Traumatic brain injury in pedestrian–vehicle collisions: Convexity and suitability of some functionals used as injury metrics

Background and Objective: Abrupt accelerations or decelerations can cause large strain in brain tissues and, consequently, different forms of Traumatic Brain Injury (TBI). In order to predict the effect of the accelerations upon the soft tissues of the brain, many different injury metrics have been proposed (typically, an injury metric is a real valued functional of the accelerations). The objective of this article is to make a formal and empirical comparison, in order to identify general criteria for reasonable injury metrics, and propose a general guideline to avoid ill-proposed injury metrics. Methods: A medium-size sample of vehicle-pedestrian collisions, from Post Mortem Human Subject (PMHS) tests, is analyzed. A statistical study has been conducted in order to determine the discriminant power of the usual metrics. We use Principal Component Analysis to reduce dimensionality and to check consistency among the different metrics. In addition, this article compares the mathematical properties of some of these functionals, trying to identify the desirable properties that any of those functionals needs to fulfill in order to be useful for optimization. Results: We have found a pair-wise consistency of all the currently used metrics (any two injury metrics are always positively related). In addition, we observed that two independent principal factors explain about 72.5% of the observed variance among all collision tests. This is remarkable because it indicates that despite high number of different injury metrics, a reduced number of variables can explain the results of all these metrics. With regard to the formal properties, we found that essentially all injury mechanisms can be accounted by means of scalable, differentiable and convex functionals (we propose to call minimization suitable injury metric to any metric having these three formal properties). In addition three useful functionals, usable as injury metrics, are identified on the basis of the empirical comparisons. Conclusions: The commonly used metrics are highly consistent, but also highly redundant. Formal minimal conditions of a reasonable injury metric have been identified. Future proposals of injury metrics can benefit from the results of this study.Peer ReviewedPostprint (author's final draft

Pediatric, adult and elderly bone material properties

Age dependence; Bone; Coupon; Full field strain measurements; Quasi-static and dynamic tensile testsPostprint (published version

The influence of impact speed on chest injury outcome in whole body frontal sled impacts

While the seatbelt restraint has significantly improved occupant safety, the protection efficiency still needs further enhance to reduce the consequence of the crash. Influence of seatbelt restraint loading on chest injury under 40 km/h has been tested and documented. However, a comprehensive profiling of the efficiency of restraint systems with various impact speeds has not yet been sufficiently reported. The purpose of this study is to analyse the effect of the seatbelt load-ings on chest injuries at different impact speeds utilizing a high bio-fidelity human body Finite Element (FE) model. Based on the whole-body frontal sled test configuration, the current simulation is setup using a substitute of Post-Mortem Human Subjects (PMHS). Chest injury outcomes from simulations are analysed in terms of design variables, such as seatbelt position parameters and collision speed in a full factorial experimental design. These outcomes are specifically referred to strain-based injury probabilities and four-point chest deflections caused by the change of the parameters. The results indicate that impact speed does influence chest injury outcome. The ribcage injury risk for more than 3 fractured ribs will increase from around 40 to nearly 100% when the impact speed change from 20 to 40 km/h if the seatbelt positioned at the middle-sternum of this study. Great injuries to the chest are mainly caused by the change of inertia, which indicates that chest injuries are greatly affected by the impact speed. Furthermore, the rib fracture risk and chest deflection are nonlin-early correlated with the change of the seatbelt position parameters. The study approach can serve as a reference for seatbelt virtual design. Meanwhile, it also provides basis for the research of chest injury mechanism

