Destruction mechanism of anterior cervical discectomy and fusion in frontal impact.

The aim of this study was to quantitatively study the effect of anterior cervical discectomy and fusion (ACDF) on the risk of spinal injury under frontal impact. A head-neck finite element model incorporating active neck muscles and soft tissues was developed and validated. Based on the intact head-neck model, three ACDF models (single-level, two-level and three-level) were used to analyze the frontal impact responses of the head-neck. The results revealed that various surgical approaches led to distinct patterns of vertebral damage under frontal impact. For single-level and three-level ACDFs, vertebral destruction was mainly concentrated at the lower end of the fused segment, while the other vertebrae were not significantly damaged. For two-level ACDF, the lowest vertebra was the first to suffer destruction, followed by severe damage to both the upper and lower vertebrae, while the middle vertebra of the cervical spine exhibited only partial damage around the screws. Fusion surgery for cervical spine injuries predominantly influences the vertebral integrity of the directly fused segments when subjected to frontal impact, while exerting a comparatively lesser impact on the cross-sectional properties of adjacent, non-fused segments.

Lumbar and neck injuries of occupants in different reclining postures.

PURPOSE: With the increasing level of automation in automobiles, the advent of autonomous vehicles has reduced the tendency of drivers and passengers to focus on the task of driving. The increasing automation in automobiles reduced the drivers' and passengers' focus on driving, which allowed occupants to choose a more relaxed and comfortable sitting position. Meanwhile, the occupant's sitting position went from a frontal, upright position to a more relaxed and reclined one, which resulted in the existing restraint systems cannot to keep occupants safe and secure. This study aimed to determine the effects of different reclining states on occupants' lumbar and neck injuries. METHODS: This is an original research on the field of automotive safety engineering. Occupants in different initial sitting positions (25°, 35°, 45°, and 55°) were adapted to changes in seat back angle and restraint systems and placed in the same frontal impact environment. Neck injury indexes, lumbar axial compression force and acceleration, as well as occupant dynamic response during the impact, were compared in different sitting positions. The injury response and kinematic characteristics of occupants in different reclining positions were analyzed by the control variable method. RESULTS: As the sitting angle increased, the occupant's head acceleration decreased, and the forward-lean angle decreased. Occupants in the standard sitting position had the greatest neck injury, with an Nij of 0.95, and were susceptible to abbreviated injury scale 2+ cervical medullary injuries. As the seatback angle increased, the geometric position of the lumbar spine tended to be horizontal, and the impact load transmitted greater forces to the lumbar spine. The occupant's lumbar injury was greatest in the lying position, with a peak axial compression force on the lumbar region of 5.5 KN, which was 2.3 KN greater than in the standard sitting position. CONCLUSION: The study of occupant lumbar and neck injuries based on different recline states can provide a theoretical basis for optimizing lumbar evaluation indexes, which is conducive to the understanding of the lumbar injury mechanism and the comprehensive consideration of occupant safety protection.

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.

IIHS small overlap frontal crash test ratings and real-world driver death risk.

OBJECTIVE: To evaluate how ratings for the Insurance Institute for Highway Safety (IIHS) driver-side small-overlap frontal crash test predict real-world driver death risk in frontal impacts. METHODS: IIHS released the driver-side small-overlap frontal crash test in 2012, after manufacturers had improved vehicle designs to make good ratings in the IIHS moderate overlap frontal crash test virtually ubiquitous. In the small overlap test, the vehicle impacts a rigid barrier at 40 mph (64 km/h) with 25% of the vehicle's width overlapping the barrier. As in other IIHS tests, vehicles are rated as good, acceptable, marginal, or poor. Drivers' risk of dying in a frontal crash was estimated by dividing driver deaths by driver involvements in police-reported crashes and modeling with logistic regression to estimate the effect of crash test rating, while controlling for driver age and sex, vehicle type and curb weight, and number of vehicles in the crash. RESULTS: Drivers of good-rated vehicles were 12% less likely to die in frontal impacts than drivers of poor-rated vehicles. This estimate was 11% for acceptable-rated vehicles and 5% (not statistically significant) for marginal-rated vehicles, compared with vehicles rated poor. CONCLUSIONS: The current study demonstrates that the IIHS driver-side small-overlap crash test rating encourages vehicle designs that reduce drivers' real-world risk of dying in frontal crashes.

