Joint Reduction, Shoulder Dislocation, Posterior 

Posterior shoulder dislocations are uncommon injuries, accounting for only 4% of all shoulder dislocations. Perhaps for this reason, many posterior shoulder dislocations are missed initially by the treating physicians, and nearly all cases have delayed diagnosis.^[1] Failure to diagnose and treat posterior dislocations promptly can result in complications, including recurrent dislocations, avascular necrosis of the humeral head, degenerative disease, and chronic pain.^[1]

Posterior shoulder dislocations usually result from the forceful contractions of the internal rotators that occur during seizures and electrical shock. This mechanism can force the humeral head posteriorly, out of normal alignment and behind the glenoid. Less commonly, posterior shoulder dislocations follow trauma. The mechanism may be a direct blow to the anterior shoulder or a posteriorly directed force applied through the forward-flexed arm.

To avoid a missed diagnosis, perform a thorough examination and obtain radiographs that definitively show the orientation of the glenoid with respect to the humeral head. On an anteroposterior (AP) view of the shoulder, a posterior dislocation is very subtle. Several findings in the AP views have been described, including the “trough sign,” which is caused by a reverse Hill-Sachs deformity, or loss of overlap of the humeral head and glenoid fossa (see the images below). However, these subtle findings frequently are missed.

Radiographic projections such as an axillary view or a transscapular Y view are much more reliable and should be ordered routinely when a posterior dislocation is suspected. On both of these views, the humeral head can be seen posterior to the glenoid fossa.^[1]

A patient with a posterior dislocation presents with the affected arm held in adduction and internal rotation. Efforts by the examiner to abduct or externally rotate the extremity result in pain and very little movement. Additionally, a prominent acromion and coracoid should be noted, with the humeral head palpable posteriorly. These findings may be obscured by massive swelling or in large individuals.

A complete neurovascular examination should be performed as well, although the incidence of neurovascular injuries is lower with posterior dislocations than with anterior dislocations.^[1] Posterior shoulder dislocations are commonly associated with posterior glenoid rim fractures and anterior compression fractures of the humeral head.

• An uncomplicated posterior shoulder dislocation that is diagnosed within 6 weeks of injury may be reduced in the emergency department (ED).
• A small humeral head defect is not a contraindication to attempting a closed reduction in the ED.
• A fracture-dislocation with a nondisplaced lesser tuberosity fracture may be treated with a closed reduction.

• Delayed (>6 wk) presentation
• Large humeral head defect
• Displaced or multipart fracture-dislocations (These are treated by open reduction and internal fixation or by arthroplasty.)

• Procedural sedation and analgesia are required.
• For more information, see Procedural Sedation.

• Sheets may be used to reduce operator fatigue during the procedure.

• The patient is placed supine on a stretcher.

• A traction-countertraction method is used to reduce posterior shoulder dislocations.
• Traction is applied to the forearm of the affected extremity while countertraction is applied in reciprocation.
• To facilitate traction and reduce operator fatigue, a sheet may be looped and tied around the waist of the operator applying traction.

  • The affected extremity is then flexed at the elbow and is also placed inside the looped sheet.
  • As the operator leans back, traction is applied via the looped-and-tied sheet, and the operator’s hands are free to guide and stabilize the extremity.^[2]
• Countertraction can be applied by means of a second sheet, looped around the patient’s chest under the axilla of the affected shoulder and secured to a second operator or stationary object.^[2]
• Traction should be applied in a smooth, firm manner, with the shoulder held in adduction and internal rotation.
• An assistant may apply additional gentle pressure to the humeral head in the posterior^{[2, 3]} and lateral^{[2, 4]} directions to disengage it from the posterior glenoid.
• When the head of the humerus disengages, the arm may be externally rotated. However, the operator must exercise extreme caution here, as external rotation can cause a fracture of the humerus if it is not disengaged from the glenoid.^[5]
• A soft, palpable clunk and return of mobility usually indicate successful reduction.
• The patient may be placed in a sling and swath if the joint is stable, or, if unstable, the patient may be splinted in slight abduction and neutral rotation.^{[4, 3]}
• Routine, appropriate postreduction care includes performing and documenting a complete neurovascular examination and obtaining postreduction radiographs.
• Orthopedic referral is indicated for all posterior shoulder dislocations.

• Making the diagnosis is the critical element.

  • Radiography beyond anteroposterior (AP) views is important when clinical suspicion of an occult posterior dislocation is high.
  • Complete radiographs (Y view or axillary view) are essential for diagnosis, since posterior dislocations may be missed on AP views alone.
• Nonacute posterior dislocations and complicated fracture-dislocations most likely require open reduction and fixation.
• Procedural sedation is the standard of care and ensures pain control and muscle relaxation. Local anesthesia instillation into the joint is quite challenging in this injury but may be used by appropriately experienced providers.
• Smooth, firm traction results in successful reduction; patience is rewarded in this procedure. Yanking, placing the operator’s foot in the patient’s axilla, or other impatient maneuvers only increase the likelihood of complications.
• Appropriate aftercare includes a complete neurovascular examination and postreduction radiographs.
• Given the rare nature of this injury, consultation by an orthopedic surgeon in the emergency department is prudent.

• The most common complication of attempted closed reduction is a humeral fracture.
• Acute redislocation is also a potential complication.
• Complications of the dislocation itself include the following:

  • Osteonecrosis
  • Posttraumatic osteoarthritis
  • Joint stiffness and functional incapacity