Temporomandibular joint injuries during whiplash

Abstract

Whiplash injuries occur due to differential accelerations in the human body. Neck injuries are predominant, but a considerable body of clinical evidence suggesting a close relationship between whiplash and temporomandibular joint (TMJ) disorders has also accumulated. These soft-tissue injuries are generally treated conservatively and may take several years to resolve. The symptoms are well established but their cause is unclear as the validity of retrospective clinical studies is compromised by their subjective nature. Two main injury hypotheses have been proposed, but these lack experimental evidence. This thesis presents the development and sled-testing of a physical model of the head, neck and mandible designed to simulate in vivo behaviour in a low velocity rear-end collision. Extensive instrumentation and a new angular displacement transducer for the head have given detailed kinematic information regarding mouth-opening and accelerations at the TMJ. Soft-tissue tensile tests using in vitro specimens have given an indication of the structural properties of the TMJ. The results indicate clearly that the mandible and TMJ are not harmed during a low-velocity rear-end collision. Excessive levels of mouth-opening do not occur during whiplash resulting from (triangle)v's of up to 9.2km/h. Active bracing of the jaw muscles prevents mouth-opening. A 2-D kinematic model of the head/jaw complex has been developed. The input to this model is given by the measured rotational kinem atics of the model head. Sim ulations have shown a good correlation w ith experim ental data and a parametric analysis showed remarkable stability of the model. The latter indicates that normal geometric variations are unlikely to influence loading at the TMJ significantly. The model was used to estimate the magnitude of loading at the TMJ during retroflexion. Comparison with a simple free body diagram of the mandible shows that reactive forces across the TMJ in functional chewing are much higher. These results are in direct conflict with the predominant Inertial Injury Theory. In contrast, the results of this thesis are in agreement with the post-accident neuro-muscular changes proposed by the Late TMJ Injury Theory.