Deflection corridors of abdomen and thorax in oblique side impacts using equal stress equal velocity approach: comparison with other normalization methods.

The first objective of the study was to determine the thorax and abdomen deflection time corridors using the equal stress equal velocity approach from oblique side impact sled tests with postmortem human surrogates fitted with chestbands. The second purpose of the study was to generate deflection time corridors using impulse momentum methods and determine which of these methods best suits the data. An anthropometry-specific load wall was used. Individual surrogate responses were normalized to standard midsize male anthropometry. Corridors from the equal stress equal velocity approach were very similar to those from impulse momentum methods, thus either method can be used for this data. Present mean and plus/minus one standard deviation abdomen and thorax deflection time corridors can be used to evaluate dummies and validate complex human body finite element models.

Influence of morphological variations on cervical spine segmental responses from inertial loading.

OBJECTIVES: The objective of this study was to investigate the influence of morphological variations in osteoligamentous lower cervical spinal segment responses under postero-anterior inertial loading. METHODS: A parametric finite element model of the C5-C6 spinal segment was used to generate models. Variations in the vertebral body and facet depth (anteroposterior), posterior process length, intervertebral disc height, facet articular process height and slope, segment orientation ranging from lordotic to straight, and segment size were parameterized. These variations included male-female differences. A Latin hypercube sampling method was used to select parameter values for model generation. Forces and moments associated with the inertial loading were applied to the generated model segments. The 7 parameters were grouped as local or global depending on the number of spinal components involved in the shape variation. Four output responses representing overall segmental and soft tissue responses were analyzed for each model variation: response angle of the segment, anterior longitudinal ligament stretch, anterior capsular ligament stretch, and facet joint compression in the posterior region. Pearson's correlation coefficient was used to compute the correlations of these output responses with morphological variations. RESULTS: Fifty models were generated from the parameterized model using a Latin hypercube sampling technique. Variation in response angle among the models was 4° and was most influenced by change in the combined dimension of vertebral body and facet depth, followed by size of the segment. The maximum anterior longitudinal ligament stretch varied between 0.1 and 0.3 and was strongly influenced by the change in the segment orientation. The anterior facet joint region sustained tension, whereas the posterior region sustained compression. For the anterior capsular ligament stretch, the most influential global variation was segment orientation, whereas the most influential local variations were the facet height and facet angle parameters. In the case of posterior facet joint compression, segment orientation was again most influential, whereas among the local variations, the facet angle had the most influence. CONCLUSION: Shape variations in the intervertebral disc influenced segmental rotation and ligament responses; however, the influence of shape variations in the facet joint was confined to capsular ligament responses. Response angle was most influenced by the vertebral body depth variations, explaining greater segmental rotations in female spines. Straighter spine segments sustained greater posterior facet joint compression, which may offer an explanation for the higher incidence of whiplash-associated disorders among females, who exhibit a straighter cervical spine. The anterior longitudinal ligament stretch was also greater in straighter segments. These findings indicate that the morphological features specific to the anatomy of the female cervical spine may predispose it to injury under inertial loading.

Normalized frontal impact biofidelity kinematic corridors using post mortem human surrogates.

Due to reducing cost and powerful computing resources and the ability of finite element human body models (FEHBM) to predict human body response more realistically, they are gaining acceptance to be a substitute for mechanical surrogates. Unlike mechanical surrogates, FEHBM can realistically simulate human kinematics and kinetics. Moreover, an array of quantities can be directly measured from FEHBMs. However, similar to Anthropomorphic Test Devices (ATDs), in order to evaluate the biofidelity, these models must be validated using PMHS response corridors. Therefore, availability of such PMHS corridors that can be used to validate both ATD and FEHBM kinematics is of primary importance. The current study presents normalized biofidelity corridors of head CG, T1, T12, and sacrum accelerations using PMHS frontal sled tests that were previously conducted. In addition, rotational accelerations and displacements of the head are also presented. The experimental data were collected using four specimens. Each specimens were tested with non-injurious pulses using two different velocities (low: 3.6m/s and medium: 6.9m/s). These data were normalized using mass-based technique to represent mid-sized United States population. Using the normalized data, average and plus/minus one standard deviation response corridors were generated that can be used to evaluate the biofidelity of ATDs and FEHBMs.

