A hangman’s fracture is a fracture which involves both pars interarticularis of C2, and is as a result of hyperextension and distraction. This is known as a judical lesion as these are the forces delivered by a noose, which contrary to most ill-informed depictions, was placed with the knot towards the side of the neck, next to the angle of the mandible / mastoid process.

Treatment can be bracing or more typically internal fixation.

References:
WheelessOnline
Wikipedia – hanging

Credit: Dr Frank Gaillard
http://www.radpod.org