Small Female Occupant Response in Reclined and Upright Seated Postures in Frontal Impacts.

The objective of this study was to compare the kinematics of the head-neck, torso, pelvis, and lower extremities and document injuries and their patterns to small female occupants in frontal impacts with upright and reclined postures using an experimental model. Six postmortem human surrogates (PMHS) with a mean stature of 154 ± 9.0 cm and mass of 49 ± 12 kg were equally divided between upright and reclined groups (seatback: 25 deg and 45 deg), restrained by a three-point integrated belt, positioned on a semirigid seat, and exposed to low and moderate crash velocities (15 km/h and 32 km/h respectively). The response between the upright and reclined postures was similar in magnitude and curve morphology. While none of the differences were statistically significant, the thoracic spine demonstrated increased downward (+Z) displacement, and the head demonstrated an increased horizontal (+X) displacement for the reclined occupants. In contrast, the upright occupants showed a slightly increased downward (+Z) displacement at the head, but the torso displaced primarily along the +X direction. The posture angles between the two groups were similar at the pelvis and different at the thorax and head. At 32 km/h, both cohorts exhibited multiple rib failure, with upright specimens having a greater number of severe fractures. Although MAIS was the same in both groups, the upright specimens had more bi-cortical rib fractures, suggesting the potential for pneumothorax. This preliminary study may be useful in validating physical (ATDs) and computational (HBMs) surrogates.

Three-Dimensional-Digital Image Correlation Methodology for Kinematic Measurements of Non-Penetrating Blunt Impacts.

Blunt force trauma remains a serious threat to many populations and is commonly seen in motor vehicle crashes, sports, and military environments. Effective design of helmets and protective armor should consider biomechanical tolerances of organs in which they intend to protect and require accurate measurements of deformation as a primary injury metric during impact. To overcome challenges found in velocity and displacement measurements during blunt impact using an integrated accelerometer and two-dimensional (2D) high-speed video, three-dimensional (3D) digital image correlation (DIC) measurements were taken and compared to the accepted techniques. A semispherical impactor was launched at impact velocities from 14 to 20 m/s into synthetic ballistic gelatin to simulate blunt impacts observed in behind armor blunt trauma (BABT), falls, and sports impacts. Repeated measures Analysis of Variance resulted in no significant differences in maximum displacement (p = 0.10), time of maximum displacement (p = 0.21), impact velocity (p = 0.13), and rebound velocity (p = 0.21) between methods. The 3D-DIC measurements demonstrated equal or improved percent difference and low root-mean-square deviation compared to the accepted measurement techniques. Therefore, 3D-DIC may be utilized in BABT and other blunt impact applications for accurate 3D kinematic measurements, especially when an accelerometer or 2D lateral camera analysis is impractical or susceptible to error.

Occupant Injury and Response on Oblique-Facing Aircraft Seats: A Computational Study.

Increased interest in the airline industry to enhance occupant comfort and maximize seating density has prompted the design and installation of obliquely mounted seats in aircraft. Previous oblique whole-body sled tests demonstrated multiple failures, chiefly distraction-associated spinal injuries under oblique impacts. The present computational study was performed with the rationale to examine how oblique loading induces component level responses and associated injury occurrence. The age-specific human body model (HBM) was simulated for two oblique seating conditions (with and without an armrest). The boundary conditions consisted of a 16 g standard aviation crash pulse, 45 deg seat orientation, and with restrained pelvis and lower extremities. The overall biofidelity rating for both conditions ranged from 0.5 to 0.7. The validated models were then used to investigate the influence of pulse intensity and seat orientation by varying the pulse from 16 g to 8 g and seat orientation from 0 deg to 90 deg. A total of 12 parametric simulations were performed. The pulse intensity simulations suggest that the HBM could tolerate 11.2 g without lumbar spine failure, while the possibility of cervical spine failure reduced with the pulse magnitude <9.6 g pulse. The seat orientation study demonstrated that for all seat angles the HBM predicted failure in the cervical and lumbar regions at 16 g; however, the contribution of the tensile load and lateral and flexion moments varied with respect to the change in seat angle. These preliminary outcomes are anticipated to assist in formulating safety standards and in designing countermeasures for oblique seating configurations.

