Her research interest concerns Biomechanics of the musculoskeletal system especially children deformities (torsion of lower limbs, Legg-Calvès Perthès Disease, congenital dislocation of the hip, clubfeet and scoliosis) and adult arthroplasties (hip, shoulder and knee). The research in children deformities consists in the quantification of the cause of the deformity and their consequences on the joints. The evolution of these deformities with growth is also studied. The objectives are to get a better comprehension of the children deformities and to perform an optimised planification of surgical or orthopaedic treatment. The adult arthroplasties research basically consists in the evaluation of the mechanical behavior of the implants in bone, in vitro and in vivo situation.
Methodologies developed are Bone and Joints modeling and characterization coupled with medical imaging techniques. She introduced the development of numerical models with individualized mechanical and geometric properties derived from medical images and the multiscale characterization of the musculo-skeletal tissue (organ, tissue, cellular and molecular). Most of her research are performed in collaboration with companies and clinicians.
She served as a council member of the ESB (European Society of Biomechanics) 1996-2004 and was vice president (2000-04). Since 2006, she is a member of the World Council for Biomechanics. She served as an expert at the National Committee of Scientific Research (CNRS), 2002-2008 and currently expert in the National Agency of Education and Research Evaluation (AERES), and National Agency of Research (ANR) and international funding agencies.
Abstract: PURPOSE: To cross-validate the magnetic resonance elastography (MRE) technique with a clinical device, based on an ultrasound elastometry system called Fibroscan. MATERIALS AND METHODS: Ten healthy subjects underwent an MRE and a Fibroscan test. The MRE technique used a round pneumatic driver at 60 Hz to generate shear waves inside the liver. An elastogram representing a map of the liver stiffness was generated allowing for the measurement of the average liver stiffness inside a region of interest. The Fibroscan technique used an ultrasound probe (3.5 MHz) composed of a vibrator that sent low-frequency (50 Hz) shear waves inside the right liver lobe. The probe acts as an emitter-receptor that measures the velocity of the waves propagated inside the liver tissue. RESULTS: The mean shear stiffness measured with the MRE and Fibroscan techniques were 1.95+/-0.06 kPa and 1.79+/-0.30 kPa, respectively. A higher standard deviation was found for the same subject with Fibroscan. CONCLUSION: This study shows why MRE should be investigated beyond the Fibroscan. The MRE technique provided elasticity of the entire liver, meanwhile the Fibroscan provided values of elasticity locally.
Abstract: The aim of this study is to assess density and elastic properties of Wistar rat cortical bone from growth to senescence and to correlate them with morphological and physico-chemical properties of bone. During growth (from 1 to 9 months), bone density and Young's modulus were found to increase from 1659+/-85 to 2083+/-13 kg m(-3) and from 8+/-0.8 to 19.6+/-0.7 GPa respectively. Bone microporosity was found to decrease from 8.1+/-0.7% to 3.3+/-0.7%. Physico-chemical investigations exhibited a mineralization of bone matrix and a maturation of apatite crystals, as protein content decreased from 21.4+/-0.2% to 17.6+/-0.6% and apatite crystal size and carbonate content increased (c-axis length: from 151 to 173 A and CO(3)W%: from 4.1+/-0.3% to 6.1+/-0.2%). At adult age, all properties stabilized. During senescence, a slow decrease of mechanical properties was first observed (from 12 to 18 months, rho=2089+/-14 to 2042+/-30 kg m(-3) and E(3)=19.8 +/-1.3 to 14.8+/-1.5 GPa), followed by a stabilization. Physico-chemical properties stabilized while microporosity increased slightly (from 3.3% to 4%) but not significantly (p>0.05). A multiple regression analysis showed that morphological and physico-chemical properties had significant effects on density regression model. Microporosity had a greater effect on Young's modulus regression model than physico-chemical properties. This study showed that bone structure, mineralization and apatite maturation should be considered to improve the understanding of bone mechanical behaviour.
Abstract: BACKGROUND: The porosity of human cortical bone is one of the major parameters conditioning bone strength. The purpose of this study was to validate the characterization of human cortical bone microarchitecture using microcomputed tomography (microCT). To validate this microCT technique, the structural measurements were compared with other methods such as ultrasonic techniques and scanning electron microscopy (SEM). METHODS: Nineteen cortical samples were extracted from the superior, middle, and inferior shaft of three human femurs (FI, FII, FIII). The samples were scanned by microCT with an isotropic resolution of 8 microm. Most of the structural parameters used for trabecular microarchitecture were calculated to characterize the network of pores. On the same cortical samples, (1) ultrasound measurements were performed using contact transmission emitter-receptor to determine elastic coefficient and Young's modulus; (2) SEM was performed on femoral cross sections from FII to evaluate the porosity. RESULTS: The morphological parameters showed a wide range of variation depending of the level of the diaphysis. Porosity measured by microCT was significantly correlated with porosity measured by SEM (r = 0.91, P < 0.05). Moreover, all the morphological parameters showed high correlation coefficients with the elastic coefficient and Young's modulus, leading to validation of our three-dimensional analysis. CONCLUSIONS: The strong correlations between the structural and mechanical properties obtained with the three techniques allowed us to validate the microCT technique used to characterize cortical bone microstructure. Porosity measurements might be of importance for clinicians and researchers to obtain a better understanding and evaluation of bone fracture in elderly patients.
