A human model for road safety: from geometrical acquisition to model validation with radioss

Review of non-penetrating ballistic testing techniques for protection assessment: From biological data to numerical and physical surrogates

Human surrogates have long been employed to simulate human behaviour, beginning in the automotive industry and now widely used throughout the safety framework to estimate human injury during and after accidents and impacts. In the specific context of blunt ballistics, various methods have been developed to investigate wound injuries, including tissue simulants such as clays or gelatine ballistic, physical dummies and numerical models. However, all of these surrogate entities must be biofidelic, meaning they must accurately represent the biological properties of the human body. This paper provides an overview of physical and numerical surrogates developed specifically for blunt ballistic impacts, including their properties, use and applications. The focus is on their ability to accurately represent the human body in the context of blunt ballistic impact.

Thoughts and perspectives on biomechanical numerical models under impacts: Are women forgotten from research?

The present paper explores a series of articles in the literature which deal with impact biomechanics of the head and thorax/abdomen segments, investigating the "sex specific properties/data" used in the studies. Statements in these studies are analyzed and point out, the use of male or female subjects for the developments of finite element models and their validation against experimental data. The present analysis raises the question about "androcentrism," and how biomechanical engineering findings and the design of the derived protecting devices are focused on male subjects.

Finite element analysis for better evaluation of rib fractures: A pilot study

INTRODUCTION

Modeling rib fracture stability is challenging. Computer-generated finite element analysis (FEA) is an option for assessment of chest wall stability (CWS). The objective is to explore FEA as a means to assess CWS, hypothesizing it is a reliable approach to better understand rib fracture pathophysiology.

METHODS

Thoracic anatomy was generated from standardized skeletal models with internal/external organs, soft tissue and muscles using Digital Imaging and Communications in Medicine data. Material properties were assigned to bone, cartilage, skin and viscera. Simulation was performed using ANSYS Workbench (2020 R2, Canonsburg, PA). Meshing the model was completed identifying 1.3 and 2.1 million elements and nodes. An implicit solver was used for a linear/static FEA with all bony contacts identified and applied. All material behavior was modeled as isotropic/linear elastic. Six load cases were evaluated from a musculoskeletal AnyBody model; forward flexion, right/left lateral bending, right/left axial rotation and 5-kg weight arm lifting. Standard application points, directions of muscle forces, and joint positions were applied. Ten fracture cases (unilateral and bilateral) were defined and 66 model variations were simulated. Forty-three points were applied to each rib in the mid/anterior axillary lines to assess thoracic stability. Three assessment criteria were used to quantify thoracic motion: normalized mean absolute error, normalized root mean square error, and normalized interfragmentary motion.

RESULTS

All three analyses demonstrated similar findings that rib fracture deformation and loss of CWS was highest for left/right axial rotation. Increased number of ribs fracture demonstrated more fracture deformation and more loss of CWS compared with a flail chest segment involving less ribs. A single rib fracture is associated with ~3% loss of CWS. Normalized interfragmentary motion deformation can increases by 230%. Chest wall stability can decrease by over 50% depending on fracture patterns.

CONCLUSION

Finite element analysis is a promising technology for analyzing CWS. Future studies need to focus on clinical relevance and application of this technology.

LEVEL OF EVIDENCE

Diagnostic Tests or Criteria; Level IV.

