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The trend towards patient-specific medical orthopedic prostheses has led to an increased use of 3D-printed surgical implants made of Ti6Al4V. However, uncertainties arise due to varying printing parameters, particularly with regards to the fatigue limit. This necessitates time-consuming and costly experimental validation before they can be safely used on patients. To address this issue, this study aimed to employ a stress-life fatigue analysis approach coupled with a finite element (FE) simulation to estimate numerically the fatigue limit and location of failure for 3D-printed surgical osteosynthesis plates and to validate the results experimentally. However, predicting the fatigue life of 3D components is not a new concept and has previously been implemented in the medical device field, though without experimental validation. Then, an experimental fatigue test was conducted using a proposed modification to the staircase method introduced in ISO 12107. Additionally, a FE model was developed to estimate the stress cycles on the plate. The stress versus number of cycles to failure curve (S-N) obtained from the minimum mechanical properties of 3D-printed Ti6AI4V alloy according to ASTM F3001-14 to predict the fatigue limit. The comparison between experimental results and fatigue numerical predictions showed very good agreement. It was found that a linear elastic FE model was sufficient to estimate the fatigue limit, while an elastic-plastic model led to an accurate prediction throughout the implant’s cyclic life. The proposed method has great potential for enhancing patient-specific implant designs without the need for time-consuming and costly experimental regulatory testing.

Influence of footwear on posture in athletes is poorly documented despite its potential impact on biomechanics and injury risk. The aim of this study was to investigate effects of different footwear geometries on comfort and posture on a cohort of 48 elite rugby players. Spine posture was characterized by photogrammetry, while center of pressure was measured by means of a force platform. Three different footwear outsoles architectures (one rugby shoe with flat outsole, one rugby shoe with a 10 mm heel rise and foot arch support, and a running shoe with a 10mm heel rise and foot arch support) were compared to non-shod in randomized order. Then comfort felt at the level of foot and spine was also estimated by subjective questionnaires. Compared to the flat rugby model, both other models induced significantly (p

Objective: Proprioceptive senses play an important role in human body reflex and movement, so far implementing physiological mathematical models of proprioceptors in the musculoskeletal model and investigating their effects have not been sufficiently investigated. The purpose of the present study was to establish a compact framework for a lower limb musculoskeletal model by considering both ascending signals from central nervous system and descending feedback neural signal from physiologically realistic proprioceptors and evaluate it with progressive experimental data as well as investigating the effects of the proprioceptive feedback on the human movement. Methods: The simulation framework was established by combining a lower limb musculoskeletal model, the forward dynamic tool from OpenSim codes, and an executive program based on Python codes. The physiological mathematical models of the muscle spindle and Golgi tendon organs were included in the feedback control loop for the model. The model was evaluated through both previous literature data and currently implemented volunteer reflex experiments from the neural organ level to the monosynaptic reflex loop, and finally the complicated movement, such as the firing rate of the proprioceptors, the knee-jerk reflex, and the normal gait. Simultaneously, the effects of the proprioceptors on human normal gait were initially investigated. Results: The reliability of the framework was properly evaluated by comparing the experimental data of neural firing rate, electromyography signals, and joint kinematics. The gait analysis indicated that the introduction of the proprioceptors in the motor control loop can substantially resist the external disturbance. Conclusion: The established framework has been evaluated at different levels, and it can be extended and applied to different musculoskeletal models for human movement analysis and evaluate the effects of the proprioceptors on them.

The development of artificial prosthetic lower limbs aims to improve patient’s mobility while avoiding secondary problems resulting from the use of the prostheses themselves. The residual limb is a pressure-sensitive area where skin injuries and pain are more likely to develop. Requirements for adequate prosthetic limbs have now become urgent to improve amputee’s quality of life. This study aims to understand how socket design parameters related to geometry can influence pressure distribution in the residual limb. A finite element model was developed to simulate the mechanical loading applied on the residual limb of a below-knee amputee while walking. A sensitivity analysis to socket initial geometry, scaling the socket downward in the horizontal plane, was performed. Recordings include stress levels on the skin and in the residual limb deep soft tissues. Peak stress was reduced by up to 51% with a limited reduction of the socket size. More important scale reduction of the residual limb would lead to possible negative effects, such as stress concentrations in sensitive areas. This result confirms the interest of the prosthetist to develop a well-fitting socket, possibly a little smaller than the residual limb itself, in order to avoid residual limb mobility in the socket that could cause friction and stress concentrations. Non-homogeneous geometrical reductions of the socket should be further investigated.

Purpose The aim of this study is to evaluate the morphological variability in mandibles with different types of edentulism, comparing the use of traditional morphometrics and tridimensional geometric morphometrics. Methods Traditional morphometrics and geometric morphometrics (GM) exploratory analysis, by principal components (PCs) and PC scores, were performed on a sample of 24 cadaveric hemi mandibles. A digital reconstruction of 3D surfaces of each specimen was obtained by CT scans segmentation. The mandibles were divided in three groups: full dentition (G1), partial edentition (G2) and total edentition (G3). The results of the two methods were compared in relation to the morphological variability determined with each method. Results Both methods were consistent in terms of morphological variability between the defined groups. The main shape variations observed were a decrease in mandibular body height, a widening of the cross sectional morphology on the symphysis, a shorten-narrowed Ramus and a deeper sigmoid notch, in the partially or totally edentition groups, compared to the full dentition group. Discussion The general patterns of morphological variations associated with edentulism that have been reported in literature could be visualized with GM method, which had not been previously used for this purpose. The GM methods could offer a more detailed definition of shape variations, which is critical in a clinical context. Moreover, GM allowed defining configurations of mean morphologies and an image library with different types of morphological variations.