Surface wave analysis of the skin for penetrating and non-penetrating projectile impact in porcine legs.

Secondary blast injuries may result from high-velocity projectile fragments which ultimately increase medical costs, reduce active work time, and decrease quality of life. The role of skin penetration requires more investigation in energy absorption and surface mechanics for implementation in computational ballistic models. High-speed ballistic penetration studies have not considered penetrating and non-penetrating biomechanical properties of the skin, including radial wave displacement, resultant surface wave speed, or projectile material influence. A helium-pressurized launcher was used to accelerate 3/8″ (9.525 mm) diameter spherical projectiles toward seventeen whole porcine legs from seven pigs (39.53 ± 7.28 kg) at projectile velocities below and above V50. Projectiles included a mix of materials: stainless steel (n = 26), Si3N4 (n = 24), and acetal plastic (n = 24). Tracker video analysis software was used to determine projectile velocity at impact from the perpendicular view and motion of the tissue displacement wave from the in-line view. Average radial wave displacement and surface wave speed were calculated for each projectile material and categorized by penetrating or non-penetrating impacts. Two-sample t-tests determined that non-penetrating projectiles resulted in significantly faster surface wave speeds in porcine skin for stainless steel (p = 0.002), plastic (p = 0.004), and Si3N4 ball bearings (p = 0.014), while ANOVA determined significant differences in radial wave displacement and surface wave speed between projectile materials. Surface wave speed was used to quantify mechanical properties of the skin including elastic modulus, shear modulus, and bulk modulus during ballistic impact, which may be implemented to simulate accurate deformation behavior in computational impact models.

Male and Female Cervical Spine Biomechanics and Anatomy: Implication for Scaling Injury Criteria.

There is an increased need to develop female-specific injury criteria and anthropomorphic test devices (dummies) for military and automotive environments, especially as women take occupational roles traditionally reserved for men. Although some exhaustive reviews on the biomechanics and injuries of the human spine have appeared in clinical and bioengineering literatures, focus has been largely ignored on the difference between male and female cervical spine responses and characteristics. Current neck injury criteria for automotive dummies for assessing crashworthiness and occupant safety are obtained from animal and human cadaver experiments, computational modeling, and human volunteer studies. They are also used in the military. Since the average human female spines are smaller than average male spines, metrics specific to the female population may be derived using simple geometric scaling, based on the assumption that male and female spines are geometrically scalable. However, as described in this technical brief, studies have shown that the biomechanical responses between males and females do not obey strict geometric similitude. Anatomical differences in terms of the structural component geometry are also different between the two cervical spines. Postural, physiological, and motion responses under automotive scenarios are also different. This technical brief, focused on such nonuniform differences, underscores the need to conduct female spine-specific evaluations/experiments to derive injury criteria for this important group of the population.

Cervical spine injuries, mechanisms, stability and AIS scores from vertical loading applied to military environments.

PURPOSE: The purpose of this study was to determine injuries to osteo-ligamentous structures of cervical column, mechanisms, forces, severities and AIS scores from vertical accelerative loading. METHODS: Seven human cadaver head-neck complexes (56.9 ± 9.5 years) were aligned based on seated the posture of military soldiers. Army combat helmets were used. Specimens were attached to a vertical accelerator to apply caudo-cephalad g-forces. They were accelerated with increasing insults. Intermittent palpation and radiography were done. A roof structure mimicking military vehicle interior was introduced after a series of tests and experiments were conducted following similar protocols. Upon injury detection, CT and dissection were done. Temporal force responses were extracted, peak forces and times of occurrence were obtained, injury severities were graded, and spine stability was determined. RESULTS: Injuries occurred in tests only when the roof structure was included. Responses were tri-phasic: initial thrust, secondary tensile, tertiary roof contact phases. Peak forces: 1364-4382 N, initial thrust, 165-169 N, secondary tensile, 868-3368 N tertiary helmet-head roof contact phases. Times of attainments: 5.3-9.6, 31.7-42.6, 55.0-70.8 ms. Injuries included fractures and joint disruptions. Multiple injuries occurred in all but one specimen. A majority of injury severities were AIS = 2. Spines were considered unstable in a majority of cases. CONCLUSIONS: Spine response was tri-phasic. Injuries occurred in roof contact tests with the helmeted head-neck specimen. Multiplicity and unstable nature of AIS = 2 level injuries, albeit at lower severities, might predispose the spine to long-term accelerated degenerative changes. Clinical protocols should include a careful evaluation of sub-catastrophic injuries in military patients.