Thorax Dynamic Modeling and Biomechanical Analysis of Chest Breathing in Supine Lying Position

During respiration, the expansion and contraction of the chest and abdomen are coupled with each other, presenting a complex torso movement pattern. A finite element (FE) model of chest breathing based on the HUMOS2 human body model was developed. One-dimensional muscle units with active contraction functions were incorporated into the model based on Hill's active muscle model so as to generate muscle contraction forces that can change over time. The model was validated by comparing it to the surface displacement of the chest and abdomen during respiration. Then, the mechanism of the coupled motion of the chest and abdomen was analyzed. The analyses revealed that since the abdominal wall muscles are connected to the lower edge of the rib cage through tendons, the movement of the rib cage may cause the abdominal wall muscles to be stretched in both horizontal and vertical in a supine position. The anteroposterior and the right-left diameters of the chest will increase at inspiration, while the right-left diameter of the abdomen will decrease even though the anteroposterior diameter of the abdomen increases. The external intercostal muscles at different regions had different effects on the motion of the ribs during respiration. In particular, the external intercostal muscles at the lateral region had a larger effect on pump handle movement than bucket handle movement, and the external intercostal muscles at the dorsal region had a greater influence on bucket handle movement than pump handle movement.

Head contacts in second-row pediatric occupants when the front-seat is reclined during automated emergency braking

Seating configurations for autonomous driving will include reclined front seated occupants, which may expose child occupants seated directly behind to head impacts even in pre-crash scenarios. This study used mathematical modelling to investigate head contact for second-row child occupants seated behind a reclined front-seat during an automatic emergency braking (AEB) scenario. Although characterized by low speed (<1 m/s), head contacts were observed for a seatbelt-restrained 10-year-old and a 6-year-old in a low-back booster when the front-seat was reclined and in an aftward track position. Future seating configurations should consider the potential for head contact by second-row child occupants during crash-avoidance scenarios.

Blunt injury of liver: mechanical response of porcine liver in experimental impact test

OBJECTIVE

The liver is frequently injured in blunt abdominal trauma caused by road traffic accidents. The testing of safety performance of vehicles, e.g. belt usage, head support, seat shape, or air bag shape, material, pressure and reaction, could lead to reduction of the injury seriousness. Current trends in safety testing include development of accurate computational human body models (HBMs) based on the anatomical, morphological, and mechanical behavior of tissues under high strain.

APPROACH

The aim of this study was to describe the internal pressure changes within porcine liver, the severity of liver injury and the relation between the porcine liver microstructure and rupture propagation in an experimental impact test. Porcine liver specimens (n = 24) were uniformly compressed using a drop tower technique and four impact heights (200, 300, 400 and 500 mm; corresponding velocities: 1.72, 2.17, 2.54 and 2.88 m s^-1). The changes in intravascular pressure were measured via catheters placed in portal vein and caudate vena cava. The induced injuries were analyzed on the macroscopic level according to AAST grade and AIS severity. Rupture propagation with respect to liver microstructure was analyzed using stereological methods.

MAIN RESULTS

Macroscopic ruptures affected mostly the interface between connective tissue surrounding big vessels and liver parenchyma. Histological analysis revealed that the ruptures avoided reticular fibers and interlobular septa made of connective tissue on the microscopic level.

SIGNIFICANCE

The present findings can be used for evaluation of HBMs of liver behavior in impact situations.

Development and validation of an optimized finite element model of the human orbit

INTRODUCTION

The authors' main purpose was to develop a detailed finite element model (FEM) of the human orbit and to validate it by analyzing its behavior under the stress of blunt traumas.

MATERIALS AND METHODS

A pre-existing 3D FEM of a human head was modified and used in this study. Modifications took into account preliminary research carried out on PubMed database. Data from a CT scan of the head were computed with Mimics^® software to re-create the skull geometry. The mesh production, the model's properties and the simulations of blunt orbital traumas were conducted on Hyperworks^® software.

RESULTS

The resulting 3D FEM was composed of 640 000 elements and was used to perform blunt trauma simulations on an intact orbit. A total of 27 tests were simulated. Fifteen tests were realized with a metallic cylinder impactor; 12 tests simulated a hit by a closed fist. In all the tests conducted (27/27), the orbital floor was fractured. Fracture patterns were similar to those found in real clinical situations according to the buckling and hydraulic theories of orbital floor fractures.

DISCUSSION

The similitude between the fracture patterns produced on the model and those observed in vivo allows for a validation of the model. This model constitutes, at the authors knowledge, the most sophisticated one ever developed.

