Presentation
Painful shoulder post motorbike accident, unable to abduct right arm
Patient Data
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 suboptimal but does confirm the dislocation. No fracture seen.
Case Discussion
Posterior glenohumeral 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.
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