Light bulb sign - posterior shoulder dislocation

Case contributed by Mohammad Taghi Niknejad
Diagnosis almost certain

Presentation

Work up for trauma.

Patient Data

Age: 25 years
Gender: Male
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Info

The humeral head is forced into the internal rotation as it dislocates posteriorly, giving the appearance of a light bulb sign.

There is also a small cortical fracture in the lateral aspect of the humeral head.

Case Discussion

Posterior dislocation of the right shoulder on frontal projection can be difficult to identify. Note the poor congruency of the glenohumeral line, not forming a nice lens and the light bulb shape of the rotated humeral head. 

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