Evaluation of 6 and 10 Year-Old Child Human Body Models in Emergency Events

Emergency events can influence a child’s kinematics prior to a car-crash, and thus its interaction with the restraint system. Numerical Human Body Models (HBMs) can help understand the behaviour of children in emergency events. The kinematic responses of two child HBMs–MADYMO 6 and 10 year-old models–were evaluated and compared with child volunteers’ data during emergency events–braking and steering–with a focus on the forehead and sternum displacements. The response of the 6 year-old HBM was similar to the response of the 10 year-old HBM, however both models had a different response compared with the volunteers. The forward and lateral displacements were within the range of volunteer data up to approximately 0.3 s; but then, the HBMs head and sternum moved significantly downwards, while the volunteers experienced smaller displacement and tended to come back to their initial posture. Therefore, these HBMs, originally intended for crash simulations, are not too stiff and could be able to reproduce properly emergency events thanks, for instance, to postural control.

Development of a Gravid Uterus Model for the Study of Road Accidents Involving Pregnant Women

Car accident simulations involving pregnant women are well documented in the literature and suggest that intra-uterine pressure could be responsible for the phenomenon of placental abruption, underlining the need for a realistic amniotic fluid model, including fluid-structure interactions (FSI). This study reports the development and validation of an amniotic fluid model using an Arbitrary Lagrangian Eulerian formulation in the LS-DYNA environment. Dedicated to the study of the mechanisms responsible for fetal injuries resulting from road accidents, the fluid model was validated using dynamic loading tests. Drop tests were performed on a deformable water-filled container at acceleration levels that would be experienced in a gravid uterus during a frontal car collision at 25 kph. During the test device braking phase, container deformation induced by inertial effects and FSI was recorded by kinematic analysis. These tests were then simulated in the LS-DYNA environment to validate a fluid model under dynamic loading, based on the container deformations. Finally, the coupling between the amniotic fluid model and an existing finite-element full-body pregnant woman model was validated in terms of pressure. To do so, experimental test results performed on four postmortem human surrogates (PMHS) (in which a physical gravid uterus model was inserted) were used. The experimental intra-uterine pressure from these tests was compared to intra uterine pressure from a numerical simulation performed under the same loading conditions. Both free fall numerical and experimental responses appear strongly correlated. The relationship between the amniotic fluid model and pregnant woman model provide intra-uterine pressure values correlated with the experimental test responses. The use of an Arbitrary Lagrangian Eulerian formulation allows the analysis of FSI between the amniotic fluid and the gravid uterus during a road accident involving pregnant women.

An anatomic and morphometric analysis of splenic variability using 3D reconstruction and spatial orientation from computed tomography

INTRODUCTION

In terms of frequency, the spleen is the first organ affected in abdominal trauma, resulting even today in a high rate of mortality (10%). Nevertheless, very few studies have investigated splenic quantitative morphometry as to shape and spatial orientation. Therefore, we analysed healthy spleen variability in order to integrate it in its environment and to correlate its morphometric parameters to anthropometric characteristics.

METHODS

Ninety abdominopelvic CT-scans performed on patients over 16 years with no splenic pathology were retrospectively selected among a Mediterranean population. Three age groups ([16-30], [30-60] and [over 60 years]), equally distributed among genders, were created. Parameters, such as volume, characteristic checkpoints, orientation, and morphology, were measured on the spleen, the 11th thoracic vertebra and the 10th ribs in three-dimensional reconstructions. Anthropometric parameters were characterised by waist circumference, costo-xiphoid angle, abdominal height and chest depth.