Background Prosthetic rehabilitation improves the overall quality of life of patients, despite discomfort and medical complications. No quantitative assessment of prosthesis-patient interaction is used in routine protocols and prosthesis quality still results from the manufacturer's know-how. Objective Our objective is to investigate whether pressure can be a relevant factor for assessing socket adequacy. Methods A total of 8 transtibial amputee volunteers took part in this experimental study. The protocol included static standing and 2 minutes walking tests while the stump-to-socket interface pressures were measured. Questionnaires on comfort and pain were also conducted. Results During static standing test, maximum pressures were recorded in the proximal region of the leg, with a peak value reaching 121.1 ± 31.6 kPa. During dynamic tests, maximum pressures of 254.1 ± 61.2 kPa were recorded during the loading phase of the step. A significant correlation was found between the pain score and static maximum recorded pressure (r= 0.81). Conclusions The protocol proposed and evaluated in this study is a repeatable, easy-to-set quantified analysis of the patient to socket interaction while standing and walking. This approach is likely to improve feedback for prosthesis manufacturers and consequently the overall design of prostheses.

Computational biomechanics for human body modeling has generally been categorized into two separated domains: finite element analysis and multibody dynamics. Combining the advantages of both domains is necessary when tissue stress and physical body motion are both of interest. However, the method for this topic is still in exploration. The aim of this study is to implement unique controlling strategies in finite element model for simultaneously simulating musculoskeletal body dynamics and in vivo stress inside human tissues. A finite element lower limb model with 3D active muscles was selected for the implementation of controlling strategies, which was further validated against in-vivo human motion experiments. A unique feedback control strategy that couples together a basic Proportion-Integration-Differentiation (PID) controller and generic active signals from Computed Muscle Control (CMC) method of the musculoskeletal model or normalized EMG singles was proposed and applied in the present model. The results show that the new proposed controlling strategy show a good correlation with experimental test data of the normal gait considering joint kinematics, while stress distribution of local lower limb tissue can be also detected in real-time with lower limb motion. In summary, the present work is the first step for the application of active controlling strategy in the finite element model for concurrent simulation of both body dynamics and tissue stress. In the future, the present method can be further developed to apply it in various fields for human biomechanical analysis to monitor local stress and strain distribution by simultaneously simulating human locomotion.

Summary Purpose The aim of this study was to perform an exploratory analysis of the morphological variations of mandibles at diverse states of edentulousness using tridimensional geometric morphometrics. Methods Twelve cadaveric mandibles were selected and divided in three groups: dentate (G1), partially edentate (G2) and totally edentate (G3). CT scans, segmentation and digital reconstruction of 3D surfaces of each specimen was made. Thirteen landmarks were defined; the measurement error was determined and 3D morphometrics exploratory analysis by principal components (PCs) and PC scores was performed. Results The principal shape variations in G2 and G3 compared to G1 can be summarized as follows: (1) decrease in the mid body mandibular height of 24% in G2 and 41% in G3, (2) decrease of symphysis height of 16% in G2 and 37% in G3, (3) a decrease in posterior mandibular height of 30% in both G1 and G2, (4) a deeper sigmoid notch also in both groups and finally (5) a widening of 7.7% in the cross sectional morphology on the symphysis in G3. Conclusions The 3D morphometric methods, combined with surface morphing tools confirmed the main patterns of bone changes in edentulous mandibles, referenced in the literature. The average 3D mandibular morphologies of each edentulousness state group was also defined. These methods could offer more accurate definition of shape variations, which is critical in a clinical context. This study provides clinicians with highlights of 3D morphological mandibular variations at different states of edentulism and not only in 2D projections as they are currently described. The 3D surface model for each group in PDF3D file format, are include in supplementary material.

Finite element analysis (FEA) has been widely used to study foot biomechanics and pathological functions or effects of therapeutic solutions. However, development and analysis of such foot modeling is complex and time-consuming. The purpose of this study was therefore to propose a method coupling a FE foot model with a model order reduction (MOR) technique to provide real-time analysis of the dynamic foot function. A generic and parametric FE foot model was developed and dynamically validated during stance phase of gait. Based on a design of experiment of 30 FE simulations including four parameters related to foot function, the MOR method was employed to create a prediction model of the center of pressure (COP) path that was validated with four more random simulations. The four predicted COP paths were obtained with a 3% root-mean-square-error (RMSE) in less than 1 s. The time-dependent analysis demonstrated that the subtalar joint position and the midtarsal joint laxity are the most influential factors on the foot functions. These results provide additionally insight into the use of MOR technique to significantly improve speed and power of the FE analysis of the foot function and may support the development of real-time decision support tools based on this method.

Background Today there is still a controversy surrounding the existence of mobility between the bones of the skull, the foundation on which cranial osteopathy techniques are based. The lack of total closure for the sutures of young people or simply the suture discontinuity of the elderly would mean there is residual mobility or at least a weakness area. Objectives The goal of our work was to study skull deformation as an indicator of possible mobility or altered stiffness area under slow loading on either side of the sagittal suture using a digital-image-correlation based system. Methods Quasi-static load trials under compression were performed on 4 human skulls at a displacement rate of 0.5 mm/s. The digital image correlation technique was used to measure the maximum and minimum principal strain on the sagittal suture. Results The results of this study show that the strain field remains homogeneous in the areas observed, even when compression force reaches values exceeding 100 N. Conclusion No particular concentration of strain in the immediate vicinity of the suture was detected with our measurement method, which would have suggested a relative displacement or a weakness area in the region of the two bones margins on the sagittal suture.