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.

Evaluation of synthetic clear gelatin as an acceptable surrogate for low-velocity penetrating impacts using the depth of penetration calibration standard.

Ballistic gelatin has been extensively used in ballistics research for decades, but calibration standards were established on limited datasets, and only few studies have attempted to recreate these experiments with biological tissues. Recent studies have demonstrated better biofidelity with 20% ordnance ballistic gelatin, but researchers have discredited the use of synthetic gelatin claiming different behavior than ordnance gelatin. To investigate the use of synthetic clear gelatin as an acceptable surrogate of biological tissue, depth of penetration was compared between low-velocity impacts of various projectiles into porcine tissue (n = 192), post-mortem human subjects (n = 29), and Clear Ballistics synthetic gelatin (n = 39). The predicted depth of penetration of the 0.177" steel BB (38.1 mm) was consistent with the manufacturer's calibration standard (31.75-44.45 mm) and within calibration bounds of recently proposed empirical equations. Compared to impacts in biological tissue, synthetic gelatin demonstrated the least variability in depth of penetration (R2 = 0.96). Using ANCOVA, velocity was a significant covariate (p < 0.001), and there were no significant differences in normalized depth of penetration over density between porcine tissue, post-mortem human subjects, and 20% synthetic gelatin (p = 0.22). Ultimately, this study confirmed the use of 20% synthetic gelatin as an acceptable tissue simulant using standard calibration methods for use in future ballistic studies.

Penetration Thresholds of Porcine Limbs for Low Sectional Density Projectiles in High-Rate Impact.

INTRODUCTION: With similar prevalence to injuries from fires, stings, and natural disasters, soft tissue injuries may occur from fireworks, industrial accidents, or other explosives. Surgeons are less familiar with treating high-velocity penetration from small debris, which may increase the chance of infection and subsequent fatality. Penetration risk curves have been developed to predict V50, the velocity with 50% probability of penetration, for various sized projectiles. However, there has been limited research using nonmetallic materials to achieve lower density projectiles less than 1 g cm-2, such as sand or rocks. MATERIAL AND METHODS: To emulate the size and density of these energized particles, 14 ball bearings of stainless steel, silicon nitride, or Delrin acetal plastic ranging from 1.59 mm (1/16") to 9.53 mm (3/8") with sectional densities between 0.3 g cm-2 and 5 g cm-2 were launched toward porcine legs at a range of velocities to determine the penetration thresholds. High-speed videography was captured laterally at 40 kHz and impact velocity was captured using a physics-based tracking software. A generalized linear model with repeated measures and a logit link function was used to predict probability of penetration for each projectile. A total of 600 impacts were conducted to achieve at least 15 penetrating impacts for each projectile over a range of velocities. RESULTS: Higher impact velocities were required to penetrate the skin as sectional density of the projectile decreased, and the relationship between velocity and sectional density exhibited an exponential relationship (V50, $ = 184.6*S{D^{ - 0.385}}$, R2 = 0.95) with substantial change for nonlinearity in sectional densities ranging from 0.3 g cm-2 to 1 g cm-2. Compared to previous studies, the empirical relationship was consistent in the linear region (2-5 g cm-2), and novel experimentation filled in the gaps for sectional densities less than 1 g cm-2, which expressed more nonlinearity than previously estimated. For low-density projectiles with diameters of 1.59 (1/16") or 3.18 (1/8"), 32 impacts were lodged into the epidermis but did not penetrate through the dermis; however, penetration was defined as displacement into or through the dermis. CONCLUSIONS: These experimental results may be used to develop and validate finite element simulations of low-density projectile impacts to address complex, multivariate loading conditions for the development of protective clothing to reduce wounding and subsequent infection rates.

In vitro skin puncture methodology for material characterization.