RESULTS

Observed variations in splenic morphology were divided into three groups: cupped (66.7%), coiled (17.8%), and flat (15.5%). Splenic morphometry tends to be abdominal-shaped (54.5%) or dorsal-shaped (45.5%). The mean of the angle between the main axis of the spleen and the CT-scan horizontal axis was 40±14°. Correlations were highlighted between volume and gender (p<0.05), splenic morphology and liver morphometry (p<0.05) as well as between orientation of hilar surface and splenic morphometry (p<0.01). Moreover, the spleen is more horizontal in women (p<0.05), in the elderly (p<0.05) and in the obese (p<0.01).

CONCLUSION

This study defines three groups based on shape and highlights correlations between parameters describing healthy splenic variability and its anthropometric characteristics, which are of great importance for numerical modelling in splenic studies.

Characterizing the importance of free space in the numerical human body models

The geometric fidelity of the inner organs on finite-element model (FEM) of the human body and the choice to use discontinuous mesh engender the appearance of empty spaces that do not reflect the real-life situation of human body cavities. The aim of this study is to assess the influence of these empty spaces on the behavior of a simplified FEM built with three different structures in interaction which properties are relevant with the abdominal cavity. This FEM is made up of a large sphere (peritoneum) containing two hemispheres (liver and spleen). The space between peritoneum and inner organs was defined with two different approaches and assessed under impact conditions. The first is a meshfree space (Mfs) approach, e.g., consider the space as a perfect gas. The second approach, meshed space (MS), entailed adding volumetric elements in the empty space. From each approach, one optimal configuration was identified regarding the recorded force versus compression, the mobility of inner organs, and the space incompressibility. This space has a considerable influence on the behavior of the FEM and mainly on the applied loadings of inner organs (difference reaching 70% according to the configuration). For the first approach, the incompressible gas is designated because it guarantees space incompressibility (vf/vi = 1) and inner organs loading with the lowest delay (for high impact velocity: Peak force = 89 N, compression 47%). For the second approach, the discontinuous volumetric mesh is preferred because it promotes space incompressibility (vf/vi = 0.94) and acceptable force reaction (for high impact velocity: Peak force = 97 N, compression 49%). The current study shows the importance of this space on the human FEMs cavities behavior and proposes two configurations able to be used in a future study including detailed FEM.

Posterior urethral injuries associated with motorcycle accidents and pelvic trauma in adolescents: analysis of urethral lesions occurring prior to a bony fracture using a computerized finite-element model

Adolescent males involved in motorcycle accidents are particularly at risk for pelvic injury, which may provoke a posterior urethral injury. The aim of this study was to develop a model to analyze the association between injuries and fractures of the pelvic ring and the risk of posterior urethral injury.

METHOD

Based on experience with traffic accident modeling, a computerized finite-element model was extrapolated from a computerized tomography scan of a 15-year-old boy. The anatomic structures concerned in urethral and pelvic ring trauma were isolated, rendered in 3D and given biomechanical properties. The model was verified according to available experiments on pelvic ring trauma.

RESULTS

To apply the model, we recreated three impact mechanisms on the pelvic ring: lateral impact, antero-posterior impact and a real car‒motorcycle accident situation (postero-lateral impact). In all three situations, stretching of the posterior urethra was identified prior to bony fracture visualization.

CONCLUSION

Application of this model allowed us to analyze precisely the link between trauma of the pelvic ring and lesions of the posterior urethra. The results should help to establish guidelines for urethral catheterization in male adolescents in cases of pelvic trauma, even when no bony fracture is present, in order to prevent iatrogenic worsening of a misdiagnosed posterior urethral trauma.

Petrous bone fracture: a virtual trauma analysis

OBJECTIVE

The temporal bone shields sensorineural, nervous, and vascular structures explaining the potential severity and complications of trauma related to road and sport accidents. So far, no clear data are available on the exact mechanisms involved for fracture processes. Modelization of structures helps to answer these concerns. Our objective was to design a finite element model of the petrous bone structure to modelize temporal bone fracture propagation in a scenario of lateral impact.

