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*INRA, Station de science du sol, Montfavet (FRA) Diffusion du document : INRA, Station de science du sol, Montfavet (FRA); National audience

International audience; Low back pain represents a major economic and societal challenge due to its high prevalence. Lumbar orthoses are one of the recommended treatments. Even if previous results showed their clinical effects, the detailed mode of action is still poorly known, making the device design difficult. A renewed instrumentation and experimental protocol should bring better insight into the lumbar brace–trunk mechanical interaction. This instrumentation should give detailed information on the basic physical or geometrical parameters: the pressure applied on the trunk, the body shape and the strain in the belt. The principal objective of this study was to propose and validate a new measurement protocol, based on pressure mapping systems and full-field shape and strain measurement. The feasibility of the protocol was tested along with its validity and repeatability. The influence of various parameters, which could cause changes in the measurements, was tested with six different belt configurations on one subject. Measurements were also performed to study the impact of posture on pressure and strain. Both pressure and strain appeared to be asymmetric from left to right. The pressure applied by the lumbar belt on the back varies with breathing and with posture. This study showed that full-field measurements were necessary to render the high variability of pressure or strain around the trunk, under recommendations of their use to guarantee a satisfying repeatability.

International audience; Lumbar belts are one of the possible indication among therapeutic strategies for low back-pain management, but few studies and insufficient data have been reported to evaluate their clinical effects.Recently, a semi-analytical model has been developed for in-silico trials of lumbar belts on patients' morphologies (Molimard et al., 2019a), incorporating for the first time the trunk deformation and providing an estimation of the pressure applied on the trunk. A unique indicator of the belt mechanical efficiency was proposed: Pressure is integrated into a bending moment, calculated at the center of curvature in the lumbar region, characterizing the action of reducing lumbar spine lordosis. One important finding of this study indicates that patient BMI impacts belt efficacy, suggesting that overweight is predictive of decreased belt effectiveness. However, more morphologies in the high Body Mass Index (BMI) range were needed to confirm this trend, showing the importance of controlling the cohort characteristics.To investigate this association between belt efficacy and morphological indicators, 24 different morphologies were artificially generated using a Proper Orthogonal Decomposition (POD) from a base of 13 experimental trunk geometries, with most of them being overweight. They were used for a new in-silico clinical trial using one lumbar belt model and the waist-to-hip (WHR) ratio as a morphological indicator. The results confirmed our hypothesis showing that an increase in WHR is associated with a decrease in bending moment. In addition, no difference in these trends could be found between experimental and in-silico patients, nor between men and women.

International audience; Low back pain is a major public health problem in European Countries. In France, about 50% of population is suffering of this pathology every year (Fassier 2011). Because of health care cost and sick leave (Fassier 2011; Leclerc et al. 2009), low back pain has both societal and economic adverse consequences. Many treatments are proposed. However no guideline is provided to physician. Treatment depends on patient, on low back pain type and evolution and also on physician knowledge and believes. Medical devices, as lumbar belt might be proposed to treat low back pain. Several clinical trials have shown their efficacy (Calmels et al. 2009). Nevertheless, both mechanical and physiological effects of lumbar belts remain unclear. In this study, the application of a lumbar belt on the trunk is simulated by a finite element model. It is often assumed that the pain comes from the toe of the intervertebral discs and is related only to the intradiscal pressure and the thoracolumbar posture. Beside, abdominal pressure is used by belt manufacturers as a marker of the lumbar belt efficiency, because a change in the abdominal pressure could bring a change in the thoracolumbar posture and consequently on the intradiscal pressure. That's why the goal of this study is to determine the mechanical effect of wearing lumbar belt: i) on abdominal pressure; ii) on thoracolumbar posture; iii) on intervertebral disc pressure.

International audience; Every year, about 50% of French population is suffering of low back pain [Fassier, 2011]. A usual part of treatment is lumbar belt wearing. Nevertheless the biomechanical and physiological impacts are not clearly understood. In this study, the application of lumbar belt on the trunk is simulated by a finite element model. The objective of this model is to determine the impacts of wearing lumbar belt in abdominal pressure, spine posture and inter-vertebral disc pressure.

