MANUAL MINORS
Posterior shoulder dislocation is a less common type of shoulder dislocation, accounting for about 2-4% of all shoulder dislocations. It occurs when the humeral head is displaced backward, out of the glenoid cavity of the scapula.
This type of dislocation is typically associated with indirect trauma, such as a fall onto an internally rotated outstretched arm or electrical convulsions, which generate a force pushing the humeral head backward. Due to its less obvious presentation, posterior dislocations are often diagnosed late or overlooked.
Diagnosis
Clinical diagnosis can be challenging because the deformity is less noticeable than in anterior dislocations. Patients present with pain and severe limitation of shoulder movement, with the arm in adduction and internal rotation. On physical examination, there is marked stiffness in external rotation.
Anteroposterior and axillary X-rays are essential for diagnosis, but the scapular “Y” view is also helpful. X-rays may show the “light bulb sign,” where the humeral head appears rounded and symmetrical due to internal rotation.
Differential Diagnosis
Pathology | Characteristics |
|---|---|
Anterior shoulder dislocation | Visible deformity, with the arm in abduction and external rotation |
Humeral neck fracture | Shoulder deformity without joint dislocation |
Rotator cuff tear | Shoulder pain and weakness without visible dislocation |
Acromioclavicular dislocation | Deformity at the top of the shoulder without humeral displacement |
Shoulder contusion | Mild pain and limitation without significant deformity or dislocation |
Emergency Management
Emergency management includes closed reduction of the dislocation, typically performed under sedation or anaesthesia. Reduction may be achieved with traction and external rotation techniques, although it is more challenging than anterior dislocations.
A thorough neurovascular assessment is crucial before and after reduction to check for potential damage to the brachial plexus or blood vessels. After reduction, the position is confirmed with X-rays, and the shoulder is immobilised with a sling or splint for 3 to 6 weeks.
Definitive Treatment
Definitive treatment depends on the stability of the shoulder after reduction and the presence of associated injuries. In uncomplicated dislocations, conservative treatment involves immobilisation followed by physiotherapy to restore mobility and muscle strength.
In cases of chronic or recurrent dislocations, or if there are associated injuries such as fractures of the humeral head or glenoid labrum (reverse Bankart lesion), surgery may be necessary. This could involve arthroscopic stabilisation or capsulolabral repair to prevent future instability.
Comments