Cervical vertebral and spinal cord injuries in rollover occupants.

BACKGROUND: Rollover crashes continue to be a substantial public health issue in North America. Previous research has shown that the cervical spine is the most injured spine segment in rollovers, but much of the past research has focused on risk factors rather than the actual cervical spine injuries. We sought to examine how different types of cervical spine injuries (vertebral and/or cord injury) vary with different occupant-related factors in rollovers and to compare these with non-rollovers. METHODS: We obtained crash and injury information from the National Automotive Sampling System-Crashworthiness Data System (NASS-CDS) for 2005-2015 and Crash Investigation Sampling System (CISS) for 2017-2022. Based on weighted data, we calculated relative risks to assess how occupant sex, seat belt use, ejection status, and fatal outcome relate to the rate of different cervical spine injuries in rollovers and non-rollovers. RESULTS: In NASS-CDS occupants with cervical spine injuries (N = 111,040 weighted cases), about 91.5% experienced at least one vertebral injury whereas only 11.3% experienced a spinal cord injury (most of which had a concomitant vertebral fracture). All types of cervical spine injuries we examined were 3.4-5.2 times more likely to occur in rollovers compared to non-rollovers. These relative risks were similar for both sexes, belted and unbelted, non-ejected, and non-fatal occupants. The number of weighted CISS occupants with cervical spine injuries (N = 42,003) was smaller than in the NASS analysis, but cervical spine injuries remained 6.25 to 6.36 times more likely in rollovers compared to non-rollovers despite a more modern vehicle fleet. CONCLUSIONS: These findings underscore the continued need for rollover-specific safety countermeasures, especially those focused on cervical spine injury prevention, and elucidate the frequency, severity and other characteristics of the specific vertebral and spinal cord injuries being sustained in rollovers. Our findings suggest that countermeasures focused on preventing cervical vertebral fractures will also effectively prevent most cervical spinal cord injuries.

Knockout of formyl peptide receptor 1 reduces osteogenesis and bone healing.

AIMS: Formyl peptide receptor 1 (FPR1), from a G-protein coupled receptor family, was previously well-characterized in immune cells. But the function of FPR1 in osteogenesis and fracture healing was rarely reported. This study, using the FPR1 knockout (KO) mouse, is one of the first studies that try to investigate FPR1 function to osteogenic differentiation of bone marrow-derived stem cells (BMSCs) in vitro and bone fracture healing in vivo. MATERIALS AND METHODS: Primary BMSCs were isolated from both FPR1 KO and wild type (WT) mice. Cloned mouse BMSCs (D1 cells) were used to examine role of FoxO1 in FPR1 regulation of osteogenesis. A closed, transverse fracture at the femoral midshaft was created to compare bone healing between KO and WT mice. Biomechanical and structural properties of femur were compared between healthy WT and KO mice. KEY FINDINGS: FPR1 expression increased significantly during osteogenesis of both primary and cloned BMSCs. Compared to BMSCs from FPR1 KO mice, WT BMSCs displayed considerably higher levels of osteogenic markers as well as mineralization. Osteogenesis by D1 cells was inhibited by either an FPR1 antagonist cFLFLF or a specific inhibitor of FoxO1, AS1842856. In addition, the femur from WT mice had better biomechanical properties than FPR1 KO mice. Furthermore, bone healing in WT mice was remarkably improved compared to FPR1 KO mice analyzed by X-ray and micro-CT. SIGNIFICANCE: These findings indicated that FPR1 played a vital role in osteogenic differentiation and regenerative capacity of fractured bone, probably through the activation of FoxO1 related signaling pathways.

CCR2 monocytes as therapeutic targets for acute disc herniation and radiculopathy in mouse models.

