Finite element analysis of whiplash injury for women
Whiplash injuries are among the most common injuries reported for low velocity car accidents, particularly for rear-end impacts. Although they are mainly minor injuries they result in a great deal of suffering and cost. Surprisingly, female car occupants have a 1.5-2 times higher risk of soft tissue neck injury than men. Moreover, females are more prone to long-term injury. There is no direct explanation for this gender
difference; the whiplash injury mechanism itself has not been fully established and so few theories have pursued what is undoubtedly seen as a side issue. The problem is exacerbated by the fact that most research is influenced by international safety standards, leading to the average female car occupant being poorly represented by an average 50th percentile male model or a 5th percentile female model during experiments, let alone during the car safety design process. Summing up, it is apparent that it is timely and necessary to investigate the mystery of female whiplash injury. The existing Nottingham Trent FE model of a male head-neck complex grafted onto a standard Hybrid III dummy model was gradually refined and adapted to represent the average woman. The first part of the study showed that females cannot be represented by a simple, scaled down male model and proved that there was a need for a more sophisticated female model. Subsequent models developed with explicit female anatomical and physiological characteristics showed significant gender differences in
their head-neck kinematics during rear-end impact simulation. The results were in agreement with experimental data. The influence of head-head restraint horizontaldistance was also investigated. On the basis of this interim success, the male and female models were further developed and extended to include active muscle response. It was found that the active muscle response principally influenced the head-neck motion by reducing the peak head rotation and the axial forces on ligaments. Furthermore, by simulating different onset times and force levels for the muscle response, the head-neck kinematics and the loads on the neck soft tissue were shown to be related to an occupant's awareness of an oncoming impact. However, of most direct interest to the subject of this thesis, the results indicated higher intervertebral rotation, greater head retraction and increased ligament forces on females than males, particularly for the female model in the "surprised" condition, where the impact is totally unexpected. Female models also had
greater peak intervertebral displacements in the horizontal and vertical directions, together with simultaneous higher rotation. This could suggest impingement of the synovial folds, which would lead to neck pain. Female flexor muscles also underwent greater length contraction in comparison to male muscles. The results of tjos research give a possible explanation for the higher risk of whiplash injuries among female car occupants. However, the many limitations pointed out in the thesis show that further complementary experimental and computational research is required before definite recommendations can be made for changes to the design of car
seats and head restraints in order to reduce the risk of soft tissue injury to women. Nevertheless, the findings of this study show that female gender is a crucial but neglected problem in the car safety industry and suggest a revision of test programmes and regulations, whcih are currently based on the average male, in order to improve overall female car occupant safety.