• Clinical science

Shoulder dislocation

Abstract

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.

Epidemiology

  • Most common joint dislocation
  • Sex: >
  • Peak incidence: 20–29 years

References:[1][2]

Epidemiological data refers to the US, unless otherwise specified.

Etiology

  • 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)

References:[1][3]

Classification

  • > 95 % anterior (subcoracoid) and/or anterior-inferior (subglenoid)
  • ∼ 4% posterior
  • ∼ 1% inferior

References:[4][5]

Clinical features

  • 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
    • The humeral head can usually be palpated below the coracoid process.
    • Loss of shoulder contour: a prominent acromion and flattening of the deltoid muscle
    • The arm is typically held in external rotation and slight abduction.
  • 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!

References:[3][1]

Diagnostics

  • Physical examination
  • Shoulder x‑ray
    • AP view and lateral view to confirm dislocation and exclude fracture
      • For posterior shoulder dislocation: axillary and/or scapular lateral views
      • An AP view may show the lightbulb sign, which is diagnostic of posterior shoulder dislocation.
    • Hill-Sachs lesion
      • 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
      • Can be seen on an AP view x-ray of the shoulder joint
      • Leads to an increased risk of recurrent shoulder dislocation and cartilage or joint capsule injury[1]
  • MRI
    • Indicated to assess soft tissue damage or if a Hill-Sachs lesion is present
    • Bankart lesion: injury of the anterior inferior lip of the glenoid labrum due to traumatic anterior shoulder dislocation
      • Soft Bankart: only the labrum is involved
      • Bony Bankart: when there is associated avulsion fracture of the anterior inferior glenoid
      • Can be seen on MRI
      • Leads to an increased risk of recurrent shoulder dislocation

References:[3][1]

Treatment

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.

  • Emergent management:
    • Immobilization of the joint with a splint/sling
    • Analgesia
  • Conservative management:
    • Closed reduction
    • Indications:
      • 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
    • Types of repair:
      • Open
      • Arthroscopic
    • Indications:
      • Unsuccessful closed reduction
      • Concomitant dislocated fracture of humerus, clavicle, or scapula
      • Displaced Bankart lesion
      • Recurrent shoulder dislocations
      • Young and active individuals may require early surgery to prevent recurrent dislocations in the future.

Continuous neurovascular monitoring/evaluation before and after reduction is important for prevention and early detection of axillary nerve and artery damage!

References:[3][1]

Complications

References:[3][1][4]

We list the most important complications. The selection is not exhaustive.

Prognosis

  • High rate of recurrence
  • After rotator cuff repair, the rate of recurrence is significantly lower.

References:[3]