Acute Dislocation of Shoulder – Mechanism of Injury

The shoulder joint is formed by four articulations

• Sternoclavicular joint
• Acromioclavicular Joint
• Glenohumeral joint
• Scapulothoracic joint

All of these joints work together  for smooth functioning of the shoulder.

Acute traumatic dislocation of shoulder is quite a common injury. The normal shoulder can become unstable as a result of trauma. Although the shoulder can be dislocated by direct trauma such as a blow directed at the proximal humerus, indirect force is the most common cause of shoulder sprain, subluxation, or dislocation.

Dislocation of shoulder can be of following types

Anterior Dislocation

Over 95% of shoulder dislocation cases are anterior. It could be  sub-coracoid. Sub-glenoid; subclavicular; and, very rarely, intrathoracic. The subtypes denote position of the dislocated head

Posterior Dislocation
Posterior dislocations are occasionally due to electrocution or seizure and may be caused by strength imbalance of the rotator cuff muscles.  It is a relatively uncommon injury.

Inferior Dislocation

It is the least common the three  occurring in less than 1% of all shoulder dislocation cases. This condition is also called luxatio erecta because the arm appears to be permanently held upward or behind the head. It is caused by a hyper abduction of the arm that forces the humeral head against the acromion.

Inferior dislocations have a high complication due to  vascular, neurological, tendon, and ligament injuries.

Mechanism

Anterior dislocation is caused by a combination of abduction, extension, and external rotation forces. Due to this force is indirectly transferred  to the anterior capsule and ligament resulting in dislocation. Trauma is the most common cause of anterior dislocation.

Posterior dislcation is generally caused by convulsive disorders. However convulsive disorders can result in anterior dislocations as well through indirect forces.

Apart from trauma and convulsion disorders, dislocations may result from violent muscle contraction, by electrical shock and sudden jerky force to shoulder.

A direct force applied to the anterior shoulder  an indirect posterior force applied through the arm up to the shoulder may also result in dislocations

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Related posts:

1. Acute Dislocation of Shoulder – Clinical Presentation
2. Acute Anterior Dislocation of Shoulder – Treatment
3. Sternoclavicular Dislocation-Mechanisms of Injury
4. Posterior Dislocation of Shoulder – Presentation and Treatment
5. Radiographic Studies In Shoulder Dislocation