A study on correlation of pedestrian head injuries with physical parameters using in-depth traffic accident data and mathematical models

Objective. The aim of this study was to investigate head injuries, injury risks, and corresponding tolerance levels of children in car-to–child pedestrian collisions. Methods. An in-depth accident analysis was carried out based on 23 accident cases involving child pedestrians. These cases were collected with detailed information about pedestrians, cars, and road environments. All 23 accidents were reconstructed using the MADYMO program with mathematical models of passenger cars and child pedestrians developed at Chalmers University of Technology. The contact properties of the car models were derived from the European New Car Assessment Program (EuroNCAP) subsystem tests. Results. The accident analysis demonstrated that the head was the most frequently and severely injured body part of child pedestrians. Most accidents occurred at impact speeds lower than 40 km/h and 98% of the child pedestrians were impacted from the lateral direction. The initial postures of children at the moment of impact were identified. Nearly half (47%) of the children were running, which was remarkable compared with the situation of adult pedestrians. From accident reconstructions it was found that head impact conditions and injury severities were dependent on the shape and stiffness of the car front, impact velocity, and stature of the child pedestrian. Head injury criteria and corresponding tolerance levels were analyzed and discussed by correlating the calculated injury parameters with the injury outcomes in the accidents. Conclusions. Reducing head injuries should be set as a priority in the protection of child pedestrians. HIC is an important injury criterion for predicting the risks of head injuries in child pedestrian accidents. The tolerance level of head injuries can have a considerable variation due to individual differences of the child pedestrians. By setting a suitable speed limit and improving the design of car front, the head injury severities of child pedestrians can be reduced.

Head-to-vehicle contact boundary condition and criteria and corresponding thresholds of head injuries are crucial in evaluation of vehicle safety performance for pedestrian protection, which need a constantly updated understanding of pedestrian head kinematic response and injury risk in real-world collisions. Thus, the purpose of the current study is to investigate the characteristics of pedestrian head-to-vehicle contact boundary condition and pedestrian AIS3+ (Abbreviated Injury Scale) head injury risk as functions of kinematic-based criteria, including HIC (Head Injury Criterion), HIP (Head Impact Power), GAMBIT (Generalized Acceleration Model for Brain Injury Threshold), RIC (Rotational Injury Criterion), and BrIC (Brain Injury Criteria), in real-world collisions. To achieve this, 57 vehicle-to-pedestrian collision cases were employed, and a multi-body modeling approach was applied to reconstruct pedestrian kinematics in these real-world collisions. The results show that head-to-windscreen contacts are dominant in pedestrian collisions of the analysis sample and that head WAD (Wrap Around Distance) floats from 1.5 to 2.3 m, with a mean value of 1.84 m; 80% of cases have a head linear contact velocity below 45 km/h or an angular contact velocity less than 40 rad/s; pedestrian head linear contact velocity is on average 83 ± 23% of the vehicle impact velocity, while the head angular contact velocity (in rad/s) is on average 75 ± 25% of the vehicle impact velocity in km/h; 77% of cases have a head contact time in the range 50–140 ms, and negative and positive linear correlations are observed for the relationships between pedestrian head contact time and WAD/height ratio and vehicle impact velocity, respectively; 70% of cases have a head contact angle floating from 40° to 70°, with an average value of 53°; the pedestrian head contact angles on windscreens (average = 48°) are significantly lower than those on bonnets (average = 60°); the predicted thresholds of HIC, HIP, GAMBIT, RIC, BrIC2011, and BrIC2013 for a 50% probability of AIS3+ head injury risk are 1,300, 60 kW, 0.74, 1,470 × 104, 0.56, and 0.57, respectively. The findings of the current work could provide realistic reference for evaluation of vehicle safety performance focusing on pedestrian protection.