OBJECTIVE: Back pain and radiculopathy caused by disc herniation are major health issues worldwide. While macrophages are key players in disc herniation induced inflammation, their roles and origins in disease progression remain unclear. We aim to study the roles of monocytes and derivatives in a mouse model of disc herniation. METHODS: Using a CCR2-CreER; R26R-EGFP (Ai6) transgenic mouse strain, we fate-mapped C-C chemokine receptor type 2 (CCR2) expressing monocytes and derivatives at disc herniation sites, and employed a CCR2RFP/RFP mouse strain and a CCR2-specific antagonist to study the effects of CCR2+ monocytes on local inflammatory responses, pain level, and disc degeneration by immunostaining, flow cytometry, and histology. RESULTS: CCR2+ monocytes (GFP+) increased at the sites of disc hernia over postoperative day 4, 6, and 9 in CCR2-CreER; Ai6 mice. F4/80+ cells increased, and meanwhile, CD11b+ cells trended downward. Co-localization analysis revealed that both GFP+CD11b+ and GFP+F4/80+ constituted the majority of CD11b+ and F4/80+ cells at disc hernia sites. Fluorescence activated cell sorter purified GFP+ cells exhibited higher cytokine expressions than GFP- cells. Inhibition of CCR2 signaling reduced infiltration of monocytes and macrophages, alleviated pain, maintained disc height, and reduced osteoclast activity in adjacent cortical bone for up to 1 month. CONCLUSION: Our findings suggest that circulating CCR2+ monocytes play important roles in initiating and promoting the local inflammatory responses, pain sensitization, and degenerative changes after disc herniation, and thus may serve as therapeutic targets for disc herniation induced back and leg pain.

Comparison of thoracolumbar spine kinematics and injuries in reclined frontal impact sled tests between mid-size adult female and male PMHS.

Disparities in injury tolerance and kinematic response remain understudied despite field data highlighting sex-based differences in injury risk. Furthermore, the automotive industry anticipates occupants will prefer reclined seating in highly automated vehicles. This study aimed to compare thoracolumbar spine kinematics and injuries between mid-size female and male post-mortem human subjects (PMHS) in reclined frontal impacts. Seven adult PMHS (three female, four male) were tested in reclined (50°) 50 km/h frontal impacts. The PMHS were seated on a semi-rigid seat and restrained by a prototype three-point seat belt system designed to mitigate submarining. The 3-D motions of five vertebrae and the pelvis were measured by an optical motion tracking system. Pressure transducers were inserted into intervertebral discs at three locations along the lumbar spine to track timing of lumbar vertebra fractures. Due to variations in the geometry of the pelvis and soft tissue surrounding the pelvis compared to the male subjects, the female subjects could not be positioned in the seat the same as the males, and, as a result, the females and their belt anchors needed to be translated forward in the seat to maintain similar belt geometry relative to the males. The females exhibited similar pre-test spinal curvatures and kinematics to the males. An L1 fracture was observed in one of three female subjects and two of four male subjects, and timing of these fractures were both similar (61 âˆ¼ 65 ms) and close to the time of peak downward seat force. Generally, the female and male subjects exhibited similar kinematic and injury responses in this reclined frontal impact sled test condition.

The Effects of Recline Angle and Restraint Geometry on Lap Belt-Pelvis Interaction for Above-Normal BMI Motor Vehicle Occupants.

