Whip-lash injuries is caused due to

This injury occurs due to rear end automobile collision. The body of victim is accelerated by the impact force but the head is left behind. Sudden hyperextension followed by sudden hyperflexion occurs. It is mentioned that in mild forms only subtle hyperextension injuries are found in X Ray. So hyperextension being the primary injury is most impoant answer. Ref: Krishan Vij textbook of forensic medicine, 5th edition pg : 287