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Acute posterior glenohumeral dislocation — MSRA MCQ

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HardShoulder InjuriesAcute posterior glenohumeral dislocationMSRA

A 36-year-old man presents to general practice 4 days after a witnessed tonic–clonic seizure. Since then, he has had severe right shoulder pain and cannot use the arm to dress. At the emergency department on the day of the seizure, a single anteroposterior shoulder radiograph was reported as showing no fracture or dislocation, and he was discharged with analgesia. He holds the arm adducted and internally rotated. There is posterior fullness of the shoulder and he cannot actively or passively externally rotate beyond neutral because of pain and a firm block. Abduction is also markedly restricted. Distal pulses, hand neurology and sensation over the lateral upper arm are normal. There is no fever, neck pain or recurrent seizure activity. What is the most appropriate management now?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: B — Refer to the emergency department now for orthogonal shoulder imaging and urgent reduction assessment, maintaining sling support and avoiding manipulation in general practice

Explanation lettering: B = shown as A · E = shown as B · D = shown as C · C = shown as D · A = shown as E

This presentation is highly suggestive of a missed posterior glenohumeral dislocation. A convulsion is a characteristic mechanism because powerful internal rotator contraction can dislocate the humeral head posteriorly. The fixed adducted, internally rotated posture, posterior shoulder fullness and, particularly, marked loss of passive external rotation indicate a mechanical joint abnormality rather than pain-limited rotator-cuff dysfunction. A single anteroposterior radiograph can appear normal in posterior dislocation. Axillary, modified axial/Velpeau or scapular-Y imaging is needed to establish glenohumeral congruity; urgent assessment is necessary because delayed recognition increases the risk of a locked dislocation and more complex treatment. Reduction should occur in an acute setting with appropriate analgesia, imaging and orthopaedic support, not in general practice. A is inappropriate because physiotherapy before excluding dislocation risks delay. B is plausible after seizure-associated shoulder weakness, but cuff pathology does not explain a fixed passive external-rotation block or posterior fullness. C delays assessment of a time-critical missed dislocation. D may later be useful for associated bony or soft-tissue injury, but MRI is not the first investigation or disposition when dislocation remains unexcluded.

Reference: Missed posterior shoulder fracture dislocations: a new protocol from a London major trauma centre (2020) — https://pubmed.ncbi.nlm.nih.gov/32193195/ Dislocated shoulder (2023) — https://www.nhs.uk/conditions/dislocated-shoulder/?src=conditionswidget