Abstract

This analysis provides a structured overview of glenohumeral joint dislocation, identifying it as the most frequent large joint dislocation. Anatomically, the joint's inherent instability is attributed to the size mismatch between the large humeral head and the shallow glenoid fossa, stabilized primarily by the glenoid labrum and the rotator cuff muscles. Dislocations are classified into three main types: anterior (most common, 96%), posterior (2–4%), and inferior (rare, <1%). The mechanisms, characteristic clinical presentations (including arm position), and common associated injuries—such as Hill-Sachs/Bankart lesions (anterior) and reverse Hill-Sachs/reverse Bankart lesions (posterior)—are detailed. Neurovascular compromise, particularly axillary nerve injury, is a significant complication. Diagnosis relies chiefly on history, physical examination, and radiographic imaging (AP and lateral views, often requiring an axillary view for subtle posterior dislocations). Management requires closed reduction, followed by immobilization and subsequent physical therapy, with surgical intervention reserved for recurrent instability.

Clinical Summary of Glenohumeral Dislocation

• 0:09 Definition and Incidence: Glenohumeral joint dislocation (shoulder dislocation) is the separation of the humerus from the shoulder joint. It is the most common dislocation of a large joint.
• 0:14 Anatomy and Instability: The glenohumeral joint is a synovial ball-and-socket joint that prioritizes range of motion over stability. The humeral head is approximately four times larger than the shallow glenoid fossa, contributing to inherent instability.
• 0:48 Stabilization Structures: Key stabilizing structures include the glenoid labrum (fibrocartilage ring), supporting ligaments, and the four rotator cuff muscles (supraspinatus, infraspinatus, teres minor, and subscapularis). The biceps tendon also provides a depressive stabilizing effect on the humerus.
• 1:30 Dislocation Types: Dislocations are categorized as anterior, posterior, or inferior. Superior dislocation is generally prevented by the coracoacromial arch.

Anterior Dislocation (Most Common)

• 1:43 Prevalence and Mechanism: Anterior dislocation is the most common type due to the joint capsule being weakest in this area. It results from abduction, extension, and external rotation, often following direct trauma or a fall onto an outstretched arm.
• 2:02 Associated Lesions: This type is closely linked to Hill-Sachs lesions (compression fractures on the posterolateral humeral head) and Bankart lesions (rupture of the anterior glenoid labrum). Avulsion fractures accompanying Bankart lesions are termed bony Bankart lesions.
• 2:33 Clinical Presentation: The arm is typically held in external rotation with abduction, with pain upon any movement. There is a loss of the normal deltoid contour, and the acromion may appear prominent.

Posterior Dislocation (Uncommon)

• 2:48 Prevalence and Mechanism: Posterior dislocations account for only 2–4% of cases, occurring when the humeral head is forced posteriorly while in internal rotation. It is most commonly associated with generalized tonic-clonic seizures, electrocution (including ECT), or trauma (falls onto an outstretched arm).
• 3:22 Associated Lesions: Can cause reverse Hill-Sachs lesions (impaction on the anteromedial humeral head) and reverse Bankart lesions (rupture of the posterior glenoid labrum). A tear of the subscapularis muscle is also frequent.
• 3:44 Clinical Presentation: The arm is typically held in internal rotation and adduction, with limited external rotation. Loss of the deltoid contour is possible but less frequent than in anterior dislocations, and neurovascular complications are less common.

Inferior Dislocation (Rare)

• 4:03 Classification and Mechanism: Rare (<1% of cases), also termed luxatio erector because the arm is held upwards in fixed abduction, often with the patient placing their hand on their head. It typically results from forced hyperabduction.

• 4:25 Neurovascular Complications: Potential for injury exists during both the incident and reduction. The axillary nerve is injured in nearly 40% of anterior dislocations, leading to sensory loss over the lateral shoulder and deltoid weakness/atrophy. Injury to the brachial plexus and axillary vessels is also possible.

• 4:53 Instability and Recurrence: Soft tissue damage (ligament/rotator cuff tears) is common and predisposes to recurrent dislocation. Approximately 40% of traumatic anterior dislocations recur within one year.

• 5:13 Diagnosis and Imaging: Diagnosis is based on history, physical exam, and imaging. X-rays (AP and lateral views minimum) are standard. CT and MRI can detail soft tissue injuries or subtle fractures. Ultrasound can be used for point-of-care confirmation of reduction.

• 6:14 Radiographic Features: Posterior dislocations are subtle and missed initially in up to 50% of cases, necessitating an axillary view. AP signs of posterior dislocation include the "rim sign" (glenohumeral joint space >6mm) and the "light bulb sign" (fixed internal rotation of the humeral head).

• 6:54 Management: Treatment involves closed reduction (repositioning without opening the skin), typically performed with sedation and analgesia. This is followed by a period of sling stabilization and gradual physiotherapy.

• 7:23 Recurrence and Surgery: In cases of recurrent dislocation, surgical stabilization may be required.