A coupled physical – computational methodology for the investigation of short fall related infant head impact

Head injury in childhood is the single most common cause of death or permanent disability from injury. Little understanding exists of the response of a child’s head to injurious loading, thus in clinical practice, head injured infants are difficult to assess. Developing an understanding of injurious events from practical experience and epidemiology alone is a significant challenge, since there are many age dependent and biomechanical variables that are poorly understood at the bedside. Without a comprehensive biomechanical characterisation of the primary injury mechanics, interpretation of the pathophysiological consequences will remain rudimentary. Experimentation on living infants is inconceivable and Postmorterm-Human-Surrogates (PMHSs) rare. A further limitation is technological, since, researchers out of experimental necessity, typically derive impact acceleration data by calculation, dividing peak impact force by head mass, to produce a ‘global’ acceleration approximation. A need exists for a new experimental methodology, to provide specific regional and localised response data and characterisation of a range of biomechanical variables. A coupled physical–computational methodology was developed. An infant 3D-CAD head model was created from high resolution CT and MR images, from which a physical and equivalent computational Finite-Element (FE) model was developed. The physical model was 3D-printed with tissue response matched co-polymers, a gelatin-brain and polyamide/latex-patch-scalp and validated against the PMHS impact response. Impact response, linear and angular velocities and accelerations, strains and strain rates, was optically measured by Digital-Image-Correlation. An infant FE head was subsequently developed and validated against impact response data, both ‘regionally and locally’ from the physical model and ‘globally’ against the PMHS, Abstract iv showing good agreement with both. Fracture risk was investigated by FE simulation of injurious PMHS impacts; and a parametric analysis conducted to investigate the effects of fall height on maximum stress response and fracture risk probability. During impact of different regions of the coupled models, certain areas produced ‘local’ acceleration responses two to three times greater than the related global acceleration. Local translational acceleration was very different at different points on the skull and sensitive to impact location. In contrast, the global translational impact acceleration was not, providing justification for challenging the ‘global’ approach, a form of overall “averaging”, and related injury thresholds. There were different local angular accelerations in different structures, at different times and significant variation at different impact heights and significant structural deformation during impact. Angular acceleration data is extremely valuable for quantifying local and regional deformational accelerations for determining both impact nature and injury risks. Strain was ten times greater in the suture and fontanelle areas than bone. The coupled-methodology proved to be significant in characterising infant head impact injury mechanics and skull fracture risk, which is anticipated to inform clinical and forensic management and injury prevention strategies into the future