Hangman's fracture: A broken neck involving a fracture of an upper cervical vertebra similar to the injury suffered in death by hanging. The fracture always affects the vertebra called the axis -- the second cervical vertebra (C2) -- with or without subluxation (slippage) of C2 on C3. A hangman's fracture often causes death by suffocation, as nearly occurred to the actor/director Christopher Reeves when he was injured in an equestrian accident.