Pierre-Yves Rohan

École nationale supérieure d'arts et métiers | ENSAM · Institut de Biomecanique Humaine Georges Charpak (IBHGC)

This paper proposes a proof of concept application of a biphasic constitutive model to identify the mechanical properties of in vivo human skin under extension. Although poromechanics theory has been extensively used to model other soft biological tissues, only a few studies have been published for skin, and most have been limited to ex vivo or in...

Background Transmission of loads between the prosthetic socket and the residual limb is critical for the comfort and walking ability of people with transfemoral amputation. This transmission is mainly determined by the socket tightening, muscle forces, and socket ischial support. However, numerical investigations of the amputated gait, using modeli...

Errors in biomechanical simulations arise from modelling and discretization. Discretization errors can be quantified with a posteriori error estimates. The relevance of such error estimates for practical biomechanics problems is rarely adressed. In this contribution, we propose an implementation of a posteriori error estimates targeting a user-defi...

Soft biological tissues demonstrate strong time-dependent and strain-rate mechanical behavior, arising from their intrinsic visco-elasticity and fluid-solid interactions. The time-dependent mechanical properties of soft tissues influence their physiological functions and are related to several pathological processes. Poro-elastic modeling represent...

Background In vivo mechanical characterisation of biological soft tissue is challenging, even under moderate quasi-static loading. Clinical application of suction-based methods is hindered by usual assumptions of tissues homogeneity and/or time-consuming acquisitions/postprocessingObjective Provide practical and unexpensive suction-based mechanical...

We propose a novel image-informed glioblastoma mathematical model within a reactive multiphase poromechanical framework. Poromechanics offers to model in a coupled manner the interplay between tissue deformation and pressure-driven fluid flows, these phenomena existing simultaneously in cancer disease. The model also relies on two mechano-biologica...

Soft biological tissues demonstrate strong time-dependent and strain-rate mechanical behavior, arising from their intrinsic viscoelasticity and fluid-solid interactions especially at sufficiently large time scales. The time-dependent mechanical properties of soft tissues influence their physiological functions and are linked to several pathological...

We propose a novel image-informed glioblastoma mathematical model within a reactive multiphase poromechanical framework. Poromechanics offers to model in a coupled manner the interplay between tissue deformation and pressure-driven fluid flows, these phenomena existing simultaneously in cancer disease. The model also relies on two mechano-biologica...

Clinical management of cancer has continuously evolved for several decades. Biochemical, molecular and genomics approaches have brought and still bring numerous insights into cancerous diseases. It is now accepted that some phenomena, allowed by favorable biological conditions, emerge via mechanical signaling at the cellular scale and via mechanica...

OBJECTIVE: 2D Ultrasound (US) imaging has been recently investigated as a more accessible alternative to 3D Magnetic Resonance Imaging (MRI) for the estimation of soft issue motion under external mechanical loading. In the context of pressure ulcer prevention, the aim of this pilot MRI study was to design an experiment to characterize the sacral so...

Pressure ulcers are a severe disease affecting patients that are bedridden or in a wheelchair bound for long periods of time. These wounds can develop in the deep layers of the skin of specific parts of the body, mostly on heels or sacrum, making them hard to detect in their early stages. Strain levels have been identified as a direct danger indica...

Impingement with surrounding tissues is a major cause of failure of anterior cruciate ligament reconstruction. However, the complexity of the knee kinematics and anatomical variations make it difficult to predict the occurrence of contact and the extent of the resulting damage. Here we hypothesise that a description of wear between the reconstructe...

Pressure ulcers are a severe disease affecting patients that are bedridden or in a wheelchair bound for long periods of time. These wounds can develop in the deep layers of the skin of specific parts of the body, mostly on heels or sacrum, making them hard to detect in their early stages. Strain levels have been identified as a direct danger indica...

Objective 2D Ultrasound (US) imaging has been recently investigated as a more accessible alternative to 3D Magnetic Resonance Imaging (MRI) for the estimation of soft issue motion under external mechanical loading. In the context of pressure ulcer prevention, the aim of this pilot MRI study was to design an experiment to characterize the sacral sof...

Clinical management of cancer has continuously evolved for several decades. Biochemical, molecular, and genomics approaches have brought and still bring numerous insights into cancerous diseases. It is now accepted that some phenomena, allowed by favorable biological conditions, emerge via mechanical signaling at the cellular scale and via mechanic...