International audience; Interface pressure applied by compression bandages is the therapeutic action of the treatment of some venous or lymphatic pathologies. The so-called Static Stiffness Index, which quantifies the pressure increase from supine to standing position, is usually used to differentiate compression bandages. It was hypothesized that this pressure increase was the consequence of a change in leg geometry (blood and muscle falling down) and a change in calf soft tissue mechanical properties (muscles contraction). Calf soft tissue global stiffness of both legs of 25 patients was characterized in a sitting and standing position. This characterization was combined with interface pressure measurements applied by six different bandages. Though soft tissue mechanical properties significantly increased from sitting to standing position, no correlation was observed with the corresponding pressure increase. Thus, pressure increase is mainly attributed to a change in leg geometry.

International audience; Objective: A numerical 3D model of the human trunk was developed to study the biomechanical effects of lumbar belts used to treat low back pain. Methods: This model was taken from trunk radiographies of a person and simplified so as to make a parametric study by varying morphological parameters of the patient, characteristic parameters of the lumbar belt and mechanical parameters of body and finally to determine the parameters influencing the effects of low back pain when of wearing the lumbar belt. The loading of lumbar belt is modelled by Laplace's law. These results were compared with clinical study. Results: All the results of this parametric study showed that the choice of belt is very important depending on the patient's morphology. Surprisingly, the therapeutic treatment is not influenced by the mechanical characteristics of the body structures except the mechanical properties of intervertebral discs. Discussion: The numerical model can serve as a basis for more in-depth studies concerning the analysis of efficiency of lumbar belts in low back pain. In order to study the impact of the belt's architecture, the pressure applied to the trunk modelled by Laplace's law could be improved. This model could also be used as the basis for a study of the impact of the belt over a period of wearing time. Indeed, the clinical study shows that movement has an important impact on the distribution of pressure applied by the belt.; Objectif : Un modèle numérique 3D du tronc humain a été développé pour étudier les effets biomécaniques des ceintures lombaires utilisées pour traiter les lombalgies. Méthodes : Ce modèle a été pris à partir de radiographies du tronc d'une personne et simplifié de manière à faire une étude paramétrique en faisant varier les paramètres morphologiques du patient, les paramètres caractéristiques de la ceinture lombaire et les paramètres mécaniques du corps et enfin à déterminer les paramètres influençant les effets de la lombalgie lors du port de la ceinture lombaire. La charge de la ceinture lombaire est modélisée par la loi de Laplace. Ces résultats ont été comparés à ceux d'une étude clinique. Résultats : Tous les résultats de cette étude paramétrique ont montré que le choix de la ceinture est très important en fonction de la morphologie du patient. De façon surprenante, le traitement thérapeutique n'est pas influencé par les caractéristiques mécaniques des structures corporelles, à l'exception des propriétés mécaniques des disques intervertébraux. Discussion : Le modèle numérique peut servir de base à des études plus approfondies concernant l'analyse de l'efficacité des ceintures lombaires dans les lombalgies. Afin d'étudier l'impact de l'architecture de la ceinture, la pression appliquée sur le tronc modélisée par la loi de Laplace pourrait être améliorée. Ce modèle pourrait également servir de base à une étude de l'impact de la ceinture sur une période de port. En effet, l'étude clinique montre que le mouvement a un impact important sur la répartition de la pression appliquée par la ceinture.

Fabric-to-fabric friction is involved in the action mechanism of medical compression devices such as compression bandages or lumbar belts. To better understand the action of such devices, it is essential to characterize, in their use conditions (mainly pressure and stretch), the frictional properties of the fabrics they are composed of. A characterization method of fabric-to-fabric friction was developed. This method was based on the customization of the fourth instrument of the Kawabata Evaluation System, initially designed for fabric roughness and friction characterization. A friction contactor was developed so that the stretch of the fabric and the applied load can vary to replicate the use conditions. This methodology was implemented to measure the friction coefficient of several medical compression bandages. In the ranges of pressure and bandage stretch investigated in the study, bandage-to-bandage friction coefficient showed very little variation. This simple and reliable method, which was tested for commercially available medical compression bandages, could be used for other medical compression fabrics.

