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International audience; To prevent spinal and back injuries in snowboarding, back protector devices (BPDs) have been increasingly used. The biomechanical knowledge for the BPD design and evaluation remains to be explored in snowboarding accident conditions. This study aims to evaluate back-to-snow impact conditions and the associated back injury mechanisms in typical snowboarding backward falls. A previously validated snowboarder multi-body model was first used to evaluate the impact zones on the back and the corresponding impact velocities in a total of 324 snowboarding backward falls. The biomechanical responses during back-to-snow impacts were then evaluated by applying the back-to-snow impact velocity to a full human body finite element model to fall on the snow ground of three levels of stiffness (soft, hard, and icy snow). The mean values of back-to-snow normal and tangential impact velocities were 2.4 m/s and 7.3 m/s with maximum values up to 4.8 m/s and 18.5 m/s. The lower spine had the highest normal impact velocity during snowboarding backward falls. The thoracic spine was found more likely to exceed the limits of flexion-extension range of motions than the lumbar spine during back-to-snow impacts, indicating a higher injury risk. On the hard and icy snow, rib cage and vertebral fractures were predicted at the costal cartilage and the posterior elements of the vertebrae. Despite the possible back injuries, the back-to-snow impact force was always lower than the force thresholds of the current BPD testing standard. The current work provides additional biomechanical knowledge for the future design of back protections for snowboarders.

Introduction This study aims at identifying mechanical characteristics under bi-axial loading conditions of extracted swine pia mater (PM) and dura and arachnoid complex (DAC). Methods 59 porcine spinal samples have been tested on a bi-axial experimental device with a pre-load of 0.01 N and a displacement rate of 0.05 mm.s−1. Post-processing analysis included an elastic modulus, as well as constitutive model identification for Ogden model, reduced Gasser Ogden Holzapfel (GOH) model, anisotropic GOH model, transverse isotropic and anisotropic Gasser models as well as a Mooney-Rivlin model including fiber strengthening for PM. Additionally, micro-structure of the tissue was investigated using a bi-photon microscopy. Results Linear elastic moduli of 108±40 MPa were found for DAC longitudinal direction, 53±32 MPa for DAC circumferential direction, with a significant difference between directions (p Statement of Significance This study is the first to present biaxial tensile test of pia mater as well as constitutive model comparisons for dura and arachnoid complex tissue based on such tests. Collagen structures observed by semi-quantitative analysis of two photon microscopy confirmed the use of anisotropic Gasser model for pia mater and existence of fenestration. While clear identification of fibre population was not possible in DAC, results from anisotropic Gasser model depicted better fitting on experimental data as per this protocol. Bi-axial mechanical testing allows quasi-static characterization under conditions closr to the physiological context and the results presented could be used for further simulations of physiology. Indeed, the inclusion of meningeal tissue in finite element models will allow more accurate and reliable numerical simulations.

International audience; BackgroundDegenerative Cervical Myelopathy results from spine degenerations narrowing the spinal canal and inducing cord compressions. Prognosis is challenging. This study aimed at simulating typical spinal cord compressions observed in patients with a realistic model to better understand pathogenesis for later prediction of patients' evolution.MethodsA 30% reduction in cord cross-sectional area at C5-C6 was defined as myelopathy threshold based on Degenerative Cervical Myelopathy features from literature and MRI measurements in 20 patients. Four main compression types were extracted from MRIs and simulated with a comprehensive three-dimensional finite element spine model. Median diffuse, median focal and lateral types were modelled as disk herniation while circumferential type additionally involved ligamentum flavum hypertrophy. All stresses were quantified along inferior-superior axis, compression development and across atlas-defined spinal cord regions.FindingsAnterior gray and white matter globally received the highest stress while lateral pathways were the least affected. Median diffuse compression induced the highest stresses. Circumferential type focused stresses in posterior gray matter. Along inferior-superior axis, those two types showed a peak of constraints at compression site while median focal and lateral types showed lower values but extending further.InterpretationMedian diffuse type would be the most detrimental based on stress amplitude. Anterior regions would be the most at risk, except for circumferential type where posterior regions would be equally affected. In addition to applying constraints, ischemia could be a significant component explaining the early demyelination reported in lateral pathways. Moving towards patient-specific simulations, biomechanical models could become strong predictors for degenerative changes.