Effect of hip flexion angle on lower limb injuries of occupants in autonomous vehicle crashes.

This study aims to determine the influence of the hip flexion angle on the injury trends of lower limbs. An impact model was established using a hybrid human body model and an accurate vehicle model. Simulations were performed in two boundary environments of 25 and 40% overlap impacts under different hip flexion angles. The analysis of the dynamic responses indicated that the hip flexion angle significantly affected the injury trends. The maximum femur index of different overlaps was all found at the minimum hip angle, except for the left femur at 25% overlap rate. Meanwhile, the maximum acetabular stress was all found at the minimum hip angle (approximately 0.09-0.20 GPa). This study provides mechanistic insights into the lower limb injuries associated with complex human postures.

Study on the influence of seating orientation during frontal impacts by child occupant human body model response analysis.

OBJECTIVE: Autonomous driving cars must be developed to ensure that children will have the highest level of protection in case of collision. Changes to the vehicle cabin design (different seat orientations, fully reclining seats, etc.) may significantly impact child occupant safety. Understanding child occupant responses under these new conditions is necessary to decrease risk and enhance child safety. In this study, child occupant response in different seating orientations exposed to frontal impacts with a focus on the head injuries and kinematics was analyzed. METHODS: Finite elements simulations were performed using the PIPER 6-year-old human body model (HBM). All simulations were carried out in a generic full vehicle environment. The child model was positioned in an adequate generic car restraint system (CRS) in the left rear vehicle seat in 4 seating orientations: 0° (forward-facing position), 30°, 60°, and 90° (living room position). Two scenarios were evaluated for all seating orientations according to the left front seat backrest position: reclined position nominal upright and rest position (55°). All seat configurations were subjected to the mobile progressive deformable barrier frontal impact (European New Car Assessment Programme [Euro NCAP] frontal impact testing protocol). A total of 8 scenarios were simulated in LS-DYNA. RESULTS: Based on the Euro NCAP injury risk rate, 90° seating orientation (living room position) was the safest among all selected scenarios independent of the left front seat backrest position. The worst case was found in 60° seat rotation. The highest values for Head Injury Criterion (HIC) and head acceleration (Acc 3 ms) were noted for this case. Higher Brain Injury Criterion (BrIC) values were observed at higher seat rotation angles. Hence, a 90° seating orientation showed the highest BrIC value. Attending to the skull stress, greater head injuries were caused principally by contact with the vehicle interior (seat headrest). Maximum stress values were reached at 30° and 60° seating orientations with the front seat in rest position. In 90° seating orientation, high stress values were also identified. CONCLUSIONS: These results show that attending to these new seating orientations, current child safety standards are not sufficient to ensure children the highest level of protection. Other additional criteria such as BrIC or skull stress that offer a way to capture brain injuries should be used.

A Comparison of the Mid-Size Male THOR and Hybrid III ATDs in Vehicle Frontal Crash Tests.

In order to evaluate the THOR-50M as a front impact Anthropomorphic Test Device (ATD) for vehicle safety design, the ATD was compared to the H3-50M in matching vehicle crash tests for 20 unique vehicle models from 2 vehicle manufacturers. For the belted driver condition, a total of fifty-four crash tests were investigated in the 56.3 km/h (35 mph) front rigid barrier impact condition. Four more tests were compared for the unbelted driver and right front passenger at 40.2 km/h (25 mph) in the flat frontal and 30-degree right oblique rigid barrier impact conditions. The two ATDs were also evaluated for their ability to predict injury risk by comparing their fleet average injury risk to Crash Investigation Sampling System (CISS) accident data for similar conditions. The differences in seating position and their effect on ATD responses were also investigated. This study showed that the belted THOR-50M injury responses were higher than the H3-50M by 25%-180%, in all reported ATD responses, except chest acceleration. For one unbelted condition, the THOR-50M reported 200%-300% higher neck responses than the H3-50M, primarily due to head contact to the roof structure in a mid-sized sedan. The THOR-50M overpredicted the injury risk based on chest deflection compared to the CISS accident data by at least a factor of 4 times. The THOR-50M also overpredicted the injury risk based on BrIC by at least a factor of 10 times. Future work is needed to investigate these overpredictions with respect to ATD construction, injury risk curves, and seating procedures.