As the use of electric self-balancing scooters (ESSs) increases, so does the number of related traffic accidents. Because of the special control method, mechanical structure and driving posture, ESSs are prone to various single-vehicle accidents, such as collisions with fixed obstacles and falls due to mechanical failures. In various ESS accident scenarios, the rider's head injury is the most frequent injury type. In this study, several typical single-ESS accident scenarios are reconstructed via computational methods, and the risk of riders' head/brain injury is assessed in depth using various injury criteria. Results showed that two types of ESSs (solo- and two-wheeler) do not have clear differences in head kinematics and head injury risks; the head kinematics (or falling posture) and ESS accident scenario exhibit a distinct effect on the head injury responses; half of the analysed ESS riders have a 50% probability of skull fracture, a few riders have a 50% risk of abbreviated injury scale (AIS) 4+ brain injury, and none has a diffuse axonal injury; the ESS speed plays an important role in producing the head/brain injury in ESS riders, and generally, higher ESS speed generates higher level of predicted head injury parameters. These findings will provide theoretical support for preventing head injury among ESS riders and data support for developing and legislating ESSs.

There are a very limited number of reports concerning the relationship between pedestrian head injuries and collision parameters through a combination of statistical analysis methods and finite element method (FEM). This study aims to explore the characteristics of pedestrian head injuries in car–pedestrian collisions at different parameters by using the two means above. A retrospective analysis of pedestrian head injuries was performed based on detailed investigation data of 61 car–pedestrian collision cases. The head damage assessment parameters (head injury criterion (HIC), peak stress on the skull, maximal principal strain for the brain) in car–pedestrian simulation experiments with four contact angles and three impact velocities were obtained by FEM. The characteristics of the pedestrian head injuries were discussed by comparing and analyzing the statistical analysis results and finite element analysis results. The statistical analysis results demonstrated a significant difference in skull fractures, contusion and laceration of brain and head injuries on the abbreviated injury scale (AIS)3+ was found at different velocities (p < 0.05) and angles (p < 0.05). The simulation results showed that, in pedestrian head-to-hood impacts, the values of head damage assessment parameters increased with impact velocities. At the same velocity, these values from the impact on the pedestrian’s back were successively greater than on the front or the side. Furthermore, head injury reconstruction and prediction results of two selected cases were consistent with the real injuries. Overall, it was further spelled out that, for shorter stature pedestrians, increased head impact velocity results in greater head injury severity in car–pedestrian collision, especially in pedestrian head-to-hood impacts. Under a back impact, the head has also been found to be at greater damage risk for shorter stature pedestrians, which may have implications on automotive design and pedestrian protection research if prevention and treatment of these injuries is to be prioritized over head injuries under a front or side impact.

Finite element (FE) models are often used to study the biomechanical effects of traumatic brain injury (TBI). Measures based on mechanical responses, such as principal strain or invariants of the strain tensor, are used as a metric to predict the risk of injury. However, the reliability of inferences drawn from these models depends on the correspondence between the mechanical measures and injury data, as well as the establishment of accurate thresholds of tissue injury. In the current study, a validated anisotropic FE model of the human head is used to evaluate the hypothesis that strain in the direction of fibers (axonal strain) is a better predictor of TBI than maximum principal strain (MPS), anisotropic equivalent strain (AESM) and cumulative strain damage measure (CSDM). An analysis of head kinematics-based metrics, such as head injury criterion (HIC) and brain injury criterion (BrIC), is also provided. Logistic regression analysis is employed to compare binary injury data (concussion/no concussion) with continuous strain/kinematics data. The threshold corresponding to 50% of injury probability is determined for each parameter. The predictive power (area under the ROC curve, AUC) is calculated from receiver operating characteristic (ROC) curve analysis. The measure with the highest AUC is considered to be the best predictor of mTBI. Logistic regression shows a statistical correlation between all the mechanical predictors and injury data for different regions of the brain. Peaks of axonal strain have the highest AUC and determine a strain threshold of 0.07 for corpus callosum and 0.15 for the brainstem, in agreement with previously experimentally derived injury thresholds for reversible axonal injury. For a data set of mild TBI from the national football league, the strain in the axonal direction is found to be a better injury predictor than MPS, AESM, CSDM, BrIC and HIC.