Abstract: The human skin is an exceedingly complex and multi-layered material. This paper aims to introduce the application of the finite element analysis (FEA) to the in vivo characterization of the non-linear mechanical behaviour of three human skin layers. Indentation tests combined with magnetic resonance imaging (MRI) technique have been performed on the left dorsal forearm of a young man in order to reveal the mechanical behaviour of all skin layers. Using MRI images processing and a pre and post processor allows to make numerically individualized 2D model which consists of three skin layers and the muscles. FEA has been applied to simulate indentation tests. Neo-Hookean slightly compressible material model of two material constants (C(10), K) has been used to model the mechanical behaviour of the three skin layers and the muscles. The identification of material model parameters was done by applying Levenberg-Marquardt algorithm (LMA). Our methodology of identification provides a range of values for each constant. Range of values of different material properties of epidermis, dermis, hypodermis are respectively, C10(E)=0.12+/-0.06 MPa, C10(D)=1.11+/-0.09 MPa, C10(H)=0.42+/-0.05 KPa, K(E)=5.45+/-1.7 MPa, K(D)=29.6+/-1,28 MPa, K(H)=36.0+/-0.9 KPa.
Abstract: The kinematic magnetic resonance imaging technique has been developed to provide a functional examination of the knee. Technical limitations require this examination to be performed in supine position, and the knee motion is represented by an assembly of static positions at different knee angles. However, the main knee function is to support the body weight and perform continuous motion, e.g. parallel squat. Our study quantified the knee kinematics of 20 healthy subjects in different motion conditions (finite and continuous) and in different mechanical conditions (continuous unloaded and continuous loaded). We evaluated the angular and localisation difference of a finite helical axis of the knee motion for parallel squat, continuous knee extension in supine position and the finite set of knee extension in supine position. We found large inter-individual dispersion. The majority of subjects had equivalent knee kinematics between continuous knee extension and the finite set of knee extension in supine position, but not between continuous knee extension in supine position and the parallel squat. Therefore, results from a functional examination of a finite set of knee extensions in supine position do not represent the knee motion in a parallel squat. Our results suggest that functional examination of the knee from magnetic resonance imaging do not necessarily reflect the physiological kinematics of the knee. Further investigation should focus on a new magnetic resonance imaging acquisition protocol that allows image acquisition during weight bearing or includes a special device which reproduces the loaded condition.
Abstract: BACKGROUND: Most in vivo knee kinematic analyses are based on external markers attached to the shank and the thigh. Literature data show that markers positioning and soft tissues artifacts affect the kinematic parameters of the bones true movement. Most of the techniques of quantification used were invasive. The aim of the present study was to develop and apply a non-invasive methodology to compute the relative movement between the bones and the markers. METHODS: Magnetic resonance imaging acquisitions were performed on the right knee of eleven volunteers without knee injury. The subjects were equipped with external magnetic resonance imaging-compatible marker sets. A foot drive device allowed the subjects to perform an actively loaded knee extension. The whole volume of the subject's knee was processed for four sequentially held knee flexion positions during the knee movement. The bones and external marker sets geometry were reconstructed from magnetic resonance imaging images. Then a registration algorithm was applied to the bones and the relative movement of the thigh and shank marker sets with respect to their underlying bones was computed. FINDINGS: The protocol resulted in a good geometrical accuracy and reproducibility. Marker sets movement differ from that of the bones with a maximum of 22 mm in translation and 15 degrees in rotation and it affects the knee kinematics. INTERPRETATION: Marker sets relative movement modify the knee movement finite helical axes direction (range 10-35 degrees ) and localization (range 0-40 mm). The methodology developed can evaluate external marker set system to be used for kinematic analysis in a clinical environment.
Abstract: Carpal skeleton shows drastic developmental changes during embryogenesis. At this stage, the cartilaginous matrices appear and later form models of the limb bones. The purpose of this study was to investigate the morphometry of carpal bones in humans during embryological development. We obtained digitalized histological serial sections of 18 human embryos and early fetuses from the Institute of Anatomy in Paris. Surfdriver and MSC.Patran software were used for three-dimensional reconstruction and morphometry. There was a strong correlation between the volume of the carpal cartilaginous structure and the size of the embryos (P<0.001) and an exponential correlation between the carpal volume and the percentage of volume presented by the proximal carpal row (P=0.005). According to inertia parameters, the geometry of carpal cartilaginous structure, initially plane, becomes curved during embryogenesis. Carpal bones growth follows non-homothetic transformation. The innovations in embryo reconstruction serve as new tool for scientific investigation. A hypothesis of carpal development is proposed.
Abstract: The purpose of the study was to investigate changes in passive mechanical properties of the soleus muscle of the rat during the first year of life. These mechanical changes were quantified at a macroscopic (whole muscle) and a microscopic level (fiber) and were correlated with biochemical and morphological properties. Three passive mechanical tests (a relaxation test, a ramp stretch test and a stretch release cycle test) with different amplitudes and velocities were performed on isolated soleus muscles and fibers in rats at ages 1 (R1), 4 (R4) and 12 (R12) months. Mechanical parameters (dynamic and static forces, stresses and normalized stiffness) were recorded and measured. The morphological properties (size of fibers and muscles) for the three groups of rats were assessed by light microscopy which allowed us to observe the evolution of the fiber type (I, IIc and IIa) in the belly region and along the longitudinal axis of the muscle. In addition, biochemical analyses were performed at the level of the whole muscle in order to determine the collagen content. The results of the passive mechanical properties between the macroscopic (muscle) and microscopic (fiber) levels showed a similar evolution. Thus, an increase of the dynamic and static forces appeared between 1 and 4 months while a decrease of the passive tension occurred between 4 and 12 months. These mechanical changes were correlated to the morphological properties. In addition, the size of the three fibers type which grew with age could explain the increase of forces between 1 and 4 months. Furthermore, the biochemical analysis showed an increase of the collagen content during the same period which could also be associated with the increase of the passive forces. After 4 months, the passive tension decreased while the size of the fiber continued to increase. The biochemical analysis showed a decrease of the collagen content after 4 months, which could explain the loss of passive tension in the whole muscle. Concerning the similar loss at the fiber level, other assumptions are required such as a myofibril loss process and an increase of intermyofibrillar spaces. The originality of this present study was to compare the passive mechanical properties between two different levels of anatomical organization within the soleus muscle of the rat and to explain these mechanical changes in terms of biochemical and morphological properties.
