HEAD, NECK, AND MANDIBLE DYNAMICS GENERATED BY WHIPLASH

That injuries to the temporomandibular joint (TMJ) can be imposed by s hort-acting forces generated during rear-end collisions of motor vehic les was first proposed more than 50 years ago. Since that time, numero us anecdotal and clinical reports relating the onset of TMJ symptoms t o low-velocity rear-end collisions have appeared in the literature. Va rious mechanisms of injury to the TMJ occurring during extension and f lexion phases of 'whiplash' have been proposed. However, transient for ces 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-fl exion dynamic data to develop linear and angular force-time histories experienced at the TMJ. Fourteen test collisions of motor vehicles uti lizing seven live test subjects were conducted in July 1993. Linear an d 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 impa ct velocity changes in the range tested (3.9-10.9 km/h). Mandibular op ening responses were measured on three test subjects. Neither neck hyp erflexion nor hyperextension occurred for any subject on any trial. At some point in the series, all test subjects experienced neck muscle s train 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 injur y threshold appears to be reached in the 8.0 km/h range. Linear and ro tational forces generated at the TMJ in rear-end impacts below the 11. 0 km/h velocity-change level do not appear to be injurious. (C) 1998 P ublished by Elsevier Science Ltd. All rights reserved.