"type I: Avulsion fracture of the upper dens; usually stable"
"type II: Transverse fracture of the base of dens; unstable"
"type III: Fracture at the body of C2"
"AO Spine classification of upper cervical injuries: not specific to the dens, but rather bony and ligamentous injuries involving the occipital condyles, atlas (C1), or axis (C2)"
"Mach effect"
"type I: Avulsion fracture of the upper dens; usually stable"
"type II: Transverse fracture of the base of dens; unstable"