Abstract: The objective of this study is to quantify the effect of three biomechanical factors, which include forces, bone material properties and bone remodelling coefficient, on the long term cement less Total Hip Arthroplasty (THA) results. Bone physiological remodelling algorithm is proposed to describe bone adaptation behaviour after operation. Two typical cases, which are obtained from simulated results, are compared with real clinical cases. Statistical analyses are performed to quantify the relationship between the long term variation of bone density and biomechanical factors. The results show that all the factors considered and their combination have relevant effects on the bone remodelling results.
Abstract: Investigations of bone mechanical properties are of major importance for bone pathology research, biomaterials, and development of in vivo bone characterization devices. Because of its complex multiscale structure, assessment of bone microstructure is an important step for understanding its mechanical behavior. In this study, we have investigated the strain rate influence on the mechanical properties of interstitial lamellae on two human femur bone samples. Nanoindentation tests were performed with the continuous stiffness measurement technique. Young’s modulus and hardness were calculated using the Oliver and Pharr method. A statistical significant influence of strain rate on hardness was found (p < 0.05) showing a viscoplastic behavior of interstitial bone at the micrometer scale. This phenomenon may reflect the role of the organic component in the bone matrix mechanical behavior.
Abstract: The purpose of this study is to quantify the spatial distribution of acoustic velocities and elastic properties (elastic constants) on Human femoral cortical bone. Four cross sections (average thickness of 2.09+/-0.27 mm) have been cut transversally between 40% and 70% of the total length and between them parallelepiped samples in each quadrant have been cut. Ultrasonic technique in transmission with immersion focused transducers at 5 MHz and contact transducers 2.25 MHz were used on the cross sections and parallelepiped samples, respectively. The first technique allows relative spatial distribution of velocities to be obtained, meanwhile the second technique allows the direct assessment of elastic constants. For both techniques, bulk velocities were found to be lower at the posterior side with an increase along the length (from 40% to 70% total length) (p < 0.05). Densities and elastic constants show equivalent pattern of variation. These variations are mainly due the cortical porosity related to vascularisation environment. The spatial distribution of velocities exhibits significant radial variation from the endosteal to the periosteal region. This is in agreement with variation of the porosity at that location. Same range of velocities was obtained with both techniques. The range of longitudinal velocities values varies from 3548 to 3967 m/s and between 18.5 and 33.1 GPa for the bulk velocities and axial elastic constants, respectively. Our results are within the range with those found in the literature. However, it must be noted that the range of acoustic and elastic properties variation is concerning the same bone. So, our new results show the ability of the technique to quantify accurately local variation of acoustic and elastic properties (within the section and along the length) of human cortical bone. Furthermore, our immersion technique could be used to assess the spatial distribution of the elastic constants with the knowledge of spatial distribution of densities.
Abstract: OBJECTIVE: To investigate and compare the spatial distribution of velocity with that of the microstructural properties (dimension of the haversian canal, percentage of porosity) on cross section of cortical bone. DESIGN: Experimental investigations permitted to quantify variation of acoustic properties related with that of the microstructural properties. BACKGROUND: Transmission ultrasonic techniques have been used in vitro and in vivo to assess the elastic and acoustic properties of Human bone, but few investigated the relationship between their variation with that of the microstructure. METHODS: Two scanning techniques (in transmission with a focused transducer at 5 MHz and an environmental scanning electronic microscope at 20 KV) enabled to obtain the spatial distribution of relative acoustic velocities and the microstructural properties (pore size and porosity). RESULTS: Increase of the velocities is related with the decrease of pore size and porosity. Around the periphery of the sections, the velocities were found to be significantly lower in the posterior side with a significant increase along the length. Radial variations are correlated to the spatial distribution of the microstructure where the endocortical region is more porous compared to the periosteal region. CONCLUSION: Significant alterations of the microstructural properties of the cortical bone reflect small variation of velocity suggesting that the velocities are not so sensitive to microstructural changes. RELEVANCE: These results are of importance for the clinicians and researchers to get a better understanding (advantages and limitation) of the use of ultrasound technique to assess material and structural properties of cortical bone. Our study suggested that velocity could be an index of porosity. Then it would be of interest to improve the clinical assessment of bone quality by describing bone both by a mineralization index and a microstructural index.
