- Clinical science
Because the head of the humerus is substantially larger than the glenoid fossa, shoulder dislocation is the most common type of joint dislocation. The head of the humerus can dislocate completely or partially (subluxation) in three directions: anteriorly (most common), posteriorly, or inferiorly. Shoulder dislocation is usually the result of trauma. Typical symptoms include pain and restricted range of motion. Examination reveals a palpable dent in the shoulder caused by the empty glenoid fossa, while the head of the humerus may be palpable inferior to the glenoid fossa. X-rays of the shoulder in two views are necessary to rule out fractures and confirm the diagnosis. With adequate analgesia and muscle relaxation, the head of the humerus can be carefully repositioned into the glenoid fossa through various maneuvers. Reduction is followed by immobilization and subsequent physiotherapy. Patients with concomitant soft tissue lesions or recurrent shoulder dislocation may require surgery to stabilize the shoulder joint. Possible complications of shoulder dislocation include neurovascular damage (most commonly axillary nerve palsy), continued instability, restricted range of motion, and rotator cuff injury.
- Most common joint dislocation
- Sex: ♂ > ♀
- Peak incidence: 20–29 years
Epidemiological data refers to the US, unless otherwise specified.
- Anatomy: The head of the humerus is larger than the shallow glenoid fossa, which accounts for the high incidence of shoulder dislocation.
- Trauma (e.g., falling on an outstretched arm)
- Predisposing factors for recurrent shoulder dislocation
- For posterior dislocation: uncoordinated muscle contraction (e.g., seizure, electrical shock)
- > 95 % anterior (subcoracoid) and/or anterior-inferior (subglenoid)
- ∼ 4% posterior
- ∼ 1% inferior
- Severe shoulder pain
- Inability to move the shoulder
- Empty glenoid fossa: A palpable dent may be present at the point where the head of the humerus is supposed to lie.
- In anterior or anterior-inferior dislocation
In posterior dislocation
- Prominence of the posterior shoulder with anterior flattening
- Prominent coracoid process
- The arm is held in adduction and internal rotation, with the patient unable to actively rotate it in the outward direction.
In inferior dislocation
- The arm is held above the head, with the patient unable to actively adduct the arm.
- Neurologic dysfunction, especially with involvement of the axillary nerve, is common.
Posterior shoulder dislocation is frequently overlooked during clinical examination!
- Look for signs of fracture.
- Check for neurovascular deficits.
AP view and lateral view (Y view) to confirm dislocation and exclude fracture
- For posterior shoulder dislocation: axillary and/or scapular lateral views (Y view)
- The lightbulb sign is diagnostic of posterior shoulder dislocation.
- Seen in 35–40 % of patients with an anterior dislocation
- An indentation on the posterolateral surface of the humeral head caused by the glenoid rim
- AP view and lateral view (Y view) to confirm dislocation and exclude fracture
The primary aim of treatment is to reposition the humeral head into the glenoid cavity and restore full range of motion. This may be achieved by either closed reduction or surgical repair.
- Immobilization of the joint with a splint/sling
- Closed reduction
- Inferior dislocation and most anterior dislocations (except subclavicular or intrathoracic displacements)
- Uncomplicated posterior dislocations presenting early (< 6 weeks)
- Cases with no evidence of major arterial injury, associated injuries (Bankart, Hill-Sachs, disruption of the labrum), or associated fractures
- Surgical management
Continuous neurovascular monitoring/evaluation before and after reduction is important for prevention and early detection of axillary nerve and artery damage!
Damage to the axillary nerve
- Numbness or sensory loss over the lateral surface of the shoulder
- Malfunction of the deltoid muscle, resulting in an inability to abduct the arm
- Injury to the brachial plexus, axillary artery, and/or axillary vein
- Avulsion fracture of the major and/or minor tubercles
- Shoulder joint instability
We list the most important complications. The selection is not exhaustive.
- High rate of recurrence
- After rotator cuff repair, the rate of recurrence is significantly lower.