Sex, Age and Stature Affects Neck Biomechanical Responses in Frontal and Rear Impacts Assessed Using Finite Element Head and Neck Models.

The increased incidence of injury demonstrated in epidemiological data for the elderly population, and females compared to males, has not been fully understood in the context of the biomechanical response to impact. A contributing factor to these differences in injury risk could be the variation in geometry between young and aged persons and between males and females. In this study, a new methodology, coupling a CAD and a repositioning software, was developed to reposture an existing Finite element neck while retaining a high level of mesh quality. A 5th percentile female aged neck model (F0575YO) and a 50th percentile male aged neck model (M5075YO) were developed from existing young (F0526YO and M5026YO) neck models (Global Human Body Models Consortium v5.1). The aged neck models included an increased cervical lordosis and an increase in the facet joint angles, as reported in the literature. The young and the aged models were simulated in frontal (2, 8, and 15 g) and rear (3, 7, and 10 g) impacts. The responses were compared using head and relative facet joint kinematics, and nominal intervertebral disc shear strain. In general, the aged models predicted higher tissue deformations, although the head kinematics were similar for all models. In the frontal impact, only the M5075YO model predicted hard tissue failure, attributed to the combined effect of the more anteriorly located head with age, when compared to the M5026YO, and greater neck length relative to the female models. In the rear impacts, the F0575YO model predicted higher relative facet joint shear compared to the F0526YO, and higher relative facet joint rotation and nominal intervertebral disc strain compared to the M5075YO. When comparing the male models, the relative facet joint kinematics predicted by the M5026YO and M5075YO were similar. The contrast in response between the male and female models in the rear impacts was attributed to the higher lordosis and facet angle in females compared to males. Epidemiological data reported that females were more likely to sustain Whiplash Associated Disorders in rear impacts compared to males, and that injury risk increases with age, in agreement with the findings in the present study. This study demonstrated that, although the increased lordosis and facet angle did not affect the head kinematics, changes at the tissue level were considerable (e.g., 26% higher relative facet shear in the female neck compared to the male, for rear impact) and relatable to the epidemiology. Future work will investigate tissue damage and failure through the incorporation of aged material properties and muscle activation.

Comparison of Upper Neck Loading in Young Adult and Elderly Volunteers During Low Speed Frontal Impacts.

Cervical pain and injuries are a major health problem globally. Existing neck injury criteria are based on experimental studies that included sled tests performed with volunteers, post-mortem human surrogates and animals. However, none of these studies have addressed the differences between young adults and elderly volunteers to date. Thus, this work analyzed the estimated axial and shear forces, and the bending moment at the craniocervical junction of nine young volunteers (18-30 years old) and four elderly volunteers (>65 years old) in a low-speed frontal deceleration. Since the calculation of these loads required the use of the mass and moment of inertia of the volunteers' heads, this study proposed new methods to estimate the inertial properties of the head of the volunteers based on external measurements that reduced the error of previously published methods. The estimated mean peak axial force (Fz) was -164.38 ± 35.04 N in the young group and -170.62 ± 49.82 N in the elderly group. The average maximum shear force (Fx) was -224.42 ± 54.39 N and -232.41 ± 19.23 N in the young and elderly group, respectively. Last, the estimated peak bending moment (My) was 13.63 ± 1.09 Nm in the young group and 14.81 ± 1.36 Nm in the elderly group. The neck loads experienced by the elderly group were within the highest values in the present study. Nevertheless, for the group of volunteers included in this study, no substantial differences with age were observed.

How muscle stiffness affects human body model behavior.

