Head, neck, and mandible dynamics generated by 'whiplash'

That injuries to the temporomandibular joint (TMJ) can be imposed by short-acting forces generated during rear-end collisions of motor vehicles was first proposed more than 50 years ago. Since that time, numerous anecdotal and clinical reports relating the onset of TMJ symptoms to low-velocity rear-end collisions have appeared in the literature. Various mechanisms of injury to the TMJ occurring during extension and flexion phases of 'whiplash' have been proposed. However, transient forces developed at the TMJ in impact velocity changes on the order of 8.0 kilometers per hour (km/h) have been shown to be well within typical physiologic ranges. This study applies current head/neck extension-flexion dynamic data to develop linear and angular force-time histories experienced at the TMJ. Fourteen test collisions of motor vehicles utilizing seven live test subjects were conducted in July 1993. Linear and angular accelerometers and high-speed photographic cameras recorded the vehicle and human-subject responses. Head accelerations and forces generated at the TMJ bore a generally linear relationship to the impact velocity changes in the range tested (3.9-10.9 km/h). Mandibular opening responses were measured on three test subjects. Neither neck hyperflexion nor hyperextension occurred for any subject on any trial. At some point in the series, all test subjects experienced neck muscle strain symptoms lasting 1-3 days. No TMJ symptoms were experienced. The head, neck, and mandible motions occurring in the 'whiplash' maneuver are more complex than previously described. The cervical muscle injury threshold appears to be reached in the 8.0 km/h range. Linear and rotational forces generated at the TMJ in rear-end impacts below the 11.0 km/h velocity-change level do not appear to be injurious.