The interaction of the three-point seat belt with the occupant, particularly the lap belt with the pelvis, is affected by a multitude of intrinsic and extrinsic factors, including the torso recline angle, lap belt angle, and occupant body mass index (BMI). While field data analyses have shown the strong safety benefit for seat belt use regardless of occupant size or crash direction, the term "submarining" historically has been used to describe a scenario in which the lap belt loads the abdominal soft tissue and organs, superior and posterior to the pelvic bone. While contemporary restraint systems work to effectively address the risk of submarining in occupants properly seated and properly belted, scenarios in which the lap belt may not properly engage the load-bearing pelvis remain. These scenarios, including a reclined torso angle or shallow lap belt angle, require further study. In this research study, eight non-injurious seated belt pull tests were conducted on two constrained whole-body cadavers of above-normal BMI (≥ 25 kg/m2) with controlled variation of torso and lap belt-pelvis angles. Test factors affecting belt engagement with the pelvis were identified for each subject. Belt engagement was largely affected by the initial placement of the lap belt. The initial belt placement was affected by the torso angle which influenced the distribution of the abdominal soft tissue. The belt disengagement thresholds differed between subjects due to the inter-subject differences in soft tissue distribution, which affected the lap belt kinematics relative to the pelvis. In addition to improving the understanding of this particular submarining mechanism, this study provides a dataset for future validation of human body model soft tissue deformation response from lap belt loading.

Development of an Injury Risk Function for the Anterior Pelvis Under Frontal Lap Belt Loading Conditions.

Iliac wing fractures due to lap belt loading have been identified in laboratory tests for almost 50 years and an analysis of recent data suggests these injuries are also occurring in the field. With the introduction of highly autonomous vehicles on the horizon, vehicle manufacturers are exploring open cabin concepts that permit reclined postures and separation of the occupant from the knee bolster and instrument panel. This will result in greater reliance on the lap belt and lap belt/pelvis loading to restrain occupants. No injury criteria exist for iliac wing fractures resulting from lap belt loading like that seen in frontal crash conditions. This study tested the tolerance of isolated iliac wings in a controlled lap belt-like loading environment while incorporating the effect of loading angle after analyzing lap belt loading experiments from a previous study. Twenty-two iliac wings were tested; nineteen of them sustained fracture (exact), but the loading input was insufficient to cause fracture in the other three (right censored). The fracture tolerance of the tested specimens ranged widely (1463-8895 N) and averaged 4091 N (SD 2381 N). Injury risk functions were created by fitting Weibull survival models to data that integrated censored and exact failure observations.

Effect of axial compression on stiffness and deformation of human lumbar spine in flexion-extension.

OBJECTIVE: The goal of this study was to evaluate the effect of axial compression, employed with a follower-load mechanism, on the response of the lumbar spine in flexion and extension bending. Additional goals include measurement of both the kinetic (stiffness) and kinematic (deformation distribution) responses, evaluating how the responses vary across specimens, and to develop response corridors that can be used to evaluate human body models (HBMs) and anthropomorphic test devices (ATDs). METHODS: Seven mid-sized male adult lumbar spines (T12-S1) from postmortem human surrogates were tested in subinjurious flexion and extension bending with 0, 900, and 1800 N of superimposed axial compression. Tests were performed in load-control with a 6-DOF robotic test system that applied pure flexion and extension moments to the specimens, and axial compression was directed along the spine's curvature via a follower load mechanism powered by force-controlled linear actuators. Load-deformation response data were captured and used to characterize the kinetic response of the lumbar spine in flexion/extension, and how it varies with axial compression. Individual vertebral kinematics were captured using 3D motion capture and the data was used to illustrate the distribution of bending deformation across each intervertebral joint of the spine, as well has how that distribution changes with axial compression. These response data were used to develop elliptical path-length parameterized response corridors for surrogate biofidelity evaluation. RESULTS: The lumbar spine was found to be generally stiffer in extension than in flexion, but this difference decreased with increasing axial compression. The lumbar spine exhibited a nonlinear kinetic (moment vs. angle) response in flexion that became more linear and stiffer with the addition of axial compression. In flexion without axial load, the majority of the bending deformation occurred at the L5-S1 joint, whereas in extension, deformation was more evenly distributed across the different intervertebral levels, but the locus of deformation was located in the mid-proximal lumbar at L2-L3. CONCLUSIONS: The superposition of axial compression in the lumbar spine affects the kinetic and kinematic response of the lumbar spine in flexion and extension. The response data and approach detailed in this study permit better assessment of ATD and HBM biofidelity.