MATERIALS AND METHODS

A finite element model of the petrous bone structure was designed based on computed tomography data. A 7-m/s lateral impact was simulated to reproduce a typical lateral trauma. Results of model analysis was based on force recorded, stress level on bone structure up to induce a solution of continuity of the bony structure.

RESULTS

Model simulation showed that bone fractures follow the main axes of the petrous bone and occurred in a 2-step process: first, a crush, and second, a massive fissuration of the petrous bone. The lines of fracture obtained by simulation of a lateral impact converge toward the middle ear region. This longitudinal fracture is located at the mastoid-petrous pyramid junction.

DISCUSSION

Using this model, it was possible to map petrous bone fractures including fracture chronology and areas of fusion of the middle ear region. This technique may represent a first step to investigate the pathophysiology of the petrous bone fractures, aiming to define prognostic criteria for patients' care.

Posterior urethral injuries associated with pelvic injuries in young adults: computerized finite element model creation and application to improve knowledge and prevention of these lesions

INTRODUCTION

Young adult males involved in motorcycle accidents are particularly at risk for posterior urethral injury whenever pelvic injury occurs. Posterior urethral injuries remain problematic because their diagnosis may be missed, and during the initial treatment response the urethral injury can be aggravated by urethral catheterization. Few anatomical and clinical tools exist that establish a correlation between injuries and fractures of the pelvic ring and the risk of posterior urethral injury.

METHOD

Based on experience with traffic accident modeling, a computerized finite element model was conceived integrating the specific anatomic structures concerned. This model was extrapolated from a CAT scan of a young adult. The anatomic structures concerned in urethral and pelvic ring trauma (PRT) were isolated, placed in 3D and given biomechanical properties. The model was verified according to available experiments on PRT.

RESULTS

To apply the model, we recreated a lateral impact mechanism on the pelvic ring. Stretching between the prostatic and membranous portions of the urethra (before and after visualization of a pelvic fracture) as well as timing of injury was studied.

CONCLUSION

The model's application permitted us to analyze precisely the link between lateral impact trauma of the pelvic ring and lesions of the posterior urethra and to identify an urethra stretching prior to visualization of a pelvic fracture. Utilization of the model with other mechanisms of injury should allow for better comprehension of this associated trauma, improved prevention, iatrogenic aggravation of, and care for, these serious injuries.

Technique for chestband contour shape-mapping in lateral impact

The chestband transducer permits noninvasive measurement of transverse plane biomechanical response during blunt thorax impact. Although experiments may reveal complex two-dimensional (2D) deformation response to boundary conditions, biomechanical studies have heretofore employed only uniaxial chestband contour quantifying measurements. The present study described and evaluated an algorithm by which source subject-specific contour data may be systematically mapped to a target generalized anthropometry for computational studies of biomechanical response or anthropomorphic test dummy development. Algorithm performance was evaluated using chestband contour datasets from two rigid lateral impact boundary conditions: Flat wall and anterior-oblique wall. Comparing source and target anthropometry contours, peak deflections and deformation-time traces deviated by less than 4%. These results suggest that the algorithm is appropriate for 2D deformation response to lateral impact boundary conditions.

A pseudo-elastic effective material property representation of the costal cartilage for use in finite element models of the whole human body

OBJECTIVE

Injury-predictive finite element (FE) models of the chest must reproduce the structural coupling behavior of the costal cartilage accurately. Gross heterogeneities (the perichondrium and calcifications) may cause models developed based on local material properties to erroneously predict the structural behavior of cartilage segments. This study sought to determine the pseudo-elastic effective material properties required to reproduce the structural behavior of the costal cartilage under loading similar to what might occur in a frontal automobile collision.