STUDY DESIGN Continuous measurements and computation of absolute metrics of cervical subarachnoid space (CSS) and spinal cord (SC) geometries proposed are based on in vivo magnetic resonance imaging and 3D reconstruction. OBJECTIVE The aim of the study is to offer a new methodology to continuously characterize and to quantify the detailed morphology of the CSS and the cervical SC in 3D for healthy subjects in both neutral supine and flexion. SUMMARY OF BACKGROUND DATA To the best of our knowledge, no study provides a morphological quantification by absolute indices based on the 3D reconstruction of SC and CSS thanks to in vivo magnetic resonance imaging. Moreover, no study provides a continuous description of the geometries. METHODS Absolute indices of SC (cross-sectional area, compression ratio, position in the canal, length) and of CSS (cross-sectional area, occupational ratio, lengths) were computed by measures from 3D semi-automatic reconstructions of high resolution in vivo magnetic resonance images (3D T2-SPACE sequence) on healthy subjects (N = 11) for two postures: supine neutral and flexion neck positions. The variability induced by the semi-automatic reconstruction and by the landmarks positioning were investigated by preliminary sensitivity analyses. Inter and intra-variability were also quantified on a randomly chosen part of our population (N = 5). RESULTS The length and cross-sectional area of SC are significantly different (P

Introduction Isometric manipulation is a current practice in osteopathy and treatment benefits have been reported in the literature. Such benefits could be assessed using experimental non-invasive cervical mobility measurements. The main objective was to quantitatively measure the effects of isometric manipulation on principal and compensatory cervical motions. Methods 101 healthy volunteers were included in this study. 51 healthy volunteers selected randomly underwent the experimental protocol before and after isometric treatment and were compared to 50 healthy volunteers who underwent a placebo treatment. Osteopathic diagnosis was performed on each healthy volunteer before and after the treatment. The experimental protocol included measurements by a motion capture system focusing on principal range of motion and compensatory motions. Results In both the isometric and the placebo sample, respectively including 51 (age: 29.2 ± 8.1, BMI: 22.2 ± 3.5) and 50 healthy volunteers (age: 27.4 ± 6.8, BMI: 22.9 ± 2.8), a pre-treatment diagnosis revealed a light cervical dysfunction in all subjects, mainly in levels C3 and C4. Altered ranges of motion thresholds (C3/C4 alterations) were identified: 113.2° for flexion, 130.0° for rotation and 90.2° for lateral flexion. After manipulations, the volunteers who underwent the isometric treatment presented a slight increase in amplitude for lateral flexion (p \textless 0.04), which was not found in the volunteers who underwent the placebo treatment. Compensatory motions showed differences pre and post isometric treatment without reaching significant values. Conclusion Principal ranges of motion were found significantly higher after osteopathic treatment when compared to the placebo treatment. Osteopathic palpatory diagnosis showed significant correlation with range of motions before treatment.

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.

44th Congress of the Société de Biomécanique, Poitiers, FRANCE, 28-/10/2019 - 30/10/2019; The mechanical phenomena which occur in the subarachnoid space have been studied either from a structural point of view particularly focusing on the spinal cord (SC) or from a fluid point of view focusing on the cerebrospinal fluid (CSF) flow. Fluid-structure interaction (FSI) approaches provide new perspectives to numerically describe the physiological phenomenon. It has been showed that the CSF acts in a passively way on the central nervous system as shock absorber in compressive spinal cord injuries (Fradet et al. 2016). However, we are not aware of any study that provide stress values induced by the active physiological role of the pulsatile CSF flow profile on the spinal cord in 3D. The purpose of this study is to quantify the maximum Von Mises stress generated in the spinal cord induced by an healthy pulsatile flow profile of the CSF.

Trunk range of motion (ROM) could be divided into two anatomical parts: the movements of the thorax and the lumbar spine. The trunk mobility is largely described with gait, but few studies are inte...

44th Congress of the Société de Biomécanique, Poitiers, FRANCE, 28-/10/2019 - 30/10/2019; Recent news in Rugby Union highlight the necessity to prevent concussions and injuries during training and matches. The number of concussions has indeed been reported to increase in the last decades (Finch et al. 2013). This is mostly due to the anatomy of professional rugby players (muscular development, higher body mass index- BMI).While the rugby union rules have been changing to promote safer practice in scrum, the players get highly injured during tackles (Fuller et al. 2010). Multiple influences on injury risks, such as the impact conditions or the player's morphology, have not been fully studied. In tackling, both the tackler (T) and the ball carrier (BC), their morphology and initial position need to be studied to fully describe the tackle impacts. Experimentally, on field data can be acquired with sensors and epidemiological studies have been carried to correlate the type of injury with the impact conditions (Kuster et al. 2012)

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).