International audience; Objective: A numerical 3D model of the human trunk was developed to study the biomechanical effects of lumbar belts used to treat low back pain. Methods: This model was taken from trunk radiographies of a person and simplified so as to make a parametric study by varying morphological parameters of the patient, characteristic parameters of the lumbar belt and mechanical parameters of body and finally to determine the parameters influencing the effects of low back pain when of wearing the lumbar belt. The loading of lumbar belt is modelled by Laplace's law. These results were compared with clinical study. Results: All the results of this parametric study showed that the choice of belt is very important depending on the patient's morphology. Surprisingly, the therapeutic treatment is not influenced by the mechanical characteristics of the body structures except the mechanical properties of intervertebral discs. Discussion: The numerical model can serve as a basis for more in-depth studies concerning the analysis of efficiency of lumbar belts in low back pain. In order to study the impact of the belt's architecture, the pressure applied to the trunk modelled by Laplace's law could be improved. This model could also be used as the basis for a study of the impact of the belt over a period of wearing time. Indeed, the clinical study shows that movement has an important impact on the distribution of pressure applied by the belt.; Objectif : Un modèle numérique 3D du tronc humain a été développé pour étudier les effets biomécaniques des ceintures lombaires utilisées pour traiter les lombalgies. Méthodes : Ce modèle a été pris à partir de radiographies du tronc d'une personne et simplifié de manière à faire une étude paramétrique en faisant varier les paramètres morphologiques du patient, les paramètres caractéristiques de la ceinture lombaire et les paramètres mécaniques du corps et enfin à déterminer les paramètres influençant les effets de la lombalgie lors du port de la ceinture lombaire. La charge de la ceinture lombaire est modélisée par la loi de Laplace. Ces résultats ont été comparés à ceux d'une étude clinique. Résultats : Tous les résultats de cette étude paramétrique ont montré que le choix de la ceinture est très important en fonction de la morphologie du patient. De façon surprenante, le traitement thérapeutique n'est pas influencé par les caractéristiques mécaniques des structures corporelles, à l'exception des propriétés mécaniques des disques intervertébraux. Discussion : Le modèle numérique peut servir de base à des études plus approfondies concernant l'analyse de l'efficacité des ceintures lombaires dans les lombalgies. Afin d'étudier l'impact de l'architecture de la ceinture, la pression appliquée sur le tronc modélisée par la loi de Laplace pourrait être améliorée. Ce modèle pourrait également servir de base à une étude de l'impact de la ceinture sur une période de port. En effet, l'étude clinique montre que le mouvement a un impact important sur la répartition de la pression appliquée par la ceinture.

International audience; Objective: To develop a new method for the prediction of interface pressure applied by medical compression bandages. Methods: A finite element simulation of bandage application was designed, based on patient-specific leg geometries. For personalized interface pressure prediction, a model reduction approach was proposed, which included the parametrization of the leg geometry. Pressure values computed with this reduced model were then confronted to experimental pressure values. Results: The most influencing parameters were found to be the bandage tension, the skin-to-bandage friction coefficient and the leg morphology. Thanks to the model reduction approach, it was possible to compute interface pressure as a linear combination of these parameters. The pressures computed with this reduced model were in agreement with experimental pressure values measured on 66 patients' legs. Conclusion: This methodology helps to predict patient-specific interface pressure applied by compression bandages within a few minutes whereas it would take a few days for the numerical simulation. The results of this method show less bias than Laplace's Law, which is for now the only other method for interface pressure computation.

International audience; Lower back pain is a major public health problem. Despite claims that lumbar belts change spinal posture due to applied pressure on the trunk, no mechanical model has yet been published to prove this treatment. This paper describes a first model for belt design, based on the one hand on the mechanical properties of the fabrics and the belt geometry, and on the other hand on the trunk geometrical and mechanical description. The model provides the estimation of the pressure applied to the trunk, and a unique indicator of the belt mechanical efficiency is proposed: pressure is integrated into a bending moment characterizing the belt delordosing action on the spine. A first in-silico clinical study of belt efficiency for 15 patients with 2 different belts was conducted. Results are very dependent on the body shape: in the case of high BMI patients, the belt effect is significantly decreased, and can be even inverted, increasing the lordosis. The belt stiffness proportionally increases the pressure applied to the trunk, but the influence of the design itself on the bending moment is clearly outlined. Moreover, the belt/trunk interaction, modeled as sticking contact and the specific way patients lock their belts, dramatically modifies the belt action. Finally, even if further developments and tests are still necessary, the model presented in this paper seems suitable for in-silico pre-clinical trials on real body shapes at a design stage.

