Light bulb sign (posterior shoulder dislocation)

Last revised by Dr Daniel J Bell on 15 May 2021

The light bulb sign refers to the abnormal AP radiograph appearance of the humeral head in posterior shoulder dislocation.

When the humerus dislocates it also internally rotates such that the head contour projects like a light bulb when viewed from the front 1.

See also

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Cases and figures

  • Figure 1: a traditional light bulb
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  •  Case 1
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  • Case 2: lightbulb sign - posterior shoulder dislocation
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  • Case 3
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  • Case 4
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