Etude biomécanique d'un nouvel implant rachidien pour préserver la croissance et la mobilité dans le traitement des scolioses

Le "gold-standard" du traitement chirurgical des scolioses est l'arthrodèse, qui consiste, à l'aide d'une instrumentation adaptée, à corriger et redresser les déformations scoliotiques, puis fusionner les vertèbres du segment pathologique afin de consolider la correction réalisée. Cette fusion entraine la destruction de la biomécanique physiologique du rachis, en supprimant sa mobilité et sa croissance. Les travaux réalisés dans le cadre de cette thèse portent sur le développement et la validation d'un nouveau concept d'instrumentation rachidienne ayant pour objectifs de réduire voire d'arrêter l'évolution des déformations rachidiennes, en conservant croissance et mobilité. Ce nouveau dispositif a nécessité une étude biomécanique large, partant du concept nouveau de cet implant, passant par la mise au point d'une méthodologie expérimentale, la conception et la réalisation de prototypes, puis leur validation à travers des études numériques, mécaniques, tribologiques et in vivo sur gros animal. La caractérisation in vitro du dispositif porte sur des essais mécaniques de caractérisation de matériau et des essais tribologiques de caractérisation du frottement. La caractérisation in vivo consiste en deux études menées sur gros animal, le modèle de porc Landrace, une première sur l'étude de l'arrachement de vis pédiculaires, puis une seconde, de validation de concept, avec 2 mois d'implantation du montage. Les premières conclusions tirées de ces travaux sont positives quant au bon fonctionnement du système. Des études en cours et à venir permettront de compléter ces résultats, et de valider le système dans son ensemble, afin de permettre sa future mise sur le marché.The "gold standard" of surgical treatment of scoliosis is arthrodesis, which, with an appropriate instrumentation, corrects and straightens the deformities and fuses the vertebra of the pathologic segment to consolidate the correction. This fusion leads to the destruction of the physiological biomechanics of the spine, destroying growth and mobility. The work done in this thesis focuses on the development and validation of a new concept of spinal instrumentation which objectives are to reduce or even stop the development of spinal deformities, maintaining growth and mobility. This device is composed of materials used in new ways, leading to friction issues that do not exist in the current spinal systems. Thus, the system required a large biomechanical study, starting from the new concept of this implant, carrying on the development of an experimental methodology, designing and prototyping and then validation through numerical, mechanical, tribological and large animal in vivo studies. In vitro characterization of the device involves characterization of material through mechanical tests, and characterization of the tribological behavior of the system. In vivo characterization consists of two studies on large animal, the Landrace pig model : a first one on pedicle screws pullout, and a second one with 2 months of implantation, to validate the concept. The initial findings from this work are positive about the correct behavior of this system. Ongoing and future studies will complement those results, and validate the system as a whole, to allow future marketing

Bone Damage Evolution Around Integrated Metal Screws Using X-Ray Tomography : In situ Pullout and Digital Volume Correlation

Better understanding of the local deformation of the bone network around metallic implants subjected to loading is of importance to assess the mechanical resistance of the bone-implant interface and limit implant failure. In this study, four titanium screws were osseointegrated into rat tibiae for 4 weeks and screw pullout was conducted in situ under x-ray microtomography, recording macroscopic mechanical behavior and full tomographies at multiple load steps before failure. Images were analyzed using Digital Volume Correlation (DVC) to access internal displacement and deformation fields during loading. A repeatable failure pattern was observed, where a ∼300–500 μm-thick envelope of bone detached from the trabecular structure. Fracture initiated close to the screw tip and propagated along the implant surface, at a distance of around 500 μm. Thus, the fracture pattern appeared to be influenced by the microstructure of the bone formed closely around the threads, which confirmed that the model is relevant for evaluating the effect of pharmacological treatments affecting local bone formation. Moreover, cracks at the tibial plateau were identified by DVC analysis of the tomographic images acquired during loading. Moderate strains were first distributed in the trabecular bone, which localized into higher strains regions with subsequent loading, revealing crack-formation not evident in the tomographic images. The in situ loading methodology followed by DVC is shown to be a powerful tool to study internal deformation and fracture behavior of the newly formed bone close to an implant when subjected to loading. A better understanding of the interface failure may help improve the outcome of surgical implants

Home Environmental Interventions for the Prevention or Control of Allergic and Respiratory Diseases: What Really Works.

International audienceHome health care workers interventions have been implemented in western countries to improve health status of patients with respiratory diseases especially asthma and allergic illnesses. Twenty-six controlled studies dealing with prevention and control of these diseases through home environmental interventions were reviewed. After a comprehensive description of the characteristics of these studies, the effectiveness of each intervention was then evaluated in terms of participants' compliance with the intervention program, improvement of quality of the indoor environment, and finally improvement of health outcomes, in detailed tables. Limitations and biases of the studies are also discussed. Overall, this review aims at giving a toolbox for home health care workers to target the most appropriate measures to improve health status of the patient depending on his and/or her environment and disease. Only a case-by-case approach with achievable measures will warrant the efficacy of home interventions. This review will also provide to the research community a tool to better identify targets to focus in future evaluation studies of home health care workers action

THREE-DIMENSIONAL OSTEOCYTE LACUNO-CANALICULAR NETWORK AT THE BONE IMPLANT INTERFACE

International audienc

Pullout strength of all suture anchors in the repair of rotator cuff tears: a biomechanical study

International audienc

THE OSTEOCYTE LACUNO-CANALICULAR NETWORK AT THE BONE-IMPLANT INTERPHASE IMAGED WITH FOCUSED ION BEAM -SCANNING ELECTRON MICROSCOPY

International audienc

Numerical simulation of stress-shielding at the bone-implant interface under shear loading

International audienceInserting a titanium implant in bone tissue may modify its physiological loading and therefore cause bone resorption, a phenomenon known as stress-shielding [1]. While monitoring and preventing stress-shielding is necessary to ensure the surgical success, it remains difficult to experimentally retrieve information on the properties of the interfacial tissues at the scale of 1-100 μm from the implant surface, where this phenomenon is localized. Numerical modelling represents a complementary tool to better understand phenomena related to the coupled bone-implant system due to the difficulty of measuring the stress distribution in vivo. The aim of this study is to investigate numerically the influence of various geometrical and material parameters on the local stress field around a bone-implant interface (BII) subject to shear loading

THREE-DIMENSIONAL OSTEOCYTE LACUNO-CANALICULAR NETWORK AT THE BONE IMPLANT INTERFACE

International audienc

Numerical simulation of stress-shielding at the bone-implant interface under shear loading

International audienceInserting a titanium implant in bone tissue may modify its physiological loading and therefore cause bone resorption, a phenomenon known as stress-shielding [1]. While monitoring and preventing stress-shielding is necessary to ensure the surgical success, it remains difficult to experimentally retrieve information on the properties of the interfacial tissues at the scale of 1-100 μm from the implant surface, where this phenomenon is localized. Numerical modelling represents a complementary tool to better understand phenomena related to the coupled bone-implant system due to the difficulty of measuring the stress distribution in vivo. The aim of this study is to investigate numerically the influence of various geometrical and material parameters on the local stress field around a bone-implant interface (BII) subject to shear loading