Biomedical subjects

D Périé

Publications and source records attributed to D Périé.

10 recordsLinked to original sources

PubMed2005

Assessment of compressive modulus, hydraulic permeability and matrix content of trypsin-treated nucleus pulposus using quantitative MRI.

A clinical strength MRI and intact bovine caudal intervertebral discs were used to test the hypotheses that (1) mechanical loading and trypsin treatment induce changes in NMR parameters, mechanical properties and biochemical contents; and (2) mechanical properties are quantitatively related to NMR parameters. MRI acquisitions, confined compression stress-relaxation experiments, and biochemical assays were applied to determine the NMR parameters (relaxation times T1 and T2, magnetization transfer ratio (MTR) and diffusion trace (TrD)), mechanical properties (compressive modulus H(A0) and hydraulic permeability k(0)), and biochemical contents (H(2)O, proteoglycan and total collagen) of nucleus pulposus tissue from bovine caudal discs subjected to one of two injections and one of two mechanical loading conditions. Significant correlations were found between k(0) and T1 (r=0.75,p=0.03), T2 (r=0.78, p=0.02), and TrD (r=0.85, p=0.007). A trend was found between H(A0) and TrD (r=0.56, p=0.12). However, loading decreased these correlations (r=0.4, p=0.2). The significant effect of trypsin treatment on mechanical properties, but not on NMR parameters, may suggest that mechanical properties are more sensitive to the structural changes induced by trypsin treatment. The significant effect of loading on T1 and T2, but not on H(A0) or k(0), may suggest that NMR parameters are more sensitive to the changes in water content enhanced by loading. We conclude that MRI offers promise as a sensitive and non-invasive technique for describing alterations in material properties of intervertebral disc nucleus, and our results demonstrate that the hydraulic permeability correlated more strongly to the quantitative NMR parameters than did the compressive modulus; however, more studies are necessary to more precisely characterize these relationships.

Animals↗

PubMed2004

Biomechanical modelling of orthotic treatment of the scoliotic spine including a detailed representation of the brace-torso interface.

As part of the development of new modelling tools for the simulation and design of brace treatment of scoliosis, a finite element model of a brace and its interface with the torso was proposed. The model was adapted to represent one scoliotic adolescent girl treated with a Boston brace. The 3D geometry was acquired using multiview radiographs. The model included the osseo-ligamentous structures, thoracic and abdominal soft tissues, brace foam and shell, and brace-torso interface. The simulations consisted of brace opening to include the patient's trunk followed by brace closing. To validate the model, the resulting geometry was compared with the real in-brace geometry, and the resulting contact reaction forces at the brace-torso interface were compared with the equivalent forces calculated from pressure measurements made on the in-brace patient. Differences between coronal equivalent and reaction forces were less than 7N. However, sagittal reaction forces (47N) were computed on the abdomen, whereas negligible equivalent forces were measured. The simulated geometry presented partially reduced coronal Cobb angles (1-4 degrees), over-corrected sagittal Cobb angles and maximum deformation plane (5 degrees), completely corrected coronal shift, and sagittal shift and rib humps that were not corrected. This study demonstrated the feasibility of a new approach that represents the load transfer from the brace to the spine more realistically than does the direct application of forces.

Adolescent↗

PubMed2003

Correlation between nucleus zone migration within scoliotic intervertebral discs and mechanical properties distribution within scoliotic vertebrae.