Objectives Elevated head injury incidence in infants compared to toddlers involved as occupants in motor vehicle crashes has been demonstrated in multiple population-representative crash databases. Further, experimental studies have revealed a potential injury mechanism via impact between a rear-facing, CRS-restrained child and the back of the vehicle seat or console on the row in front of the CRS. Subsequently, experimental studies have suggested that bracing the CRS against the seat immediately in front of the CRS could mitigate head injury, but also indicated that more research was necessary. Thus, we investigated the effect of bracing against the front seat, as well as distance from the front seat with rear-facing infant carriers and rear-facing convertibles, with a focus on changes to measured head, neck and chest injury metrics in rear facing CRSs. Further, we examined the effect of using the infant carrier with and without a base on these injury metrics. Methods 34 frontal sled tests at 30 or 35 mph were conducted using a simulated rear-row vehicle seat and structure representing the front seatback. A Q1.5 anthropomorphic test device (ATD) was placed in a single make/model LATCH-affixed rear-facing convertible or single make/model infant carrier; infant carrier without base was affixed with lap and shoulder belt. To evaluate the effect of bracing and distance, tests were conducted with a 300, 140, 70, or 15 mm gap between the CRS seatback and the front seatback, or a touching (0 mm) or braced (-20 mm) condition. Bayesian regression models quantified the effects of various predictors and model uncertainty. Results For tests with the convertible CRS, no head contact was observed between the head and the front vehicle seatback. For the infant carrier, head contact occurred at both 70 and 140 mm distances but not the other distances. On average, the −20, 0, or 15 mm distances yielded a 60% reduction in head injury criterion with 15 millisecond window (HIC15), and a 60% to 80% reduction in neck tension, compared to the 70 and 140 mm distances; chest acceleration also decreased for the convertible seat only. In the case of both carriers and convertibles, each mm of distance the CRS moves away from the front seatback up to 70 mm, adds 5.3 HIC15 points (95% Credible Interval (CrI):[4.6, 6.2]), and 3.5 Newtons (95% CrI: [2.2, 4.8]) of neck tension, on average. Conclusions Placing a rear facing CRS, both convertibles and infant carriers, against or close to the seatback of the seat immediately in front of the CRS reduces head and tensile neck injury criteria in ATDs. The amount of gap between the front seat and the rear facing CRS is strongly and positively correlated with HIC for both convertibles and infant carriers. RF infant carriers with and without a base yield comparable injury metrics and kinematics when touching or nearly touching the back of the front vehicle seatback.

Proper evaluation of ski helmet designs and safety standards should rely on head impact conditions involved in skiing and snowboarding head injuries. To study these impacts, main crash scenarios involving head injuries are numerically replicated. Multibody models of skiers and snowboarders were developed to investigate five common crash scenarios involved in traumatic brain injury: forward and sideways skiing falls, snowboarding backward falls, collisions between users and collisions with obstacles. For each scenario, the influence of crash conditions on head impact (location, speed, linear and rotational accelerations) and risk of injury are evaluated. Crash conditions were initial velocity, user height, position and approach angle, slope steepness, obstacles, and snow stiffness. One thousand one hundred forty-nine crashes were simulated and three significant levels of impact conditions were discriminated over the investigated crash scenarios: 1) the smallest normal-to-slope impact velocities (6 km·h; 22 km·h) and peak linear accelerations (42g; 75g) were obtained during forward and sideways skiing falls; 2) snowboarding backward falls and collisions between users were associated with high normal-to-surface impact velocities (26 km·h; 32 km·h) and head accelerations (80g; 149g) above one published threshold for mild traumatic brain injury but below the pass/fail criteria of helmet standard tests; 3) collisions with obstacles were associated with high normal-to-surface impact velocities (19 km·h; 35 km·h) and the highest head accelerations (626g; 1885g). Current impact conditions of helmet standard evaluations consistently replicate collisions with obstacles, but need to be revised to better reflect other significant crash scenarios leading to traumatic brain injury.