BACKGROUND: Active human body models (AHBM) consider musculoskeletal movement and joint stiffness via active muscle truss elements in the finite element (FE) codes in dynamic application. In the latest models, such as THUMS™ Version 5, nearly all human muscle groups are modeled in form of one-dimensional truss elements connecting each joint. While a lot of work has been done to improve the active and passive behavior of this 1D muscle system in the past, the volumetric muscle system of THUMS was modeled in a much more simplified way based on Post Mortem Human Subject (PMHS) test data. The stiffness changing effect of isometric contraction was hardly considered for the volumetric muscle system of whole human body models so far. While previous works considered this aspect for single muscles, the effect of a change in stiffness due to isometric contraction of volumetric muscles on the AHBM behavior and computation time is yet unknown. METHODS: In this study, a simplified frontal impact using the THUMS Version 5 AM50 occupant model was simulated. Key parameters to regulate muscle tissue stiffness of solid elements in THUMS were identified for the material model MAT_SIMPLIFIED_FOAM and different stiffness states were predefined for the buttock and thigh. RESULTS: During frontal crash, changes in muscle stiffness had an effect on the overall AHBM behavior including expected injury outcome. Changes in muscle stiffness for the thigh and pelvis, as well as for the entire human body model and for strain-rate-dependent stiffness definitions based on literature data had no significant effect on the computation time. DISCUSSION: Kinematics, peak impact force and stiffness changes were in general compliance with the literature data. However, different experimental setups had to be considered for comparison, as this topic has not been fully investigated experimentally in automotive applications in the past. Therefore, this study has limitations regarding validation of the frontal impact results. CONCLUSION: Variations of default THUMS material model parameters allow an efficient change in stiffness of volumetric muscles for whole AHBM applications. The computation time is unaffected by altering muscle stiffness using the method suggested in this work. Due to a lack of validation data, the results of this work can only be validated with certain limitations. In future works, the default material models of THUMS could be replaced with recently published models to achieve a possibly more biofidelic muscle behavior, which would even allow a functional dependency of the 1D and 3D muscle systems. However, the effect on calculation time and model stability of these models is yet unknown and should be considered in future studies for efficient AHBM applications.

The influence of car passengers' sitting postures in intersection crashes.

Car passengers are frequently sitting in non-nominal postures and are able to perform a wide range of activities since they are not limited by tasks related to vehicle control, contrary to drivers. The anticipated introduction of Autonomous Driven vehicles could allow "drivers" to adopt similar postures and being involved in the same activities as passengers, allowing them a similar set of non-nominal postures. Therefore, the need to investigate the effects of non-nominal occupant sitting postures during relevant car crash events is becoming increasingly important. This study aims to investigate the effect of different postures of passengers in the front seat of a car on kinematic and kinetic responses during intersection crashes. A Human Body Model (HBM) was positioned in a numerical model of the front passenger seat of a midsize Sports Utility Vehicle (SUV) in a total of 35 postures, including variations to the lower and upper extremities, torso, and head postures. Three crash configurations, representative of predicted urban intersection crashes, were assessed in a simulation study; two side impacts, a near-side and a far-side, respectively, and a frontal impact. The occupant kinematics and internal loads were analyzed, and any deviation between the nominal and altered posture responses were quantified using cross-correlation of signals to highlight the most notable variations. Posture changes to the lower extremities had the largest overall influence on the lower extremities, pelvis, and whole-body responses for all crash configurations. In the frontal impact, crossing the legs allowed for the highest pelvis excursions and rotations, which affected the whole-body response the most. In the two side-impacts, leaning the torso in the coronal plane affected the torso and head kinematics by changing the interaction with the vehicle's interior. Additionally, in far-side impacts supporting the upper extremity on the center console resulted in increased torso excursions. Moreover, the response of the upper extremities was consistently sensitive to posture variations of all body regions.

The Effect on Head-Neck Injuries of Six-Year-Old Child Occupant by Misusing the Restraint System / 医用生物力学

Objective To explore the effect of restraint system misuse on head-neck injuries for rear occupant of 6-year-old children in frontal impact crashes. Methods Based on the previously validated 6-year-old child occupant finite element model, in terms of ECE R44 testing regulations, the impact crash under right and wrong use of restraint system was simulated in Pam-Crash software. Results The force and moment of the neck were the minimum by merely using booster seat, but the maximum intracranial pressure, the maximum stress and the maximum principal strain were larger than their damage threshold and would cause fatal brain damage in child head. The only use of adult safety belt would cause more serious damage in child neck with larger force and moment. Conclusions Two ways of misusing the restraint system would aggravate head-neck injuries of the 6-year-old child. The proper use of the restraint system can provide the best protective effect for head and neck of the 6-year-old child occupant.

Feasibility study of a safe sled environment for reclined frontal deceleration tests with human volunteers.