The role of the above-knee socket is to ensure the load transfer via the coupling of residual limb-prosthesis with minimal discomfort and without damaging the soft tissues. Modelling is a potential tool to predict socket fit prior to manufacture. However, state-of-the-art models only include the femur in soft tissues submitted to static loads negle...

In this short technical note, we are interested in the constitutive equations used to model macroscopically the mechanical function of soft tissues under mechanical loading. Soft tissues have the ability to undergo large elastic reversible deformations under quasi-static loading and are usually modelled using hyperelastic constitutive laws. Several...

Background Pressure-induced tissue strain is one major pathway for Pressure Ulcer development and, especially, Deep Tissue Injury. Biomechanical investigation of the time-dependent stress–strain mechanical behaviour of skeletal muscle tissue is therefore essential. In the literature, a viscoelastic formulation is generally assumed for the experimen...

Background Physiologic aging is associated with loss of mobility, sarcopenia, skin atrophy and loss of elasticity. These factors contribute, in the elderly, to the occurrence of a pressure ulcer (PU). Brightness mode ultrasound (US) and shear wave elastography (SWE) have been proposed as a patient-specific, bedside, and predictive tool for PU. Howe...

Abstract as conference proceeding: https://doi.org/10.1080/10255842.2021.1978758

This paper investigates the complex time-dependent behavior of cortex tissue, under adiabatic condition, using a two-phase flow poroelastic model. Motivated by experiments and Biot’s consolidation theory, we tackle time-dependent uniaxial loading, confined and unconfined, with various geometries and loading rates from 1μm/s to 100μm/s. The cortex t...

Spheroids encapsulated within alginate capsules are emerging as suitable in vitro tools to investigate the impact of mechanical forces on tumor growth since the internal tumor pressure can be retrieved from the deformation of the capsule. Here we focus on the particular case of Cellular Capsule Technology (CCT). We show in this contribution that a...

The proper management of the local mechanical environment within soft tissuesSoft tissue is a key challenge central the prevention ofPressure ulcer (PUs) Pressure Ulcers (PUs). Magnetic Resonance (MR) imaging is the preferred imaging modality to measure geometrical features associated with PUs. It is a very time-consuming method and it represents a...

Skin Marker (SM) based motion capture is the most widespread technique used for motion analysis. Yet, the accuracy is often hindered by Soft Tissue Artifact (STA). This is a major issue in clinical gait analysis where kinematic results are used for decision-making. It also has a considerable influence on the results of rigid body and Finite Element...

Soft tissue deformation(STD) causes the most prominent source of error in skin marker (SM) based motion analysis, commonly referred to as Soft Tissue Artifact (STA). To compensate for its effect and to accurately assess in vivo joint kinematics, quantification of STD in three-dimension (3D) is essential. In the literature, different invasive and ra...

Subject-specific tensioning of ligaments is essential for the stability of the knee joint and represents a challenging aspect in the development of finite element models. We aimed to introduce and evaluate a new procedure for the quantification of ligament prestrains from biplanar X-ray and CT data. Subject-specific model evaluation was performed b...

Résumé Introduction Chez l’enfant ayant été traité pour un pied bot varus équin idiopathique (PBVE), le lien entre défauts morphologiques constatés cliniquement ou par radiographie standard et anomalies fonctionnelles est difficile à établir objectivement. Le but de ce travail est de démontrer la faisabilité d’une étude combinée par reconstruction...

Spheroids encapsulated within alginate capsules are emerging as suitable in vitro tools to investigate the impact of mechanical forces on tumor growth since the internal tumor pressure can be retrieved from the deformation of the capsule. Here we focus in particular on the Cellular Capsule Technology (CCT). We show that a modeling approach accounti...

Finite Element Analysis is a numerical modelling tool vastly employed in research facilities to analyse and predict load transmission between the human body and a medical device, such as a prosthesis or an exoskeleton. Yet, the use of FEM in a framework compatible with clinical constraints is hindered by, amongst others, heavy and time-consuming as...

Introduction In children treated for idiopathic equinovarus clubfoot (EVCF), the relation between morphologic defects on clinical examination and standard X-ray on the one hand and functional abnormalities on the other is difficult to objectify. The aim of the present study was to demonstrate the feasibility of combined 3D analysis of the foot and...