Human Lumbar Spine Injury Risk in Dynamic Combined Compression and Flexion Loading.

Anticipating changes to vehicle interiors with future automated driving systems, the automobile industry recently has focused attention on crash response in novel postures with increased seatback recline. Prior research found that this posture may result in greater risk of lumbar spine injury in the event of a frontal crash. This study developed a lumbar spine injury risk function (IRF) that estimated injury risk as a function of simultaneously applied compression force and flexion moment. Force and moment failure data from 40 compression-flexion tests were utilized in a Weibull survival model, including appropriate data censoring. A mechanics-based injury metric was formulated, where lumbar spine compression force and flexion moment were normalized by specimen geometry. Subject age was incorporated as a covariate to further improve model fit. A weighting factor was included to adjust the influence of force and moment, and parameter optimization yielded a value of 0.11. Thus, the normalized compression force component had a greater effect on injury risk than the normalized flexion moment component. Additionally, as force was nominally increased, less moment was required to produce injury for a given age and specimen geometry. The resulting IRF may be utilized to improve occupant safety in the future.

Failure tolerance of the human lumbar spine in dynamic combined compression and flexion loading.

Vehicle safety systems have substantially decreased motor vehicle crash-related injuries and fatalities, but injuries to the lumbar spine still have been reported. Experimental and computational analyses of upright and, particularly, reclined occupants in frontal crashes have shown that the lumbar spine can be subjected to simultaneous and out-of-phase combined axial compression and flexion loading. Lumbar spine failure tolerance in combined compression-flexion has not been widely explored in the literature. Therefore, the goal of this study was to measure the failure tolerance of the lumbar spine in combined compression and flexion. Forty lumbar spine segments with three vertebrae (one unconstrained) and two intervertebral discs (both unconstrained) were pre-loaded with axial compression (2200N, 3300N, or 4500N) and then subjected to rotation-controlled dynamic flexion bending until failure. Clinically relevant middle vertebra fractures were observed in twenty-one of the specimens, including compression and burst fractures. The remaining nineteen specimens experienced failure at the potting-grip interface. Failure tolerance varied within the sample and were categorized by the appropriate data censoring, with clinically relevant middle vertebrae fractures characterized as uncensored or left-censored and potting-grip fractures characterized as right-censored. Average failure force and moment were 3290N (range: 1580N to 5042N) and 51Nm (range: 0Nm to 156 Nm) for uncensored data, 3686N (range: 3145N to 4112N) and 0Nm for left-censored data, and 3470N (range: 2138N to 5062N) and 101Nm (range: 27Nm to 182Nm) for right-censored data. These data can be used to develop and improve injury prediction tools for lumbar spine fractures and further research in future safety systems.

Effect of Temperature and Freezing on Human Adipose Tissue Material Properties Characterized by High-Rate Indentation: Puncture Testing.

The characterization of human subcutaneous adipose tissue (SAT) under high-rate loading is valuable for development of biofidelic finite element human body models (FE-HBMs) to predict seat belt-pelvis interaction and injury risk in vehicle crash simulations. While material characterization of SAT has been performed at 25 °C or 37 °C, the effect of temperature on mechanical properties of SAT under high-rate and large-deformation loading has not been investigated. Similarly, while freezing is the most common preservation technique for cadaveric specimens, the effect of freeze-thaw on the mechanical properties of SAT is also absent from the literature. Therefore, the aim of this study was to determine the effect of freezing and temperature on mechanical properties of human SAT. Fresh and previously frozen human SAT specimens were obtained and tested at 25 °C and 37 °C. High-rate indentation and puncture tests were performed, and indentation-puncture force-depth responses were obtained. While the chance of material failure was found to be different between temperatures and between fresh and previously frozen tissue, statistical analyses revealed that temperature and freezing did not change the shear modulus and failure characteristics of SAT. Therefore, the results of the current study indicated that SAT material properties characterized from either fresh or frozen tissue at either 25 °C or 37 °C could be used for enhancing the biofidelity of FE-HBMs.

