Biomechanical analysis of whiplash injuries; women are not scaled down men

Mordaka J Gentle C R Nottingham Trent University Whiplash is the most common soft tissue injury sustained in car accidents. The term is commonly associated with hyperextension of the neck as the head rotates backwards in rear end collisions but the exact injury mechanism is not fully understood because the neck is an anatomically and mechanically complex structure. Experimental studies of the mechanism of injury are limited by several ethical and practical factors, so biomechanical computational simulation, based upon experimental research and mathematical modelling, appears to be the most appropriate method of investigation. During the last decade, significant progress has been made in improving car occupant safety through the use of safety devices, such as airbags and advanced seat belts, as well as the construction of the car body itself. Much still needs to be done, especially for female occupants, because statistically they incur twice the risk of whiplash injury as male car occupants. No simple explanation has so far been found for this difference. It is thought that the anatomic dissimilarity of the sexes is the principal reason, but there are undoubtedly a number of secondary, sociological reasons: women tend to drive smaller cars than men and are more likely to be passengers. The lack of a full explanation arises from the fact that, although there have been several FE-models of the male cervical spine reported, female models are rarely documented. This paper addresses the problem by developing a biomechanical FEM model of the 50th and the 5th percentile female cervical spines, based on the earlier published male model created at the Nottingham Trent University, which relies on grafting a detailed biomechanical model of the neck and head onto a standard HYBRID III dummy model. All numerical analyses have been undertaken using LS-DYNA. Special attention was paid to the behaviour of the scaled down male model in comparison with the model, which included female characteristic features. FEM models of males and females in a representative seat were therefore subjected to 9.5 km/h rear-end simulated collisions and were compared against reported experimental tests. The detailed behaviour varied significantly with gender. The female models revealed greater and earlier peak horizontal acceleration of the head and smaller peak relative extension than the male models. It was concluded that the presented FE models were reasonably in accordance with available crash data on instrumented volunteers in terms of head motion.