Orientation of the Intercostal Muscle Fibers in the Human Rib Cage

Great improvement was achieved to protect vehicle occupants in case of a motor vehicle crashes thanks to the development of restraint systems such as seat belts and airbags . These systems increase the mechanical coupling between the human body and the vehicle to minimize the risk of severe injuries to the thorax and the head during a crash. As a result, they may induce injuries, such as rib fractures because of the loading applied to the thorax by the seat belt. Predict- ing and preventing injuries to the thorax is of particular interest as severe injuries occurred predominantly in the thorax in side impact (Welsh et al. 2009) and in elderly subjects. Significant efforts were put in the development of computational finite element models of the thorax to accurately predict the rib fractures created because of an impact (Li et al. 2010). While the mechanical response of the individual human ribs has been widely studied (Charpail et al. 2005; Kindig 2009), only few studies reported on the contribution of the inter- costal muscles (ICM) on the rib cage impact response (Vezin & Berthet 2009). Furthermore, computational studies designed to assess the con- tribution of the ICM in the thorax impact response had to face the lack of detailed description of the ICM structure such as their thickness, and their fiber orientation (Poulard & Subit 2015). Therefore, the goal of this study was to measure the orientation of the fibers in the ICM layers in the human thorax

Biofidelity Corridors for Sternum Kinematics in Low-Speed Side Impacts

Objective: Field data show that side impact car crashes have become responsible for a greater proportion of the fatal crashes compared to frontal crashes, which suggests that the protection gained in frontal impact has not been matched in side impact. One of the reasons is the lack of understanding of the torso injury mechanisms in side impact. In particular, the deformation of the rib cage and how it affects the mechanical loading of the individual ribs have yet to be established. Therefore, the objective of this study was to characterize the ribcage deformation in side impacts by describing the kinematics of the sternum relative to the spine. Methods: The 3D kinematics of the 1st and of the 5th or 6th thoracic vertebrae and of the sternum were obtained for three Post Mortem Human Subjects (PMHS) impacted laterally by a rigid wall traveling at 15 km/h. The experimental data were processed to express the kinematics of the sternum relative to the spine throughout the impact event. Methods were developed to interpolate the kinematics of the vertebrae for which experimental data were not available. Results: The kinematics of the sternocostal junction for ribs 1 to 6 as well as the orientation of the sternum were expressed in the vertebra coordinate systems defined for each upper thoracic vertebra (T1 to T6). Corridors were designed for the motion of the sternum relative to each vertebra. In the experiments, the sternum moved upward for all rib levels (1 to 6), and away from the spine with an amplitude that increased with the decreasing rib level (from rib 1 to rib 6). None of the differences observed in the kinematics could be correlated to the occurrence of rib fractures. Conclusions: This study provides both qualitative and quantitative information for the ribcage skeletal kinematics in side impact. This data set provides the information required to better evaluate computational models of the thorax for side impact simulations. The corridors developed in this study provide new biofidelity targets for the impact response of the ribcage. This study contributes to augmenting the state of knowledge of the human chest deformation in side impact to better characterize the rib fracture mechanisms.The analysis performed in this study has been funded by and carried out in association with SAFER - Vehicle and Traffic Safety Centre at Chalmers University of Technology, Sweden. D. Subit thanks European Union for its financial support through the Marie Curie International Incoming Fellowship (FP7-PEOPLE-2013-IIF, project BioAge # 622905). F. M ¨ ohler gratefully acknowledges the financial support from the Franco-German University through the Franco-German double degree program between ENSAM and KIT. The views expressed in this article are those of the authors and do not necessarily represent the views of the funding bodies

Pediatric, adult and elderly bone material properties

Age dependence; Bone; Coupon; Full field strain measurements; Quasi-static and dynamic tensile testsPostprint (published version

Upper Body Skeletal Posture of the Average Pedestrian Male from Upright High-Resolution X-ray Images – Comparison to the THUMS Pedestrian Model

No Abstrac

The Contribution of Pre-impact Posture on Restrained Occupant Finite Element Model Response in Frontal Impact.