Evidence is still inconclusive for the benefits of bracing in patients with knee osteoarthritis. To assess the effect of REBEL RELIEVER unloading knee brace in conservative treatment of knee osteoarthritis, a randomized controlled trial was conducted in 67 patients with symptomatic medial knee osteoarthritis, who randomly received 6-week treatment with either REBEL RELIVER unloading knee brace + usual care (Brace group, N = 32) or usual care alone (Control group, N = 35). Primary outcome was the global last 24h-pain relief (100-mm visual analogic scale [VAS]) at 6 weeks. Secondary endpoints included pain on motion (100-mm VAS), function (Lequesne index), safety and observance. At 6 weeks, mean [SD] last 24h-pain decreased significantly more in Brace group versus Control group (−41.35 [3.37] vs −15.37 [3.23], difference −25.98, 95% CI −41.64 to −10.33, P

International audience; Objective: To develop a decision-making tool (DMT) to facilitate the prescription of knee orthoses for patients with osteoarthritis (OA) in daily practice. Methods: A steering committee gathered a multidisciplinary task force experienced in OA management/clinical research. Two members performed a literature review with qualitative analysis of the highest-quality randomized controlled trials and practice guidelines to confirm evidence concerning knee orthosis for OA. A first DMT draft was presented to the task force in a 1-day meeting in January 2016. The first version of the DMT was criticized and discussed regarding everyday practice issues. Every step was discussed and amended until consensus agreement was achieved within the task force. Then 4 successive consultation rounds occurred by electronic communication, first withprimary-and secondary-carephysicians, then with international experts. All corrections and suggestions by each member were shared with the rest of the task force and included to reach final consensus. The final version was validated by the steering committee. Results: The definition and indication of several types of knee orthoses (sleeve, patello-femoral, hinged or unicompartmental offloading braces) were detailed. Orthoses may be proposed in addition to first-line non-pharmacological treatment if patient acceptance is considered good. At every step, a specific clinical assessment is needed. Discussion/conclusion: Based on the latest high-level evidence, practice guidelines, and an expert panel, a DMT to facilitate daily practice prescription of knee orthoses for OA patients was designed. An evaluation of DMT implementation in a wide range of health professionals is still needed. (C) 2018 The Author(s). Published by Elsevier Masson SAS.

International audience; Compression therapy with stockings or bandage is the most common treatment for venous or lymphatic disorders. The objective of this study was to investigate the influence of bandage mechanical properties, application technique and subject morphology on the interface pressure, which is the key of this treatment. Bandage stretch and interface pressure measurements (between the bandage and theleg) were performed on 30 healthy subjects (15 men and 15 women) at two different heights on the lower leg and in two positions (supine and standing). Two bandages were applied with two application techniques by a single operator. The statistical analysis of the results revealed: no significant difference in pressure between men and women, except for the pressure variation between supine and standing position; a very strong correlation between pressure and bandage mechanical properties (p

International audience

International audience

International audience; Compression bandages are commonly used in the treatment of some venous or lymphatic pathologies. The success of the treatment relies on the applied pressure, which depends on several parameters related to the bandage but also to patients’ morphology. A previous experimental study showed that patient’s morphology and bandage elastic properties were not sufficient to explain interface pressure distribution [1]. However, these two parameters are the only one taken into account in Laplace’s Law, actual reference method to explain interface pressure distribution.

Objective Compression bandages are commonly used in the treatment of some venous or lymphatic pathologies. The success of the treatment relies on the applied pressure, which depends on several parameters, especially the bandage properties but also patients’ morphology. A previous experimental study showed that considering only patient's morphology and bandage elastic properties were not sufficient to explain interface pressure distribution. However, these two parameters are the only one taken into account in Laplace's Law, current standard method to explain interface pressure distribution. The objective of the study is to characterize and model compression bandages pressure generation mechanisms. Material and methods A patient-specific numerical simulation of 4 bandages application [Biflex ® 16 and Biflex ® 17 (Thuasne) applied with 2 and 3 layers on the leg] was developed for 5 subjects. The inputs of this simulation are the subjects’ morphology, the bandage's and soft tissues’ elastic properties and the application technique. The results of this simulation were then confronted to the experimental results and pressure values computed with Laplace's Law: P = nT/r, with P the pressure [N/mm 2 ], n the number of layers, T the bandage tension [N/mm] and r the local radius of curvature [mm]. Results The numerical simulation provides the complete pressure distribution over the leg but also considers the deformations of the leg, induced by bandage application. The comparison with the results given by Laplace's law highlighted the influence of these leg geometry changes on the applied pressure. However, the 4 parameters considered in this simulation (leg morphology and deformations, bandage elastic properties and application technique) are not sufficient to completely explain pressure generation, and differences with the experiments still persist. Discussion/Conclusion Numerical simulation still needs to be enriched to consider other parameters which may impact interface pressure such as bandage to bandage interaction for example.

