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Posterior Shoulder Dislocation

Summary:

  • Posterior shoulder dislocations are rare compared to anterior shoulder dislocations and occur most commonly from an axial load while the arm is internally rotated and in the adducted position.
  • Initial imaging includes plain radiographs: AP view & axillary view.
  • Complications include: Reverse Bankart lesion, Reverse Hill-Sachs lesion, fractures, and recurrent posterior instability.
  • Reductions should be done in consultation with orthopedic surgery since some cannot be reduced by closed techniques, but rather need either arthroscopic stabilization or open surgery.

Posterior Shoulder Reduction

    Normal Shoulder X-ray

    Normal Shoulder X-Ray AP View
    X-Ray of Posterior Dislocation

    Posterior Shoulder Dislocation


    Background Info
    • Less common than anterior dislocations (~ 2% of shoulder dislocations)

    • Patients will commonly present with the arm internally rotated and in the adducted position with resulting pain if attempts to externally rotate or abduct occur

    • Humeral head can be palpated in posterior shoulder just below the acromion process

    • Classically associated with convulsive seizures and electrocution though still uncommon

    Mechanism of Injury
    • An axial load applied to the arm while it is in an adducted and internally rotated arm where the humeral head is forced posteriorly.

    • The reason that a seizure or electrocution could cause a posterior dislocation has to do with the differing strengths of the rotator cuff muscles (where the internal rotator cuff muscles are stronger than the external muscles and thus a sudden contraction of the internal muscle can cause a dislocation).

    Imaging Considerations
    • Axillary or Scapular "Y" view:
      • The humeral head will be behind or posterior to the glenoid
      • May be helpful in seeing a reverse Hill Sachs lesion
    • AP of the Shoulder:
      • If there is > 6 mm of space between the anterior rim of glenoid and humeral head, then highly concerning for a dislocation
      • Since the arm is internally rotated the greater tuberosity should be in front of the humeral head instead of laterally
    • AP Shoulder Perpendicular to the Body (not scapula):
      • You may see a loss of elliptical overlap since the humeral head would normally overlap the posterior aspect of the glenoid and is now gone
    Subtypes of Dislocations
    • Subcoracoid (most common)
    • Subclavicular
    • Subglenoid
    Complications

    Other possible associated injuries include:

    • Reverse Bankart lesion (detachment of the posterior labrum)
    • Reverse Hill-Sachs lesion (a defect in the anterior portion of the humeral head produced by the posterior rim of the glenoid; seen on axillary radiographic view
    • Lesser tuberosity fracture
    • POLPSA lesion (Posterior Labrocapsular Periosteal Sleeve Avulsion)
    • Recurrent posterior instability
    Management Considerations
    • Check neurovascular status.

    • In many cases the shoulder will reduce on its own, but if not then consult with an orthopedic surgeon prior to reducing as prolonged dislocations (i.e., > 3 weeks as seen in some elderly patients) or the presence of an anterior humeral articular injury are contraindications to doing a closed reduction.

    • Closed reduction technique (if not contraindicated): gentle, prolonged axial traction along the humerus while applying gentle anteriorly directed pressure to get the humeral head over the glenoid rim.

    • If closed reduction is not appropriate for the patient, then orthopedic surgery may consider doing an arthroscopic stabilization procedure or open surgical methods which include: postero-inferior capsular shift, McLaughlin procedure, allograft reconstruction.

    • Once stabilized, consider external rotator cuff muscle strengthening (mainly infraspinatus muscle).

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    References
    1. Kroner K, Lind T, Jensen J. The epidemiology of shoulder dislocations. Arch Orthop Trauma Surg 1989;108(5):288-90.
    2. Zhang AL, Montgomery SR, Ngo SS, Hame SL, Wang JC, Gamradt SC. Arthroscopic versus open shoulder stabilization: current practice patterns in the United States. Arthroscopy 2014;30(4):436-43.
    Editors & Reviewers

    Editors: 

    • Anthony J. Busti, MD, PharmD, FNLA, FAHA
    • Dylan Kellogg, MD

    Last Updated:  June 2015