Factors influencing the effectiveness of occupant retention under far-side impacts: A parametric study.

The occupant retention and injuries under far-side impact are invariably dependent upon the effectiveness of the seatbelt restraint system, which is largely driven by parameters such as seatbelt pre-tensioner limiting load, D-ring position above and behind the shoulder, and friction coefficient between the torso and the seatbelt. The cumulative effect of systematic variation of these parameters on occupant kinematics under far-side is rarely studied in the literature. In this study, a systematic and detailed analysis was performed to understand the effect of these parameters on occupant retention. A rigid buck assembly with Global Human Body Model Consortium Human Body Model, validated with post mortem human surrogate experiments was used under two different impact scenarios-lateral and oblique. A simulation matrix of 16 cases was designed by varying the magnitude of the parameters for each impact scenario. Each case was graded as good, moderate, or poor retention based on the position of the shoulder seatbelt at the time of rebound. Head accelerations and excursions, chest compression, rib fractures, and neck moments of the HBM were analyzed to understand the effect of improved retention on occupant kinematics. Results showed that higher pre-tensioner limiting load, higher seatbelt friction, and backward position of D-ring improved retention in both lateral and oblique scenarios. Head acceleration, and excursions and chest compression decreased from poor retention cases to good retention cases for both impact scenarios. Rib fractures were higher in cases with poor retention as compared to those with good retention. The peak lateral neck moments changed marginally from poor to good retention; however, the rate of loading of the neck was significantly higher in good retention. Thus, the current study suggested that the backward D-ring position coupled with higher pretensioner limiting load and friction is likely to improve retention in far-side impacts and prevent injuries from the occupant slipping out of the restraint system. Better retention reduced occupant acceleration, excursion, chest compression and number of rib fractures, on the contrary it might instill higher injury vulnerability to neck and brain.

Biomechanics of Lumbar Motion-Segments in Dynamic Compression.

Recent epidemiology studies have reported increase in lumbar spine injuries in frontal crashes. Whole human body finite element models (FEHBM) are frequently used to delineate mechanisms of such injuries. However, the accuracy of these models in mimicking the response of human spine relies on the characterization data of the spine model. The current study set out to generate characterization data that can be input to FEHBM lumbar spine, to obtain biofidelic responses from the models. Twenty-five lumbar functional spinal units were tested under compressive loading. A hydraulic testing machine was used to load the superior ends of the specimens. A 75N load was placed on the superior PMMA to remove the laxity in the joint and mimic the physiological load. There were three loading sequences, namely, preconditioning, 0.5 m/s (non-injurious) and 1.0 m/s (failure). Forces and displacements were collected using six-axis load cell and VICON targets. In addition, acoustic signals were collected to identify the times of failures. Finally, response corridors were generated for the two speeds. To demonstrate the corridors, GHBMC FE model was simulated in frontal impact condition with the default and updated lumbar stiffness. Bi-linear trend was observed in the force versus displacement plots. In the 0.5 m/s tests, mean toe- and linear-region stiffnesses were 0.96±0.37 and 2.44±0.92 kN/mm. In 1.0 m/s tests, the toe and linear-region stiffnesses were 1.13±0.56 and 4.6±2.5 kN/mm. Lumbar joints demonstrated 2.5 times higher stiffness in the linear-region when the loading rate was increased by 0.5 m/s.

Evaluation of kinematics and injuries to restrained occupants in far-side crashes using full-scale vehicle and human body models.