International audience; Compression bandages are a common treatment for some lymphatics or venous pathologies. The treatment success directly depends on the pressure which is applied on the external surface of the leg and which is then transmitted to the internal tissues. This interface pressure (between the limb and the bandage) depends mainly on the following parameters:- the bandage components (padding layers, …)- their mechanical properties- the bandage stretch- the application technique (spiral, …) and number of layers (overlap)- patient’s leg morphology- other parameters such as friction between the different bandage layers.Though the efficacy of this treatment is admitted [1], its action mechanism and the pressure it applies on the leg remain poorly understood [2].For now, the reference method for the computation of interface pressure applied by compression bandage is Laplace’s Law:P = n T / r (1)with P the local pressure, n the number of layers of the bandage, T the bandage tension (i.e. force to stretch the bandage), r the local radius of curvature of the limb. However, this law, which only considers the non-deformed state of the limb, is unable to accurately predict interface pressures [3].The aim of this communication is to present a combined experimental and numerical approach for the assessment of interface pressure applied by compression bandages.

International audience; Low back pain is a pain felt in the lumbar region of the spine. Among a large series of care strategies, lumbar belt might be used to treat this pathology. Several clinical trials have shown the efficiency of lumbar belts [1]. Despite the high quantity of affected patients each year (about 80 % of the French population have /will suffer back pain in their life), few authors investigated the mechanism of action of belts. It is usually reported that the main mechanical effect of a lumbar belt is the pressure applied on the trunk. This pressure on the abdominal skin and muscles induce an increase of intra-abdominal pressure, a decrease of intra-discal pressure, and a proprioceptive reaction of the posture. Unfortunately, the link between the textile characteristics, the belt design and the pressure applied on the trunk has been poorly studied.Recently, Bonnaire [2] proposed a clinical study using optical methods and pressure map sensors; Munoz [3] proposed a detailed finite element model, closely linked to medical imaging showing the load release in the intervertebral disc, but resorting to a clinical study is a tedious task, and some early stage information should be of great help when designing new belts.The purpose of this communication is an assessment of the applied pressure by a lumbar belt onto the trunk from the mechanical properties of fabrics and the trunk shape. It gives a way to estimate the mechanical efficiency of belts at the design stage.

International audience; Goal: A non-invasive method is proposed to identify in vivo the passive mechanical properties of deep soft tissues in the human leg.How: Force-displacement curves in response to a localized compression of the calf are measured with a custom made experimental setup. The material parameters of a finite element model are then calibrated against the experimental curves using a genetic algorithm. A thorough investigation of the efficacy of this method to identify such mechanical properties is conducted through a design of experiments analysis and mixed numerical - experimental validations. Results: It is the first time that a thorough analysis is conducted to really separate the contribution of deep and superficial tissues in the response to compression tests and this permits to estimate the parameters of deep soft tissues on four subjects independently of the response of their other tissues. Two strain energy density functions are compared. It is shown that a 2nd order reduced polynomial better describes the passive mechanical behavior of the deep soft tissues of the leg than the neo-Hookean model.

International audience; Compression of the lower leg by bandages is a common treatment for the advanced stages of some venous or lymphatic pathologies. The outcomes of this treatment directly result from the pressure generated onto the limb. Various bandage configurations are proposed by manufacturers: the study of these configurations requires the development of reliable methods to predict pressure distribution applied by compression bandages. Currently, clinicians and manufacturers have no dedicated tools to predict bandage pressure generation. A numerical simulation approach is presented in this work, which includes patient-specific leg geometry and bandage. This model provides the complete pressure distribution over the leg. The results were compared to experimental pressure measurements and pressure values computed with Laplace’s law. Using an appropriate surrogate model, this study demonstrated that such simulation is appropriate to account for phenomena which are neglected in Laplace’s law, like geometry changes due to bandage application.

International audience; Compression of the lower leg using medical compression stockings or bandages is a widely used treatment. We submit that the mechanical properties of soft tissues in the lower limb play a major role during compressive treatments of venous deficiency [1] and that predictive biomechanical models could help to better adapt the treatment to the specificity of each patient. A challenging step of the development of such models is to identify the mechanical properties of soft tissues for each patient [2]-[4].We recently developed a non-invasive and fast inverse approach to address this challenge. In this communication, the approach is described and assessed on several volunteers, showing promising results for an extension to large-size cohort of patients.