Abstract: Currently, the predominant hypothesis explains cellular differentiation as an essentially genetic intracellular process. The goal of this paper is to suggest that cell growth and differentiation may be, simply, the result of physical and chemical constraints.Bone growth occurs at the level of cartilage conjunction (growth plate) in a zone of lesser constrain. It appears that this growth also induces muscle, tendon, nerve and skin elongation. This cartilage growth by itself seems to explain the elongation of the hand. Growth stops at puberty likely because of feed-back from an increasing muscle load. The ossification (that is differentiation of cartilage into bone) appears to result from the shear stress induced. The study of bone age, obtained by X-ray picture of the hand, shows that ossification of epiphyses is very precise both in time and space. Computer modelization suggests that this ossification occurs where shear stress is greatest. The cartilage which does not ossify (joint, nose, larynx, ear, bronchus, etc.) is not exposed to high shear.Shear stress induces the secretion of extracellular matrix and a change of the biochemical environment of the cell. Precipitation of calcium phosphate, as in ossification, seems related to the alkalosis induced by shear stress.To speak in more general terms, loss of cellular differentiation, as occurs with cancer, can result from a change in the physical-chemical environments.
Abstract: The objective of the paper is to address the methodology developed to model bone and joints with individualised geometric and material properties from medical image data. An atlas of mechanical properties of human bone has been investigated demonstrating individual differences. From these data, predictive relationships has been established between mechanical properties and quantitative datas derived from measurements on medical images. Subsequently, geometric and numerical models of bones with individualised geometrical and mechanical properties has been developed from the same source of image datas. The advantages of this modelling technique is its ability to study the ‘patient’ specificity. This should be of importance for quantifying bone and joint deformities and performing individualised preoperative planning surgery or orthopaedic treatment. In the same way, the efficiency of orthopaedic treatment with customised orthese or mechanical behavior of implant in bone could be evaluated Results would suggest improvement or development of new design.
Abstract: An in vivo method based on CT images and finite element meshing had been developed to quantify and visualize the bone density distribution of scoliotic vertebrae. CT examination (axial acquisition of the apical, superior and inferior adjacent vertebral bodies) had been performed on seven girls presenting an idiopathic scoliosis. Using an in-house image processing software and the pre-post processor Patran, a surfacic finite element mesh of each body slice was proposed allowing an automatic mapping of the cancellous bone slices and a volumic mesh for the bone density distribution visualization. In the coronal plane, compared to the body geometrical centre, the body mechanical centre was shifted forward in the concavity of the curvature for six patients and in the convexity for one patient. For each patient, this shift forward was made in a same way for the three vertebrae. In the sagittal plane, the body mechanical inertia centre was shifted forward in the posterior side for 12 vertebrae, in the anterior side for 3 vertebrae and was not shifted forward for 6 vertebrae. This shift forward was made in the anterior side for the inferior adjacent vertebra. The shift forward by slice was made in a same way for each slice, excepted at the end plates. Besides, one can observe that the scoliotic deformation evolution seemed to modify the mechanical property distribution. The results may also suggest predictive criteria of evolution of the scoliotic deformities.
Abstract: MRI has been clinically only used for investigation of intervertebral disc disorders. In this study, MR images were used and a new 3D modelling of the intervertebral discs was proposed. MRI examination had been performed on fourteen girls presenting an idiopathic scoliosis and wearing a first CTM brace. Using an in-house image processing software and the pre-post processing software Patran, geometrical models were obtained with and without brace for each patient. These models included the outline of the intervertebral high intensity zone, composed of the nucleus and a part of the annulus. The shift forward between disc high intensity zone centres and body centres was found to be varying from 0 to 8mm. The sagittal and coronal shifts forward appeared in the curvature convexity and were maximum at the curvature apex. The intervertebral disc wedging was found to be varying from -10 degrees to +10 degrees. On these fourteen analysed patients, the CTM brace decreased the coronal shift forward between disc high intensity zone centres and body centres, and increased the sagittal intervertebral wedging. The intervertebral disc informations obtained represented new data in the scoliotic deformation description. But this method was not adapted for a clinical use. The qualitative and quantitative data obtained will help the orthopaedist in the brace design and also the clinician in the scoliosis comprehension.
Abstract: The aim of the study was to investigate the mechanisms of the Cheneau-Toulouse-Munster (CTM) brace in the correction of scoliotic curves, at night in the supine position. Magnetic resonance imaging (MRI) and Computer tomography (CT) acquisitions were performed in vivo on eight girls having an idiopathic scoliosis and being treated for the first time using a personalized CTM brace. Personalized 3D finite element models of the spine were developed for each patient, and an optimisation approach was used to quantify the forces generated by each brace on each scoliotic spine. A sensitivity study was undertaken to test the assumptions about intervertebral behaviour and load transmission from the brace to the spine. The computed CTM brace forces were 9-216N in the coronal plane and 2-72N in the sagittal plane. Personalized spinal stiffness properties should be included in spine models because, in this study, partial correction resulted from the application of higher estimated forces than for total correction. Partially reduced spines should be stiffer than totally reduced spines. The sensitivity study showed that the computed brace forces were proportional to the intervertebral Young's modulus and should be analysed as estimated data. Better knowledge of brace forces should be helpful in brace design to achieve the best correction of first scoliotic deformities.