Report of sacroiliac morphology changes during growth is limited in the literature and the interest of such morphology and its consequence for surgery is increasing.Aims of this work are (1) to anatomically define the sacroiliac joint (SIJ), and (2) to assess the influence of growth on the sacroiliac morphology and the pelvic parameters.Forty-nine young subjects from 6 months to 18 years old (y/o) and 20 adults aged from 18 to 50 y/o were selected from our institutional patient database.They underwent a computed tomography (CT) examination on a 128-MDCT (GE Healthcare Optima CT660). Transverse CT image datasets were reconstructed, anonymized, and segmented with ITK-SNAP. Landmarks and surfaces were selected and a SIJ orientation analysis was performed using costumed Python scripts.The subjects were divided into four groups: infants (1.9±1 y/o), children (6.9±1.7 y/o), adolescents (13.7±1.8 y/o), and adults (27.3±5.6 y/o). Differences between SIJ orientation were found significant between young subject groups for synovial sacrum SIJ orientation (p.001) and iliac total SIJ orientation (p=.036). Both orientations of younger subjects were found significantly different from the adult group (p.035). SIJ synovial sacrum and iliac total orientations correlated significantly with age (p.03). All orientations correlated with pelvic incidence (p.04) except for synovial sacrum SIJ orientation (p=.2). No gender or symmetrical differences were found significant in any group.Morphologic definition of the SIJ confirmed the independency of the gender during growth. Such results will be beneficial for the analysis and management of vertebral pathology.

Background Literature is still limited regarding reports of non-invasive assessment of the cervical range of motion in normal subjects. Investigations into compensatory motions, defined as the contribution of an additional direction to the required motion, are also limited. The objectives of this work were to develop and assess a reliable method for measuring the cervical range of motion in order to investigate motion and compensatory strategies. Methods and data collection Ninety-seven no neck-related pain subjects (no severe cervical pathology, 57 women, age: 28.3 ± 7.5y. old, BMI: 22.5 ± 3.2 kg/m2) underwent a non-invasive cervical range of motion assessment protocol. In-vivo head’s motion relative to the thorax was assessed through the measurement of the main angular amplitudes in the 3 directions (flexion/extension, axial rotations and lateral inclinations) and associated compensatory motions using an opto-electronic acquisition system. Results The principal motion reproducibility resulted in intra-class correlation coefficients ranging from 0.81 to 0.86. The following maximum ranges of motion were found: 127.4 ± 15.1° of flexion/extension, 89.3 ± 12° of lateral inclinations and 146.4 ± 13° of axial rotations after 6 outlier exclusions. Compensatory motions highly depend on the associated principal motion: for flexion/extension: (3.5 ± 7.6;-2.1 ± 7.8°), for rotation: (25.7 ± 17.9°;0.4 ± 4.7)°, for inclination: (22.9 ± 34.7°;-0.04 ± 8.7°). Age, BMI and weight significantly correlated with flexions (p

Purpose To determine whether left atrial (LA) strain quantification with cardiac magnetic resonance (MR) imaging feature tracking is associated with the severity of LA fibrofatty myocardial remodeling at histologic analysis. Materials and Methods This prospective case-control study was approved by the institutional review board. LA strain was evaluated with cardiac MR feature tracking between January 2014 and March 2015 in 13 consecutive patients (mean age, 61 years ± 19; nine male) with mitral regurgitation in the 24 hours before mitral valve surgery and 13 age- and sex-matched healthy control subjects. LA strain parameters were compared first between control subjects and patients and then according to atrial fibrillation and mitral regurgitation status. Associations between LA strain and histology of preoperative biopsies were reported by using receiver operating characteristic curve analysis and Spearman correlation. Results Peak longitudinal atrial strain (PLAS) was significantly lower in patients with mitral regurgitation than in healthy control subjects (P < .001). Increased LA remodeling was significantly related to altered LA strain, and the strongest association was found between PLAS and the degree of fibrofatty myocardial replacement at histologic analysis (r = -0.75, P = .017). LA end-diastolic volume was increased in patients with mitral regurgitation when compared with that in healthy volunteers (P < .001) because of volume overload; however, volume did not correlate with the histologic degree of LA fibrofatty replacement (r = -0.35, P = .330). Conclusion LA strain, especially PLAS, correlates strongly with the degree of fibrofatty replacement at histologic analysis. Such functional imaging biomarker in combination with LA volumetry could help to guide clinical decisions, since myocardial structural remodeling is a known morphologic substrate of LA dysfunction leading to atrial fibrillation with adverse outcome. © RSNA, 2017 Online supplemental material is available for this article.