Objective: The goal of the study was to assess the feasibility of a safe crash environment for volunteer tests in reclined seating positions. An iterative multimodal approach was chosen, consisting of full-body human body model (HBM) simulations, anthropomorphic test device (ATD) physical testing, and volunteer testing.Methods: To estimate a noninjurious deceleration pulse, the iterative inclination of the seat was supported through HBM simulations and physical ATD testing. One male volunteer was exposed to 5 low-speed frontal sled impacts with stepwise reclined seat angles. The volunteer was restrained with a non-pretensioned 3-point seat belt. All procedures were approved by the relevant ethics boards.Results: Volunteer sled tests in 3 different seat configurations were performed with one volunteer at noninjurious deceleration levels. Inclination of the seat and the absence of a footrest resulted in elevated axial seat reaction forces and almost pure translational motion of the human body.Conclusions: A maximum speed of 7.1 km/h and peak deceleration of 3.0 g was found to be a safe pulse for volunteer testing in frontal impacts with a rigid reclined seat. Larger soft tissue deformations were observed when reclined, possibly associated with higher shear loads within the soft tissue. Preliminary results highlight trade-offs between the degree of seat angulation, friction force, and restraint capability of a 3-point seat belt, thus causing forward translation and/or axial spinal compression of the occupant that may need to be addressed in the future.

Relationship between frontal car-to-car test result and vehicle crash compatibility evaluation in mobile progressive deformable barrier test.

Objective: In 2020, the world's first crash compatibility rating test will be introduced in the European mobile progressive deformable barrier (MPDB) test. In this research, the quantitative change in partner protection performance of large vehicles in car-to-car (C2C) impacts was studied if these large vehicles were designed in future based on MPDB tests addressing crash compatibility ratings. Methods: Representative vehicles of the European fleet were selected and a Computer Aided Engineering (CAE) parameter study was conducted. In particular, by changing an indicator of structural interaction performance (SD; i.e., the degree of uniformity of barrier deformation)/mass/stiffness of large vehicles systematically in a step-by-step approach, the compatibility evaluation results of large vehicles in MPDB and the occupant injury score of small vehicles in C2C impacts were compared. The CAE result was evaluated compared to that of C2C physical impact tests. Results: The CAE parameter study showed that in the C2C impact condition, the effects on occupant injury in a small vehicle due to changes in the large vehicle were as follows: (1) SD change: The effect was minor except for small overlap condition. (2) Mass and stiffness change: The effect was relatively major. On the other hand, compatibility evaluation in the MPDB showed a tendency to overestimate the effect of SD change in comparison with the above-mentioned C2C impact condition. In addition, physical impact tests showed that, based on SD evaluation, the large vehicle with a relatively inferior compatibility rating compared to those with superior compatibility ratings showed a contradicting trend of better compatibility performance in the C2C test. Conclusions: The currently proposed compatibility evaluation method of the MPDB test showed some tendency to overestimate the effect of SD change and resulted in quantitatively inconsistent outcomes regarding occupant injury in the partner car in C2C impact conditions.

Objective Evaluation of Whole Body Kinematics in a Simulated, Restrained Frontal Impact.

The use of human body models as an additional data point in the evaluation of human-machine interaction requires quantitative validation. In this study a validation of the Global Human Body Models Consortium (GHBMC) average male occupant model (M50-O v. 4.5) in a restrained frontal sled test environment is presented. For vehicle passengers, frontal crash remains the most common mode, and the most common source of fatalities. A total of 55-time history traces of reaction loads and kinematics from the model were evaluated against corresponding PMHS data (n = 5). Further, the model's sensitivity to the belt path was studied by replicating two documented PMHS cases with prominent lateral and medial belt paths respectively. Results were quantitatively evaluated using open source CORA software. A tradeoff was observed; better correlation scores were achieved on gross measures (e.g. reaction loads), whereas better corridor scores were achieved on localized measures (rib deflections), indicating that subject specificity may dominate the comparison at localized anatomical regions. On an overall basis, the CORA scores were 0.68, 0.66 and 0.60 for force, body kinematics and chest wall kinematics. Belt force responses received the highest grouped CORA score of 0.85. Head and sternum kinematics earning a 0.8 and 0.7 score respectively. The model demonstrated high sensitivity to belt path, resulting in a 20-point increase in CORA score when the belt was routed closer to analogous location of data collection. The human model demonstrated overall reasonable biofidelity and sensitivity to countermeasures in frontal crash kinematics.

