Presentation
Shoulder pain following a seizure.
Patient Data
Both frontal views, including what is supposed to be an external rotation view, are in internal rotation. Impaction fracture medial humeral head (reverse Hill-Sachs fracture). The scapular Y view shows posterior dislocation of the glenohumeral joint with posterior displacement of the humeral head with respect to the glenoid.
Case Discussion
When the humeral head dislocates posteriorly, it is often "stuck" in internal rotation. Because the shoulder is locked in internal rotation, the internal and external rotation views will both be in internal rotation. The smooth appearance of the internally rotated humeral head has been likened to a light bulb, so a posteriorly dislocated humeral head locked in internal rotation has been called the lightbulb sign.
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