Infantile atlantooccipital instability. The potential danger of extreme extension.

During early infancy, adventitious sliding and slipping movements between the vertebral column and skull are possible in the cadaver. In ten of 17 infants, the posterior arch of the atlas inverted through the foramen magnum during extension of the head on the atlas, resulting in the anatomic potential of bilateral vertebral artery compression. These anatomic conditions may be the basis for a chain of events that contributes to death in some neonates and infants with conventioanl diseases and may be one source of unanticipated death.