Objective: The objective of this study was to discuss the influence of the pre-impact posture to the response of a finite element human body model (HBM) in frontal impacts. Methods: This study uses previously published cadaveric tests (PMHS), which measured six realistic pre-impact postures. Seven postured models were created from the THUMS occupant model (v4.0): one matching the standard UMTRI driving posture as it was the target posture in the experiments, and six matching the measured pre-impact postures. The same measurements as those obtained during the cadaveric tests were calculated from the simulations, and biofidelity metrics based on signals correlation (CORA) were established to compare the response of the seven models to the experiments. Results: The HBM responses showed good agreement with the PMHS responses for the reaction forces (CORA = 0.80 ± 0.05) and the kinematics of the lower part of the torso but only fair correlation was found with the head, the upper spine, rib strains (CORA= 0.50 ± 0.05) and chest deflections (CORA = 0.67 ± 0.08). All models sustained rib fractures, sternal fracture and clavicle fracture. The average number of rib fractures for all the models was 5.3 ± 1.0, lower than in the experiments (10.8 ± 9.0). Variation in pre-impact posture greatly altered the time histories of the reaction forces, deflections and the rib strains, mainly in terms of time delay, but no definite improvement in HBM response or injury prediction was observed. By modifying only the posture of the HBM, the variability in the impact response was found to be equivalent to that observed in the experiments. The postured HBM sustained from 4 to 8 rib fractures, confirming that the pre-impact posture influenced the injury outcome predicted by the simulation. Conclusions: This study tries to answer an important question: what is the effect of occupant posture on kinematics and kinetics. Significant differences in kinematics observed between HBM and PMHS suggesting more coupling between the pelvis and the spine for the models which makes the model response very sensitive to any variation in the spine posture. Consequently, the findings observed for the HBM cannot be extended to PMHS. Besides, pre-impact posture should be carefully quantified during experiments and the evaluation of HBM should take into account the variation in the predicted impact response due to the variation in the model posture.This work was supported by funds from Toyota Collaborative SafetyResearch Center (ToyotaCSRC). The experimentswere funded by the NHTSA and the Japan Automobile Research Institute (JARI). The views expressed in this article are those of the authors and do not necessarily represent or reflect the views of the sponsors. The authors acknowledge Masao Muraji and Corinne Uskali (Toyota Motor Engineering & Manufacturing, North America) for their contribution to the design of the study

Experimental investigation of the effect of occupant characteristics on contemporary seat belt payout behavior in frontal impacts.

Objective: The goal of this study was to investigate the influence of the occupant characteristics on seat belt force vs. payout behavior based on experiment data from different configurations in frontal impacts. Methods: The data set reviewed consists of 58 frontal sled tests using several anthropomorphic test devices (ATDs) and postmortem human subjects (PMHS), restrained by different belt systems (standard belt, SB; force-limiting belt, FLB) at 2 impact severities (48 and 29 km/h). The seat belt behavior was characterized in terms of the shoulder belt force vs. belt payout behavior. A univariate linear regression was used to assess the factor significance of the occupant body mass or stature on the peak tension force and gross belt payout. Results: With the SB, the seat belt behavior obtained by the ATDs exhibited similar force slopes regardless of the occupant size and impact severities, whereas those obtained by the PMHS were varied. Under the 48 km/h impact, the peak tension force and gross belt payout obtained by ATDs was highly correlated to the occupant stature (P = .03, P = .02) and body mass (P = .05, P = .04), though no statistical difference with the stature or body mass were noticed for the PMHS (peak force: P = .09, P = .42; gross payout: P = .40, P = .48).With the FLB under the 48 km/h impact, highly linear relationshipswere noticed between the occupant body mass and the peak tension force (R2 =0.9782) and between the gross payout and stature (R2 =0.9232) regardless of the occupant types. Conclusions: The analysis indicated that the PMHScharacteristics showed a significant influence on the belt response, whereas the belt response obtained with the ATDs was more reproducible. The potential cause included the occupant anthropometry, body mass distribution, and relative motion among body segments specific to the population variance. This study provided a primary data source to understand the biomechanical interaction of the occupant with the restraint system. Further research is necessary to consider these effects in the computational studies and optimized design of the restraint system in a more realistic manner.The experiments reviewed in this study were funded by the NHTSA and Autoliv Research. The opinions expressed herein are solely those of the authors

