A Traumatic Dislocation of the Atlas from the Axis in a Patient with Atlantooccipital Assimilation.

Atlantooccipital assimilation is defined as the complete or partial fusion of the caudal portion of the occiput with the cranial portion of the atlas. We report an extremely rare case of a traumatic dislocation of the atlas from the axis (C1 from C2), which lead to internal decapitation in a patient with atlantooccipital assimilation. This report reviews the background of atlantooccipital assimilations and their clinical relevance.