Posterior shoulder dislocation
Painful shoulder post motorbike accident, unable to abduct right arm.
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On the AP projection the humeral head has the classic light bulb appearance of posterior shoulder dislocation. This appearance occurs because of internal rotation of the humeral head accompanying the dislocation. The lateral view in this case is sub-optimal but does confirm the dislocation. No fracture seen.
Posterior dislocations are rare and occur in 2 to 4% of shoulder dislocations; the humeral head is displaced posteriorly due to axial loading of the adducted, internally rotated arm. Often this injury will happen during violent muscular contractions, electric shock, or convulsive seizures. 86% of posterior dislocations will have impacted fractures of the anteromedial portion of the humeral head, otherwise known as a reverse Hill-Sachs lesion 1-3.
Unlike anterior dislocation which are usually easily identified on an AP projection, posterior shoulder dislocations can be difficult to identify without further views.
- 1. Pope TL. Harris & Harris' Radiology of Emergency Medicine. Lippincott Williams & Wilkins. (2012) ISBN:145110720X. Read it at Google Books - Find it at Amazon
- 2. Hawkins RJ, Neer CS, Pianta RM et-al. Locked posterior dislocation of the shoulder. J Bone Joint Surg Am. 1987;69 (1): 9-18. Pubmed citation
- 3. Clough TM, Bale RS. Bilateral posterior shoulder dislocation: the importance of the axillary radiographic view. Eur J Emerg Med. 2001;8 (2): 161-3. Pubmed citation