Background The axial motion of aortic root (AR) due to ventricular traction was previously suggested to contribute to ascending aorta (AA) dissection by increasing its longitudinal stress, but AR in-plane motion effects on stresses have never been studied. The objective is to investigate the contribution of AR in-plane motion to AA stress levels. Methods The AR in-plane motion was assessed on magnetic resonance imagining data from 25 healthy volunteers as the movement of the AA section centroid. The measured movement was prescribed to the proximal AA end of an aortic finite element model to investigate its influences on aortic stresses. The finite element model was developed from a patient-specific geometry using LS-DYNA solver and validated against the aortic distensibility. Fluid–structure interaction (FSI) approach was also used to simulate blood hydrodynamic effects on aortic dilation and stresses. Results The AR in-plane motion was 5.5 ± 1.7 mm with the components of 3.1 ± 1.5 mm along the direction of proximal descending aorta (PDA) to AA centroid and 3.0 ± 1.3 mm perpendicularly under the PDA reference system. The AR axial motion elevated the longitudinal stress of proximal AA by 40% while the corresponding increase due to in-plane motion was always below 5%. The stresses at proximal AA resulted approximately 7% less in FSI simulation with blood flow. Conclusions The AR in-plane motion was comparable with the magnitude of axial motion. Neither axial nor in-plane motion could directly lead to AA dissection. It is necessary to consider the heterogeneous pressures related to blood hydrodynamics when studying aortic wall stress levels. Electronic supplementary material The online version of this article (10.1186/s12938-019-0632-7) contains supplementary material, which is available to authorized users.

Statement of problem Implant prosthodontics provides high-quality outcomes thanks to recent technological developments and certification procedures such as International Organization for Standardization (ISO) 14801. However, these certification tests are costly, and the result is highly uncertain as the influence of design variables (materials and structure) is still unknown. The design process could be significantly improved if the influence of design parameters were identified. Purpose The purpose of this in vitro study was to use finite element analysis (FEA) to assess the influence of design parameters on the mechanical performance of an implant in regard to testing conditions of ISO 14801 standard. Material and methods An endosseous dental implant was loaded under ISO 14801 testing conditions by numerical simulation, with 4 parameters evaluated under the following conditions: conditions of the contact surface area between the implant and the loading tool, length of the fixation screw, implant embedding depth, and material used for implant stiffness. FEA was used to compare the force that needed to reach the implant’s yield and fracture strength. Results A dental implant’s fracture point can be increased by 41% by improving the contact surface area, by 20% depending on the type of material, by 4% depending on the length of the fixation screw, and by 1.4% by changing the implant embedding depth. Conclusions FEA made it possible to evaluate 4 performance parameters of a dental implant under ISO 14801 conditions. Under these conditions, the contact surface area was found to be the major parameter influencing implant performance. This observation was validated experimentally in a fatigue test under ISO 14801 conditions.

Leg length discrepancies (LLD) are a common reason for podiatry consultations and can affect up to 90% of the overall population. Furthermore, it is widely recognized that intensive participation in certain sports can alter bone development. The aim of this study is to explore any possible relation between playing soccer and the appearance or evolution of LLD, by means of a retrospective study based on the analysis of case reports of patients followed for foot or plantar troubles. Case reports were selected in the archives of a podiatric clinic for the period between 2002 and 2016 among patients who declared regular to intensive soccer playing, aged 13 years or more. LLD was detected in the vast majority of cases (95 cases out of 104). Pearson correlation coefficients were computed and revealed a strong correlation between the laterality of the kicking limb and that of the shorter leg. The shorter limb was on the side of the kicking leg in 96% of the cases when considering the players who began practice before the age of 13, and only 53% of the cases for others. Intensive soccer playing at a young age may encourage the appearance and evolution of a real LLD.

This study documents the development of adverse fetal outcome predictors dedicated to the analysis of road accidents involving pregnant women. To do so, a pre-existing whole body finite element model representative of a 50th percentile 26 weeks pregnant woman was used. A total of 8 accident scenarios were simulated with the model positioned on a sled. Each of these scenarios was associated to a risk of adverse fetal outcome based on results from real car crash investigations involving pregnant women from the literature. The use of airbags and accidents involving unbelted occupants were not considered in this study. Several adverse fetal outcome potential predictors were then evaluated with regard to their correlation to this risk of fetal injuries. Three predictors appeared strongly correlated to the risk of adverse fetal outcome: (1) the intra uterine pressure at the placenta fetal side area (r = 0.92), (2) the fetal head acceleration (HIC) (r = 0.99) and (3) area of utero-placental interface over a strain threshold (r = 0.90). Finally, sensitivity analysis against slight variations of the simulation parameters was performed and assess robustness of these criteria.

44th Congress of the Société de Biomécanique, Poitiers, FRANCE, 28-/10/2019 - 30/10/2019; With aging of the global population, the number of aortic flow related cardiovascular diseases (CVD) as aneurysm, dissection and atherosclerosis are increasing (Craiem et al. 2017). In such pathologies the part of the flow in the physio-pathological mechanism has still to be described and proven. In aneurysm, wall shear stress changes have been shown to be related to occurrence of burst (Vorp 2007). Additionally, wall shear stress has also been proven to be correlated with the changes in aortic tissue in ascending aorta (van Ooij et al. 2015; Lantz et al. 2011). In dissection, a study has revealed that the increase in WSS was related to alterations of the aortic morphology (Chi et al. 2017). The morphology of aorta as well as material properties of the wall changes with gender, age and body Surface Area (Biaggi et al. 2009). However the current aortic flow simulations rarely take into account the changes in the morphology (van Ooij et al. 2016). Additionally in vascular and thoracic surgery, description of the aortic morphology through a centreline has enable to describe a normal morphology according with the patient data. Aortic shapes description has also involved architectural concept as Gothic arch (Ou et al. 2006).

