A Hangman's fracture causes a break in the pedicle(s) of the axis. The pedicles is a connecting portion of the vertebrae between the main body and the tansverse process. The transverse process is a projection from the side of the vertebra. This piece of bone has a place for the rib to attach. They also provide a place for ligaments and muscles to attach.
The injury that causes this type of fracture is usually forcible hyperextension of the head. The term originated from death by hanging. The noose placed below the condemned person's chin forced the head back. When the subject was dropped, hyperextension with the full weight of the body caused enough force to fracture the axis.
In today's world, this injury is still seen sometimes. But the cause is more likely from sports injuries or car accidents. In hangings from suicide, asphyxia (lack of air) is the usual cause of death. Accidental injuries of this type may require surgery to stabilize the spine.