Lightbulb 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

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

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 lightbulb shape of the rotated humeral head. 

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