Is optimized restraint system for an occupant with obesity different than that for a normal BMI occupant?

OBJECTIVE: To optimize the components of restraint systems for protecting obese (BMI = 35 kg/m2) and normal BMI (BMI = 25) human body models (HBMs) in frontal crash simulations, and to compare the two optimized designs. METHODS: The Life Years Lost metric, which incorporates the risk of injury and long-term disability to different body regions, was used as the optimization objective function. Parametric simulations, sampled from a 15-parameter design space using the Latin Hypercube technique, were performed and metamodels of the HBM responses were developed. A genetic algorithm was applied to the metamodels to identify the optimized designs. RESULTS: While most of the restraint parameters between the optimized design for obese and normal BMI HBMs were similar, the main difference was that the restraint for the obese HBM included an under-the-seat airbag, which mitigated its lower extremity excursion, improved its torso kinematics, and decreased its lower extremity and lumbar spine injury risks. The optimized designs for both HBMs included an inflatable seat belt, which reduced the risk of thoracic injury. CONCLUSIONS: The design recommendations from this study should be considered to improve safety of occupants with obesity.

Effect of various restraint configurations on submarining occurrence across varied seat configurations in autonomous driving system environment.

OBJECTIVE: Self-driving technology will bring novelty in vehicle interior design and allow for a wide variety of occupant seating choices. Previous studies have shown that the increased risk of submarining exhibited by reclined occupants cannot be fully mitigated by changes in the seat configuration alone. This study aims to investigate the effects of three restraint countermeasures on cases with marginal submarining events and estimate their effect on submarining risk and injury prediction metrics. METHODS: Vehicle environment frontal crash Finite Element (FE) simulations were performed with the two simplified Global Human Body Model Consortium (GHBMC) occupant models: small female and midsize male. The baseline occupant restraints consisted of a frontal airbag, a seatback-integrated 3-point belt with a lap belt anchor pre-tensioner, and a retractor-mounted pre-tensioner and load limiter. Based on submarining thresholds identified in previous studies, three baseline configurations were identified for each occupant size. For each baseline case three restraint system modifications were evaluated. The modifications consisted of the introduction of a pelvis restraint cushion airbag (PRC), the use of a knee airbag (KAB) and the modification of the of the passenger airbag location (PAB). Simulations were performed using the USNCAP 56 km/h frontal crash pulse. Occupant kinematic data was extracted from each simulation to investigate how changes in the restraint system configuration affects submarining. RESULTS: Overall, in only one of the investigated cases did the proposed restraint modification prevent submarining occurrence, however each of the restraint modifications reduced the pelvis excursion over the baseline scenario. The presence of the PRC airbag showed the highest reduction in pelvis forward excursion for the female model. The presence of the KAB and the modified location of the PAB also contributed to reductions in excursion to a smaller degree. For the male surrogate, the KAB showed the highest reduction in pelvis forward excursion. The presence of the PRC led to a reduction in the lumbar spine shear force. CONCLUSIONS: Submarining may be a major challenge to overcome for reclined occupants in autonomous driving systems. This suggests that there may not be a single generalizable currently-existing countermeasure able to effectively prevent marginal submarining cases in reclined positions.

Multidirectional mechanical properties and constitutive modeling of human adipose tissue under dynamic loading.