Feature tracking (FT) is an emerging approach for the evaluation of both left atrium (LA) and left ventricular (LV) myocardial strain from cine MRI. We aimed to: 1) perform a simultaneous evaluation of LA and LV strain in patients with aortic valve stenosis (A VS) and 2) evaluate associations of LA strain measurements with LV remodeling (LVmass/LVend-diastolic volume) and strain. We studied 55 patients (34 AVS:71±11 years, 21 controls :66±9 years) with preserved LV ejection fraction (LVEF). FT was applied to cine MRI to extract LV longitudinal, circumferential and radial strain as well as LA longitudinal strain and radial motion fraction for the reservoir, conduit and LA contraction phases. All LV strains decreased significantly in AVS. Similarly, all LA indices showed a decreasing trend in AVS patients as compared to controls. While reservoir and conduit phases LA strains were significantly associated with LV remodeling and strain (r>0.42), lower correlations were found for comparisons with LA contraction phase strains (r

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.

Background Diastolic dysfunction is a major cause of morbidity in obese individuals. We aimed to assess the ability of magnetic resonance imaging (MRI) derived left atrial (LA) strain to detect early diastolic dysfunction in individuals with obesity and type 2 diabetes, and to explore the association between cardiac adipose tissue and LA function. Methods Twenty patients with obesity and T2D (55 ± 8 years) and nineteen healthy controls (48 ± 13 years) were imaged using cine steady state free precession and 2-point Dixon cardiovascular magnetic resonance. LA function was quantified using a feature tracking technique with definition of phasic longitudinal strain and strain rates, as well as radial motion fraction and radial velocities. Results Systolic left ventricular size and function were similar between the obesity and type 2 diabetes and control groups by MRI. All patients except four had normal diastolic assessment by echocardiography. In contrast, measures of LA function using magnetic resonance feature tracking were uniformly altered in the obesity and type 2 diabetes group only. Although there was no significant difference in intra-myocardial fat fraction, Dixon 3D epicardial fat volume(EFV) was significantly elevated in the obesity and type 2 diabetes versus control group (135 ± 31 vs. 90 ± 30 mL/m2, p Conclusions LA MRI-strain may be a sensitive tool for the detection of early diastolic dysfunction in individuals with obesity and type 2 diabetes and correlated with BMI and epicardial fat supporting a possible association between adiposity and LA strain. Trials Registration Australian New Zealand Clinical Trials Registry No. ACTRN12613001069741

International audience; Objectives: The valve-in-valve (VinV) procedure may be used in high-risk patients with failed mitral surgical bioprostheses. The objective of this in vitro study was to assess the hemodynamic function of different VinV configurations. Methods: A double activation duplicator was used to test 11 valve configurations (surgical bioprostheses alone) and 15 VinV configurations (Sapien [Edwards Lifesciences, Irvine, Calif] implanted within the surgical bioprosthesis) under 8 different hemodynamic conditions. The internal orifice diameter (IOD) of the surgical bioprosthesis was measured with a Smartscope (OGP Multi Sensor Measuring Instruments, Singapore). Results: The VinV procedure was associated with significant deterioration in antegrade hemodynamic parameters compared with valve configuration (effective orifice area, 1.51 +/- 0.21 cm 2 vs 1.65 +/- 0.37 cm 2; P 20%, and IOD > 23 mm was associatedwith higher risk of paravalvular regurgitation when oversizing was 20%. Significant paravalvular regurgitation is rare and occurs with larger IODs and lower percentage of oversizing (8%).