Correlations between intervertebral disc degeneration and bone mass were investigated previously, but never on scoliotic patients. Using MRI measurements of intervertebral discs behavior and vertebral bone tomodensitometry, correlations between nucleus zone displacement within intervertebral discs and mechanical center migration within vertebral bodies were investigated in vivo on scoliotic patients. The protocol, performed on eleven scoliotic girls, was composed of a CT scan acquisition of apical and adjacent vertebrae followed by a MRI acquisition of the thoracolumbar spine. The displacement between the vertebral body centroid and inertia center was computed from the CT images and called the mechanical migration. The displacement between nucleus zones and vertebral body centroids was quantified from MRI and called the nucleus zone migration. For apical vertebrae, a significant correlation was found in the coronal plane (r = 0.766, p < 0.01), but not in the sagittal plane (r = -0.349, p > 0.05). For adjacent vertebrae, significant correlations were found in both coronal (r = -0.633, p < 0.05) and sagittal (r = -0.797, p < 0.01) planes. The nucleus zone migration occurred in the convexity of the curvature whereas the mechanical migration occurred in the concavity.Known secondary mechanical phenomenon of scoliosis was quantified using new parameters describing intervertebral discs and vertebral bodies. Further investigations should be performed to explain the mechanical evolution of scoliosis and to use these parameters in predictive criteria of scoliosis.

Bone Density↗

PubMed2002

Biomechanical evaluation of Cheneau-Toulouse-Munster brace in the treatment of scoliosis using optimisation approach and finite element method.

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.

Adolescent↗

PubMed2002

Evaluation and calibration of an electromagnetic tracking device for biomechanical analysis of lifting tasks.

Electromagnetic motion tracking devices are increasingly used as a kinematic measuring tool. The aim of this study was to evaluate a long-range transmitter in an environment with a conventional force plate present in order to assess its suitability for further biomechanical applications. Using a calibration apparatus developed in our lab and Optotrack measurements, the performances of the Motion Star were evaluated. Positions and orientations were measured in a 140 x 80 x 120 cm(3) space centered on the force plate. Using a mathematical model developed at Queen's University, these data were calibrated. Errors on position and orientation were less than 150 mm and 10 degrees before calibration of the Motion Star, and less than 20mm and 2 degrees after calibration, with no differences between data collected with the force plate switched on/off. These errors did not depend on sensor orientation. Variability of the signal was small indicating minimal noise. Field distortion was the largest source of measurement error, which increased with the distance between the transmitter and the sensor and the proximity of the sensor to the force plate. Before its use for biomechanical analysis of lifting tasks and validation of dynamic models using force plate data, the data from electromagnetic motion tracking devices must be calibrated to decrease the errors due to electromagnetic field distortion.

Biomechanical Phenomena↗

PubMed2002

Personalised mechanical properties of scoliotic vertebrae determined in vivo using tomodensitometry.

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?

Child↗

PubMed2002

Personalized biomechanical modeling of Boston brace treatment in idiopathic scoliosis.

The aim of this study was to describe how the Boston brace modify the scoliotic curvatures using a finite element (FE) model and experimental measurements. The experimental protocol, applied on 12 scoliotic girls, was composed of the pressure measurement at the brace-torso interface followed by two radiographic acquisitions of the patient's torso with and without brace. A 3D FE model of the trunk was built for each unbraced patient. The brace treatment was represented by two different modeling approaches: 1) using equivalent forces calculated from the measured pressures; 2) by an explicit personalized FE model of the brace (hexahedral elements) and its interface with the torso (contact elements). In the first model, measured brace forces less than 40N and up to 113N induced respectively less than 21% and up to 87% of real correction. Thoracic forces induced the main correction, affecting partially both lumbar and thoracic curves, in agreement with the literature. In the second model, the brace closing reduced the curves up to 35% of real correction. Contact reaction forces (16-79N) were similar to real brace forces (11-72N). The results suggested that other mechanisms than brace pads contribute to the equilibrium of the patients. Postural control by the muscular system remains a problem to address in a future study. The second model represented more realistically the load transfer from the brace to the spine than external forces application. With such model, it is expected to predict the effect of a brace before its design and manufacturing, and also to improve its design.

Adolescent↗

PubMed2001

In vivo geometrical evaluation of Cheneau-Toulouse-Munster brace effect on scoliotic spine using MRI method.

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.

Adolescent↗

PubMed2001

Tomodensitometry measurements for in vivo quantification of mechanical properties of scoliotic vertebrae.

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?

Child↗

PubMed2001

Intervertebral disc modeling using a MRI method: migration of the nucleus zone within scoliotic intervertebral discs.

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.

Analysis of Variance↗