Three-dimensional kinematic corridors of the head, spine, and pelvis for small female driver seat occupants in near- and far-side oblique frontal impacts.

OBJECTIVES: Analyses of recent automotive accident data indicate an increased risk of injury for small female occupants compared to males in similar accidents. Females have been shown to be more susceptible to spinal injuries than males. To protect this more vulnerable population, advanced anthropomorphic test devices (ATDs) and computer human body models are being developed and require biofidelity curves for validation. The aim of this study is to generate female-specific 3D kinematic corridors in near- and far-side oblique frontal impacts for the head, spine, and pelvis. METHODS: Eight specimens were procured and prescreened for mass, stature, and quantitative computed tomography bone mineral density and preexisting injuries to minimize biologic variability. Sets of 4 noncolinear retroreflective targets were placed on the back of the head; dorsal spine at T1, T8, and L2; and posterior sacrum. Instrumented computed tomography scans were obtained to measure the orientation and position of the markers relative to anatomic fiducials. The specimens were placed on a buck representative of a generic automotive driver's seat environment designed to minimize lower-extremity and pelvic motion. The buck was oriented such that the buck centerline was seated 30° from the impact vector in either a near- or far-side oblique frontal configuration. Preposition of the occupant was specified to the 50th percentile male H-point location, thigh and tibial angles, and torso angle. Impact was delivered via a servo-acceleration sled to the base of the buck with a 30 km/h 9 g trapezoidal pulse. Occupants were restrained by a standard 3-point belt that had a custom load-limiter device set to 2 kN at the D-ring side of the shoulder belt. Target motion was recorded at 1 kHz using a 3D optical motion capture system. Anatomic motion of the head, spine, and pelvis was calculated relative to the seat, and the average response was determined from 4 near-side and 4 far-side tests. The borders of the corridor were determined by calculating a standard deviational ellipse in the x, y, and z planes at each time step. RESULTS: Plots of the biofidelity corridors for near- and far-side tests are shown in planes parallel to the seat from the lateral, rear, and overhead directions. Averaged peak excursions in the fore/aft and lateral directions are compared for the near- and far-side corridors. Near-side female and male tests are similarly compared. CONCLUSIONS: In general, average peak excursions were greater in the far-side configuration than in the near-side configuration. Peak excursion results compared well with similar tests conducted on male postmortem human subjects (PMHS). The kinematic corridors developed in the current study serve as a set of biofidelity corridors for the development of current and future physical and computational surrogates.

Injury risk functions for frontal oblique collisions.

OBJECTIVE: The objective of this article was the construction of injury risk functions (IRFs) for front row occupants in oblique frontal crashes and a comparison to IRF of nonoblique frontal crashes from the same data set. METHOD: Crashes of modern vehicles from GIDAS (German In-Depth Accident Study) were used as the basis for the construction of a logistic injury risk model. Static deformation, measured via displaced voxels on the postcrash vehicles, was used to calculate the energy dissipated in the crash. This measure of accident severity was termed objective equivalent speed (oEES) because it does not depend on the accident reconstruction and thus eliminates reconstruction biases like impact direction and vehicle model year. Imputation from property damage cases was used to describe underrepresented low-severity crashes-a known shortcoming of GIDAS. Binary logistic regression was used to relate the stimuli (oEES) to the binary outcome variable (injured or not injured). RESULTS: IRFs for the oblique frontal impact and nonoblique frontal impact were computed for the Maximum Abbreviated Injury Scale (MAIS) 2+ and 3+ levels for adults (18-64 years). For a given stimulus, the probability of injury for a belted driver was higher in oblique crashes than in nonoblique frontal crashes. For the 25% injury risk at MAIS 2+ level, the corresponding stimulus for oblique crashes was 40 km/h but it was 64 km/h for nonoblique frontal crashes. CONCLUSIONS: The risk of obtaining MAIS 2+ injuries is significantly higher in oblique crashes than in nonoblique crashes. In the real world, most MAIS 2+ injuries occur in an oEES range from 30 to 60 km/h.

Application of energy derivative method to determine the structural components' contribution to deceleration in crashes.