Background: The prolonged standing position is an important factor in the onset of foot musculoskeletal disorders among workers. Safety shoes, designed to protect against the physical constraints of the work environment, do not address this issue to date. Objectives: The goal of this study is to assess the possible benefits of custom-made foot orthoses among prolonged standing workers. Study design: repeated measures without control group. Methods: Thirty-four standing workers who suffer from foot pain volunteered for the study. Custom-made foot orthoses, designed by a podiatrist, were 3D-printed and distributed to each volunteer. Static balance as well as static and dynamic plantar pressure measurements were carried out with sensors inserted in the safety shoes, before and after three weeks of wearing foot orthoses daily. A questionnaire on pain and comfort was also distributed before and after treatment. Results: Feelings of pain, discomfort and heavy legs were found to be significantly reduced after wearing 3D-printed orthoses (p

International audience; Blunt aortic injuries are common and severe in motor vehicle crash accidents (MVCAs), but the injury mechanisms, which can be categorised as kinematics and hydrodynamics aspects, remain to be uncertain. In this study, a finite element model was developed for the aorta-heart system with fluid–structure interaction methods, aimed to study both kinds of mechanisms simultaneously. The aortic blood flow was generated by simulating left ventricle contraction. This model was further integrated with a human body model to reconstruct a real car crash case. The aorta-heart model was validated against ventricular volume, blood pressure, velocity, flow rate and wall shear stress. The integrated model predicted aorta isthmus laceration and other injuries consistent with the case injury reports. The cardiac output during the accident was more intense than the physiological output, proving the ability of current simulation approach to capture the blood flow modification by the thoracic compressive loadings during accidents.

Plantar heel pain is one of the most common musculoskeletal disorders and generally causing long term discomfort of the patients. The objective of the present study is to combine in vivo experimental measurements and finite element modelling of the foot to investigate the influences of stiffness and thickness variation of individual plantar tissues especially the heel pad on deformation behaviours of the human foot. The stiffness and thickness variance of individuals were measured through supersonic shear wave elastography considering detailed heel pad layers refered to in literature as: dermis, stiffer micro-chamber layer, softer macro-chamber layer. A corresponding foot model with separated heel pad layers was established and used to a sensitivity analysis related to the variance of above-mentioned tissue characteristics. The experimental results show that the average stiffness of the micro-chamber layer ranged from 24.7 (SD 2.4) kPa to 18.8 (SD 3.5) kPa with the age group increasing from 20–29 years old to 60–69 years old, while the average macro-chamber stiffness is 10.6 (SD 1.5) kPa that appears to slightly decrease with the increasing age. Both plantar soft tissue stiffness and thickness of male were generally larger than that of female. The numerical simulation results show that the variance of heel pad strain level can reach 27.5% due to the effects of stiffness and thickness change of the plantar tissues. Their influences on the calcaneus stress and plantar pressure were also significant. This indicates that the most appreciate way to establish a personalized foot model needs to consider the difference of both individual foot anatomic geometry and plantar soft tissue material properties.

We present an original method using a low cost accelerometer and a Kalman-filter based algorithm to monitor cardiopulmonary resuscitation chest compressions (CC) depth. A three-axis accelerometer connected to a computer was used during CC. A Kalman filter was used to retrieve speed and position from acceleration data. We first tested the algorithm for its accuracy and stability on surrogate data. The device was implemented for CC performed on a manikin. Different accelerometer locations were tested. We used a classical inertial navigation algorithm to reconstruct CPR depth and frequency. The device was found accurate enough to monitor CPR depth and its stability was checked for half an hour without any drift. Average error on displacement was ±0.5mm. We showed that depth measurement was dependent on the device location on the patient or the rescuer. The accuracy and stability of this small low-cost accelerometer coupled to a Kalman-filter based algorithm to reconstruct CC depth and frequency, was found well adapted and could be easily implemented.

This study proposed to broadly examine vehicle use by pregnant women in order to improve realism of accident simulations involving these particular occupants. Three research pathways were developed: the first consisted in a questionnaire survey examining the driving habits of 135 pregnant women, the second obtained measurements of 15 pregnant women driving position in their own vehicle from the 6th to the 9th month of pregnancy by measuring distances between body parts and vehicle parts, and the third examined car accidents involving pregnant occupants. Results obtained indicate that between 90% and 100% of pregnant women wore their seat belts whatever their stage of pregnancy, although nearly one third of subjects considered the seat belt was dangerous for their unborn child. The measurements obtained also showed that the position of the pregnant woman in her vehicle, in relation to the various elements of the passenger compartment, changed significantly during pregnancy. In the studied accidents, no correlation was found between the conditions of the accident and the resulting fetal injury. Results reveal that pregnant women do not modify significantly the seat setting as a function of pregnancy stage. Only the distance between maternal abdomen and steering wheel change significantly, from 16 cm to 12 cm at 6 and 9 month respectively. Pregnant women are mainly drivers before 8 months of pregnancy, passengers after that. Car use frequency falls down rapidly from 6 to 9 months of pregnancy. Real crashes investigations indicate a low rate of casualties, i.e. 342 car accidents involving pregnant women for a period of 9 years in an approximately 1.7 million inhabitants area. No specific injury was found as a function of stage of pregnancy.

Soccer is the most popular sport in the world and generates great financial revenue. It is also a sport whose practice has evolved considerably in terms of intensity and commitment, and in which the intrinsic risk of injury (not directly related to an interaction with the environment) is particularly high. In this context, the cleated shoe as a major component of soccer equipment may play a key role in the overexposure to injury. Soccer shoe evolution is all the more challenging, because design and mechanical structure differ in many points compared to other modern shoes developed for sports such as running, tennis and basketball.This critical review aims to elucidate the characteristics of modern soccer footwear and their possible link to soccer-specific injuries, focusing on the following areas: (1) ergonomics, comfort and proprioception; (2) shoe mechanical characteristics; (3) field surfaces and shoe design.