OBJECTIVE: The objective of the current study was to perform a parametric study with different impact objects, impact locations, and impact speeds by analyzing occupant kinematics and injury estimations using a whole-vehicle and whole-body finite element-human body model (FE-HBM). To confirm the HBM responses, the biofidelity of the model was validated using data from postmortem human surrogate (PMHS) sled tests. METHODS: The biofidelity of the model was validated using data from sled experiments and correlational analysis (CORA). Full-scale simulations were performed using a restrained Global Human Body Model Consortium (GHBMC) model seated on a 2001 Ford Taurus model using a far-side lateral impact condition. The driver seat was placed in the center position to represent a nominal initial impact condition. A 3-point seat belt with pretensioner and retractor was used to restrain the GHBMC model. A parametric study was performed using 12 simulations by varying impact locations, impacting object, and impact speed using the full-scale models. In all 12 simulations, the principal direction of force (PDOF) was selected as 90°. The impacting objects were a 10-in.-diameter rigid vertical pole and a movable deformable barrier. The impact location of the pole was at the C-pillar in the first case, at the B-pillar in the second case, and, finally, at the A-pillar in the third case. The vehicle and the GHBMC models were defined an initial velocity of 35 km/h (high speed) and 15 km/h (low speed). Excursion of the head center of gravity (CG), T6, and pelvis were measured from the simulations. In addition, injury risk estimations were performed on head, rib cage, lungs, kidneys, liver, spleen, and pelvis. RESULTS: The average CORA rating was 0.7. The shoulder belt slipped in B- and C-pillar impacts but somewhat engaged in the A-pillar case. In the B-pillar case, the head contacted the intruding struck-side structures, indicating higher risk of injury. Occupant kinematics depended on interaction with restraints and internal structures-especially the passenger seat. Risk analysis indicated that the head had the highest risk of sustaining an injury in the B-pillar case compared to the other 2 cases. Higher lap belt load (3.4 kN) may correspond to the Abbreviated Injury Scale (AIS) 2 pelvic injury observed in the B-pillar case. Risk of injury to other soft anatomical structures varied with impact configuration and restraint interaction. CONCLUSION: The average CORA rating was 0.7. In general, the results indicated that the high-speed impacts against the pole resulted in severe injuries, higher excursions followed by low-speed pole, high-speed moving deformable barrier (MDB), and low-speed MDB impacts. The vehicle and occupant kinematics varied with different impact setups and the latter kinematics were likely influenced by restraint effectiveness. Increased restraint engagement increased the injury risk to the corresponding anatomic structure, whereas ineffective restraint engagement increased the occupant excursion, resulting in a direct impact to the struck-side interior structures.

Lower Leg Injury Reference Values and Risk Curves from Survival Analysis for Male and Female Dummies: Meta-analysis of Postmortem Human Subject Tests.

OBJECTIVE: Derive lower leg injury risk functions using survival analysis and determine injury reference values (IRV) applicable to human mid-size male and small-size female anthropometries by conducting a meta-analysis of experimental data from different studies under axial impact loading to the foot-ankle-leg complex. METHODS: Specimen-specific dynamic peak force, age, total body mass, and injury data were obtained from tests conducted by applying the external load to the dorsal surface of the foot of postmortem human subject (PMHS) foot-ankle-leg preparations. Calcaneus and/or tibia injuries, alone or in combination and with/without involvement of adjacent articular complexes, were included in the injury group. Injury and noninjury tests were included. Maximum axial loads recorded by a load cell attached to the proximal end of the preparation were used. Data were analyzed by treating force as the primary variable. Age was considered as the covariate. Data were censored based on the number of tests conducted on each specimen and whether it remained intact or sustained injury; that is, right, left, and interval censoring. The best fits from different distributions were based on the Akaike information criterion; mean and plus and minus 95% confidence intervals were obtained; and normalized confidence interval sizes (quality indices) were determined at 5, 10, 25, and 50% risk levels. The normalization was based on the mean curve. Using human-equivalent age as 45 years, data were normalized and risk curves were developed for the 50th and 5th percentile human size of the dummies. RESULTS: Out of the available 114 tests (76 fracture and 38 no injury) from 5 groups of experiments, survival analysis was carried out using 3 groups consisting of 62 tests (35 fracture and 27 no injury). Peak forces associated with 4 specific risk levels at 25, 45, and 65 years of age are given along with probability curves (mean and plus and minus 95% confidence intervals) for PMHS and normalized data applicable to male and female dummies. Quality indices increased (less tightness-of-fit) with decreasing age and risk level for all age groups and these data are given for all chosen risk levels. CONCLUSIONS: These PMHS-based probability distributions at different ages using information from different groups of researchers constituting the largest body of data can be used as human tolerances to lower leg injury from axial loading. Decreasing quality indices (increasing index value) at lower probabilities suggest the need for additional tests. The anthropometry-specific mid-size male and small-size female mean human risk curves along with plus and minus 95% confidence intervals from survival analysis and associated IRV data can be used as a first step in studies aimed at advancing occupant safety in automotive and other environments.