Importance of left atrial (LA) phasic function evaluation is increasingly recognized for its incremental value in terms of prognosis and risk stratification. LA phasic deformation in the pathway of normal aging has been characterized using echocardiographic speckle tracking. However, no data are available regarding age-related variations using feature-racking (FT) techniques from standard cine magnetic resonance imaging (MRI). We studied 94 healthy adults (41 ± 14 yr, 47 women), who underwent MRI and Doppler echocardiography on the same day for left ventricular (LV) diastolic function evaluation. From cine MRI, longitudinal strain and strain rate, radial motion fraction, and radial relative velocity, respectively, corresponding to the reservoir, conduit, and LA contraction phases, were measured using dedicated FT software. Longitudinal strain and radial motion fraction decreased gradually and significantly with aging for both reservoir ( r > 0.31, P < 0.003) and conduit ( r > 0.54, P < 0.001) phases, whereas they remained unchanged during the LA contraction phase. Subsequently, the LA contraction-to-reservoir ratio increased significantly with age ( r > 0.44, P < 0.001). Longitudinal strain rate and radial relative velocity significantly decreased with age (reservoir: r = 0.39, P < 0.001, conduit: r > 0.54, P < 0.001), and these associations tended to be stronger in women than in men. Finally, associations of LA functional indexes with age were stronger in individuals with lower transmitral early-to-atrial maximal velocity ratio and mitral annulus maximal longitudinal velocity, as well as higher transmitral early maximal-to-mitral annulus maximal longitudinal velocity ratio, highlighting the LV-LA interplay. Age-related changes in LA phasic function indexes were quantified by cine MRI images using a FT technique and were significantly related to age and LV diastolic function.

Background The aim of this study was to automatically assess global and regional left atrium (LA) strain in Cushing’s syndrome (CD). Modifications of LA and LV function in patients have been highlighted followed by the restoration of myocardial function after radical treatment and cortisol normalization. Our hypothesis was that a feature-tracking method could improve the understanding of the mechanisms of LA alteration concerning its reservoir, conduit, and atrial contraction phases.

Background Left atrial (LA) structural and functional changes are determinant steps on the pathway toward heart failure with preserved ejection fraction in hypertensive (HT) patients. Most LA studies are based on LA volumes evaluation in CMR and echocardiography or on echocardiographic speckle tracking estimation. Since LA functional evaluation by CMR is now emerging we aimed at 1) evaluating LA function by CMR in controls and hypertensive patients (moderate and severe HT) using feature tracking technique on conventional cine data; 2) evaluating the relationship between the components of LA function (reservoir, conduit, atrial contraction) and left ventricular (LV) remodeling.

Background: Transcatheter valve replacement has emerged as a viable alternative in high and intermediate risk patients with severe aortic stenosis. However, the durability of transcatheter valves remains currently largely unknown. Moderate valve oversizing (OS)(5–20% in area) is recommended to

Background Cardiac Magnetic resonance (CMR) imaging is able to characterize with high accuracy left atrial (LA) size and volumes as well as dense myocardial fibrosis. The addition of functional parameters such as LA myocardial strain would enhance CMR usefulness for a comprehensive LA characterization. Our aim was to evaluate the ability of strain values obtained by CMR to characterize LA functional alterations in the setting of aortic valve stenosis (AVS).

Introduction Observations of EDWARDS SAPIEN prosthesis (ED SA) once deployed in vivo, shows a frequent elliptic geometry, which can cause inadequate transvalvular hemodynamic and the occurence of valvular regurgitation (intra and/or para). Objectives This study aims to quantify in vitro, hemodynamic and valvular regurgitation of ED SA in circular and elliptic deployment conditions. Method A pulsed simulator reproducing the human circulation was used. ED SA 23 and 26 were implanted in circular annulus with increasing diameter (18, 20, 22mm for the size 23 and 21, 23 , 25mm for 26) and in 4 elliptic annulus for each size prosthesis (3 annulus with increasing Eccentricity Index (EI) at 0.17, 0.26, 0.33 starting to a small fixed diameter and 1 with the smallest and biggest diameters of circular annulus). The Effective Orifice Area (EOA) was calculated by the continuity equation and mean transvalvular gradient (TVG) were obtained by Doppler. The performance index (PI=100x(EOA/annulus area) was calculated. The ultrasound allowed the research of regurgitation, quantified by flow measurement. Results The highest TVG were observed for circular annulus 18 and 20mm, respectively 17.7 and 12.2mmHg, which was correlated with the lowest EOA (1.27 and 1.44 cm 2 ). We observed a mismatch leaflets-stent for annulus 18 with plicature of leaflets. Hemodynamic parameters and mean PI (48.5 vs 43.2) were better with elliptic geometry than circular. No significant intraprosthetic regurgitation was observed. Just 1 paraprosthetic regurgitation occured for the ED SA 26 in the elliptic annulus with largest EI. Conclusion Hemodynamic parameters of ED SA obtained in vitro with elliptic geometry appear to be better than those with circular. A “leaflets-stent mismatch” can occur in the case of undersizing in annulus with smaller area.