Influence of bone microstructure on the mechanical properties of skull cortical bone – A combined experimental and computational approach

The strength and compliance of the dense cortical layers of the human skull have been examined since the beginning of the 20th century with the wide range in the observed mechanical properties attributed to natural biological variance. Since this variance may be explained by the difference in structural arrangement of bone tissue, micro-computed tomography (μCT) was used in conjunction with mechanical testing to study the relationship between the microstructure of human skull cortical coupons and their mechanical response. Ninety-seven bone samples were machined from the cortical tables of the calvaria of ten fresh post mortem human surrogates and tested in dynamic tension until failure. A linear response between stress and strain was observed until close to failure, which occurred at 0.6% strain on average. The effective modulus of elasticity for the coupons was 12.01 ± 3.28 GPa. Porosity of the test specimens, determined from μCT, could explain only 51% of the variation of their effective elastic modulus. Finite element (FE) models of the tested specimens built from μCT images indicated that modeling the microstructural arrangement of the bone, in addition to the porosity, led to a marginal improvement of the coefficient of determination to 54%. Modulus for skull cortical bone for an element size of 50 μm was estimated to be 19 GPa at an average. Unlike the load bearing bones of the body, almost half of the variance in the mechanical properties of cortical bone from the skull may be attributed to differences at the sub-osteon ( < 50 μm) level. ANOVA tests indicated that effective failure stress and strain varied significantly between the frontal and parietal bones, while the bone phase modulus was different for the superior and inferior aspects of the calvarium. The micro FE models did not indicate any anisotropy attributable to the pores observable under μCT.This research was sponsored by contract no. N00421-11-C-0004 from the U.S. Naval Air Warfare Center, Aircraft Division, Patuxent River, MD