Oblique Loading in Post Mortem Human Surrogates from Vehicle Lateral Impact Tests using Chestbands.

While numerous studies have been conducted to determine side impact responses of Post Mortem Human Surrogates (PMHS) using sled and other equipment, experiments using the biological surrogate in modern full-scale vehicles are not available. The present study investigated the presence of oblique loading in moving deformable barrier and pole tests. Threepoint belt restrained PMHS were positioned in the left front and left rear seats in the former and left front seat in the latter condition and tested according to consumer testing protocols. Three chestbands were used in each specimen (upper, middle and lower thorax). Accelerometers were secured to the skull, shoulder, upper, middle and lower thoracic vertebrae, sternum, and sacrum. Chestband signals were processed to determine magnitudes and angulations of peak deflections. The magnitude and timing of various signal peaks are given. Vehicle accelerations, door velocities, and seat belt loads are also given. Analysis of deformation contours, peak deflections, and angulations indicated that the left rear seated specimen were exposed to anterior oblique loading while left front specimens in both tests sustained essentially pure lateral loading to the torso. These data can be used to validate human body computational models. The occurrence of oblique loading in full-scale testing, hitherto unrecognized, may serve to stimulate the exploration of its role in injuries to the thorax and lower extremities in modern vehicles. It may be important to continue research in this area because injury metrics have a lower threshold for angled loading.

Normalizing and scaling of data to derive human response corridors from impact tests.

It is well known that variability is inherent in any biological experiment. Human cadavers (Post-Mortem Human Subjects, PMHS) are routinely used to determine responses to impact loading for crashworthiness applications including civilian (motor vehicle) and military environments. It is important to transform measured variables from PMHS tests (accelerations, forces and deflections) to a standard or reference population, termed normalization. The transformation process should account for inter-specimen variations with some underlying assumptions used during normalization. Scaling is a process by which normalized responses are converted from one standard to another (example, mid-size adult male to large-male and small-size female adults, and to pediatric populations). These responses are used to derive corridors to assess the biofidelity of anthropomorphic test devices (crash dummies) used to predict injury in impact environments and design injury mitigating devices. This survey examines the pros and cons of different approaches for obtaining normalized and scaled responses and corridors used in biomechanical studies for over four decades. Specifically, the equal-stress equal-velocity and impulse-momentum methods along with their variations are discussed in this review. Methods ranging from subjective to quasi-static loading to different approaches are discussed for deriving temporal mean and plus minus one standard deviation human corridors of time-varying fundamental responses and cross variables (e.g., force-deflection). The survey offers some insights into the potential efficacy of these approaches with examples from recent impact tests and concludes with recommendations for future studies. The importance of considering various parameters during the experimental design of human impact tests is stressed.

Optimized lower leg injury probability curves from postmortem human subject tests under axial impacts.