Quantifying the mechanical behavior of skin has been foundational in applications of cosmetics, surgical techniques, forensic science, and protective clothing development. However, previous puncture studies have lacked consistent and physiological boundary conditions of skin. To determine natural skin tension, excision of in situ porcine skin resulted in significantly different diameter reduction (shrinkage) in leg (19.5 %) and abdominal skin (38.4 %) compared to flank skin (28.5 %) (p = 0.047). To examine effects of initial tension and pre-conditioning, five conditions of initial tension (as percentage of diameter increase) and pre-conditioning were tested in quasistatic puncture with a 5 mm spherical impactor using an electrohydraulic load frame and custom clamping apparatus. Samples with less than 5 % initial tension resulted in significantly greater (p = 0.011) force at failure (279.2 N) compared to samples with greater than 25 % initial tension (195.1 N). Eight pre-conditioning cycles of 15 mm displacement reduced hysteresis by 45 %. The coefficient of variance was substantially reduced for force, force normalized by cutis thickness, displacement, stiffness, and strain energy up to 46 %. Pre-conditioned samples at physiological initial tension (14-25 %) resulted in significantly greater (p = 0.03) normalized forces at failure (278.3 N/mm) compared to non-conditioned samples of the same initial tension (234.4 N/mm). Pre-conditioned samples with 14-25 % initial tension, representing physiological boundary conditions, resulted in the most appropriate failure thresholds with the least variation. For in vitro puncture studies, the magnitude of applied initial tension should be defined based on anatomical location, through a shrinkage experimentation, to match natural tension of skin. Characterizing the biological behavior and tolerances of skin may be utilized in finite element models to aid in protective clothing development and forensic science analyses.

Sex-related disparities in vehicle crash injury and hemodynamics.

Objective: Multiple studies evaluate relative risk of female vs. male crash injury; clinical data may offer a more direct injury-specific evaluation of sex disparity in vehicle safety. This study sought to evaluate trauma injury patterns in a large trauma database to identify sex-related differences in crash injury victims. Methods: Data on lap and shoulder belt wearing patients age 16 and up with abdominal and pelvic injuries from 2018 to 2021 were extracted from the National Trauma Data Bank for descriptive analysis using injuries, vital signs, International Classification of Disease (ICD) coding, age, and injury severity using AIS (Abbreviated Injury Scale) and ISS (Injury Severity Score). Multiple linear regression was used to assess the relationship of shock index (SI) and ISS, sex, age, and sex*age interaction. Regression analysis was performed on multiple injury regions to assess patient characteristics related to increased shock index. Results: Sex, age, and ISS are strongly related to shock index for most injury regions. Women had greater overall SI than men, even in less severe injuries; women had greater numbers of pelvis and liver injuries across severity categories; men had greater numbers of injury in other abdominal/pelvis injury regions. Conclusions: Female crash injury victims' tendency for higher (AIS) severity of pelvis and liver injuries may relate to how their bodies interact with safety equipment. Females are entering shock states (SI > 1.0) with lesser injury severity (ISS) than male crash injury victims, which may suggest that female crash patients are somehow more susceptible to compromised hemodynamics than males. These findings indicate an urgent need to conduct vehicle crash injury research within a sex-equity framework; evaluating sex-related clinical data may hold the key to reducing disparities in vehicle crash injury.

Expanded Combined Loading Injury Criterion for the Human Lumbar Spine Under Dynamic Compression.

Contemporary injury tolerance of the lumbar spine for under-body blast references axial compression and bending moments in a limited range. Since injuries often occur in a wider range of flexion and extension with increased moment contribution, this study expands a previously proposed combined loading injury criterion for the lumbar spine. Fifteen cadaveric lumbar spine failure tests with greater magnitudes of eccentric loading were incorporated into an existing injury criterion to augment its applicability and a combined loading injury risk model was proposed by means of survival analysis. A loglogistic distribution was the most representative of injury risk, resulting in optimized critical values of Fr,crit = 6011 N, and My,crit = 904 Nm for the proposed combined loading metric. The 50% probability of injury resulted in a combined loading metric value of 1, with 0.59 and 1.7 corresponding to 5 and 95% injury risk, respectively. The inclusion of eccentric loaded specimens resulted in an increased contribution of the bending moment relative to the previously investigated flexion/extension range (previous My,crit = 1155 Nm), with the contribution of the resultant sagittal force reduced by nearly 200 N (previous Fr,crit = 5824 N). The new critical values reflect an expanded flexion/extension range of applicability of the previously proposed combined loading injury criterion for the human lumbar spine during dynamic compression.

