• 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

• 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).

• 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

• Subcoracoid (most common)
• Subclavicular
• Subglenoid

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

• 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).

To see other related content select from an item below:

• Radiology:  Anterior Shoulder Dislocation 
  

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: 

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

Last Updated:  June 2015