An anatomically detailed rhesus monkey brain FE model was developed to simulate in vivo responses of the brain of sub-human primates subjected to rotational accelerations resulting in diffuse axonal injury (DAI). The material properties used in the monkey model are those in the GHBMC 50th percentile male head model (Global Human Body Model Consortium). The angular loading simulations consisted of coronal, oblique and sagittal plane rotations with the center of rotation in neck to duplicate experimental conditions. Maximum principal strain (MPS) and Cumulative strain damage measure (CSDM) were analyzed for various white matter structures such as the cerebrum subcortical white matter, corpus callosum and brainstem. The MPS in coronal rotation were 45% to 54% higher in the brainstem, 8% to 48% higher in the corpus callosum, 13% to 22% higher in the white matter when compared to those in oblique and sagittal rotations, suggesting that more severe DAI was expected from coronal and oblique rotations as compared to that from sagittal rotation. The level 1+ DAI was associated with 1.3 to 1.42 MPS and 50% CSDM (0.5) responses in the brainstem, corpus callosum and cerebral white matter. The mass scaling method, sometimes referred to as Holbourn's inverse 2/3 power law, used for development of human brain injury criterion was evaluated to understand the effect of geometrical and anatomical differences between human and animal head. Based on simulations conducted with the animal and human models in three different planes - sagittal, coronal and horizontal - the scaling from animal to human models are not supported due to lack of geometrical similitude between the animal and human brains. Thus, the scaling method used in the development of brain injury criterion for rotational acceleration/velocity is unreliable.

Decrease of morbidity in road traffic accidents in a high income country – an analysis of 24,405 accidents in a 21 year period

IntroductionSeveral case–control studies have assessed the effectiveness of the bicycle helmet against head and face injuries. This is the first case–control study in a non anglo-saxon setting; it is based...

A proposed tolerance criterion for diffuse axonal injury in man

Objective The present study aimed to compare white matter hyperintensity (WMH) and white matter microbleed (WMM) proportions in trauma patients with intracranial hemorrhage (ICH) to published participants without ICH. When WMH or WMM proportions were associated with head trauma, these proportions were assessed to determine their associations with multiple undesirable outcomes. Methods The study population had ICH on CT, an admission Glasgow Coma Scale (GCS) score of 3-15, and blunt trauma. MRI was reviewed to determine the presence of WMH and WMM. The prevalence of non-trauma WMH and WMM by age was collated from the literature. The CT ICH mass effect (ME) scores reflect the presence or absence of lateral ventricular compression, basal cistern compression, and midline shift (0-3). The CT ICH Abbreviated Injury Scale (AIS) scores were obtained from the trauma registry (1-5). The total ICH score was determined by calculating AIS + ME + WMM (presence = 1; absence = 0) (range 1-9). An adverse outcome included hospital deaths, intensive care stay ≥2 days, or hospital stay >5 days. Multivariate analyses were used to determine independent associations. Results Of 1,545 patients, MRI was performed in 173 (mean age, 64.7 years). The WMH proportion was lower in patients with ICH (117/173; 67.6%) than in non-ICH age-matched counterparts (3,385/4,073; 83.1%; p < 0.0001). Mean ages with and without WMH were 72.4 and 48.6 years, respectively (p < 0.0001). The WMM proportion was greater in patients with ICH (96/173; 55.5%) than in non-ICH age-matched counterparts (473/3,216; 14.7%; p < 0.0001). Macrobleed on CT (ME + AIS scores) had univariate associations (p < 0.02 to < 0.001) with hospital deaths, intensive care and hospital lengths of stay, an adverse outcome, and failure to follow commands at discharge. Hospital mortality had an independent association with total ICH score (GCS 3-12, p > 0.1000; ME + AIS score, p > 0.1000; total ICH score, p = 0.0151). An ICU stay of ≥2 days was independently associated with total ICH score (GCS 3-12, p = 0.0004; ME + AIS score, p > 0.1000; total ICH score, p = 0.0004). Similarly, a hospital stay exceeding five days was significantly associated with total ICH score (GCS 3-12, p = 0.0004; ME + AIS score, p > 0.1000; total ICH score, p = 0.0071). An adverse outcome also showed an independent association with total ICH score (GCS 3-12, p = 0.0031; ME + AIS score, p > 0.1000; total ICH score, p = 0.0046). Additionally, failure to follow commands at three months was independently associated with total ICH score (GCS 3-12, p = 0.8283; ME + AIS score, p = 0.0948; total ICH score, p = 0.0443). The ME + AIS score did not show significant independent associations with these outcomes (p > 0.1000). Conclusions WMMs were indicative of traumatic axonal brain injury, whereas WMHs were associated with advancing age. Macrobleed on CT had univariate associations with multiple undesirable outcomes. The combination of macrobleeds identified on CT (ME + AIS) and microbleeds detected on MRI (WMM) showed independent associations with poor outcomes. However, CT-detected macrobleeds without microbleed status did not demonstrate an independent association. Findings from this study underscore the need for further investigation into the quantification of CT macrobleeds and MRI microbleeds and their correlation with both in-hospital and long-term clinical outcomes.