Analysis of experimental injuries to obese occupants with different postures in frontal impact.

The objective of the present study was to analyze injuries and their patterns to obese occupants in frontal impacts with upright and reclined postures using experimental data. Twelve obese post-mortem human subjects (PMHS) were positioned on a sled buck with seatback angles of 250 or 450 from the vertical, termed as upright and reclined postures. They were restrained with a seat belt and pretensioner. Frontal impact tests were conducted at 8.9 or 13.9 m/s, termed as low and high velocities. After the test, x-rays and CTs were taken, and an autopsy was conducted. The Maximum AIS (MAIS) and Injury Severity Score (ISS) were calculated, and injury patterns were analyzed. The mean age, stature, total body mass, and body mass indexes were 67 years, 112 kg, and 1.7 m, and 38 kg/m2. None of these parameters were statistically significantly different between any groups. The mean thickness of the soft tissues in the left anterior lateral, central, and right anterior lateral aspects were 44 mm, 24 mm, and 46 mm. In the low-velocity tests, the ISS data were 9, 18, and 9 for the upright, and 9, 9, and 4 for the reclined specimens, and in the high velocity tests, they were 29, 17, and 27 for the upright, and 27, 13, and 27 for the reclined postures. Other data are given in the paper. For both postures at the low velocity, injuries were concentrated at one body region, and the ISS data were in the mild category; in contrast, at the high velocity, other body regions also sustained injuries, and the ISS data were in the major trauma category. From MAIS perspectives, injuries to obese occupants did not change between postures and were independent of the energy input to the system. The association of chest with pelvis injuries in upright and reclined postures to obese occupants may have additional consequences following the initial injury to this group of our population.

Effect of muscle activation scheme in human head-neck model on estimating cervical spine ligament strain from military volunteer frontal impact data.

Cervical spine (c-spine) injuries are a common injury during automobile crashes. The objective of this study is to verify an existing head-neck (HN) finite element model with military volunteer frontal impact kinematics by varying the muscle activation scheme from previous literature. Proper muscle activation will allow for accurate percent elongation (strain) of the c-spine ligaments and will serve to establish ligamentous response during non-injury frontal impacts. Previous human research volunteer (HRV) frontal impact sled tests reported kinematic data that served as the input for HN model simulation. Peak sled acceleration (PSA) was varied between 10G and 30G for HRVs. Muscle activation was shifted to begin at 0 ms at start of impact to allow for proper muscle contraction in the HN model. Then, extensor muscle activation magnitude was varied between 20 and 100% to determine the proper activation necessary to match kinematic outputs from the model with experimental results. The model was validated against 10G test recorded response. Ligament strain was measured from multiple ligaments along the c-spine once the model was verified. The 40% activated extensor muscle scheme was deemed the most biofidelic, with CORA scores of 0.743 and 0.686 for head X linear acceleration and angular Y acceleration for 10G pulse. All PSA groups scored well with this muscle activation. Most ligaments were buffered well by the active simulation, with only the interspinous ligament nearing physiologic injury. With the HN model verified against additional kinematic data, simulations with higher accelerations to predict areas of injury in real life crash scenarios are possible.

Comparison of Axial Force Attenuation Characteristics in Two Different Lower Extremity Anthropomorphic Test Devices.

INTRODUCTION: Any type of boot or footwear is designed to attenuate and distribute loading to the bottom of the foot. Anthropomorphic test device (ATDs) are used to assess potential countermeasures against these loads. The specific aims of this study were to compare and quantify force attenuation characteristics as a function of input energy for Hybrid-III and Mil-Lx ATD human surrogates. MATERIALS AND METHODS: Two lower leg ATD surrogates (Mil-Lx and Hybrid-III) were tested to investigate the influence of a commercially available military boot on lower extremity force response and assess such differences against previously published postmortem human surrogate studies. The testing apparatus impacted the bottom of the foot using a rigid plate at velocities from 2 to 10 m/s. Tests were conducted on each ATD to obtain axial force response with and without boots as a function of input energy. RESULTS: Peak forces ranged from 1 to 16.4 kN for the Hybrid-III, and 1 to 8.4 kN for the Mil-Lx for similar input conditions. The average force attenuation for the Hybrid-III at upper and lower load cells was 71% (59%-80%) and 70% (58%-78%). The average attenuation for the Mil-Lx at upper and lower load cells was 20% (13%-28%) and 37% (36%-37%), respectively. At the knee load cell, the attenuated peak loads ranged from 62% to 81% for the Hybrid-III and 16% to 30% for the Mil-Lx. CONCLUSIONS: Force attenuation characteristics in the booted vs unbooted configuration of the Mil-Lx were significantly different than force attenuation characteristics of the H3 and may better represent in vivo forces during vertical impact injuries, such as IED blasts. Hence for military relevant applications where boots are used, the Mil-Lx may provide a more conservative evaluation of lower extremity protection systems.