METHODS

Twenty-eight segments of cadaveric costal cartilage were subjected to cantilever-like, dynamic loading. Three limited-mesh FE models were then developed for each specimen, having element sizes of 10 mm (typical of current whole-body FE models), 3 mm, and 2 mm. The cartilage was represented as a homogeneous, isotropic, linear elastic material. The elastic moduli of the cartilage models were optimized to fit the anterior-posterior (x-axis) force versus displacement responses observed in the experiments. For a subset of specimens, additional model validation tests were performed under a second boundary condition.

RESULTS

The pseudo-elastic effective moduli ranged from 4.8 to 49 MPa, with an average and standard deviation of 22 ± 13.6 MPa. The models were limited in their ability to reproduce the lateral (y-axis) force responses observed in the experiments. The prediction of the x-axis and y-axis forces in the second boundary condition varied. Neither the effective moduli nor the model fit were significantly affected (Student's t-test, p < 0.05) by the model mesh density. The average pseudo-elastic effective moduli were significantly (p < 0.05) greater than local costal cartilage modulus values reported in the literature.

CONCLUSIONS

These results are consistent with the presence of stiffening heterogeneities within the costal cartilage structure. These effective modulus values may provide guidance for the representation of the costal cartilage in whole-body FE models where these heterogeneities cannot be modeled distinctly.

The Contribution of the Perichondrium to the Structural Mechanical Behavior of the Costal-Cartilage

The costal-cartilage in the human ribcage is a composite structure consisting of a cartilage substance surrounded by a fibrous, tendonlike perichondrium. Current computational models of the human ribcage represent the costal-cartilage as a homogeneous material, with no consideration for the mechanical contributions of the perichondrium. This study sought to investigate the role of the perichondrium in the structural mechanical behavior of the costal-cartilage. Twenty-two specimens of postmortem human costal-cartilage were subjected to cantileveredlike loading both with the perichondrium intact and with the perichondrium removed. The test method was chosen to approximate the cartilage loading that occurs when a concentrated, posteriorly directed load is applied to the midsternum. The removal of the perichondrium resulted in a statistically significant (two-tailed Student’s t-test, p≤0.05) decrease of approximately 47% (95% C.I. of 35–58%) in the peak anterior-posterior reaction forces generated during the tests. When tested with the perichondrium removed, the specimens also exhibited failure in the cartilage substance in the regions that experienced tension from bending. These results suggest that the perichondrium does contribute significantly to the stiffness and strength of the costal-cartilage structure under this type loading, and should be accounted for in computational models of the thorax and ribcage.

A Three-Dimensional Human Trunk Model for the Analysis of Respiratory Mechanics

Over the past decade, road safety research and impact biomechanics have strongly stimulated the development of anatomical human numerical models using the finite element (FE) approach. The good accuracy of these models, in terms of geometric definition and mechanical response, should now find new areas of application. We focus here on the use of such a model to investigate its potential when studying respiratory mechanics. The human body FE model used in this study was derived from the RADIOSS® HUMOS model. Modifications first concerned the integration and interfacing of a user-controlled respiratory muscular system including intercostal muscles, scalene muscles, the sternocleidomastoid muscle, and the diaphragm and abdominal wall muscles. Volumetric and pressure measurement procedures for the lungs and both the thoracic and abdominal chambers were also implemented. Validation of the respiratory module was assessed by comparing a simulated maximum inspiration maneuver to volunteer studies in the literature. Validation parameters included lung volume changes, rib rotations, diaphragm shape and vertical deflexion, and intra-abdominal pressure variation. The HUMOS model, initially dedicated to road safety research, could be turned into a promising, realistic 3D model of respiration with only minor modifications.

Experimental tests for the validation of active numerical human models

The development of numerical human models is a topic of current interdisciplinary research. In the field of automotive safety these models can be applied for the optimization of protection systems. In forensic research human models can be used for the investigation of injury mechanisms and for the prediction and reproduction of injury patterns. However, up to now human models have been validated on the basis of PMHS tests without considering the effects of muscle activity. This paper shows two experimental volunteer test set-ups for the generation of experimental validation data. In a pendulum set-up the influence of muscle activity on the human kinematics was investigated. A drop test set-up was developed for the analysis of the effects of muscle activity on impact response characteristics of muscle tissue. Experimental results, presented in this paper, can be used for the validation and optimization of active numerical human models.