International audience; The purpose of this study is to evaluate the possible use of four “FSA” thin and flexible resistive pressure mapping systems, designed by Vista Medical (Winnipeg, Manitoba, Canada), for the measurement of interface pressure exerted by lumbar belts onto the trunk. These sensors were originally designed for the measurement of low pressure applied by medical devices on the skin. Two types of tests were performed: standard metrology tests such as linearity, hysteresis, repeatability, reproducibility and drift, and specific tests for this application such as curvature, surface condition and mapping system superposition.The linear regression coefficient is between 0.86 and 0.98; hysteresis is between 6.29% and 9.41%. Measurements are repeatable. The location, time and operator, measurement surface condition and mapping system superposition have a statistically significant influence on the results. A stable measure is verified over the period defined in the calibration procedure, but unacceptable drift is observed afterward. The measurement stays suitable on a curved surface for an applied pressure above 50mmHg.To conclude, the sensor has acceptable linearity, hysteresis and repeatability. Calibration must be adapted to avoid drift. Moreover, when comparing different measurements with this sensor the location, the time, the operator and the measurement surface condition should not change; the mapping system must not be superimposed.

International audience; In France, 50% of the population per year is suffering from low back pain. Lumbar belt are frequently proposed as a part of the treatment of this pathology. However mechanical ways of working of this medical device is not clearly understood, but abdominal pressure is often related. So an optical method was developed in this study to measure strain in lumbar belt and trunk interface and to derive a pressure estimation. Optical method consisted of coupling fringe projection and digital image correlation (DIC). Measurement has been carried out on the right side of a manikin wearing a lumbar belt. Average strain is 0.2 and average pressure is 1 kPa. Continuation of this study will be comparison of strain and pressure in different areas of lumbar belt (left side, front and back) and comparison of different lumbar belts. Results will be used in a finite elements model to determine lumbar belt impact in intern body. In long term, this kind of study will be done on human.

International audience; Low back pain is a major public health problem in European Countries. In France, about 50% of population is suffering of this pathology every year [Fassier, 2011]. Because of health care cost and sick leave [Fassier, 2011], [Leclerc, 2009], low back pain as both societal and economic adverse consequences. Concerning medical devices, such as lumbar belts, several clinical trials have shown their efficiency [Calmels, 1999]. It might be essential to know which parameters are important so as to increase the efficiency of their medical effects on patients. Nevertheless, both mechanical and physiological effects of lumbar belts remain unclear.In this study, a parametrical method is used in order to identify which parameters are more important than others through numerical simulation. This study is indispensable to design lumbar belts.

International audience; Elastic compression bandage is a common treatment for venous or lymphatic disorders. Even though the efficacy of this treatment is admitted, its mechanism remains poorly understood. The success of the treatment depends on the applied pressure, which depends on the bandage tension and the curvature of the limb (Laplace’s Law), the number of layers of the bandage, its components (padding layer, crepe …) and elastic properties, and the interactions between bandages and leg. To better understand the action of compression bandage, many interface pressure measurements have been done, but those measurements only give local information and for now, the whole pressure distribution on the leg is not known. Also, due to complex leg curvature and to bandage-leg and bandage-bandage interactions, the Laplace’s law is not sufficient to give a fine description of the pressure fields. Some simulations of the leg compression exist. Most of them are modeling the action of a compression sock on a leg [1][2], whose mechanical properties are more or less complex [3]. As far as we know, the simulation of bandage application on the leg has never been done yet. The aim of this communication is to present a first numerical model of the action mechanisms of bandages onto the skin developed through an experimental-numerical approach. A subject-specific FE model of bandage application is developed and compared with experimental measurements on two subjects.

International audience; Low back pain is pain affecting the lumbar segment of the spine. It is characterized depending on its origin and its duration. In this study, only common subacute or chronic low back pain, i.e. with a mechanical origin, is studied [1]. One of the treatments suggested is the use of a lumbar orthotic device. However, few studies exist so as to clearly elucidate the mechanism of action of these devices.In our study, a single type of lumbar orthotic, used in the treatment of common subacute or chronic low back pain was analyzed using a numerical model: lumbar support belts. The objective is to perform an overall study elucidating how belts work, in order to determine main parameters influencing on the treatment of low back pain using a FE trunk model. The studied parameters will be related to the patient's morphology, the belt and the mechanical characteristics of the human trunk.