OBJECTIVE: Derive optimum injury probability curves to describe human tolerance of the lower leg using parametric survival analysis. METHODS: The study reexamined lower leg postmortem human subjects (PMHS) data from a large group of specimens. Briefly, axial loading experiments were conducted by impacting the plantar surface of the foot. Both injury and noninjury tests were included in the testing process. They were identified by pre- and posttest radiographic images and detailed dissection following the impact test. Fractures included injuries to the calcaneus and distal tibia-fibula complex (including pylon), representing severities at the Abbreviated Injury Score (AIS) level 2+. For the statistical analysis, peak force was chosen as the main explanatory variable and the age was chosen as the covariable. Censoring statuses depended on experimental outcomes. Parameters from the parametric survival analysis were estimated using the maximum likelihood approach and the dfbetas statistic was used to identify overly influential samples. The best fit from the Weibull, log-normal, and log-logistic distributions was based on the Akaike information criterion. Plus and minus 95% confidence intervals were obtained for the optimum injury probability distribution. The relative sizes of the interval were determined at predetermined risk levels. Quality indices were described at each of the selected probability levels. RESULTS: The mean age, stature, and weight were 58.2±15.1 years, 1.74±0.08 m, and 74.9±13.8 kg, respectively. Excluding all overly influential tests resulted in the tightest confidence intervals. The Weibull distribution was the most optimum function compared to the other 2 distributions. A majority of quality indices were in the good category for this optimum distribution when results were extracted for 25-, 45- and 65-year-olds at 5, 25, and 50% risk levels age groups for lower leg fracture. For 25, 45, and 65 years, peak forces were 8.1, 6.5, and 5.1 kN at 5% risk; 9.6, 7.7, and 6.1 kN at 25% risk; and 10.4, 8.3, and 6.6 kN at 50% risk, respectively. CONCLUSIONS: This study derived axial loading-induced injury risk curves based on survival analysis using peak force and specimen age; adopting different censoring schemes; considering overly influential samples in the analysis; and assessing the quality of the distribution at discrete probability levels. Because procedures used in the present survival analysis are accepted by international automotive communities, current optimum human injury probability distributions can be used at all risk levels with more confidence in future crashworthiness applications for automotive and other disciplines.

Dynamic Responses of Intact Post Mortem Human Surrogates from Inferior-to-Superior Loading at the Pelvis.

During certain events such as underbody blasts due to improvised explosive devices, occupants in military vehicles are exposed to inferior-to-superior loading from the pelvis. Injuries to the pelvis-sacrum-lumbar spine complex have been reported from these events. The mechanism of load transmission and potential variables defining the migration of injuries between pelvis and or spinal structures are not defined. This study applied inferior-to-superior impacts to the tuberosities of the ischium of supine-positioned five post mortem human subjects (PMHS) using different acceleration profiles, defined using shape, magnitude and duration parameters. Seventeen tests were conducted. Overlay temporal plots were presented for normalized (impulse momentum approach) forces and accelerations of the sacrum and spine. Scatter plots showing injury and non-injury data as a function of peak normalized forces, pulse characteristics, impulse and power, loading rate and sacrum and spine accelerations were evaluated as potential metrics related to pathological outcomes with the focus of examining the role of the pulse characteristics from inferior-to-superior loading of the pelvis-sacrum-lumbar spine complex. Interrelationships were explored between non-fracture and fracture outcomes, and fracture patterns with a focus on migration of injuries from the hip-only to hip and spine to spine-only regions. Observations indicate that injury to the pelvis and or spine from inferior-to-superior loading is associated with pulse and not just peak velocity. The role of the effect of mass recruitment and injury migration parallel knee-thigh-hip complex studies, suggest a wider application of the recruitment concept and the role of the pulse characteristics.

Military boot attenuates axial loading to the lower leg.

Biomechanical tests to understand injury mechanisms and derive injury tolerance information using Post-Mortem Human Subjects (PMHS) have not used foot protection and they have primarily focused on civilian environments such as automotive and athletic- and sports-related events. As military personnel use boots, tests with the boot are required to understand their effect on attenuating lower leg loads. The purpose of this study was therefore, to determine the modulation of human lower leg kinematics with boot compressions and share of the force absorbed by the boot from underbody blast loading. Axial impacts were delivered to the Hybrid III dummy lower leg in the neutral position. The dummy leg was instrumented with its internal upper and lower tibia load cells, and in addition, a knee load cell was attached to the proximal end. Tests were conducted at 4.4 to 8.9 m/s, with and without boots, and repeat tests were done. Morphologies of the force-time responses were similar at the three load cell locations and for all input combinations and booted and unbooted conditions. However, booted tests resulted in considerably lower maximum forces (approximately two-third reduction) than unbooted tests. These results clearly show that boots can absorb a considerable share of the impact energy and decrease impact loads transmitted to the lower leg under vertical loading, thus necessitating the generation of tolerance data using PMHS for this environment.