Human shoulder response to side impacts: a finite element study

This study aimed at developing a shoulder finite element (FE) model able to simulate the dynamic behaviour and to predict injuries in case of side impacts. This model is an updated version of the initial Human Model for Safety (HUMOS) FE model of the human body. Simulations performed with the model have been compared to experimental results of side impact tests conducted previously at INRETS. The shoulder model response under lateral impact appears to be in good agreement with experimental data such as impact force and shoulder deflections for different impact speeds and impact directions. These results seem promising for future applications such as shoulder injury prediction in simulated car crashes.

[Pregnant woman and road safety: a numerical approach. Application to a restrained third trimester pregnant woman in frontal impact]

OBJECTIVES

The goal of our work is the development of a numerical model of pregnant woman in driving position. We present an application to the study of injury mechanisms during a frontal car crash for a seat belt restrained pregnant woman in driving position.

MATERIALS AND METHODS

We integrated a digital representation of a pregnant uterus, foetus and placenta in a previous existing numerical model of non pregnant Human body in driving position, the Humos model. The realization of a numerical simulation of a frontal car crash enabled us to analyze the part played by the safety belt in the organic traumatisms.

RESULTS

Three phases were highlighted. The first phase consists of a translation forwards of the pregnant uterus during the impact. The second phase is a rotation forwards in the sagittal plan of the pregnant uterus with for axis of rotation the posterior wall of the pubis. The third phase is a vertical adjustment coupled to a translation of the uterus towards the back. This translation leads the uterus to impact the spine.

CONCLUSION

The development of a pregnant numerical model in the field of accidentology allows the analysis of organic traumatisms. That makes it possible to study the role played by the existing safety systems. This model might make it possible to develop safety systems specific to the pregnant woman.

External and internal geometry of European adults

The primary objective of the study was to bring a deeper knowledge of the human anthropometry, investigating the external and internal body geometry of small women, mid-sized men and tall men. Sixty-four healthy European adults were recruited. External measurements were performed using classical anthropometric instruments. Internal measurements of the trunk bones were performed using a stereo-radiographic 3D reconstruction technique. Besides the original procedure presented in this paper for performing in vivo geometrical data acquisition on numerous volunteers, this study provides an extensive description of both external and internal (trunk skeleton) human body geometry for three morphotypes. Moreover, this study proposes a global external and internal geometrical description of 5th female 50th male and 95th male percentile subjects. This study resulted in a unique geometrical database enabling improvement for numerical models of the human body for crash test simulation and offering numerous possibilities in the anthropometry field.

An Experimental Cadaveric Study for a Better Understanding of Blunt Traumatic Aortic Rupture

BACKGROUND

Blunt traumatic aortic rupture (BTAR) is a common catastrophic injury leading to death. Considerable uncertainty remains regarding the pathogenic cause. This study examines the comportment of the heart and the aorta during a frontal deceleration.

METHODS

Accelerometers were placed in the right ventricle of the heart, the aorta, the sternum, and the spine of six trunks removed from human cadavers. Different vertical decelerations were applied to cadavers and the relative motion of these organs was studied (19 tests).

RESULTS

The deceleration recorded in the isthmus of the aorta was always higher that the one recorded in the heart (p < 0.05). The difference of deceleration was 17% and increased with the speed's fall (extremes 5-25%). There was no significant difference of deceleration between the bony structures of the thorax. These results experimentally demonstrate for the first time that the fundamental mechanism of BTAR is sudden stretching of the isthmus of the aorta.