Aim Anorectal manometry is the most common test used to explore anorectal disorders. The recent three-dimensional high-resolution anorectal manometry (3D-HRAM) technique appears to be able to provide new topographic information. Our objective was to develop an automated analysis of 3D-HRAM images to diagnose anal sphincter defects and compare the results with those of endoanal ultrasonography (EUS), which is considered to be the gold standard. Method All patients being tested in our department for faecal incontinence or dyschezia by 3D-HRAM and EUS were eligible for the study. 3D-HRAM was used to record resting and squeeze pressure, reflecting internal and external anal sphincter function, respectively. A software platform was designed to automatically analyse the 3D-HRAM images and calculate a diagnostic score for any anal sphincter defect compared with EUS. Results A total of 206 (91% female) patients of mean age of 54 years were included in the study. A sphincter defect was diagnosed by EUS in 130 (63%). The diagnostic scores from the 3D-HRAM automated analysis for an internal anal sphincter defect showed a sensitivity of 65% and a specificity of 65%. For an external anal sphincter defect, the sensitivity was 43% and the specificity 87%. Conclusion Our study developed a method based on 3D-HRAM to automatically diagnose sphincter defects, allowing a systematic and comprehensive analysis of the test recordings. Compared with EUS, the 3D-HRAM image analysis procedure revealed poor sensitivity and specificity.

Road accidents can lead to abdominal injuries ranging from severe to lethal, that include hemorrhage of organs and their attachment system. A good understanding and prediction of abdominal injuries therefore requires investigation of the mechanical properties of the attachment systems of abdominal organs. In particular, the gastrocolic ligament (GCL) is one major link between the stomach and the transverse colon. This study aims to investigate the mechanical properties of the GCL under very low and high strain rate uniaxial tensile tests until failure. Thirty-five GCL samples were dissected from 7 embalmed cadavers and tested at a rate of 1 mm/s and 1 m/s. Incidence of freezing was also evaluated. The mechanical response of GCL samples showed an approximately bilinear curve. Within the first linear region (less than 5% of ligament strain), the apparent elastic modulus was estimated at 247±144 kPa, while in the second region, it was estimated at 690±282 kPa. The average failure stress (σfail) and failure strain (∊fail) were 131.6±50 kPa and 29%±8%, respectively. High strain rate loading also showed high sensitivity to strain rate. The estimated GCL mechanical properties in this study can be implemented in finite element models of the abdomen to further investigate the mechanical contribution of the organ attachment system under traumatic loading conditions.

A lower limb-pelvis finite element (FE) model with active three-dimensional (3D) muscles was developed in this study for biomechanical analysis of human body. The model geometry was mainly reconstructed from a male volunteer close to the anthropometry of a 50th percentile Chinese male. Tissue materials and structural features were established based on the literature and new implemented experimental tests. In particular, the muscle was modeled with a combination of truss and hexahedral elements to define its passive and active properties as well as to follow the detailed anatomy structure. Both passive and active properties of the model were validated against the experiments of Post-Mortem Human Surrogate (PMHS) and volunteers, respectively. The model was then used to simulate driver’s emergency braking during frontal crashes and investigate Knee-Thigh-Hip (KTH) injury mechanisms and tolerances of the human body. A significant force and bending moment variance was noted for the driver’s femur due to the effects of active muscle forces during emergency braking. In summary, the present lower limb-pelvis model can be applied in various research fields to support expensive and complex physical tests or corresponding device design.

Improved protection for the child pedestrian requires a precise knowledge of the biomechanics of specific injury mechanisms for this particular category of pedestrian. In the absence of tests on cadaver subjects, numerical models are a possible route of investigation for developing a predictive model for the severity of injuries. The purpose of this study was to develop an Abbreviated Injury Scale-head (AIS-head) prediction model from numerical simulations of real accident configurations between a vehicle and a child pedestrian. Fifteen real accident configurations were collected from three different databases and simulated in order to identify a realistic injury criterion. For each configuration, a complete multi-body simulation of the accident, followed by a finite element simulation of the head/hood contact, was performed. Sixteen numerical indicators of injury, related to both the kinematics and the stress distribution, were recorded at the end of each reconstruction. To assess the predictive capacity of our model, four new cases of real accidents were also simulated. Statistical analysis showed that a combination of different numerical indicators predicted the AIS-head of an accident accurately, with a mean error of 0.25.

Car driving could induce fatigue and an altered sensorimotor control of foot muscles. Also, the use of a cruise controller (CC) or an adaptive cruise controller (ACC) could delay the brake reaction time when an emergency braking response is needed. The literature brings very few information on fatigue of the leg muscles during prolonged car driving and no data was found on any lengthened brake reaction time in CC/ACC condition. We recently showed that 1 hour driving at constant speed (120 or 60 km/hour) induced fatigue of the tibialis anterior (TA) muscle. TA fatigue was associated with a reduced myotatic reflex, a situation which reduced the sensorimotor control of muscles maintaining the foot on the accelerator pedal. Driving in CC/ACC condition increased the amplitude of leg displacement during emergency braking and markedly lengthened the brake reaction time, increasing the braking distance. The brake reaction time increased with age in the CC/ACC condition. Thus, car driving modifies the sensorimotor control of foot muscles and the use of new tools to control the speed of a motor vehicle significantly lengthens the brake reaction time. This could result from an increased amplitude of leg motion and/or an age-related decrease in reflex control.

Objective: We compared the differences in the braking response to vehicle collision between an active human emergency braking [control condition] and cruise control [CC] or adaptive cruise control [ACC].Methods: In 11male subjects, age 22 to 67 years, we measured the active emergency braking response during manual driving using the accelerator pedal [control condition] or in condition mimicking CC or ACC. In both conditions, we measured the brake reaction time [BRT], delay to produce the peak braking force [PBD],total emergency braking response [BRT + PBD], and peak braking force [PBF]. Electromyograms of leg and thigh muscles were recorded during braking. The tonic vibratory response [TVR], Hoffman reflex [HR], and M-waves were recorded in leg muscles to explore the change in sensorimotor control. Results: No difference in PBF, TVR amplitude, HR latency, and Hmax/Mmax ratio were found between the control and CC/ACC conditions. On the other hand, BRT and PBD were significantly lengthened in the CC/ACC condition [240 ± 13 ms and 704 ± 70 ms, respectively] compared to control [183 ± 7 ms and 568 ± 36 ms, respectively]. BRT increased with the age of participants and the driving experience shortened PBD and increased PBF. Conclusions: In male subjects, driving in a CC/ACC condition significantly delays the active emergency braking response to vehicle collision. This could result from higher amplitude of leg motion in the CC/ACC condition and/or by the age-related changes in motor control. Car and truck drivers must take account of the significant increase in the braking distance in a CC/ACC condition.