Pelvis-Sacrum-Lumbar Spine Injury Characteristics From Underbody Blast Loading.

INTRODUCTION: Combat-related injuries from improvised explosive devices occur commonly to the lower extremity and spine. As the underbody blast impact loading traverses from the seat to pelvis to spine, energy transfer occurs through deformations of the combined pelvis-sacrum-lumbar spine complex, and the time factor plays a role in injury to any of these components. Previous studies have largely ignored the role of the time variable in injuries, injury mechanisms, and warfighter tolerance. The objective of this study is to relate the time or temporal factor using a multi-component, pelvis-sacrum-lumbar spinal column complex model. MATERIALS AND METHODS: Intact pelvis-sacrum-spine specimens from pre-screened unembalmed human cadavers were prepared by fixing at the superior end of the lumbar spine, pelvis and abdominal contents were simulated, and a weight was added to the cranial end of the fixation to account for torso effective mass. Prepared specimens were placed on the platform of a custom vertical accelerator device and aligned in a seated soldier posture. An accelerometer was attached to the seat platen of the device to record the time duration to peak velocity. Radiographs and computed tomography images were used to document and associate injuries with time duration. RESULTS: The mean age, stature, weight, body mass index, and bone density of 12 male specimens were as follows: 65 ± 11 years, 1.8 ± 0.01 m, 83 ± 13 kg, 27 ± 5.0 kg/m2, and 114 ± 21 mg/cc. They were equally divided into short, medium, and long time durations: 4.8 ± 0.5, 16.3 ± 7.3, and 34.5 ± 7.5 ms. Most severe injuries associated with the short time duration were to pelvis, although they were to spine for the long time duration. CONCLUSIONS: With adequate time for the underbody blast loading to traverse the pelvis-sacrum-spine complex, distal structures are spared while proximal/spine structures sustain severe/unstable injuries. The time factor may have implications in seat and/or seat structure design in future military vehicles to advance warfighter safety.

Temporal corridors of forces and moments, and injuries to pelvis-lumbar spine in vertical impact simulating underbody blast.

Pelvis and lumbar spine fractures occur in falls, motor vehicle crashes, and military combat events. They are attributed to vertical impact from the pelvis to the spine. Although whole-body cadavers were exposed to this vector and injuries were reported, spinal loads were not determined. While previous studies determined injury metrics such as peak forces using isolated pelvis or spine models, they were not conducted using the combined pelvis-spine columns, thereby not accounting for the interaction between the two body regions. Earlier studies did not develop response corridors. The study objectives were to develop temporal corridors of loads at the pelvis and spine and assess clinical fracture patterns using a human cadaver model. Vertical impact loads were delivered at the pelvic end to twelve unembalmed intact pelvis-spine complexes, and pelvis forces and spinal loads (axial, shear and resultant and bending moments) were obtained. Injuries were classified using clinical assessments from post-test computed tomography scans. Spinal injuries were stable in eight and unstable in four specimens. Pelvis injuries included ring fractures in six and unilateral pelvis in three, sacrum fractures in ten, and two specimens did not sustain any injuries to the pelvis or sacrum complex. Data were grouped based on time to peak velocity, and ± one standard deviation corridors about the mean of the biomechanical metrics were developed. Time-history corridors of loads at the pelvis and spine, hitherto not reported in any study, are valuable to assess the biofidelity of anthropomorphic test devices and assist validating finite element models.

Influence of bending pre-load on the tensile response of the lumbar spine.