International audience; Les ceintures lombaires sont des dispositifs médicaux utilisées pour prévenir et traiter la lombalgie, dont l’effet principal est la pression appliquée sur le tronc. L’objectif est d’évaluer quatre capteurs FSA permettant la mesure de cette pression.Matériel et méthodes. Deux types d’essai ont été réalisés : des tests classiques de métrologie (linéarité, hystérésis, répétabilité, reproductibilité et dérive) et des tests spécifiques à l’application (courbure, condition de surface et superposition de capteurs) [1].

Objective Although it is only a part of their therapeutic effect, the mechanical effect of compression or contention medical devices (CCMD) is always claimed by the manufacturers. However, the mechanism between the pressure application zone and the targeted organ is complex. It involves a purely passive mechanical effect and mechanisms related to the tonic postural system. Various strategies can be implemented to show the effectiveness of a mechanical action; among them, biomechanical modeling is a able to consider complex mechanical effects before any clinical trial. Objectives This work aims to describe the contributions of a biomechanical modeling in understanding the action of CCMD using as an illustration the lumbar belt treatment of chronic and sub-chronic back pain. Material and methods Three successive models are described: a finite elements model of the intervertebral discs, coupled with a low intensity X-ray imaging, a finite elements model of the entire trunk, including the spine but also the soft tissue of the abdomen and finally a purely analytical model based on external measurements of the trunk shape. Results These three models correspond to different questioning: the first shows that the use of lumbar belts changes the pressure in the back of intervertebral discs and therefore pain. The second allows kriging the most important parameters on posture – trunk shape, belt properties – from the others – abdominal tissues. Finally, the third model specifies the mechanical efficiency of a given lumbar belt on a specific patient. Discussion/Conclusion Each of the three proposed models answers to a specific question and cannot substitute for the other. The finite elements model used in the first two models is tedious to implement due to the geometry, obtained by segmentation of medical images, and calculation time can be high. However, this is a rich method, accurately describing the studied mechanical system and leading to detailed results. The analytical approach used in the third model requires more approximation, but its lower calculation time allows deployment in research and development units and clinics.

International audience; Interface pressure measurement is widely used to evaluate, for example, compression stockings, compression bandages and pressure ulcer prevention devices. Pneumatic [1], electro-pneumatic [1-3], resistive [2-4] or capacitive [5-6] sensors are usually used. The ideal interface pressure measurement device should be [7-8] small, thin and highly flexible, have a continuous output, be sensitive in detecting the range of pressure as low as 0-100 mmHg, be free from error of measurement on curved surfaces, be free from the effects of temperature and moisture, low cost. Despite sensors developed over the years, to our knowledge, none of them has met all the above criteria.Four “FSA” thin and flexible resistive pressure mapping systems have been designed by Vista Medical (Winnipeg, Manitoba, Canada). The objective of this study is to evaluate the FSA sensor (Vista medical, Winnipeg, Manitoba, Canada) for the measurement of interface of lumbar belts. Lumbar belt is a medical devices used to prevent and treat low back pain. The main mechanical effect of lumbar belts is the pressure applied on the trunk, which can induce a decrease of intervertebral pressure and/or modify morphological curves of the spine

International audience; Les ceintures lombaires sont largement utilisées dans le traitement de la lombalgie sub-aigüe et chronique. La compression qu'elles appliquent sur l'abdomen est supposée conduire à une variation de posture du patient diminuant la compression des disques vertébraux. Cependant, très peu d'études mécaniques sont venues confirmer ou infirmer ce mode d'action. Une étude clinique basée sur des mesures de champs de pression, de déformation des orthèses et de forme du tronc a été conduite sur 15 sujets lombalgiques. Il a été montré que le port de la ceinture diminue le niveau de douleur et que la posture est effectivement modifiée. Plus inattendu, la distribution de pression et de déformation présente des anomalies jusqu'alors jamais décrites, avec un fort déséquilibre entre le côté gauche et le côté droit du tronc.

International audience; Efficacy of lumbar belt in the treatment of low back pain has been already proven. Nevertheless, both mechanical and physiological effects remain unclear. A pilot study has been carried out to assess the mechanical effect of lumbar belts.