Brain injury tolerance limit based on computation of axonal strain

The SIMon (Simulated Injury Monitor) software package is being developed to advance the interpretation of injury mechanisms based on kinematic and kinetic data measured in the advanced anthropomorphic test dummy (AATD) and applying the measured dummy response to the human mathematical models imbedded in SIMon. The human finite element head model (FEHM) within the SIMon environment is presented in this paper. Three-dimensional head kinematic data in the form of either a nine accelerometer array or three linear CG head accelerations combined with three angular velocities serves as an input to the model. Three injury metrics are calculated: Cumulative strain damage measure (CSDM) - a correlate for diffuse axonal injury (DAI); Dilatational damage measure (DDM) - to estimate the potential for contusions; and Relative motion damage measure (RMDM) - a correlate for acute subdural hematoma (ASDH). During the development, the SIMon FEHM was tuned using cadaveric neutral density targets (NDT) data and further validated against the other available cadaveric NDT data and animal brain injury experiments. The hourglass control methods, integration schemes, mesh density, and contact stiffness penalty coefficient were parametrically altered to investigate their effect on the model's response. A set of numerical and physical parameters was established that allowed a satisfactory prediction of the motion of the brain with respect to the skull, when compared with the NDT data, and a proper separation of injury/no injury cases, when compared with the brain injury data. Critical limits for each brain injury metric were also established. Finally, the SIMon FEHM performance was compared against HIC15 through the use of NHTSA frontal and side impact crash test data. It was found that the injury metrics in the current SIMon model predicted injury in all cases where HIC15 was greater than 700 and several cases from the side impact test data where HIC15 was relatively small. Side impact was found to be potentially more injurious to the human brain than frontal impact due to the more severe rotational kinematics.

Reports from the U.S. suggest increases in the proportion and rate of head and neck injuries in skiers and snowboarders. It is important to determine if the same is true in Canada. Skiers and snowboarders (< 18 years) presenting to 16 selected emergency departments from 1991 to 1999 were assigned one body region of injury in the following order: i) brain and spine-spinal cord, ii) head and neck, iii) face, iv) other body region (i.e., controls). Crude and adjusted (age, gender, helmet use and hospital admission) odds ratios indicating the proportion of head, brain, face, and neck injury relative to controls by calendar year were estimated. Injury rates were examined for 12 to 17 year olds over the last 4 years of the study. Compared with 1997-1999, there was a lower proportion of skier head injuries from 1991-93 (adjusted odds ratio (AOR) = 0.16; 95% Confidence Interval (CI) = 0.09-0.30) and from 1995-97 (AOR = 0.71; 95% CI = 0.49-1.04). The proportion of skier brain injuries was lower from 1993-95 (AOR = 0.69; 95% CI = 0.44-1.07) and from 1995-97 (AOR = 0.56; 95% CI: 0.35-0.91). In snowboarders, however, compared with 1997-99, there was evidence that although the proportion of head injuries was lower from 1991-93 (AOR = 0.19; 95% CI = 0.05-0.80), the opposite was true for facial injuries. For 12 to 17 year olds, skier brain and snowboarder head and neck injury rates increased from 1995-99. The results suggest that head and brain injuries in skiers and head and neck injuries in snowboarders may be increasing, particularly in adolescents.