Previous full body cadaver testing has shown that both obliquely oriented seats in survivable aircraft crashes and far-side oblique crashes in vehicles present distinctive occupant kinematics that are not yet well understood. Knowledge surrounding how these loading scenarios affect the lumbar spine is particularly lacking as there exists minimal research concerning oblique loading. The current study was created to evaluate a novel experimental method through comparison with existing literature, and to examine the impact of a static bending pre-load (posture) on the load-displacement response for the whole lumbar spine loaded in non-destructive axial distraction. T12-S1 lumbar spines were tested in tension to 4 mm of displacement while positioned in one of three pre-load postures. These postures were: the spine's natural, unloaded curvature (neutral), flexed forward (flexed), and combined flexion and lateral bending (oblique). Deviations from a neutral spine position were shown to significantly increase peak loads and tensile stiffness. The presence of a flexion pre-load caused statistically significant increases in tensile stiffness, tensile force, and bending moments. The addition of a lateral bending pre-load to an already flexed spine did not significantly alter the tensile response. However, the flexion moment response was significantly affected by the additional postural pre-load. This work indicates that the initial conditions of distraction loading significantly affect lumbar spine load response. Therefore, future testing that seeks to emulate crash dynamics of obliquely seated occupants must account for multi-axis loading.

Cervical spine degeneration specific segmental angular rotational and displacements: A quantitative study.

BACKGROUND: The objective of the present isolated spine study was to evaluate the kinematic differences between groups of normal and degenerated cervical spine specimens. Previous studies on cervical spine degeneration support the existence of the unstable phase during the degeneration process; however, there is a lack of quantitative data available to fully characterize this early stage of degeneration. METHOD: For this effort five degenerated and eight normal cervical spines (C2-T1) were isolated and were subject to pure bending moments of flexion, extension, axial rotation and lateral bending. The specimen quality was assessed based on the grading scale. In the present study, the degeneration was at the C5-C6 level. A four-camera motion analysis system was used to measure the overall primary and segmental motions. FINDING: In the extension mode, the degenerated group demonstrated a significant larger angular rotation as well as antero-posterior displacement at the degenerated level (C5-C6). In contrast, in flexion mode, the degenerated group measured a drastic decrease in angular rotation, at the adjacent level (C6-C7). In other modes of loading as well as in other segmental levels, the degenerated group had similar segmental motion as the normal group. INTERPRETATION: These preliminary results provide single level degeneration specific cervical spine kinematics. The finding demonstrates the influence of degeneration on the kinematics of the normal sub adjacent segment. The degenerated group observed larger translation displacement in the extension mode, which would potentially be a critical parameter in assisting early detection of cervical spine spondylosis with just a functional X-ray scan.

Comparison of small female occupant model responses with experimental data in a reclined posture.

Objective: The objective of the current study was to compare the GHBMC female model responses with in-house sled test data for three small female post mortem human surrogates (PMHS) at 32 km/h and a seatback recline angle of 45 degrees. The kinematics and the seatbelt forces were used to compare the female PMHS and model responses. The study aimed to identify updates that may be needed to the model.Methods: In-house experimental sled test kinematic and seatbelt response data for the small females were obtained. The 5th female GHBMC was simulated with the same boundary conditions as in the experiments. In addition, using the PMHS computed tomography (CT) and test environment scans, the female model geometry was updated to a subject-specific model for one of the specimens, and the models were simulated to obtain 5th female and subject-specific model responses. The kinematic response and the seatbelt forces for the two models were compared with the average of the three experimental data.Results: The head, T8 and L4 excursions, head and pelvis accelerations and seatbelt forces for the two female models were compared with the experimental data. The model responses were in agreement with the PMHS; however, the subject-specific model showed a closer agreement with the kinematic response. The subject-specific model did not submarine as in the experiments, whereas the 5th female model submarined. However, the subject-specific model showed 20% higher seatbelt forces than the PMHS.Conclusion: This study showed that anthropometric differences may significantly alter occupant kinematics in reclined posture and need to be incorporated to investigate kinematics and injury mechanisms. The next step of the study involves incorporating age-specific material changes and investigating the subject-specific injury mechanisms. The results will be useful to develop countermeasures for autonomous vehicles.