CONCLUSION

Four mechanisms are suspected to explain the location of the rupture: two hemodynamic mechanism (sudden increase of intravascular pressure and the water-hammer effect), and two physical mechanisms (sudden stretching of the isthmus and the osseous pinch). A greater understanding of the mechanism of this injury could improve vehicle safety leading to a reduction in its incidence and severity. Future work in this area should include the creation of an inclusive, dynamic model of computer-based modeling systems. This study provides for the first time physical demonstration and quantification of the stretching of the isthmus, leading to a computerized model of BTAR.

Modeling the pregnant woman in driving position

Despite motor vehicle crashes being the leading cause of traumatic fetal morbidity, only a few researches have tried to study the automobile crashes on pregnant women. The possible negative effect of the restraint systems and the injuries mechanisms involved in car crashes with pregnant women are therefore still poorly understood. In this context, the aim of this study is to develop a numerical model of the whole human body with a gravid uterus, in order to investigate car crash scenarios and to evaluate alternative security systems to improve protection of both the woman and the fetus. A 3D reconstruction based on a set of MRI images led us to a good spatial representation of the pregnant woman in driving position. The anatomical precision will make progress possible in the field of traumatology of the pregnant woman.

Effects of static high compression on human foot-ankle: biomechanical response and injuries

To reduce road-traffic fatalities, significant improvements have been seen in the protection of vital body parts. Attention is now focused on serious injuries, which cause disability or impairment as lower limb injuries. The numerical models developed to have a better understanding of injury parameters are evaluated from human responses to load. For this objective, mechanical characterisation tests have been performed on nine human foot/ankle specimens. The responses of three foot contact points during various static loads of the tibia were studied. After each test, an autopsy was performed and the associated injuries were noticed. These tests allowed quantification of the tibia compressive force in relation to foot and ankle deformations up to injury level.

Tonic Finite Element Model of the Lower Limb

It is widely admitted that muscle bracing influences the result of an impact, facilitating fractures by enhancing load transmission and reducing energy dissipation. However, human numerical models used to identify injury mechanisms involved in car crashes hardly take into account this particular mechanical behavior of muscles. In this context, in this work we aim to develop a numerical model, including muscle architecture and bracing capability, focusing on lower limbs. The three-dimensional (3-D) geometry of the musculoskeletal system was extracted from MRI images, where muscular heads were separated into individual entities. Muscle mechanical behavior is based on a phenomenological approach, and depends on a reduced number of input parameters, i.e., the muscle optimal length and its corresponding maximal force. In terms of geometry, muscles are modeled with 3-D viscoelastic solids, guided in the direction of fibers with a set of contractile springs. Validation was first achieved on an isolated bundle and then by comparing emergency braking forces resulting from both numerical simulations and experimental tests on volunteers. Frontal impact simulation showed that the inclusion of muscle bracing in modeling dynamic impact situations can alter bone stresses to potentially injury-inducing levels.

Pedestrian lower limb injury criteria evaluation: a finite element approach

OBJECTIVE

In pedestrian traumas, lower limb injuries occur under lateral shearing and bending at the knee joint level. One way to improve injury mechanisms description and consequently knee joint safety is to evaluate the ultimate shearing and bending levels at which ligaments start being injured.

METHODS

As such data cannot easily and accurately be recorded clinically or during experiments, we show in this article how numerical simulation can be used to estimate such thresholds. This work was performed with the Lower Limb Model for Safety (LLMS) in pure lateral bending and shearing conditions, with an extended range of impact velocities.

RESULTS

One result concerns the ultimate knee lateral bending angle and shearing displacement measurements for potential failure of ligaments (posterior cruciate, medial collateral, anterior cruciates and tibial collateral). They were evaluated to be close to 16 degrees and 15 mm, respectively.

CONCLUSION

The lower leg model used in this study is an advanced FE model of the lower limb, validated under various situations. Its accurate anatomical description allows a wide range of applications. According to the validity domain of the model, it offered a valuable tool for the numerical evaluation of potential injuries and the definition of injury risk criterion for knee joint.