Patient is a 45 year old male who presented to the emergency department with left shoulder pain. Patient fell forward over the handlebars of his bike the day 2 days prior to presentation. Patient’s left shoulder pain was worse with movement. He denied any other symptoms, including extremity numbness or paresthesias. 

This is a case of posterior glenohumeral dislocation, confirmed by radiographs. The most common cause of posterior glenohumeral dislocation is trauma, as in this case, however seizure and electrocution are other common causes¹. Patients will classically present with the affected limb held flexed, adducted, and internally rotated. This patient was treated with closed reduction in the emergency department without complications.

Radiographs are generally sufficient to diagnose posterior glenohumeral dislocation. Frontal view may show widening of the glenohumeral joint, and/or the “Lightbulb Sign” due to internal rotation of the humerus. Scapular Y view may show posterior displacement of the humeral head.

One potential radiograph finding after a posterior glenohumeral dislocation is the trough line sign, due to a fracture of the anterior humeral head, as seen in this case.

Case courtesy of Dr. Emad Allam - Assistant Professor of Radiology, Loyola University Medical Center