Lionel Thollon

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

In order to investigate injury mechanisms, and to provide directions for road safety system improvements, the HUMOS project has lead to the development of a 3D finite element model of the human body in driving position. The model geometry was obtained from a 50th percentile adult male. It includes the description of all compact and trabecular bones, ligaments, tendons, skin, muscles and internal organs. Material properties were based on literature data and specific experiments performed for the project. The validation of the HUMOS model was first achieved on isolated segments and then on the whole model in both frontal and lateral impact situations. HUMOS responses were in good agreement with the experimental data used in the model validation and offers now a wide range of applications from crash simulation, optimization of safety systems, to biomedical and ergonomics.

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.

Three-dimensional Modeling of the Various Volumes of Canines to Determine Age and Sex: A Preliminary Study

Abstract:  Canines are usually used in anthropological and forensic sciences for sex and age determination. The best methods to estimate age are based on secondary dentine apposition, evaluated from periapical X‐rays. The aim of this study was to propose a new method of sex and age estimation using 3D models to obtain more precise predictions using tooth volumes. Fifty‐eight dental CT scans of patients aged 14–74 with a well‐balanced sex ratio composed the sample. One hundred and thirty‐three healthy canines were modeled (Mimics 12.0). The sample was divided into a training sample and a validation sample. An age formula was determined using the “pulp volume/tooth volume” ratio. Sex prediction was adjusted with total volumes. Applying the equations to the validation sample, no significant difference was found between the real and predicted ages, and 100% of the sex predictions were correct. This preliminary study gives interesting results, and this method is worth being tested on a larger data sample.

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° 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.

Effects of fall conditions and biological variability on the mechanism of skull fractures caused by falls

In a forensic investigation, there is considerable difficulty in distinguishing between different mechanisms that could explain the head injury sustained. The key question is often whether the injury was the consequence of a fall, a blow, or a fall caused by a blow. Better understanding of the parameters influencing the mechanism of skull fracture could be of use when attempting to distinguish between different causes of injury. Numerous parameters concerning fall conditions and biological variability are reported in the literature to influence the mechanism of skull fracture. At the current time, there are no studies that investigate both the effect of a fall and biological parameters. The aim of this paper is to study the influence of these parameters on the mechanism of skull fracture using a numerical approach. We focused on accidental falls from a standing height. A multibody model was used to estimate head impact velocities and a finite element model was used to investigate the effect of the fall conditions and of biological variability on skull fracture. The results show that the mechanism of skull fractures is influenced by a combination of at least four parameters: impact velocity, impact surface, cortical thickness and cortical density.

Mechanisms of hyoid bone fracture after modelling: Evaluation of anthropological criteria defining two relevant models

Several studies have attempted to describe the morphology of the hyoid bone, while other authors have focused on discovering the role of this bone in the occurrence of fractures. Hyoid fractures are known to be dependent on the force applied against the bone, or on the location at which the force is applied. We wished to assess the value of defining one or more models of the hyoid bone by analyzing variations in the size and angle of the various component parts of the bone relative to the sex and morphology of an individual (height and weight) in a sample of 72 bones obtained during forensic autopsy at our institution. Statistical analyses were developed using SAS software (Statistical Analysis System, version 9.2). We observed that the length of the hyoid bone and the angle between the greater horns differed significantly between men and women. Length was significantly greater in men (38.20 ± 4.67 mm) than in women (30.49 ± 7.90 mm) and the angle between the greater horns of the hyoid bone was larger in women (36.46 ± 13.77°) than in men (27.56 ± 13.02°). There was also a statistically significant correlation between the body mass index of an individual and the length of the hyoid bone. As weight increased, the hyoid bone was found to be longer. The weight of an individual was also significantly correlated with the angle of the hyoid bone, with lower weight resulting in larger angles of the bone. Furthermore, hierarchical classification enabled the hyoid bone to be differentiated into two groups or clusters according to anthropometric measurements. ROC curves were used to determine threshold values of length, width and angle to classify the hyoid bones in these two clusters: the first was composed of individuals with longer hyoid bones, and the second of individuals with greater hyoid bone widths and wider angles. Logistic regression showed male gender was more frequently associated with the first group. The morphology of the hyoid bone can be differentiated according to the gender and corpulence of an individual because these parameters are correlated. These findings are crucial in establishing a protocol for modelling the mechanism of fracture of the hyoid bone in strangulation. Two models of the hyoid bone appear to be needed to meet the practical requirements that are the purpose of these biomechanical studies.