Comparison of kinematics of GHBMC to PMHS on the side impact condition

The goal of this study was to evaluate the biofidelity of the Global Human Body Models Consortium (GHBMC) human body model under a side impact loading condition with an airbag, and analyze the effect of initial position of the model on the response. Shaw et al. conducted side impact sled tests using three Post mortem human surrogates (PMHS) with impact speeds of 4.3 ± 0.1 m/s, and used a rigid wall boundary condition with an airbag mounted to the sled. The correlation between the PMHS and the GHBMC was evaluated using the CORA rating method. The rating ranged from 0.27 to 0.69 along the body regions on a scale in which a rating of 1.0 indicated a perfect correlation between the PMHS and the GHBMC. The pelvis and thorax region showed good correlation with those of the PMHS while the spinal regions did not. In addition, the roll and yaw angle of the initial position of the PMHS had an effect on the response of subjects. The result of this research indicated two points, that the GHBMC model should be validated focusing on the internal biofidelity of the model, and that the yaw and roll angle should be carefully controlled during a side impact test.Postprint (published version

THE KINEMATICS OF HEAD IMPACTS IN CONTACT SPORT: AN INITIAL ASSESSMENT OF THE POTENTIAL OF MODEL BASED IMAGE MATCHING

Model Based Image Matching (MBIM) has potential to assess three-dimensional linear and rotational motion patterns from multiple camera views of head impact events in contact sports. The goal of this study is to assess the accuracy of the MBlM method for estimating 6DOF head kinematics in a vehicle-cadaver impact scenario for which Vicon motion analysis data are available as an independent measure. A three camera view MBlM reconstruction yielded RMS errors between 0.14-0.26 mls for change in head linear velocities ranging from 0.56-5.70 m/s, and 0.27-1.38 rad/s for change in head angular velocities ranging from 6.1041 -90 rad/s. The results from this study indicate that the MBlM method is a useful approach for measuring the kinematics of head impacts in sport

Measuring the acceleration of a rigid body

Two methods to measure the six-degree-of-freedom acceleration of a point on a rigid body are presented. The first, referred to as the periphery scheme, makes use of three clusters of accelerometers mounted orthogonal to each other and coincident with the axes of the point. One of the clusters consists of the three accelerometers attached to a cube-shaped triaxial angular rate sensor (ARS). The second method, called the compact cube scheme, uses a single 3-accelerometer/ARS cluster that may be mounted anywhere on the rigid body. During impact tests with an instrumented rigid body, both methods produced measurements that were highly correlated near the time of peak acceleration. Whereas the compact cube scheme was more economical and easier to implement, the periphery scheme produced results that were less disrupted by instrument signal errors and noisy environments

Influence of bone microstructure on the mechanical properties of skull cortical bone – A combined experimental and computational approach

The strength and compliance of the dense cortical layers of the human skull have been examined since the beginning of the 20th century with the wide range in the observed mechanical properties attributed to natural biological variance. Since this variance may be explained by the difference in structural arrangement of bone tissue, micro-computed tomography (μCT) was used in conjunction with mechanical testing to study the relationship between the microstructure of human skull cortical coupons and their mechanical response. Ninety-seven bone samples were machined from the cortical tables of the calvaria of ten fresh post mortem human surrogates and tested in dynamic tension until failure. A linear response between stress and strain was observed until close to failure, which occurred at 0.6% strain on average. The effective modulus of elasticity for the coupons was 12.01 ± 3.28 GPa. Porosity of the test specimens, determined from μCT, could explain only 51% of the variation of their effective elastic modulus. Finite element (FE) models of the tested specimens built from μCT images indicated that modeling the microstructural arrangement of the bone, in addition to the porosity, led to a marginal improvement of the coefficient of determination to 54%. Modulus for skull cortical bone for an element size of 50 μm was estimated to be 19 GPa at an average. Unlike the load bearing bones of the body, almost half of the variance in the mechanical properties of cortical bone from the skull may be attributed to differences at the sub-osteon ( < 50 μm) level. ANOVA tests indicated that effective failure stress and strain varied significantly between the frontal and parietal bones, while the bone phase modulus was different for the superior and inferior aspects of the calvarium. The micro FE models did not indicate any anisotropy attributable to the pores observable under μCT.This research was sponsored by contract no. N00421-11-C-0004 from the U.S. Naval Air Warfare Center, Aircraft Division, Patuxent River, MD

