the case.

A 34 year old insulin-dependent diabetic male presents to your ED following a “collapse” stating he thinks he has had a seizure. He has had hypoglycaemic seizures previously. He lost his glucometer 3 or 4 weeks ago and has been guessing his sugars and corresponding insulin doses by ‘how he feels’…

He has severe bilateral shoulder & upper thoracic pain. Any attempt to move, touch or examine either shoulder results in unbearable pain (plus a stream of four-letter expletives).

As part of his evaluation you get the following x-rays….

R Shoulder (OBL) R Shoulder (AP) CXR L Shoulder (AP) L Shoulder (OBL)

[DDET Interpretation:]

  • Bilateral humeral head/neck fractures
  • Right glenoid fracture with drumstick appearance of humeral head.
  • Left lesser tuberosity fragment.
  • Both humeral heads appear posteriorly subluxed on oblique view.


[DDET What would you do?:]

You are concerned about a bilateral posterior shoulder dislocation.

As we were unable to 100% decide whether these joints were in or out, we obtained a CT scan….



[DDET The CT report:]

Right Shoulder:

    • Comminuted fracture of the head, anatomical and surgical necks of humerus involving both greater & lesser tuberosity.
    • Fracture through posterior aspect of the glenoid.
    • Mild posterior subluxation of articular surface of the humeral head relative to glenoid.

Left Shoulder:

    • Comminuted fracture involving the head, anatomical & surgical necks of humerus.
    • Cortical irregularity involving inferior aspect of glenoid ?non-displaced fracture.
    • Humeral head is posteriorly dislocated and wedged on the posterior aspect of glenoid.


[DDET Posterior Shoulder Dislocations.]

Posterior Shoulder Dislocation

A rare event accounting for only ~2% of all glenohumeral dislocations. However, pay attention as this injury is missed in > 50% of initial presentations !!

Mechanics / Anatomy / History.

    • A distinct mechanism of action is required to cause a posterior shoulder dislocation (forceful internal rotation with adduction).
        • Lat dorsi, pec major & teres major overcome the smaller/weaker teres minor and infraspinatus.
    • Convulsive seizures or electrocution have been associated with this injury (a direct blow to the anterior shoulder or falls can also produce posterior dislocation).
    • Subdivided into subacromial, subglenoid & subspinous dislocations.
        • 98% are subacromial.


    • High index of suspicion based on mechanism.
        • Pain is not very reliable
    • Prominence of posterior shoulder w/ anterior flattening “squared off appearance”.
    • Arm held in adduction & internal rotation.
        • Inability to externally rotate.
        • Abduction is severely limited.


Standard AP images can be deceptively normal whereas the lateral/scapular Y-view is diagnostic. Abnormal features include;

    • Loss of ‘half-moon’ elliptical overlap of humeral head and glenoid.
    • “Rim sign”
        • Increased distance between anterior glenoid & articular surface of humeral head.
    • “Lightbulb” or “Drumstick” appearance of humeral head.
        • Occurs due to humeral profiling in internal rotation
    • Reverse Hill-Sachs deformity
        • Impaction fracture of anteromedial humeral head.


    • Urgent Orthopaedic consultation
    • Closed reduction may be attempted
        • Requires generous sedation & may be more appropriate for the OT.
        • Axial traction is applied in the line of the humeral shaft, with gentle pressure applied on the humeral head. External rotation may help.
    • ORIF may be required (+/- arthroplasty)
    • Post-reduction:
        • Shoulder immobilisation (minimum of 4 weeks).
        • Orthopaedic follow-up.

Complications of Posterior Should Dislocation.

    • Associated injuries include fractures to glenoid rim, greater tuberosity, lesser tuberosity & humeral head.
    • Subscapularis may be avulsed from the lesser tuberosity.
    • Neurovascular injury is rare (generally protected due to its anterior location).
    • 30% of patients have recurrent posterior dislocation.
    • Degenerative joint disease.


[DDET The Follow-up…]

Firstly, here are the 3D reconstructions from his CT.

Left Shoulder 3D Left Shoulder 3D1 Right Shoulder 3D

This patients’ injury had actually occurred the night before his presentation (some 14-15 hours earlier). Taking this into consideration, and given his associated humeral fractures it was decided that the relocation attempt should take place in the OT with a general anaesthetic and full muscle relaxation.

Despite multiple attempts/techniques his shoulder could not be relocated.

He returned to theatre 48 hours later for an open-reduction and internal fixation.


[DDET References.]

  1. Rosenʼs Emergency Medicine. Concepts and Clinical Approach. 7th Edition
  2. Tintinalli’s Emergency Medicine: A Comprehensive Study Guide. 7th Edition.



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