Development of a finite element model of the shoulder: application during a side impact

Abstract The shoulder is the most complex joint on the human body. Once shoulder injury occurs it can induce strong instability and a long rehabilitation period. Many studies in both fields of automotive safety and orthopaedic surgery have highlighted the fragility and the frequent injuries of the shoulder. To complete the understanding of shoulder biomechanics through usual experimental approaches, Finite Element simulation appears to be a valuable tool to investigate mechanical behaviour and failure processes involved in trauma situation (daily living, accident road, etc.). Hence, an advanced Finite Element model of the shoulder joint is under design and validation. This model aims to investigate the shoulder virtual trauma or instability problem. In this study we chose to focus on bone structure injuries especially with the clavicle fracture in side-impact situation.

Manual strangulation: experimental approach to the genesis of hyoid bone fractures.

Discovery of a fracture of the hyoid bone during forensic autopsy is a feature that raises suspicions of constriction of the neck. Studies have shown the influence of gender and build of the individual on the morphology of this bone. Our aims were to confirm these findings and to develop an experimental protocol for simulating manual strangulation in order to determine the force required to fracture the hyoid bone and the influence of anthropometric parameters on this force. A total of 77 intact hyoid bones were obtained, scanned, modeled, measured and embedded in resin. Using a hydraulic press, we applied force to the distal extremity of the greater horn. The relationships between the parameters of sex, weight and height of the subject, anteroposterior length of the hyoid, width between the greater horns, angle, fusion of the greater horns and force applied were analyzed. Our study confirmed sexual dimorphism, shown by greater length in males (>37.8 mm) than in females, and a larger angle in females (a shorter bone with a width>43.7 mm and an angle>31°01). The study confirmed the positive correlation between the length of the hyoid and the weight and height of the subject (p<0.05). Sixty-seven of the 77 hyoid bones fractured during the experiment (87% fracture rate). Of the fractures, 48% occurred at the junction between the body and the greater horns, 49% in the greater horns (mean distance from the distal extremity of the horn 17.33±4.37 mm), and 3% in the median part of the body. No significant association was found between gender and type of fracture, or between fusion or non-fusion of the horn (p>0.05). Fused bones were not more susceptible to fracture than non-fused bones. Fracture occurred at a mean force of 30.55 N (±18.189). Multiple linear regression showed a significant negative correlation between force required for fracture and age, weight and height of the subject, anteroposterior length and angle. The younger the individual, the slighter their build, the longer the bone and the smaller the angle, the greater the force required to fracture the hyoid bone.

Liver injuries in frontal crash situations a coupled numerical—experimental approach

From clinical knowledge, it has been established that hepatic traumas frequently lead to lethal injuries. In frontal or lateral crash situations, these injuries can be induced by pure deceleration effects or blunt trauma due to belt or steering wheel impact. Concerning the liver under frontal decelerations, how could one investigate organ behaviour leading to the injury mechanisms? This work couples experimental organ decelerations measurements (with 19 tests on cadaver trunks) and finite element simulation, provides a first analysis of the liver behaviour within the abdomen. It shows the influence of the liver attachment system that leads to liver trauma and also torsion effects between the two lobes of the liver. Injury mechanisms were evaluated through the four phases of the liver kinematics under frontal impact: (1) postero-anterior translation, (2) compression and sagittal rotation, (3) rotation in the transverse plane and (4) relaxation.

Finite element modelling and simulation of upper limb with radioss

Abstract The aim of this work is to understand the behaviour of the thoracic member (shoulder and arm) in case of side impact in motor vehicle accidents, and to identify tolerance criteria for this body region. In order to describe the dynamics involved in such impacts, and to focus on injuries mechanisms, a finite element model of the thoracic member was developed and validated with 3 Post Mortem Human Surrogates (PMHS). The geometry of the whole model was obtained from serial sections of a PMHS in driving position. It includes compact bones, ligaments, muscles and connective tissues, described with either shells, solids or spring elements. Concerning mechanical behaviour, bones and soft tissues are considered respectively as elastoplastic and viscoelastic materials. Numerical interfaces were also defined to model contacts between all components. The model was then integrated in a complete human model. Validation consisted of performing 6 subsystems tests (impactor) on instrumented PMHS placed in a car cockpit: a lateral load (37 kg at 7.55 ds) was applied directly on the shoulder. Displacements and acceleration of bones, as well as applied loads were measured. After each trial, a dissection was done to identify any injury on bones or ligaments.