ATYPICAL HANGMANS FRACTURES

Nineteen cases of traumatic spondylolisthesis of the axis, including 1 3 standard hangman's fractures and 6 anterolistheses of the C2 vertebr al body associated with Effendi's atypical hangman's fractures, were s tudied. Unlike the standard Effendi Type I or Type II fractures, atypi cal hangman's fractures, occurring through the posterior aspect of the vertebral body with unilateral or bilateral continuity of the posteri or cortex or pedicle, routinely narrow the spinal canal because of the fracture pattern and degree of subluxation. These atypical C2 injurie s were more frequent and more often accompanied by paralysis (33%) tha n was previously anticipated. Because of their greater potential for n eurologic compromise, it is essential that these fractures be recogniz ed as distinct from standard Types I and II C2 fractures. Larger serie s should clarify both the true incidence of paralysis and long-term re sults from these unique C2 injuries.