Abstract: This in vivo study investigated the mechanical properties of apical scoliotic vertebrae using computed tomography (CT) and finite element (FE) meshing. CT examination was performed on seven scoliotic girls. FE meshing of each vertebral body allowed automatic mapping of the CT scan and the visualisation of the bone density distribution. Centroids and mass centres were compared to analyse the mechanical properties distribution. Compared to the centroid, the mass centre migrated into the concavity of the curvature. The three vertebrae of a same patient had the same body migration behaviour because they were located at the curvature apex. This observation was verified in the coronal plane, but not in the sagittal plane. These results represent new data over few geometrical analyses of scoliotic vertebrae. Same in vivo personalisation of mechanical properties should be performed on intervertebral discs or ligaments to personalise stiffness properties of the spine for the biomechanical modelling of human torso. Moreover, do this mechanical deformation of scoliotic vertebrae, that appears before the vertebral wedging, could be a predictive tool in scoliosis treatment?
Abstract: Finite element models have been widely employed in an effort to quantify the stress and strain distribution around implanted prostheses and to explore the influence of these distributions on their long-term stability. In order to provide meaningful predictions, such models must contain an appropriate reflection of mechanical properties. Detailed geometrical and density information is now readily available from CT scanning. However, despite the use of phantoms, a method of determining mechanical properties (or elastic constants) from bone density has yet to be made available in a usable form.In this study, a cadaveric bone was CT scanned and its natural frequencies were measured using modal analysis. Using the geometry obtained from the CT scan data, a finite element mesh was created with the distribution of density established by matching the mass of the FE bone model with the mass of the cadaveric bone. The maximum values of the orthotropic elastic constants were then established by matching the predictions from FE modal analyses to the experimental natural frequencies, giving a maximum error of 7.8% over 4 modes of vibration. Finally, the elastic constants of the bone derived from the analyses were compared with those measured using ultrasound techniques. This produced a difference of <1% for both the maximum density and axial Young's Modulus. This study has thereby produced an orthotropic finite element model of a human femur. More importantly, however, is the implication that it is possible to create a valid FE model by simply comparing the FE results with the measured resonant frequency of the CT scanned bone.
Abstract: OBJECTIVE: This in vivo study investigated the mechanical properties of scoliotic vertebrae especially in the apical zone. DESIGN: A method based on computed tomography images and finite element meshing had been developed to quantify and visualise the bone density distribution of scoliotic vertebrae. BACKGROUND: Most of scoliotic studies performed considered only geometrical parameters. METHOD: Computed tomography examination had been performed on 11 girls presenting idiopathic scoliosis. Using in-house image processing software and the pre-post processor Patran, a finite element mesh of each vertebral body and a mapping of each cancellous bone slice were proposed allowing the bone density distribution to be visualised. The mechanical properties were derived from predictive relationships between Young's modulus and computed tomography number. Geometrical (unit mass) and mechanical centres were calculated and compared in order to quantify the role of mechanical property distribution on the apex zone of the scoliotic spine. RESULTS: In the coronal plane, compared to the geometrical centre, the mechanical centre was shifted forward in the concavity (0.54 mm) of the curvature except for two vertebrae. In the sagittal plane, the mechanical centre was shifted forward in the back (0.26 mm) except for three vertebrae. The shift forward by slice was made in a same way for each slice (0.63 mm), except at the end plates (0.58 mm). DISCUSSION: The result values obtained were small but significant because the curvatures were low and the vertebrae were not wedged. Besides, one can observe that the scoliotic deformation evolution seemed to modify the mechanical property distribution. RELEVANCE: This study suggested the following question: Could these CT measurements be a predictive tool in scoliosis treatment?
Abstract: OBJECTIVES: The aim was to quantify the immediate effect of the Cheneau-Toulouse-Munster brace (worn at night) on scoliotic curvatures in vivo.Design. A three-dimensional geometrical model of the spine was developed using magnetic resonance images. BACKGROUND: Many corrective ortheses were proposed for the orthopaedic treatment of idiopathic scoliosis. Simple radiographs were not sufficient to analyse the three-dimensional spinal deformations. So, three-dimensional geometrical models were developed using stereoradiography and axial tomography. MRI has been only used clinically for investigation of intervertebral disc disorders. METHOD: MRI examination had been performed on 14 girls having an idiopathic scoliosis and wearing a first Cheneau-Toulouse-Munster brace. The protocol investigated was performed with and without brace. Using an in-house image processing software and the pre-post processing software Patran, two geometrical models of the spine (spine without brace and spine with brace correction) were obtained, respectively, for each patient, the models including the vertebral bodies. RESULTS: Our method reproducibility was found to be 0.5 mm on the displacements and 2.5 degrees on the rotations. The Cheneau-Toulouse-Munster brace decreased the coronal shift forward, the coronal tilt, the axial rotation, and increased the sagittal shift forward and the sagittal vertebral tilt. DISCUSSION: The results showed that the Cheneau-Toulouse-Munster brace had a three-dimensional and personalised action on vertebrae. This technique using MRI provides no irradiation and allows the soft tissue visualisation, but actually is not dedicated for clinical use and is limited to the lying position. RELEVANCE: The qualitative and quantitative data obtained allowed a better description of the Cheneau-Toulouse-Munster brace effect on scoliotic spine, and will help the orthopaedist in the brace design and the clinician in the scoliosis comprehension.