A methodology to condition distorted acoustic emission signals to identify fracture timing from human cadaver spine impact tests.

While studies have used acoustic sensors to determine fracture initiation time in biomechanical studies, a systematic procedure is not established to process acoustic signals. The objective of the study was to develop a methodology to condition distorted acoustic emission data using signal processing techniques to identify fracture initiation time. The methodology was developed from testing a human cadaver lumbar spine column. Acoustic sensors were glued to all vertebrae, high-rate impact loading was applied, load-time histories were recorded (load cell), and fracture was documented using CT. Compression fracture occurred to L1 while other vertebrae were intact. FFT of raw voltage-time traces were used to determine an optimum frequency range associated with high decibel levels. Signals were bandpass filtered in this range. Bursting pattern was found in the fractured vertebra while signals from other vertebrae were silent. Bursting time was associated with time of fracture initiation. Force at fracture was determined using this time and force-time data. The methodology is independent of selecting parameters a priori such as fixing a voltage level(s), bandpass frequency and/or using force-time signal, and allows determination of force based on time identified during signal processing. The methodology can be used for different body regions in cadaver experiments.

Sensitivity and stability analysis of a nonlinear material model of cervical intervertebral disc under cyclic loads using the finite element method.

It is known that the human spine exhibits non-linear behavior, and its intervertebral discs play a role in the mechanism of internal load transfer. It is important to simulate its nonlinear behavior in computational models for better delineation of intrinsic responses, especially during cyclic loading activities, a mode pertinent to civilian and military populations. For developing a robust “material model” of the disc, this study used experimental tensile-compressive cyclic loading responses from four human cadaver cervical functional spinal units. Disc deformations were measured using an ultrasound system at 42 samples per second. Using experimental data, a three-network non-linear “material model” was developed using an optimization procedure and finite-element analysis. The model used 12 parameters to capture loading and unloading in tension and compression, including hysteresis. A sensitivity analysis performed to test the robustness of the “material model” indicated that seven of the 12 parameters were sensitive to tension, compressive, or both loading modes. Stability analysis was also performed under nine different loading conditions. The developed “material model” is robust and stable to capture intervertebral disc responses in tensile-compressive cyclic loading and can be used in future finite-element models.

Crash characteristics and injury patterns of restrained front seat occupants in far-side impacts.

OBJECTIVE: The study was conducted to determine the association between vehicle-, crash-, and demographic-related factors and injuries to front seat far-side occupants in modern environments. METHODS: Field data were obtained from the NASS-CDS database for the years 2009-2012. Inclusion factors included the following: adult restrained front outboard-seated occupants, no ejection or rollovers, and vehicle model years less than 10 years old at the time of crash. Far-side crashes were determined by using collision deformation classification. Injuries were scored using the Abbreviated Injury Scale (AIS). Injuries (MAIS 2+, MAIS 3+, M denotes maximum score) were examined based on demographics, change in velocity, vehicle type, direction of force, extent zone, collision partner, and presence of another occupant in the front seat. Only weighted data were used in the analysis. Injuries to the head and face, thorax, abdomen, pelvis, and upper and lower extremity regions were studied. Odds ratios and upper and lower confidence intervals were estimated from multivariate analysis. RESULTS: Out of 519,195 far-side occupants, 17,715 were MAIS 2+ and 4,387 were MAIS 3+ level injured occupants. The mean age, stature, total body mass, and body mass index (BMI) were 40.7 years, 1.7 m, 77.2 kg, and 26.8 kg/m2, respectively. Of occupants with MAIS 2+ injuries, 51% had head and 19% had thorax injuries. Of occupants with MAIS 3+ injuries, 50% had head and 69% had thorax injuries. The cumulative distribution of changes in velocities at the 50th percentile for the struck vehicle for all occupants and occupants with MAIS 2+ and MAIS 3+ injuries were 19, 34, and 42 km/h, respectively. Furthermore, 73% of MAIS 2+ injuries and 86% of MAIS 3+ injuries occurred at a change in velocity of 24 km/h or greater. Odds of sustaining MAIS 2+ and MAIS 3+ injuries increased with each unit increase in change in velocity, stature, and age, with one exception. Odds of sustaining injuries were higher with the presence of an occupant in the front seat at the MAIS 3+ level, although it was reversed at the lower level. The extent zone of 3+ increased the odds compared to the extent zones of 1 to 2 at both MAIS 2+ and MAIS 3+ injuries. Odds ratios and confidence intervals are given. CONCLUSIONS: The findings are as follows: head and thorax are the more frequently injured body regions, and the prevalence of cranium injuries is similar at both injury severities; thoracic injuries are more prevalent at the MAIS 3+ level; the presence of another front seat occupant plays a role in MAIS 3+ trauma; injuries continue to occur at changes in velocity representative of side impact environments; and mean demographic factors are close to mid-size automotive anthropometry, indicating the need to pursue this line of study. Because data were gathered from only 4 years, it would be important to include additional NASS-CDS database years, rescore injuries from previous years, and analyze other international databases to reinforce these findings for advancing safety for far-side occupants.