In 2005, the number of lower limb amputees was 1.6 million in the USA and is projected to reach 3.6 in 2050. Among causes for amputations, dysvascular diseases, trauma and diabetes are the main one and dysvascular conditions are increasing because of an ageing population [1]. The manufacturing of lower limb prosthesis is currently mainly artisanal while the use of computer assistance is still limited. As a consequence, the quality of the prosthesis will greatly depend on the prosthetist know-how. However, this is not the only factor influencing prosthesis quality, and the type of the prosthesis, its design, or the materials for both liner and socket should also be taken into account. Although prosthesis quality assessment is subjective, quantitative measurements such as pressures or temperatures in the liner and patient feedback through questionnaires can be assessed. Mechanical interactions between a stump and the prosthesis were accurately predicted using finite element method (FEM) [2,3]. Existing models mainly aim to develop a realistic model with no or limited validation. Complete optimization of the prosthesis using numerical analysis has, to the best of our knowledge, not been fully performed. Thus, the main objective of this project is to define a new FEM method to fully optimize prosthesis shape in order to improve the subject's comfort. The definition of this method will first need a validation of the FEM by comparing experiments and simulations results together with measuring the method reproducibility.

This study report documents the development of a finite element (FE) model for analyzing trauma in pregnant women involved in road accidents and help the design of a specific safety device. The model is representative of a 50th percentile pregnant woman at 26 weeks of pregnancy in sitting position. To achieve this, the HUMOS 2 model, which has been validated in a wide range of dynamic tests, was scaled to the morphology of a woman in the 50th percentile and coupled with a model of gravid uterus. During scaling, special attention was paid to the pelvic region which is known to differ considerably in morphological terms between men and women. The gravid uterus model includes a placenta, a fetus, uterosacral ligaments and the amniotic fluid by means of fluid structure interaction formulation. The uterus and the female model were coupled using an original method whereby the growth of an uterus was simulated to compress the abdominal organs in a realistic manner. The model was validated based on experimental tests described in the literature. Additional tests based on abdominal loadings with a seatbelt on Post Mortem Human Surrogates (PMHS) coupled to silicone uterus were also performed. Results highlighted the role of the possible interaction of the fetus in the pregnant woman abdominal response. Experimental corridors taking into account the presence of this fetus could therefore be proposed.

Implant-supported overdentures (IODs) are a treatment option for patients with complete edentulism. However, this treatment increases the possibilities of peri-implant complications, characterized by inflammation or partial loss of surrounding hard and soft tissues.The purpose of this finite element analysis study was to evaluate the mechanical performance of different bar-IOD designs under different clinical configurations by comparing the stress and strain distribution on the bone during secondary stabilization.A finite element model of the mandible representing a patient with complete edentulism was developed. Different designs of bar-IODs were modeled and compared. The parameters studied were the material properties (cobalt-chromium, zirconium dioxide, titanium grade 5, and titanium grade 4), diameter and bar-IOD cross-sectional shape, tilt of the posterior implants (30 degrees), presence of a distal extension cantilever in the bar-IODs (12 mm), and number of implants (4 or 6). Two different mastication loading conditions were analyzed. One- and 2-way ANOVAs and the Tukey honestly significant differences post hoc test (α=.05) were used to determine the significant von Mises stress and strain values in the bone.The 4 materials tested in the bar-IOD did not have a significant mechanical effect on the bone (P.05). A smaller diameter and structure of the bar-IOD led to significantly higher bone stress (P.001). A distal extension cantilever led to an increased stress concentration (model M1 versus model M3: P.001), which reached 50% in the event of tilting of the posterior implants (model M2 versus model M4: P.001). Tilting of the posterior implants alone, without extension, had a nonsignificant effect (model M3 versus model M4: P=.999). Model M5 supported with 6 implants reduces the stress transferred to the bone compared with model M3 supported with 4 implants (P.05).Distal extensions in bar-IODs, the tilt of the posterior implants, and the low amount of material in the cross-sectional area in the bar-IOD were the most influential parameters on the mechanical resistance of dental implants in the mandibular bone.

IntroductionAmbulance drivers often travel under stressful conditions at high speed while using vehicles with poor high-speed maneuverability. The occupant safety of ambulance vehicles has not yet been addressed by the automotive safety paradigm; particularly for the rear patient compartment. This study had two objectives: (1) to assess by survey the French Emergency Medical Services (EMS) to determine the layout of the vehicle most often used and the EMS personnel's behavior during transport; and (2) to conduct a crash test to analyze the injuries which may affect EMS personnel and patients in the rear patient compartment.MethodFirstly, a survey was distributed to the 50 largest metropolitan French EMS programs. Secondly, a crash test was performed with a Mobile Intensive Care Unit (MICU) in conditions closest to reality.ResultsForty-nine of the 50 biggest metropolitan French EMS programs responded to the survey. This represents 108 French MICUs. During the last three years, 12 of 49 EMS programs (24%) identified at least one accident with an MICU, and six of these 12 (50%) suffered at least one death in those accidents. A crash test using a typical French EMS MICU showed that after impact of a collision, the ambulance was moved more than five meters with major consequences for all passengers. A study-approved human cadaver placed in the position of a potential patient was partially thrown from the stretcher with a head impact. The accelerometric reaction of the anthropomorphic manikin head was measured at 48G.ConclusionThe crash test demonstrated a lack of safety for EMS personnel and patients in the rear compartment. It would be preferable if each piece of medical equipment were provided with a quick release system resistant to three-dimensional 10G forces. The kinetic changes undergone by the “patient” substitute on the stretcher would probably have an effect of causing injury pathology. This study highlights the need for more research and development in this area.FournierM,ChenaitiaH,MassonC,MicheletP,BehrM,AuffrayJP.Crew and patient safety in ambulances: results of a personnel survey and experimental side impact crash test.Prehosp Disaster Med.2013;28(4):1-6.