The mechanical behavior of subcutaneous adipose tissue (SAT) affects the interaction between vehicle occupants and restraint systems in motor vehicle crashes (MVCs). To enhance future restraints, injury countermeasures, and other vehicle safety systems, computational simulations are often used to augment experiments because of their relative efficiency for parametric analysis. How well finite element human body models (FE-HBMs), which are often used in such simulations, predict human response has been limited by the absence of material models for human SAT that are applicable to the MVC environment. In this study, for the first time, dynamic multidirectional unconfined compression and simple shear loading tests were performed on human abdominal SAT specimens under conditions similar to MVCs. We also performed multiple ramp-hold tests to evaluate the quasilinear viscoelasticity (QLV) assumption and capture the stress relaxation behavior under both compression and shear. Our mechanical characterization was supplemented with scanning electron microscopy (SEM) performed in different orientations to investigate whether the macrostructural response can be related to the underlying microstructure. While the overall structure was shown to be visually different in different anatomical planes, a preferred orientation of any fibrous structures could not be identified. We showed that the nonlinear, viscoelastic, and direction-dependent responses under compression and shear tests could be captured by incorporating QLV in an Ogden-type hyperelastic model. Our comprehensive approach will lead to more accurate computational simulations and support the collective effort on the research of future occupant protection systems. STATEMENT OF SIGNIFICANCE: There is an urgent need to characterize the mechanical behavior of human adipose tissue under multiple dynamic loading conditions, and to identify constitutive models that are able to capture the tissue response under these conditions. We performed the first series of experiments on human adipose tissue specimens to characterize the multi-directional compression and shear behavior at impact loading rates and obtained scanning electron microscope images to investigate whether the macrostructural response can be related to the underlying microstructure. The results showed that human adipose tissue is nonlinear, viscoelastic and direction dependent, and its mechanical response under compression and shear tests at different loading rates can be captured by incorporating quasi-linear viscoelasticity in an Ogden-type hyperelastic model.

In Vitro Mechanical Characterization and Modeling of Subcutaneous Adipose Tissue: A Comprehensive Review.

Mechanical models of adipose tissue are important for various medical applications including cosmetics, injuries, implantable drug delivery systems, plastic surgeries, biomechanical applications such as computational human body models for surgery simulation, and blunt impact trauma prediction. This article presents a comprehensive review of in vivo experimental approaches that aimed to characterize the mechanical properties of adipose tissue, and the resulting constitutive models and model parameters identified. In particular, this study examines the material behavior of adipose tissue, including its nonlinear stress-strain relationship, viscoelasticity, strain hardening and softening, rate-sensitivity, anisotropy, preconditioning, failure behavior, and temperature dependency.

Comparison of porcine and human adipose tissue loading responses under dynamic compression and shear: A pilot study.

Understanding the mechanical properties of human adipose tissue, and its influence on seat belt-pelvis interaction is beneficial for computational human body models that are developed for injury prediction in the vehicle crashworthiness simulations. While various studies have characterized adipose tissue, most of the studies used porcine adipose tissue as a surrogate, and none of the studies were performed at loading rates relevant for motor vehicle collisions. In this work, the mechanical response of human and porcine adipose tissue was studied. Two dynamic loading modes (compression and simple shear) were tested in adipose tissue extracted from the human abdomen and porcine back. An Ogden hyperelastic model was used to fit the loading response, and specific material parameters were obtained for each specimen. Two-sample t-tests were performed to compare the effective shear moduli and peak stresses from porcine and human samples. The material response of the human adipose tissue was consistent with previous studies. Porcine adipose tissue was found to be significantly stiffer than human adipose tissue under compression and shear loading. Also, when material model parameters were fit to only one loading mode, the predicted response in the other mode showed a poor fit.

Leveraging machine learning for predicting human body model response in restraint design simulations.

The objective of this study was to leverage and compare multiple machine learning techniques for predicting the human body model response in restraint design simulations. Parametric simulations with 16 independent variables were performed. Ordinary least-squares (OLS), least absolute shrinkage and selection operator (LASSO), neural network (NN), support vector regression (SVR), regression forest (RF), and an ensemble method were used to develop response surface models of the simulations. The hyperparameters of the machine learning techniques were optimized through grid search and cross-validation to avoid under-fitting and over-fitting. The ensemble method outperformed other techniques, followed by LASSO, SVR, NN, RF, and OLS. Findings indicated that optimizing the metamodel hyper-parameters are essential to predict the optimum set of restraint design parameters.