Biomechanics of human thoracolumbar spinal column trauma from vertical impact loading.

Recent studies suggest that dorsal spine injuries occur in motor vehicle crashes to restrained occupants. Compression/compression-flexion injuries occur in frontal crashes due to seat pan and vertical loading. While injuries, mechanisms and tolerances for neck injuries have been determined, thoraco-lumbar spine data are very limited. The objective of the study was to determine the biomechanical characteristics associated with such spinal injuries due to vertical loading. Upper thoracic (T2-T6), lower thoracic (T7-T11) and lumbar (T12-L5) columns from post mortem human surrogates were procured, fixed at the ends and dropped from three heights: the first two impacts designed as non-failure tests and the final was the failure test. Intermittent evaluations consisted of palpations and x-rays. Injuries were assessed using posttest x-rays and computed tomography scans. The age, stature, total body mass and body mass index of three PMHS were: 50 years, 164 cm, 66.9 kg, and 24.7 kg/m(2). The mean peak forces from 24 tests for the upper and lower thoracic and lumbar spines for varying drop heights ranged from 1.6 to 4.3, 1.3 to 5.1, and 1.3 to 6.7 kN, respectively. All peak forces increased with increasing drop heights. Injuries to the three spines included unstable vertebral body and posterior element (bipedicular and lamina) compression fractures and posterior complex disruptions. Logistic regression analysis indicated that peak forces of 3.4 and 3.7 kN are associated with 50% probability of fracture. These results indicate the initial tolerance limits of dorsal spines under vertical loading.

Oblique lateral impact biofidelity deflection corridors from Post Mortem Human Surrogates.

The objective of the study was to determine the thorax and abdomen deflection-time corridors in oblique side impacts. Data were analyzed from Post Mortem Human Surrogate (PMHS) sled tests, certain aspects of which were previously published. A modular and scalable anthropometry-specific segmented load-wall system was fixed to the platform of the sled. Region-specific forces were recorded from load cells attached to the load-wall plates. The thorax and abdomen regions were instrumented with chestbands, and deflection contours were obtained. Biomechanical responses were processed using the impulse-momentum normalization method and scaled to the mid-size male mass, 76-kg. The individual effective masses of the thorax and abdomen were used to determine the scale factors in each sled test, thus using the response from each experiment. The maximum deflections and their times of attainments were obtained, and mean and plus minus one standard deviation corridors were derived. Test-by-test thorax and abdomen force-time histories are given. Deflection-time histories for each specimen for the two body regions and corridors are presented. The mean maximum deflections for the thorax and abdomen body regions were 68.41 ± 16.1 and 68.98 ± 12.69 mm, respectively. Deflections were greater in oblique than pure lateral loading tests for both body regions, indicating the increased sensitivity of oblique side impact vector to the human response. The mean and one standard deviation responses of the thorax and abdomen serve as biofidelity corridors under oblique loading. Because modern instrumentation techniques can accommodate deflection sensors in the thorax and abdomen in devices such as WorldSID, and computer finite element models are flexible enough to extract regional and local deformation fields, the present data can be used to evaluate dummy biofidelity and validate and verify numerical models. They can be used to advance injury assessment reference values in oblique impacts.