Abstract: MRI is increasingly being used for etiologic examination of scoliosis and for intervertebral disc disorder analysis, but until now has not been applied to geometric modeling. The aim of this study was to develop a new geometric model of intervertebral discs using MRI and to quantify the migration of the nucleus zone within scoliotic intervertebral discs. Fourteen lumbar scoliotic children (Cobb angles 22 +/- 7 degrees ) were examined using MRI. The protocol consisted of sagittal and coronal plane acquisitions of the entire spine. An image processing software allowed the outline detection of the nucleus zone (intervertebral high intensity portion). The vertebral bodies were also reconstructed. Using a pre-post processor, the nucleus zone migration and a wedging angle were quantified. Statistical tests showed the repeatability of the method (p > 0.4). Nucleus zone migration was correlated to the wedging angle (r(2) = 0.488, p < 0.0001) in the coronal plane. Our results were in agreement with the literature: when two vertebrae move deforming the disc, the nucleus moves into the convexity of the curvature. But should we talk about the nucleus? Despite image processing software allowing the highlighting of image features (automatic color lookup tables applied to grayscale images using pixel intensity measurements), it is impossible to differentiate the nucleus from the annulus on T2 weighting images of adolescent spine. This new geometric model of the intervertebral disc, used for the quantification of the nucleus zone migration, should be of interest for further investigation of stiffness parameters of spine.
Abstract: An experimental study of the subtalar joint has been conducted with the aim of establishing its axis of movement as well as analysing the associated movement. For description of the axis, CT data for five positions of a single foot were reconstructed using a 3D programme, the 3D data was processed by Patran software. Measures of angular displacements were made from three amputated feet placed in a specially constructed foot frame. Four instantaneous axes of movement could be defined. Calculation of displacements showed an important rolling of the calcaneus (45 degrees). Tacking was evident in inversion, with an opposite displacement between the front and rear part of the calcaneus, whereas during eversion tacking affected only the rear part of the bone: these results were confirmed by 3D reconstructions. Henke's axis was described as that for the talonavicular joint, but acceptable for the subtalar joint. Several authors investigating the coordinates of this axis have reported large differences and described screw-like movements, the latter being incompatible with a fixed axis: instantaneous axes, however are compatible with a screw-like movement. The subtalar joint appears to work as a pivot joint during inversion and as a plane joint during eversion. Although Henke's axis has pedagogical value the subtalar joint has a series of instantaneous axes.
Abstract: In 12 infants aged under 16 months with unilateral club foot we used MRI in association with multiplanar reconstruction to calculate the volume and principal axes of inertia of the bone and cartilaginous structures of the hindfoot. The volume of these structures in the club foot is about 20% smaller than that in the normal foot. The reduction in volume of the ossification centre of the talus (40%) is greater than that of the calcaneus (20%). The long axes of both the ossification centre and the cartilaginous anlage of the calcaneus are identical in normal and club feet. The long axis of the osseous nucleus of the talus of normal and club feet is medially rotated relative to the cartilaginous anlage, but the angle is greater in club feet (10 degrees v 14 degrees). The cartilaginous structure of the calcaneus is significantly medially rotated in club feet (15 degrees) relative to the bimalleolar axis. The cartilaginous anlage of the talus is medially rotated in both normal and club feet, but with a smaller angle for club feet (28 degrees v 38 degrees). This objective technique of measurement of the deformity may be of value preoperatively.
Abstract: OBJECTIVES: A three dimensional finite element model of the femorotibial joint was developed from MR images in order to quantify in vivo the articular contact. BACKGROUND: Most of femorotibial joint models were elaborated from in vitro experiments. The stereophotogrammetric technique was used to model the geometry and mechanical testing had been performed to quantify the material properties. METHOD: MR images were performed on a normal adult knee joint, in extension position. An image processing software developed in our laboratory allowed our model geometry to be constructed, and a pre-and post-processing software allowed us to develop a three-dimensional finite element model. Experimental contact area values were obtained using a method developed in our laboratory. Theoretical contact values, areas and hydrostatic pressure were obtained with a non-linear finite element computation using a non-linear software solver. RESULTS: The results show a good agreement between theoretical and experimental contact area values. Hydrostatic pressure was found to be higher at the medial contact than at the lateral contact. CONCLUSION: This study validated the use of contact elements to quantify the contact areas. The model permitted the body weight simulation to understand the role of the menisci. RELEVANCE: The clinical application of the study was to develop a method evaluating the influence of rotational abnormalities of the lower limbs on the knee joint at short- and long-term. This consisted of quantifying the contact area and pressure values and their migration.
Abstract: OBJECTIVE: The study presents a method allowing the in vivo homogenised characteristics of the tibiae of children to be assessed. DESIGN: Studies have been performed on two groups of children: six normal children, aged from 5 to 16 yr, and on four children, aged from 8 to 11 yr with tibial deformities. We analysed the tibial transverse sections from CT scans performed on the left tibia of each child. BACKGROUND: Most tibial torsion studies have only been based on geometrical parameters. Our study integrated mechanical and geometrical considerations. METHODS: The finite element models and integration of mechanical properties were performed from CT scans. Then homogenised mechanical characteristics (tensile stiffness, flexural stiffness and torsional stiffness) were calculated. RESULTS: The homogenised mechanical characteristics decrease between 20 to 80% of the tibial length. The values increased with age for both groups of children. Children with abnormalities seem to have values of tibial rigidities comparable with those of normal tibiae. CONCLUSIONS: By considering the mechanical and geometrical properties of the tibia in our study, we showed that the bone stiffness of children is not altered with torsional deformities. RELEVANCE: Torsional tibial abnormalities of children are a frequent phenomenon which may have important consequences on gait and joints. The method developed could be used as an objective assessment of bone rigidities for analysing tibial disorders such as torsional abnormalities of varying severity.
