Spinal Curvature Update of the SAFER Human Body Model: A study on the effect of spinal curvature in frontal and run-off road crash scenarios

Abstract

The human body is a complex system made of various tissues, making it a difficult task to model in a biofidelic manner. It is of importance to be able to accurately do this in order to predict the risk of injury when exposed to large magnitudes of acceleration, e.g. in car crashes. Prior research has found that force and moment within the spine have been significant predictors of vertebral body fracture risk. This thesis implemented a spinal curvature from a prediction model, derived from volunteer data, into the SAFER HBM and evaluated its influence on the spine’s mechanical response. This was done in two ways: 1) implementing the curvature of the prediction model in the sagittal plane, as well as 2) varying the curvature in the coronal plane, to represent normal variations within the population with the assumption that the human body is not completely symmetrical. These two alternative models, together with the original SAFER HBM, were applied in paired simulations of six different crash scenarios to investigate whether the mechanical response of the vertebrae differed. The crash scenarios modelled were two frontal crashes of different severity, two oblique crashes of different impact directions as well as two run-off road scenarios with different vehicle roll motions. When reviewing the updated sagittal spinal curvature, it was seen that the predicted spinal curvature was more straight than the original SAFER HBM, showing reduced lordosis in the upper thoracic spine and reduced kyphosis in the thoracolumbar region. Then, once the updates had been applied into crash simulations, it was noted that the vertebral body trabecular bone inferior-superior strain was affected by the updated curvature, which in its own affects the vertebral body fracture risk. These differences were mainly observed in the run-off road impacts, whereas the variations of frontal impacts did not support the same findings. For these run-off road impacts, it was observed that the compressive forces exerted on the vertebrae were increased with the spinal curvature update. These compressive forces, as well as the flexion of the spine were found to be related to the peak vertebral body trabecular bone inferior-superior strain, in multiple locations in the spine supported by linear regression models. The results of the coronal plane curvature simulations supported the relations between flexion of the spine and compressive strain, as well as between the compressive force and compressive strain.