Development and validation of a C5/C6 motion segment model

Abstract

There is a large body of work investigating whiplash-associated injury in motor vehicles and its causation. Being unable to detect the actual injury and having to use the symptoms of the sufferer as a surrogate has made progress in understanding the injury causation slow. Still lacking are the causal relationships between the biomechanical load on the vehicle occupant in the crash, the resulting loading on the neck and the actual injuries suffered. The optimisation of the design of vehicle safety systems to minimise whiplash needs a better understanding of human tolerance to these injuries. This thesis describes the development of a mathematical multi-body C5/C6 motion segment model to investigate the causation of soft-tissue neck injury. This model was validated with available static in-vitro experimental data on excised motion-segments and then integrated into the existing, validated multi-body human head and neck model developed by van der Horst, to allow the application of realistic dynamic loads. The responses and injury sensing capability of the C5/C6 model were compared with available data for volunteers and cadavers in rear impacts. The head and neck model was applied to the investigation of a group of real rear impact crashes (n = 78) of vehicles equipped with a crash-pulse recorder and with known postcrash injury outcomes. The motion of the occupants in these crashes had previously been reconstructed with a MADYMO BioRID II dummy-in-seat model validated by sled testing. The occupant T1 accelerations from these reconstructions were used to drive the head and neck model. The soft-tissue loading at C5/C6 of the head and neck model was analysed during the early stage of the impact, prior to contact with the head restraint. The loading and the pain outcome from the vehicle occupants in the actual crash were compared statistically. For the longer-term whiplash-associated pain outcomes (of greater than 1 month duration) for these occupants, the C5/C6 model indicated good correlation with the magnitude of the shear loading on the facet capsule. In lower severity impacts, the model result supported a second hypothesis of injury to this motion segment: facet surface impingement.