Thoracolumbar spine kinematics and injuries in frontal impacts with reclined occupants.

OBJECTIVE: Highly automated vehicles may permit alternative seating postures, which could alter occupant kinematics and challenge current restraint designs. One predicted posture is a reclined seated position. While the spine of upright occupants is subjected to flexion during frontal crashes, the orientation of reclined occupants tends to subject the spine to high compressive loads followed by high flexion loads. This study aims to investigate kinematics and mechanisms of loading in the thoracolumbar spine for a reclined seated posture through the use of postmortem human subjects (PMHS). METHODS: Frontal impact sled tests (50 kph delta-v) were conducted on five adult midsize male PMHS seated with the torso reclined to 50 degrees with respect to the vertical. The PMHS were seated on a semi-rigid seat and restrained by a seat-integrated three-point belt with dual lap-belt pretensioners and a shoulder-belt pretensioner with a 3 kN load-limiter. 3-D kinematic trajectories of five chosen vertebrae, and the pelvis were measured relative to the vehicle buck. Intervertebral pressure transducers were installed at three locations in the lumbar column to detect load timing. RESULTS: Three PMHS suffered fractures at L1. Combined compression and flexion of the thoracolumbar spine occurred in all tests, but the magnitude of peak flexion varied across the PMHS. During the PMHS' forward excursion, the pelvis rotated anteriorly in two tests and posteriorly in two tests (lap-belt submarining occurred in one). In one test, the pelvis mount interacted with the seat, but did not affect kinematics. CONCLUSIONS: Anterior rotation of the pelvis caused increased extension of the lumbar spine, which exacerbated lumbar compression in two of the PMHS; the one subject whose pelvis kinematic tracking was lost exhibited similar compression kinematics. Posterior rotation of the pelvis enabled lumbar flexion, which decreased lumbar compression, but lead to lap-belt submarining in one case. Lumbar kinematics for these reclined frontal impacts were sensitive to changes in initial posture of the spine (magnitude of lordosis or kyphosis) and pelvis (pitch angle). To our knowledge, this study is the first to analyze thoracolumbar kinematics and resulting injuries of a reclined seating posture using PMHS.

Sensitivity of scale factor choice on injury response for equal-stress equal-velocity scaling.

OBJECTIVE: This study aims to evaluate the assumption of geometric similitude inherent to equal-stress equal-velocity scaling by determining if scale factors created with different anthropometry metrics result in different scaled injury tolerance predictions. This assumption will be evaluated when equal-stress equal-velocity scaling is employed across dissimilar (e.g., 50th male to small female) and similar (e.g., small female to a reference small female anthropometry) anthropometries. METHODS: Three average male and three small female lower extremity specimens that were tested in ankle inversion/eversion were selected for scaling analysis. Three additional female specimens were selected as a reference dataset, such that the accuracy of the scaled data could be compared to an independent measured dataset. The failure moments, total height and total weight for these donors were determined from literature. Additional anthropometry metrics (leg length, calcaneus height, and bimalleolar width) were taken from each of their respective CT scans. Scale factors were calculated from these previously determined anthropometric metrics for the six donors selected for scaling analysis by targeting the averaged anthropometry metrics of the reference small female dataset. Equal-stress equal-velocity scaling was applied to the failure moments from literature using different scale factors. The mean predicted failure tolerance and standard deviation for scaled data using different scale factors were compared to one another and to the mean failure tolerance from the reference (unscaled) small female dataset. RESULTS: When using average male data to predict ankle failure moment for a small female anthropometry, scaled moments were statistically significantly different from measured small female failure moment. Furthermore, scaled failure moments predicted using scale factors based on different anthropometry metrics were found to be significantly different from one another. Conversely, predicted mean failure moment using scaled female data of a similar size to the reference data was not significantly different from measured female failure moment, and the predicted failure moments were not significantly affected by choice of scale factor. CONCLUSIONS: This study shows that an injury metric predicted with equal-stress equal-velocity scaling is sensitive to choice of scale factor when employing scaling across occupants of dissimilar size and sex. This conclusion suggests error can be introduced into scaled response due to choice of anthropometry metric used to create a scale factor, and therefore, anthropometry metrics used to create scale factors should be justified mechanistically and shown to apply across size and sex before being employed.