The present study combines low-dose bi planar X-rays with 3D motion capture to obtain a subject-specific 3D model of transfemoral amputated subjects and multibody kinematics optimization is used to obtain a prediction of the movement of the femur relative to the socket during gait.

The present study combines low-dose bi planar X-rays with 3D motion capture to obtain a subject-specific 3D model of transfemoral amputated subjects and multibody kinematics optimization is used to obtain a prediction of the movement of the femur relative to the socket during gait. https://sb2019-poitiers.sciencesconf.org/268598 DOI: 10.1080/102558...

The main function of the intervertebral disc is biomechanical function, since it must resist repetitive high loadings, while giving the spine its flexibility and protecting the spinal cord from over-straining. It partially owes its mechanical characteristics to the lamellar architecture of its outer layer, the annulus fibrosus. Today, no non-invasi...

Background: Internal soft tissue strains have been shown to be one of the main factors responsible for the onset of Pressure Ulcers and to be representative of its risk of development. However, the estimation of this parameter using Finite Element (FE) analysis in clinical setups is currently hindered by costly acquisition, reconstruction and comp...

In an effort to improve diagnostics and treatment of knee joint laxity and to minimize post-operative complications, development of patient-specific computational models of the knee joint is subject of current interest and investigation. A key strength of computational models is that they can provide an insight on the relative contributions of the...

Errors in biomechanics simulations arise from modelling and discretization. Modelling errors are due to the choice of the mathematical model whilst discretization errors measure the impact of the choice of the numerical method on the accuracy of the approximated solution to this specific mathematical model. A major source of discretization errors i...

Successfully simulating tissue evolution in bone is of significant importance in predicting various biological processes such as bone remodeling, fracture healing and osseointegration of implants. Each of these processes involves in different ways the permanent or transient formation of different tissue types, namely bone, cartilage and fibrous tis...

Résumé Introduction L’examen clinique et l’étude radiologique en charge sont les 2 principaux moyens d’analyse des pieds et des membres inférieurs. L’anatomie et la fonction de ces 2 structures ont des conséquences réciproques. Ces 2 moyens sont sujets à la subjectivité et aux biais de projection. La radiographie biplane est devenue une alternativ...

Background: The physical examination and weight-bearing radiography are the two main available methods for assessing the feet and lower limbs. The anatomy and function of these two structures interact with each other. These two assessment methods are affected by subjectivity and projection bias. Low-dose biplanar radiography (LDBR) is now a promis...

Pressure Ulcer (PU) prevention remains a main public health issue. The physio-pathology of this injury is not fully understood, and a satisfactory therapy is currently not available. Recently, several works suggested that mechanical strains are responsible of deformation-induced damage involved in the initiation of Deep Tissue Injury (DTI). A bette...

The occurrence and management of Pressure Ulcers remain a major issue for patients with reduced mobility and neurosensory loss despite significant improvement in the prevention methods. These injuries are caused by biological cascades leading from a given mechanical loading state in tissues to irreversible tissue damage. Estimating the internal mec...

Objective: This paper reports on the quantification of passive wrist joint stiffness and investigates the potential influence of handedness and gender on stiffness estimates. Methods: We evaluated the torque-angle relationship during passive wrist movements in 2 degrees of freedom (into flexion-extension and radial-ulnar deviation) in thirteen h...

Several Finite Element (FE) models of the pelvis have been developed to comprehensively assess the onset of pathologies and for clinical and industrial applications. However, because of the difficulties associated with the creation of subject-specific FE mesh from CT scan and MR images, most of the existing models rely on the data of one given indi...

The initial assessment and postoperative monitoring of patients with various abnormalities of the foot in clinical routine practice is primarily based on the analysis of radiographs taken in the weightbearing position. Conventional x-ray imaging, however, only provides a 2-dimensional projection of 3-dimensional (3D) bony structures, and the clinic...

Bone is a tissue with the remarkable capacity to adapt its structure to an optimized microstructural form depending on variations in the loading conditions. The remodeling process in bone produces distinct tissue distributions such as cortical and trabecular bone but also fibrous and cartilage tissues. Although it has been demonstrated that mechani...

Numerous fnite element models of the knee joint have been developed to investigate knee pathology, post-surgery assessment and knee biomechanics. However, because of extensive computational efort required for preparing subject specifc model from CT-scan or MRI data, most of the models in literature are done only for one subject resulting in poor va...

