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Glenohumeral Joint Dislocation

Epidemiology

  • Most common type of dislocation
  • Occurs more frequently in adults than in children
  • Anterior dislocation is the most common type

Etiology/risk factors

  • Shoulder is exceptionally vulnerable to dislocation as it is an unstable joint
  • Shallow glenoid cavity, weak glenohumeral ligaments increase susceptibility
  • Most dislocations occur following trauma – sporting or motor vehicle injuries
  • Increased risk of dislocation in patients who have had previous shoulder injury
 Types

Anterior dislocation (most common)

  • Humerus is displaced anteriorly relative to the glenoid cavity
  • Results from a fall on externally rotated, abducted and extended arm
  • Can be further classified into subtypes depending on the position of the dislocated head
    • Preglenoid – humerus head lies in front of the glenoid
    • Subcoracoid – head lies below the coracoids process (most common type)
    • Subclavicular – head lies below the clavicle
    • Intrathoracic – rare

Posterior dislocation

  • Humerus head is displaced posteriorly relative to the glenoid cavity
  • Results from a large force directed posteriorly against internally rotated, adducted and flexed arm
  • Often occurs secondary to generalised seizures

Inferior dislocation – Luxatio Erecta (rare)

  • As a result of high energy mechanism with hyper-abduction, tearing the inferior capsule and labrum
  • Arm is permanently held upwards or behind the head

Pathologic changes

Anterior dislocation

  •    Bankart’s lesion – dislocation causes stripping of the antero-inferior glenoid labrum, a pocket forms at the front of the glenoid that allows the humeral head to dislocate into it
  •  If this is accompanied by avulsion of a piece of bone from the antero-inferior glenoid rim, then it is called a bony Bankart lesion
  • Hill-Sachs lesion – impaction fracture of the posterior aspect of humeral head left by the glenoid rim during dislocation
  • Greater tuberosity fracture
  • Damage to axillary artery and axillary nerve

Posterior dislocation

  • Reverse Bankart lesion – dislocation causes stripping of the postero-inferior labrum
  • Reverse Hill-Sachs lesion – impaction fracture of the anteromedial aspect of the humeral head following posterior dislocation
  • Lesser tuberosity fracture
  • Avulsion of the inferior glenohumeral ligament (IGHL)

Inferior dislocation

  • Neurovascular injury – greatest incidence out of all three types of shoulder dislocation s
    • Brachial plexopathy
    • Axillary artery injuries
  • Greater tuberosity fracture
  • Rotator cuff tears
  • Anterior capsule and labral tears

Clinical features

  • Severe pain with any range of motion – arm ‘locked’ in place
  • Prominent acromion
Anterior dislocation
  • Arm held externally rotated and slightly abducted
  • Affected shoulder looks flattened
  • Forearm is internally rotated, supported by the other hand
Posterior dislocation  
  • Arm held in internal rotation and adduction – external rotation is painful
  • Forearm rests on abdomen
  • Prominent coracoids process

Inferior dislocation

  • Arm held abducted over the head
  • Neurologic injury

Diagnosis

  • History of trauma
  • Physical exam
    • Dugas test – patient seated and instructed to place hand on opposite shoulder and touch elbow to chest. Pain and inability to perform indicates dislocation
    • Apprehension test – ask patient to externally rotate and abduct the shoulder whilst flexing the elbow. Examiner places one hand on the patient’s wrist and the other hand near the head of the humerus and tries to push the humerus forward. Discomfort elicits positive apprehension test, may indicate anterior dislocation
    • Calloways sign – measure girth of affected shoulder and compare to unaffected. Increased girth indicates dislocation
    • Bryant’s sign – look for lowering of axillary fold. Lower fold indicates dislocation on that side
  • X-ray – anterior and inferior dislocations are easy to visualise, but posterior dislocations can be missed
  • CT – when posterior dislocation is suspected
  • MRI – to check for soft tissue pathologies

Treatment

  • Reduction and immobilisation
    • Techniques – Cunninghams, Stimpson, Hippocratic
  • Operative
    • Open or arthroscopic Bankart repair – glenoid labrum and capsule are re-attached to the front of the glenoid rim
    • Latarjet-Bristow operation – the coracoid process and its attached muscles are transferred to the front of the glenoid. Provides anterior support to the head of the humerus

Complications

  • Rotator cuff injury
  • Brachial plexus injury
  • Shoulder instability
  • Adhesive capsulitis – especially in older patients with diabetes mellitus
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