Submarining sensitivity across varied seat configurations in autonomous driving system environment.

OBJECTIVE: Self-driving technology will bring novelty in vehicle interior design and allow for a wide variety of occupant seating choices. Thus, vehicle safety systems may be challenged to protect occupants over a wider range of potential postures. This study aims to investigate the effects of the seat cushion angle on submarining risk, lumbar spine loads and pelvis excursion for reclined occupants in frontal crashes. METHODS: Frontal crash finite element simulations were performed with two of the simplified Global Human Body Model Consortium (GHBMC) occupant models: the small female and the midsize male. Occupant restraints consisted of a frontal airbag, a seatback-integrated 3-point belt with a lap belt anchor pre-tensioner, and a retractor pre-tensioner with a force limiter. For each simulation, parameters including seat cushion angle (3°, 8°, 13°), seatback recline angle (0°, 10°, 20°, 30°), and knee bolster (KB) position relative to the occupant (baseline and no KB) were varied. A full-factorial simulation matrix was performed using the USNCAP 56 km/h frontal crash pulse. Occupant kinematics data were extracted from each simulation to investigate how changes in seat cushion angle, anthropometry, seatback angle, and KB position would affect submarining across all simulated cases. RESULTS: Overall, the F05-OS female model was more likely to submarine when compared to the male occupant model. The threshold for submarining was also affected by the seat cushion angle, seatback angle and KB distance. For the F05-OS model, increasing the seat cushion angle to 13° prevented submarining in the 10° seatback angle case, regardless of the KB position. Similarly, the 13° cushion angle prevented submarining for the M50-OS in the 30° seatback angle configuration but only in the presence of a KB. The results further show an increased lumbar flexion load with increased seat recline angle, as well as occupant-to-KB distance, although an opposite trend with the increased seat cushion angle. CONCLUSIONS: Submarining may be a major challenge to overcome for reclined occupants in autonomous driving systems. This study shows that seat cushion angle plays a role in restraining occupants in recline scenarios, but it is not sufficient to prevent submarining without additional countermeasures.

Kinematics of inboard-leaning occupants in frontal impacts.

Objective: Up to one-half of drivers swerve before a crash, which may cause vehicle motions that displace an occupant from a normal seated position. How these altered postures affect occupant restraint in a crash is unknown. The goal of this study was to quantify the effect of an initial inboard lean on occupant kinematics in a frontal impact.Methods: 30 km/h frontal impact tests were performed with three postmortem human subjects (PMHS) seated in a neutral, upright posture and in a 20° inboard-leaning posture identified from simulated swerving tests with human volunteers.Results: In comparison to the upright posture, the inboard-leaning posture increased the initial distance from the D-ring to the belted shoulder by 105-156 mm. In the inboard-leaning tests, the occupant's head displaced 45-70 mm farther forward than in the upright tests and was also located 123-147 mm farther inboard at the time of maximum forward excursion. The peak resultant velocity of the occupant's head relative to the vehicle interior increased 1.40-1.54 m/s in the inboard-leaning tests.Conclusions: The posture-induced increase in the distance between the D-ring and the shoulder permitted the increased maximum forward head displacement and increased maximum head resultant velocity relative to the vehicle interior. Thus, an initial inboard lean in a frontal impact may increase the risk and severity of a head strike to the vehicle interior, and alter the location, timing, and nature of airbag engagement.