Clinical problems of the human spine have a high prevalence, affecting more than 25.5 million people in 2012. Older adults, in particular, are susceptible to degenerative spine disorders such as deformities or osteoporosis. A basic requirement for proper management of various spinal disorders, effective injury prevention, and rehabilitation is a de...

Introduction L’évaluation en 3 dimensions du pied de l’enfant se fait par scanner ou IRM, en décharge. Cela induit des approximations d’interprétation et des biais de projection. La stéréoradiographie et les méthodes de reconstruction de modèles 3D associées ont prouvé leur intérêt comme alternative, concernant les membres inférieurs et le rachis....

Background: Lower-limb alignment in children is classically assessed clinically or based on conventional radiography, which is associated with projection bias. Low-dose biplanar radiography was described recently as an alternative to conventional imaging. The primary objective of this study was to assess the reliability of length and angle values...

Errors in biomechanics simulations arise from modeling and discretization. Modeling errors are due to the choice of the mathematical model whilst discretization errors measure the impact of the choice of the numerical method on the accuracy of the approximated solution to this specific mathematical model. A major source of discretization errors is...

Purpose: In addition to the sagittal alignment, impact of transverse plane parameters (TPP) and rotatory subluxation on patients reported outcomes were highlighted. One of the hypotheses for genesis of degenerative scoliosis is disc degeneration with increased axial vertebral (AVR) and intervertebral rotation (AIR). Therefore, TPP analysis at earl...

Introduction L’ensemble main poignet est une région complexe que les cliniciens sont amenés à explorer par différents moyens d’imagerie. La radiographie conventionnelle est une modalité fréquemment utilisée pour explorer cette région. Néanmoins, elle n’est qu’une projection 2D d’une région anatomique où il est souvent intéressant d’explorer la 3e d...

Introduction Si le rôle de l’alignement sagittal est maintenant bien connu, l’impact clinique de la dislocation rotatoire et des paramètres du plan transverse (PPT) ont été récemment soulignés. Une des hypothèses de la genèse de la scoliose dégénératives est la faillite discale, associée à une augmentation de la rotation vertébrale (AVR) et interve...

Science Arts & Métiers (SAM)

With his “physiologically oriented, dynamic model of the tongue, Joseph Perkell introduced in 1974 a new methodological approach to understanding the “relationships among phonetic models and the properties and capabilities of the speech-production mechanism.” This approach has guided a large part of our studies in the two last decades. In order to...

One of the key factors for obtaining accurate and reliable results using the Finite Element Method (FEM) is the dis-cretization of the domain. Traditionally, two main types of elements are used for three-dimensional mesh generation: tetrahedral and hexahedral elements. Tetrahedral meshes are automatically generated but standard displacement-based t...

The management of knee instability is a complex problem in orthopedic surgery. To comprehensively assess the biomechanical role of the knee joint and to investigate various aspects of knee mechanics, several Finite Element (FE) knee models have been developed. However, (i) the full validation of these models against tibio-femoral and tibio-patellar...

Generation of subject-specific 3D finite element (FE) models requires the processing of numerous medical images in order to precisely extract geometrical information about subject-specific anatomy. This processing remains extremely challenging. To overcome this difficulty, we present an automatic atlas-based method that generates subject-specific F...

Clinicians generally assume that Medical Compression Stockings (MCS) work by reducing vein luminal diameter and, in this way, help to prevent blood pooling. Conflicting results have been reported however in the case of lower leg deep veins which call into question this hypothesis. The purpose of this contribution is to study the biomechanical respo...

The purpose of this paper is to illustrate the influence of the choice of the finite element technology on the occurrence of locking and hourglass instabilities. We chose to focus on the case study of the activation of the posterior genio-glossus (GGp) that is a lingual muscle located at the root of the tongue and inserts in the front to the mandib...

La compression élastique est la thérapeutique conservatrice la plus efficace pour la prise en charge de l'insuffisance veineuse et pour le traitement de la maladie veineuse chronique et de ses complications. Malheureusement, en pratique, les objectifs thérapeutiques ne sont pas toujours atteints ce qui souligne le manque de connaissance actuel conc...

The mechanisms giving rise to vein tortuosity, which is often associated with varicosis, are poorly understood. Recent works suggest that significant biological changes in the wall of varicose veins may precede the mechanical aspects of the disease. To test the hypothesis of tortuosity being a consequence of these changes, a Finite Element model wa...