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….
- 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.
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….
- 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.
- 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.
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)
- 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.
Firstly, here are the 3D reconstructions from his CT.
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.
- Rosenʼs Emergency Medicine. Concepts and Clinical Approach. 7th Edition
- Tintinalli’s Emergency Medicine: A Comprehensive Study Guide. 7th Edition.
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