OBJECTIVE: For occupant protection, it is important to understand how a car's deceleration time history in crashes can be designed using efficient of energy absorption by a car body's structure. In a previous paper, the authors proposed an energy derivative method to determine each structural component's contribution to the longitudinal deceleration of a car passenger compartment in crashes. In this study, this method was extended to 2 dimensions in order to analyze various crash test conditions. The contribution of each structure estimated from the energy derivative method was compared to that from a conventional finite element (FE) analysis method using cross-sectional forces. METHOD: A 2-dimensional energy derivative method was established. A simple FE model with a structural column connected to a rigid body was used to confirm the validity of this method and to compare with the result of cross-sectional forces determined using conventional analysis. Applying this method to a full-width frontal impact simulation of a car FE model, the contribution and the cross-sectional forces of the front rails were compared. In addition, this method was applied to a pedestrian headform FE simulation in order to determine the influence of the structural and inertia forces of the hood structures on the deceleration of the headform undergoing planar motion. RESULT: In an oblique impact of the simple column and rigid body model, the sum of the contributions of each part agrees with the rigid body deceleration, which indicates the validity of the 2-dimensional energy derivative method. Using the energy derivative method, it was observed that each part of the column contributes to the deceleration of the rigid body by collapsing in the sequence from front to rear, whereas the cross-sectional force at the rear of the column cannot detect the continuous collapse. In the full-width impact of a car, the contributions of the front rails estimated in the energy derivative method was smaller than that using the cross-sectional forces at the rear end of the front rails due to the deformation of the passenger compartment. For a pedestrian headform impact, the inertial and structural forces of the hood contributed to peaks of the headform deceleration in the initial and latter phases, respectively. CONCLUSIONS: Using the 2-dimensional energy derivative method, it is possible to analyze an oblique impact or a pedestrian headform impact with large rotations. This method has advantages compared to the conventional approach using cross-sectional forces because the contribution of each component to system deceleration can be determined.

The influence of pre-existing rib fractures on Global Human Body Models Consortium thorax response in frontal and oblique impact.

Many post-mortem human subjects (PMHS) considered for use in biomechanical impact tests have pre-existing rib fractures (PERFs), usually resulting from cardiopulmonary resuscitation. These specimens are typically excluded from impact studies with the assumption that the fractures will alter the thoracic response to loading. We previously used the Global Human Body Models Consortium 50th percentile whole-body finite element model (GHBMC M50-O) to demonstrate that up to three lateral or bilateral PERFs do not meaningfully influence the response of the GHBMC thorax to lateral loading. This current study used the GHBMC M50-O to explore the influence of PERFs on thorax response in frontal and oblique loading. Up to six PERFs were simulated on the anterior or lateral rib regions, and the model was subjected to frontal or oblique cylindrical impactor, frontal seatbelt, or frontal seatbelt + airbag loading. Changes in thorax force-compression responses due to PERFs were generally minor, with the greatest alterations seen in models with six PERFs on one side of the ribcage. The observed changes, however, were small relative to mid-size male corridors for the loading conditions simulated. PERFs altered rib strain patterns, but the changes did not translate to changes in global thoracic response. Within the limits of model fidelity, the results suggest that PMHS with up to six PERFs may be appropriate for use in frontal or oblique impact testing.

The biomechanics of lower limb injuries in frontal-impact road traffic collisions.

AIM: We aimed to review the biomechanics of lower limb injuries caused by frontal-impact road traffic collisions. METHODS: In this narrative review, we identified articles through pubmed, Scopus and Science Direct search engines for the period of 1990-2014. Search terms included: "biomechanics", "lower limb injury", "hip injury", "knee injury", "foot and ankle injury" and "frontal impact collision". We studied factors affecting the anatomical site, frequency and severity of the injuries. RESULTS: The most common reported mechanisms of injury were: the impaction of the knee with the dashboard resulting in acetabular fracture or posterior hip dislocation; and toepan intrusion in combination with forceful application of the brake resulting in foot and ankle fractures. The probability of an occupant sustaining significant injury to the hip is increased in taller males, and being out of position during the collision. The probability of an occupant sustaining a fracture to the foot and ankle is increased in shorter female occupants with a large overlap impact or a near oblique collision. CONCLUSION: Understanding the biomechanics of frontal-impact road traffic collisions is useful in alerting clinicians to the potential lower limb injuries sustained in these collisions.