Degenerative cervical myelopathy (DCM) is a common cause of spinal cord injury for elderly population. To better understand the biomechanical interactions between the spinal central nervous system and the cerebrospinal flow in healthy population as well as the pathophysiology of DCM, biomechanical modeling is necessary. This PhD aims to provide morphometrical description of the cervical canal and mechanical description of spinal meninges which will drive to the preliminary development of numerical models with fluid-structure interactions in healthy of pathological conditions such as for DCM.In the first part, a methodology was developed for 3D MRI-based detailed morphometrical descriptions of healthy and DCM populations. This methodology could be equally used for diagnosis improvement in a clinical research context and for subject-specific geometry definition in a biomechanical context.In the secondly part, two mechanical testing protocol were performed to describe tensile mechanical properties of spinal porcine meninge as human model. Uni-axial tests firstly provided new elastic and isotropic hyperelastic description of meninges showing a tend to spinal level dependency while bi-axial tests were performed to more detailed the tissue in comparing isotropic and anisotropic hyperelastic constitutive laws. These experimental data plays a crucial role in the numerical biomechanical modelling of the interactions between the cerebrospinal fluid and the spinal central nervous system.In the third part, the mathematical formulation of a fluid-structure interaction problem between a Newtonian fluid and a linear elastic solid was developed. Thus, a preliminary simplistic FSI model was developed with an explicit solver (RADIOSS) as a proof-of -concept. Finally, others FSI approaches were discussed as alternative modelling solutions.Thus, this PhD might help scientific community to develop biomechanical models of the spinal canal in taking into account the role of cerebrospinal flow and the nervous tissues in healthy or an in pathological cases., La myélopathie cervicale dégénérative (DCM) est une cause fréquente de lésion de la moelle épinière chez les populations âgées. II est nécessaire de mieux comprendre les interactions biomécaniques entre le système nerveux central du rachis et l’écoulement du fluide céphalo-rachidien dans une population saine ainsi que mieux comprendre la physiopathologie de la DCM. Pour ce faire, la modélisation biomécanique est nécessaire. Cette thèse vise à fournir une description morphométrique du canal cervical et une description mécanique des méninges du rachis qui pourront conduire au futur développement de modèles numériques avec des interactions fluide-structure.Dans la première partie, une méthodologie a été développée pour décrire la morphométrie du canal cervical avec de nouvelles métriques à l’aide d’IRM de populations saines et avec DCM. Cette méthodologie pourrait également être utilisée pour l'amélioration du diagnostic dans un contexte de recherche clinique et pour la définition de la géométrie spécifique au sujet dans un contexte de modélisation biomécanique.Dans la deuxième partie, deux protocoles de test mécanique ont été réalisés pour décrire les propriétés mécaniques en tension les méninges de rachis porcins choisis comme un modèle similaire à l’humain. Des tests uni-axiaux ont tout d'abord permis de fournir de nouvelles données relatives à une description élastique et hyper-élastique isotrope des méninges montrant une tendance à la dépendance au niveau rachidien des propriétés mécaniques, tandis que des tests biaxiaux ont été effectués pour détailler le comportement du tissu en comparant des lois constitutives hyper-élastiques isotropes et anisotropes. Ces données expérimentales jouent un rôle crucial dans la modélisation biomécanique numérique des interactions entre le liquide céphalo-rachidien et le système nerveux central rachidien.Dans la troisième partie, la formulation mathématique d'un problème d'interaction fluide-structure entre un fluide newtonien et un solide élastique linéaire a été développée. Ainsi, un modèle FSI préliminaire et simplifié a été développé avec un solveur explicite (RADIOSS) comme preuve de concept. Enfin, d'autres approches FSI ont été discutées en tant que solutions de modélisation alternatives. Cette thèse pourrait ainsi aider la communauté scientifique à développer des modèles biomécaniques du canal rachidien en prenant en compte le rôle du flux céphalo-rachidien et des tissus nerveux dans des cas sains ou pathologiques.