UMEM Educational Pearls


30 year-old male presents with right wrist pain after falling off his bicycle. What's the diagnosis?


Scapholunate dislocation


Scapholunate Dislocation (a.k.a. “Terry Thomas” or “David Letterman” sign)

  • Increased distance between the scaphoid and lunate bones on AP wrist X-ray; the distance between the two bones should normally be less than 2mm.
  • A widened scapholunate distance suggests ligamentous injury or tear (green arrow below).
  • The widened distance resembles the famous dental diastema (i.e., tooth gap) of Terry Thomas (British comedian) and David Letterman



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