Due to the increase in time spent seated in cars, there is a risk of fatigue of the leg muscles which adjust the force exerted on the accelerator pedal. Any change in their sensorimotor control could lengthen the response to emergency braking. Fourteen healthy male subjects (mean age: 42 ± 4 years) were explored. Before and after a 1-h driving trial at 120 km h-1 , we measured the braking response, the maximal leg extension and foot inversion forces, the tonic vibratory response (TVR) in gastrocnemius medialis (GM) and tibialis anterior (TA) muscles to explore the myotatic reflex, and the Hoffmann reflex (H-reflex). During driving, surface electromyograms (EMGs) of GM and TA were recorded and the ratio between high (H) and low (L) EMG energies allowed to evaluate the recruitment of high- and low-frequency motor unit discharges. During driving, the H/L ratio decreased in TA, whereas modest and often no significant H/L changes occurred in GM muscle. After driving, the maximal foot inversion force decreased (-19%), while the leg extension force did not vary. Reduced TVR amplitude (-29%) was measured in TA, but no H-reflex changes were noted. The braking reaction time was not modified after the driving trial. Driving at constant elevated speed reduced the myotatic reflex and the recruitment of motor units in TA muscle. The corresponding changes were rarely present in the GM muscle that plays a key role in the braking response, and this could explain the absence of a reduced braking reaction time.

In the field of biomechanics, the offer of models which are more and more realistic requires to integrate a physiological response, in particular, the controlled muscle bracing and the reflexes. The following work aims to suggest a unique methodology which couples together a sensory and motor loop with a finite element model. Our method is applied to the study of the oscillation of the elbow in the case of a biceps brachial stretch reflex. The results obtained are promising in the purpose of the development of reactive human body models.

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.

Resume Objectif Determiner une loi de comportement mecanique du placenta afin de l’implementer dans les simulateurs numeriques d’accidents de la route. Patientes et methodes Etude experimentale d’indentation de 80 placentas apres delivrance de femmes enceintes francaises. Utilisation de la methode mathematique d’analyse inverse apres modelisation numerique de l’experience. Optimisation des parametres de la loi obtenue grâce aux donnees experimentales. Resultats Loi d’Ogden type Hyper-Visco-Elastique optimisee pour le placenta par les parametres μ1 = 0,0001881 Mpa, μ2 = −0,000240 Mpa, μ3 = μ4 = 0 Mpa et α1 = 2, α2 = −8, α3 = α4 = 0 en condition quasi statique. Discussion et conclusion La loi obtenue approche plus precisement le comportement mecanique du placenta que les precedentes etudes et pourrait etre utilisee dans les recherches virtuelles de lesions placentaires dans les accidents de la route.

In the field of numerical crash simulations in road safety research, there is a need to accurately define the initial conditions of a frontal impact for the car occupant. In particular, human models used to simulate such impacts barely take into account muscular contracting effects. This study aims to quantify drivers'behaviour in terms of posture and muscular activity just before a frontal impact. Experiments on volunteers were performed in order to define these conditions, both on a driving simulator and on a real moving car. Brake pedal loads, lower limbs kinematics and muscle activation were recorded. Coupling instantaneous data from both experimental protocols (simulator versus Real car), a standard emergency braking configuration could be defined as (1) joint flexion angles of 96◦, 56◦ and 13◦ for the right hip, knee and ankle respectively; (2) a maximum brake pedal load of 780 N; (3) a muscular activation of 55% for the anterior thigh, 26% for the posterior thigh, 18% for the anterior leg and 43% for the posterior leg. The first application of this research is the implementation of muscle tone in human models designed to evaluate new safety systems. Driving behaviour, Driving simulator, Electromyography, Motor vehicle crashes, Emergency braking

With recent advances obtained with numerical simulation of human body behaviour, it becomes possible to investigate the detailed behaviour of structure involved in trauma situations. Hence, does established injury criterion remain relevant with FE (finite element) modelling? In order to define standard rules for numerical simulation analysis, which methodologies could be proposed to investigate injury assumptions with an existing numerical model? A new general methodology based on a multi-level model analysis from potential tissue failure to structure kinematics was postulated and applied to a lower limb model. Standard impact situations were simulated and these demonstrate the methodology capabilities to predict the existing injury criteria threshold. Additionally, models' capabilities to provide new injury criteria (related to pedestrian impact situation) based on the general methodology were evaluated and discussed.

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.

Trauma affect between 3 and 7% of all pregnancies in industrialized countries, and the leading cause of these traumas is car crashes. The difficulty to appreciate physiologic and anatomic changes occurring during pregnancy explain that majority of studies were not based on anatomical data. We present a protocol to create a realistic anatomical model of pregnant woman using a post mortem human subject (PMHS).We inserted a physical model of the gravid uterus into the pelvis of a PMHS. 3D acceleration sensors were placed on the subject to measure the acceleration on different body segments. We simulated three frontal impact situations at 20 km/h between two average European cars.Two main kinematics events were identified as possible causes of injuries: lap belt loading and backrest impact.Cadaver experiments provide one interesting complementary approach to study injury mechanisms related to road accidents involving pregnant women. This anatomical accuracy makes it possible to progress in the field of safety devices.

