Mr. Keys was driving to work when he was hit broadside by a car that ran through the red light. When freed from his car, his breathing had stopped, and he was cyanotic. Although his heart was still beating, his pulse was fast. His head was tilted at an unusual angle, and the emergency crew stated that it appeared as though he had a fracture in the vicinity of the C2 vertebra. Given his symptoms, which of the following is most likely?