Graduate Research Assistant University of Virginia Center for Applied Biomechanics Charlottesville, Virginia
Abstract Text: In the United States, head injuries are a significant burden on public health. Of particular concern are head injuries that are the result of motor vehicle crashes (MVC). Approximately 1 out of 8 people who go to the emergency room for traumatic brain injury (TBI) do so following an MVC [1]. The automotive industry has a long history of innovating injury prevention due largely to consumer rating programs and federal regulations that evaluate, rank, and/or categorize the safety of a vehicle during a crash based on fundamental injury biomechanics data. New methods for measuring the risk and severity of an injury during a crash must undergo careful scrutiny before being incorporated into assessments. Numerous international automotive groups are currently monitoring new methods for assessing TBI in MVC, and how they may be applied to different types of vehicle occupants. During crash testing, engineers collect head kinematics data using physical anatomical test devices (ATDs) and computational finite element (FE) human body models to calculate the various injury metrics associated with different TBI mechanisms. For example, the Head Injury Criteria (HIC) quantifies the risk and severity of skull fracture as a function of linear acceleration of the head [2]. Diffuse brain injuries (i.e., concussion) are based on mechanisms related to brain deformation and axonal strain, which have demonstrated correlations with rotational head kinematics [2,3]. Brain Injury Criteria (BrIC), Universal Brain Injury Criteria (UBrIC), and Diffuse Axonal Multi-Axis General Evaluation (DAMAGE) all incorporate rotational head kinematics into account and may be a better predictor of mild and moderate TBI than HIC [4-6]. Furthermore, recent research suggests that instead of a one-size-fits-all approach to assessing injury risk, different metrics are needed when using ATDs representing a mid-sized male to a small-sized female occupant [7]. In this study, we analyzed two sets of experimental MVCs to evaluate (1) different metrics’ efficacies in predicting TBI using a small-sized female ATD, and (2) the difference in mid-sized male and small-sized female head kinematics and injury prediction for matched crash conditions. Our first analysis consisted of 27 moderate frontal crashes all performed on 5th-percentile female (F05) Hybrid-III ATDs. We used the Global Human Body Models Consortium (GHBMC) F05 brain FE model to calculate the 95th-percentile of the maximum principal strain time history (MPS-95) of brain tissue elements to serve as our reference value for assessing the accuracy of metrics based on ATD head kinematics. For the metrics, we computed HIC, and the 50th-percentile male (M50) and F05 female formulations of BrIC, UBrIC, and DAMAGE using the experimental ATD kinematics [8]. Results showed that the M50 variants of BrIC, UBrIC, and DAMAGE all overpredicted brain deformation and exhibited poorer accuracy to MPS-95 than their F05 counterparts (p < 0.05). MPS-95 case ranks exhibited greater agreement with DAMAGE-F05 (Kendall’s τ = 0.886) than HIC (Kendall’s τ = 0.744). Our second analysis consisted of 16 M50 and F05 ATD crashes with matching conditions of ATD model, occupant position, and deformable barrier overlap. Here we used head kinematics to compute HIC and sex-appropriate DAMAGE, ranking each condition according to both metrics. We observed that HIC had a reasonable agreement when comparing the vehicle rank across sexes (Kendall’s τ = 0.567), but DAMAGE exhibited a poor agreement (Kendall’s τ = 0.283). Further, this difference was most pronounced in the most severe cases. This finding suggests that using only HIC to assess TBI risk would potentially miss identifying vehicles that are severely injurious for small female occupants, but these can be detected using DAMAGE as the metric. Overall, our study suggests the need to consider both linear and angular TBI metrics when evaluating the safety of vehicles, and to use the specific metrics designed to work with the ATD surrogate used in the crash evaluation. This work is part of many studies being performed worldwide related to scrutinizing TBI metrics for use in automobile safety assessment.