Journal de Gynecologie Obstetrique et Biologie de la Reproduction - Vol. 36 - N° 6 - p. 577-581

Background Forensic investigations have been reported regarding the loss of consciousness and cardiac arrests resulting from direct mandible impact. However, the mechanisms by which the forces are transferred to the skull through direct mandible impact remain unclear. We conducted a study regarding direct mandible impact on the level of energy required to create a mandible fracture and on the energy dispersion phenomenon to the skull and to the brain. Materials and methods This study combines an experimental and numerical approach. Mandible strike was studied using experimental trials performed on post-mortem human subjects. A finite element model of the head and face of a male was also developed based on tomodensitometry scans. The model was validated with literature data and experimental trials. A parametric study was then performed to study the effect of diverse variables such as the dentition integrity, cortical bone thickness, etc. Results The forces measured on our reference model were 3000 N on the chin, 1800 N at the condyles, and 970 N in the occiput. Of all the results, we observed a decrease of approximately one-third of the efforts from the chin to the base of the skull and a lower half of the still forces at the occiput, except in the edentulous and for the lateral and frontal impact where the force is transmitted directly to the skull base area. Conclusion This study allowed us to create a 3D model of the mandible and face bones to better understand the force transfer mechanisms into and from the mandible. The parameters of the model may be modified to suit the individual characteristics for forensic investigations and legal matters.

Objective Some cardiopulmonary resuscitation (CPR) monitoring devices were released in recent years. Some of them are motion sensors. There are no guidelines were to position future or present sensors during CPR. We evaluate the possible influence of the location of motion sensors by a high-speed camera during a CPR on a manikin. Material and methods We performed a motion analysis by a high-speed camera during chest compression (CC) on a manikin to quantify chest inhomogeneous displacements and rescuer motion. Results Midline chest was found to have an inhomogeneous depth during CC (19 mm for the upper sternum, 27 mm for the middle of the sternum, and 47 mm for the xiphoid). Rescuer anatomy has a complex motion. Conclusion The direct application of the sensor under the hand performing CC seems to be the more accurate solution if the device allows it.

This study lies within the scope of passive road safety, and more particularly injury mechanisms of the abdominal area. The finite element modeling, which makes it possible to simulate a road accident and to observe the possible bone fractures or internal tissue injuries, allows large projections in the comprehension of injury mechanisms. However, the digital models already available and used in accidentology do not offer as one very simplified description of the diaphragm, as well for its geometry as for its bracing aspect and the modifications that this could induce in the behavior of abdominal organs and vessels at impact. In order to develop an accurate model of diaphragm for road safety research, a 3D reconstruction was performed, based on a sitting post-mortem Human subject sections. The resulting geometry was then turned into a segmented mechanical component (using the finite element method) and included in a full human model already available. The result is a valuable tool to improve the knowledge of injury mechanisms involved in car crashes at the abdominal level.

In the field of pedestrian injury biomechanics, knees and lower legs are highly recruited during crash situations, leading to joint damage and bones failures. This paper shows how numerical simulation can be used to complete injury mechanism analysis and then to postulate on a knee injury criteria in lateral impact. It focuses on relationships between ultimate lateral bending and shearing at the knee level and potential ligament damage, based on subsystem experimental tests. These ultimate knee lateral bendings and shearings for potential failure of ligaments (posterior cruciate, medial collateral, cruciates and tibial collateral) were estimated at 16° and 15 mm in pure lateral shearing and bending impact tests respectively. Then this methodology was applied on a full test of pedestrian impact.

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.

Insoles are known to alter plantar loads and thus plantar sensory input. We therefore hypothesised that plantar somatosensory sensation could be modified over time by use of hard metatarsal pads. A sample of 12 healthy female participants was randomly allocated to either soft metatarsal pads (n = 6, latex foam, Shore A11) or hard metatarsal pads groups (n = 6, thermoplastic, ShoreA65). All wore the same shoe type and pedometers measured daily activities. Using a bespoke actuated device, multiple mechanical stimuli were applied to the forefoot and rearfoot before and after 8 and 30 days of wearing the pads. A control test comprised estimation of multiple auditory sensations at day 0, 8 and 30. Changes in detection of the mechanical and sound stimuli were estimated using the Stevens power function, Ψ = k × Φn (estimate = Ψ; stimulus = Φ). The k coefficient measured the sensitivity, i.e. the lowest detectable load/sound, and the n coefficient the gain in perception over time. After 30 days, hard metatarsal pads group had increased plantar sensitivity in the forefoot but not the rearfoot. The soft metatarsal pads group showed no changes in plantar sensitivity and the detection of auditory sensation remained stable over the 30 days.Metatarsal pads with relatively high hardness increased the perception of the lowest mechanical stimulus in the forefoot compared to soft metatarsal pads. This provides initial evidence of the potential for changes in plantar somatosensory sensation due to choice of orthotic designs in patients with foot-related problems.

International audience; Trauma during pregnancy especially occurring during car crashes leads to many foetal losses. Numerical modelling is widely used in car occupant safety issue and injury mechanisms analysis and is particularly adapted to the pregnant woman. Material modelling of the gravid uterus tissues is crucial for injury risk evaluation especially for the abruption placentae which is widely assumed as the leading cause of foetal loss. Experimental studies on placenta behaviour in tension are reported in the literature, but none in compression to the authors' knowledge. This lack of data is addressed in this study. To complement the already available experimental literature data on the placenta mechanical behaviour and characterise it in a compression loading condition, 80 indentation tests on fresh placentae are presented. Hyperelastic like mean experimental stress versus strain and corridors are exposed. The results of the experimental placenta indentations compared with the tensile literature results tend to show a quasi-symmetrical behaviour of the tissue. An inverse analysis using simple finite element models has permitted to propose parameters for an Ogden material model for the placenta which exhibits a realistic behaviour in both tension and compression.

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.