A review of pelvic fractures in adult pedestrians: Experimental studies involving PMHS used to determine injury criteria for pedestrian dummies and component test procedures

Objectives: Perform a systematic review for the most relevant pelvic injury research involving PMHS. The review begins with an explanation of the pelvic anatomy and a general description of pelvic fracture patterns followed by the particular case of pelvic fractures sustained in pedestrian-vehicle collisions. Field data documenting the vehicle, crash, and human risk factors for pedestrian pelvic injuries are assessed. Method: A summary of full-scale PMHS tests and subsystem lateral pelvic tests is provided with an interpretation of the most significant findings for the most relevant studies. Conclusions: Based on the mechanisms of pedestrian pelvic injury, force, acceleration, and velocity and compression have been assessed as predictive variables by researchers although no consensus criterion exists.Peer ReviewedPostprint (published version

Consensus Head Acceleration Measurement Practices (CHAMP): Origins, methods, transparency and disclosure

The use of head kinematic measurement devices has recently proliferated owing to technology advances that make such measurement more feasible. In parallel, demand to understand the biomechanics of head impacts and injury in sports and the military has increased as the burden of such loading on the brain has received focused attention. As a result, the field has matured to the point of needing methodological guidelines to improve the rigor and consistency of research and reduce the risk of scientific bias. To this end, a diverse group of scientists undertook a comprehensive effort to define current best practices in head kinematic measurement, culminating in a series of manuscripts outlining consensus methodologies and companion summary statements. Summary statements were discussed, revised, and voted upon at the Consensus Head Acceleration Measurement Practices (CHAMP) Conference in March 2022. This manuscript summarizes the motivation and methods of the consensus process and introduces recommended reporting checklists to be used to increase transparency and rigor of future experimental design and publication of work in this field. The checklists provide an accessible means for researchers to apply the best practices summarized in the companion manuscripts when reporting studies utilizing head kinematic measurement in sport and military settings

The Molecular Biogeography of the Indo-Pacific: Testing Hypotheses With Multispecies Genetic Patterns

Aim: To test hypothesized biogeographic partitions of the tropical Indo-Pacific Ocean with phylogeographic data from 56 taxa, and to evaluate the strength and nature of barriers emerging from this test. \u3eLocation: The Indo-Pacific Ocean. Time Period: Pliocene through the Holocene. Major Taxa Studied: Fifty-six marine species. Methods: We tested eight biogeographic hypotheses for partitioning of the Indo-Pacific using a novel modification to analysis of molecular variance. Putative barriers to gene flow emerging from this analysis were evaluated for pairwise ΦST, and these ΦST distributions were compared to distributions from randomized datasets and simple coalescent simulations of vicariance arising from the Last Glacial Maximum. We then weighed the relative contribution of distance versus environmental or geographic barriers to pairwise ΦST with a distance-based redundancy analysis (dbRDA). Results: We observed a diversity of outcomes, although the majority of species fit a few broad biogeographic regions. Repeated coalescent simulation of a simple vicariance model yielded a wide distribution of pairwise ΦST that was very similar to empirical distributions observed across five putative barriers to gene flow. Three of these barriers had median ΦST that were significantly larger than random expectation. Only 21 of 52 species analysed with dbRDA rejected the null model. Among these, 15 had overwater distance as a significant predictor of pairwise ΦST, while 11 were significant for geographic or environmental barriers other than distance. Main Conclusions: Although there is support for three previously described barriers, phylogeographic discordance in the Indo-Pacific Ocean indicates incongruity between processes shaping the distributions of diversity at the species and population levels. Among the many possible causes of this incongruity, genetic drift provides the most compelling explanation: given massive effective population sizes of Indo-Pacific species, even hard vicariance for tens of thousands of years can yield ΦST values that range from 0 to nearly 0.5