Modélisation de la liaison os-ligament dans l'articulation du genou

This PhD thesis is devoted to the improvement of the knowledge of the soft tissues mechanical behaviour, particularly in the field of accidentology. This study aims at linking the concepts of injury used for clinical diagnostic and these of damage and failure used in mechanics. It deals with the modeling of the ligaments behaviour in the knee joint, and the role played by ligament-to-bone insertion in particular. This structure, composed of the ligament and the insertion sites, is injured either in the ligament itself (in the midsubstance) or near the ligament-to-bone transition. This problem is original according to anatomical and mechanical points of view. Anatomically there is no precise description at the microscopic level of the architecture of this transition, that seems to be very sharp at the macroscopic level, whereas it is a possible place of injury. Mechanically, it is the study of a biological tissue that is besides the transition from a mineralised hard tissue (the bone) to a non mineralised soft tissue composed of long fibres (the ligament). The methodology developed here was: understanding how the knee joint works and which injuries and traumatims occur in this joint, determining what the transition is composed of and how its components are organised, by performing a histological study, describing its mechanical behaviour and its contribution to the global behaviour of the knee, by developing an experimental protocol, and, lastly, developing a model of the mechanical behaviour of the ligament-to-bone transition. This study is devoted to the posterior cruciate and lateral collateral ligaments, the injury mechanisms of which, in the case of road accidents, were more specifically studied. The architecture of the ligament-to-bone transition was described thanks to light and electron microscopies: it is the superimposition of a mineralisation front and structural changes in the tissue (there is fibrocartilage). This transition is about 300 micrometres. The experimental tensile tests were performed on the ligament insertion - ligament - ligament insertion structure cut off from post mortem human subjects (PMHS). The structure was subjected to tensile load, either along the fiber direction, or in a realistic direction according to anatomical considerations (physiological configuration). The protocols developed in this thesis enable to perform non destructive cyclic tests, and failure tests, under quasi - static (1 mm/s and 20 mm/s) and dynamic (0.5 m/s and 1 m/s) loadings. For the physiological configuration, knees were tested with an angle of knee flexion of 180 degres (standing position) and 120 degres (driving position). The experimental results show that the ligaments dissipate energy during cyclic loading because of internal friction, and that their behaviours highly depend on the angle of knee flexion, at least in the loading range tested. Under quasi-static conditions, failure always occurs by avulsion in the cortical bone. Under dynamic conditions, in the loading range tested, there is firstly loss of cohesiveness between ligament fibres, but failure occurs most often because of deep alvusion of trabecular bone. Considering that the ligament mechanical behaviour depends on the orientation of the insertion sites, and knowing the microstructure of the insertion site, we chose an interface model to describe its behaviour. Two models of cohesive zones (coupling friction, adhesiveness, and damage) were developed to predict ligament injuries due to bone avulsion and loss of cohesiveness between ligament fibres.Cette thèse est une contribution à l'amélioration de la connaissance des comportements mécaniques des tissus biologiques, en particulier dans le contexte accidentologique. L'objectif de cette étude biomécanique est de faire le lien entre les notions de lésions utilisées en clinique et celles d'endommagement et de rupture utilisées en mécanique. Elle porte sur la modélisation du comportement des ligaments dans l'articulation du genou humain, et s'intéresse plus particulièrement à l'insertion du ligament dans l'os. Les lésions qui touchent cette structure se produisent soit dans le ligament, soit dans une région proche de la zone de transition entre l'os et le ligament. Ce problème est original sur les plans anatomique et mécanique. Sur le plan anatomique, il n'existe pas de description fine (c'est-à-dire à l'échelle microscopique) de l'architecture de cette transition, qui paraît brutale à l'oeil nu et qui est un lieu possible de lésion ligamentaire. Sur le plan mécanique, il s'agit de l'étude d'un tissu biologique, qui comprend de plus la transition entre un tissu dur minéralisé (l'os) et un tissu mou non minéralisé à fibres longues (le ligament). La méthodologie a donc été de comprendre le fonctionnement de l'articulation du genou et les lésions et traumatismes dont elle est le lieu, de connaître la composition et l'organisation des tissus qui constituent cette transition, au moyen d'un étude histologique, de décrire son comportement mécanique dans le fonctionnement du ligament, par le développement d'un protocole expérimental, et enfin de développer un modèle de comportement de l'insertion ligamentaire. L'étude porte sur les ligaments croisé postérieur et latéral externe, ligaments dont les mécanismes lésionnels dans le cas des accidents de la route ont été plus particulièrement étudiés. L'architecture de la zone de transition en microscopies optique et électronique a été décrite et a montré qu'elle est la superposition d'un front de minéralisation et d'un changement de la structure du tissu (présence de cartilage fibreux). Cette transition se fait sur une longueur d'environ 300 micromètres. Les essais expérimentaux de traction ont été réalisés sur la structure insertion ligamentaire - ligament - insertion ligamentaire prélevée sur sujets d'anatomie. La sollicitation a été appliquée soit dans la direction des fibres ligamentaires, soit une direction réaliste du point de vue physiologique. Les protocoles développés permettent de faire des essais cycliques sans endommager les tissus et des essais à rupture sous sollicitations quasi-statiques (1 mm/s et 20 mm/s) et dynamiques (0.5 m/s et 1 m/s). Pour les essais dans la configuration physiologique, les genoux ont été testés en extension complète (station érigée) et à 120 degrés de flexion (position de conduite). Les résultats expérimentaux montrent que, pour les vitesses et amplitudes testées, les ligaments dissipent de l'énergie par frottement interne et que leur comportement est très dépendant de l'angle de flexion du genou. La rupture se produit toujours par arrachement osseux au niveau de l'os cortical en quasi-statique. En dynamique, pour la vitesse testée, il y a toujours décohésion entre fibres dans le ligament, mais la rupture se produit le plus souvent par arrachement de l'os spongieux en profondeur. L'étude du comportement du ligament (influence de l'orientation de l'insertion ligamentaire) et de la micro-structure de l'insertion nous ont menés à choisir un modèle d'interface pour décrire son comportement. Deux modèles de zones cohésives (couplant frottement, adhésion et éventuellement endommagement) ont été développés pour prédire les lésions par arrachement osseux et par décohésion entre les fibres ligamentaires