Abstract: Frequency analysis of long bones has been investigated as a tool to assess bone quality or integrity. The objective of the present paper was to develop a three-dimensional finite element model of a fresh human femur with geometrical and mechanical properties derived from quantitative computer tomography images. This model was then exercised and the results were compared to those obtained from a vibration analysis technique. The percent relative error between the numerically and experimentally derived results was found about 4%. Finally, the influence of mechanical properties on the resonant spectre was studied. The results exhibit the limitations of the vibrational technique to detect slight material changes.
Abstract: Biomaterials do not escape from the general trend present in all contemporary science and technology towards increasing use of computers and information technology. In this paper the use of computer modelling for the design of biomaterials is discussed. The word 'biomaterials' is interpreted in its broadest sense, i.e. referring to any foreign object brought into the body for temporary or permanent use. Computer modelling will first be discussed as a tool to model biological structures (bones, arteries) or to investigate and simulate biological interactions at implant-host interfaces. It will then be illustrated how computer modelling, using insights gained from the modelling of the biological structures themselves, is used in the design process of dental, orthopaedic and cardiovascular prostheses. The area of computer modelling for biomaterials applications has become so vast that an exhaustive overview is impossible in the framework of one paper. Rather, some illustrative case studies will be discussed which are, in the opinion of the authors, representative of general trends in this challenging domain of science on the boundary between engineering and medicine.
Abstract: Finite element analysis modeling is an important tool in the design of total joint replacements. However, to use a finite element analysis the material properties of the studied bone must be known. The aim of the study was to measure the elastic properties of the glenoid bone in the axial, coronal, and sagittal planes with an ultrasound transmission technique. The relative density and Houndsfield computed tomography numbers were also assessed. Three pairs of scapulas were obtained from unembalmed human cadavers. Seventy-four cubic cancellous bone specimens of 6 mm were used for ultrasonic measurements. The study showed significant differences with anatomic location. Mechanical properties of cancellous bone were found to be higher near the direction of application of the resultant force, perpendicular to the articular surface of the glenoid. Mechanical properties were found to be significantly higher at the center and posterior edge of the glenoid (p < 0.01). Significant differences were also found in the three planes studied. The lateromedial Young's modulus (E1) was higher than the anteroposterior modulus (E2) and the superoinferior modulus (E3) (E1 = 372 +/- 164 MPa, E2 = 222 +/- 79 MPa, E3 = 198 +/- 75 MPa).
Abstract: Fourteen patients with acetabular dysplasia were studied by using three-dimensional computed tomography (CT) reconstructions before pelvic osteotomies. Computer manipulation of the data allowed a preoperative visual assessment of acetabular shape, assessment of potential congruency between the femoral head and acetabulum by using a mathematical best-fit sphere, and measurement of surface contact distances that depict joint coverage and relate to concentration of weight-bearing forces. Preoperative evaluation of the three-dimensional images for these 14 patients allowed improved understanding of their abnormal anatomy and better surgical planning.
Abstract: The aim of the study was to assess mechanical properties of human cancellous bone in vitro. Six hundred cubic specimens of cancellous bone were obtained from the tibia, femur, patella, lumbar spine and humerus of eight subjects. The elastic properties were assessed using an ultrasonic transmission technique developed and validated by Ashman (1). The results showed that differences exist between subjects significantly (p < 0.05) and that the mechanical properties vary along the length and the periphery (about a factor 3 to 5). Cancellous bone should be considered heterogeneous and as orthotropic materials exhibiting degrees of anisotropy varying from 2 to 4. Linear and power fit elationships for cancellous bone were found approximately equal. Powers vary from 1.3 to 1.7 for axial modulus versus density and 1.3 and 2.3 for strength versus density. Finally, these results suggest the use of appropriate mechanical properties upon the type of bone for finite element analysis.
Abstract: Mechanical properties of cortical and cancellous bone from eight human subjects were determined using an ultrasonic transmission technique. Raw computerized tomography (CT) values obtained from scans of the bones in water were corrected to Hounsfield units. The correlations between CT numbers and mechanical property estimated from cortical bone were found to be low (r2 < 0.2), while these relationships for cancellous bone were found to be higher (r2 > 0.6). These results suggest that CT values may be useful in predicting mechanical properties only for cancellous bone. Poor correlations were found between modulus in the radial or circumferential direction and modulus in the superior-inferior direction for cortical bone, whereas good correlations were found between modulus in the anterior-posterior direction or medial-lateral direction and modulus in the S-I direction for cancellous bone. These results indicate that modulus in the radial or circumferential direction could not be predicted from modulus in the S-I direction for cortical bone, but could be predicted for cancellous bone. The predictive capabilities of linear and power models evaluated for cancellous bone alone were approximately equal. However, the power function gives a better fit of data at the low and high density values. The specific relationships, depending on the types of bone, that predict elastic modulus from density and CT numbers were suggested for human cortical and cancellous bone. These specific correlations may help a number of researchers develop more accurate models; however, these hypotheses should be proven by further study.
Abstract: The bony pathoanatomy of clubfoot has been assessed by a three dimensional reconstruction of transverse CT images obtained from 27 feet in children aged 3-10 years. Principal axes of the bones were determined to quantitate interosseous deformity, while visual inspection of the reconstructed images demonstrated intraosseous deformity. "Medial spin" and midfoot adduction were analyzed on the AP view of the foot ("top" view), while hindfoot pronosupination was analyzed on the AP view of the ankle (posterior view). This technique allows visualization of deformities which normally cannot be analyzed on plain radiographs, and also shows that a variety of interosseous relationships make up the clinical entity known as clubfoot. Abnormal talar pronation ("intorsion") was an unexpected finding of this three dimensional analysis.
Abstract: The modal analysis of a human tibia consisted of characterizing its dynamic behavior by determining natural frequency, damping ratio and mode shapes. Two methods were used to perform the modal analysis: (1) a finite element method (structural model); (2) an experimental modal analysis (modal model). The experimental modal model was used to optimize the structural model. After optimization, differences in results between the two models were found to be due only to mechanical properties and mass distribution. The influences of boundary conditions and geometric properties (such as inertia and length) were eliminated by the finite element model itself. The percent relative error between the two methods was approximately 3%, corresponding to the standard deviation of the measured frequencies. For the frequency range considered, the mode shapes were bending modes in two different vibration planes (latero-medial and sagittal), with a slight torsion effect due to the twisted geometry of the tibia.
Notes: BROCKAERT H. MAZERAN P.E. RACHIK M. HO BA THO M.C. Can the nanoindentation be used to characterize the bone mechanical anisotropy? 8th International Symposium on Computer Methods in Biomechanics and Biomedical Engineering, (CMBBE), Porto, Portugal, February, 2008 (Oral)
Notes: DAO T.T. MARIN F. HO BA THO M.C. Computer-aided decision system to diagnose the pathologies of the musculoskeletal system of the lower limbs. 8th International Symposium on Computer Methods in Biomechanics and Biomedical Engineering, (CMBBE), Porto, Portugal, February, 2008 (Poster).
DAO T.T. MARIN F. HO BA THO M.C. Ontology-based computer-aided decision system : a new architecture and application concerning the musculoskeletal system of the lower limbs. 4th European Conference of the International Federation for Medical and Biological Engineering Antwerp, Belgium, November, 2008 (Oral).
DAO T.T. MARIN F. HO BA THO M.C. Predictive mathematical models based on data mining methods of the pathologies of the lower limbs. 4th European Conference of the International Federation for Medical and Biological Engineering Antwerp, Belgium, November , 2008 (Oral).
DAO T.T. MARIN F. HO BA THO M.C. Ontology of the musculo-skeletal system of lowers limbs. In Proceedings of the 29th Annual International Conference of the IEEE EMBS, pp. 386-389, Lyon, France, Août 2007 (oral).
DAO T.T. MARIN F. HO BA THO M.C. OSMMI - Diagnostic-based Ontology of the musculo-skeletal system of lowers limbs. In Proceedings of the 2nd International Conference on the Development of Biomedical Engineering, Hanoi, Vietnam, pp. 181-189, Juillet 2007 (poster).
Abstract: The human skin is a complex biological material. It consists of three layers of different thicknesses: epidermis, dermis and hypodermis. This structural complexity gives the skin of the mechanical properties of complex hyperelastic, nonlinear, viscoelastic and submitted to the pre-tension. An indentation composed of 6 loading levels and running in the MRI environment has been developed. Indentation tests were performed on the dorsal part of the left forearm of 9 subjects of ages ranging from 26 to 40 years. For each subject, 28 MRI images were built. Each image represents a slice of the forearm. The images were then processed through a medical images processing software in house in order to reconstruct skin layers, muscles and bones. Finally, a finite element model in 2D was built from MRI images at the initial configuration (without load) using a pre-processor MSC.Patran 2005. This model consists of 4 layers of different materials: three skin layers and a muscle layer. The bones were supposed rigid and fixed. The Neo-Hooke hyperelastic incompressible constitutive law with one parameter to identify C10 was used for all 4 layers of materials (C10,Epi., C10,Der., C10,Hyp., C10,Mus.) . Indentation tests were simulated using a solver MSC.Marc 2005. The error between the simulation results and those of the experiment was measured by an objective function. The identification of parameters of the constitutive law was conducted by the minimization of the objective function via Levenberg-Marquardt algorithm developed under MatLab environment. The numerical validation of the identification process has shown that the minimum is only provided when the first two layers (epidermis and dermis) behave as a single layer (C10,E+D). The identification results provide a range of values for a population of 9 subjects: C10,E+D = [60-370] kPa; C10,Hyp. = [0,04-4] kPa; C10,Mus. = [0,7-1,7] kPa. The results reflect the human variability of mechanical properties.
Abstract: This work of thesis is devoted to the mechanical analysis by the Finite Element Method of femurs with and without customized hip implant. The technique of model reconstruction is based on a preliminary CT scan exam of the specimens with or without an implant.
The mechanical behavior of the femoral bone tissues is defined by mean of either the literature for the cortical bone or the analysis of the CT images for the spongious bone.
The modelization technique by the Finite Element Method is then developed and validated in the framework of intact femurs. The different experimental tests are realized by the mean of a vibrational technique, fracture tests or strain analyses. The interest of a fine description of the bone materials is emphasized during this different simulations.
Then we work about the development and the validation of femur models equipped of a customized hip implant conceived according to the protocol of our industrial partner (EUROS ® ). The experimental tests concern the vibrational technique followed by the strain analysis.
So to demonstrate the interest of the project, we are then interested in the application of the various models. The simulation of physiological loads allows to evaluate the risk components for the bone tissue. Equally, a real clinic case concerning a revision is processed. Our analysis allows to identify the problem directly linked to the implant designing.
This work in performed in collaboration with industrial partner Euros (CIFRE Euros).
Notes: Position after PhD thesis : Engineer at MSC.Software
