Biomechanical Behaviour of Bone-Implant Interface: A Review

International audienceIn recent decades, cementless implants have been widely used in clinical practice to replace missing organs, to replace damaged or missing bone tissue or to restore joint functionality. However, there remain risks of failure which may have dramatic consequences. The success of an implant depends on its stability, which is determined by the biomechanical properties of the bone–implant interface (BII). The aim of this review article is to provide more insight on the current state of the art concerning the evolution of the biomechanical properties of the BII as a function of the implant's environment. The main characteristics of the BII and the determinants of implant stability are first introduced. Then, the different mechanical methods that have been employed to derive the macroscopic properties of the BII will be described. The experimental multi-modality approaches used to determine the microscopic biomechanical properties of periprosthetic newly formed bone tissue are also reviewed. Eventually, the influence of the implant's properties, in terms of both surface properties and biomaterials, is investigated. A better understanding of the phenomena occurring at the BII will lead to (i) medical devices that help surgeons to determine an implant's stability and (ii) an improvement in the quality of implants

The adhesive contact of viscoelastic spheres

International audienceWe have formulated the restricted self-consistent model for the adhesive contact of linear viscoelastic spheres. This model is a generalization of both the Ting (J. Appl. Mech. 33 (1966) 845) approach to the viscoelastic contact of adhesionless spheres and the restricted self-consistent model for adhesive axisymmetric bodies. We also show how the model can be used in practice by giving a few examples of numerical solutions

elastography of the bone-implant interface

International audiencethe stress distribution around endosseous implants is an important determinant of the surgical success. However, no method developed so far to determine the implant stability is sensitive to the loading conditions of the bone-implant interface (Bii). the objective of this study is to investigate whether a quantitative ultrasound (QUS) technique may be used to retrieve information on compressive stresses applied to the BII. An acousto-mechanical device was conceived to compress 18 trabecular bovine bone samples onto coin-shaped implants and to measure the ultrasonic response of the Bii during compression. the biomechanical behavior of the trabecular bone samples was modeled as Neo-Hookean. The reflection coefficient of the BII was shown to decrease as a function of the stress during the elastic compression of the trabecular bone samples and during the collapse of the trabecular network, with an average slope of −4.82 GPa −1. the results may be explained by an increase of the bone-implant contact ratio and by changes of bone structure occurring during compression. the sensitivity of the QUS response of the Bii to compressive stresses opens new paths in the elaboration of patient specific decision support systems allowing surgeons to assess implant stability that should be developed in the future. Endosseous cementless titanium implants are now widely used in orthopedic, dental and maxillofacial surgeries 1,2. However, despite a routine clinical use, osseointegration failures still occur and may have dramatic consequences. The implant surgical success is directly determined by the evolution of the biomechanical properties of the bone-implant interface (BII) 3-5. During surgery, endosseous implants are inserted in a slightly undersized bone cavity formed by drilling or cutting, leading to a pre-stressed state of the bone-implant system referred to as primary implant stability. A compromise should be found between (i) insufficient primary stability leading to excessive interfacial micromotion following surgery 6-8 , which may imply implant migration 9 and failure and (ii) excessive stresses at the BII, which may lead to bone necrosis 10,11. During healing, osseointegration phenomena, corresponding to an apposition of bone tissue around the implant surface, are stimulated by "low level" stresses applied to the BII 12 , but excessive level of stresses may damage the consolidating BII and lead to implant failure. As a consequence, the stress distribution around the implant during and after surgery is an important determinant for the implant success 13 , but it remains difficult to be assessed experimentally. X-ray based techniques 14 and magnetic resonance imaging 15 cannot be used to assess the level of stress at the BII due to diffraction phenomena related to the presence of metal. Therefore, biomechanical methods are needed. An interesting approach to assess the level of stress at the BII consists in employing finite element analysis (FEA). For example, stress and strain fields have been predicted around the BII in the context of dental 16,17 and orthopedic implants applications 18. The results showed that stresses in the range of 0-10 MPa could be obtained at the BII, depending on the physiological boundary conditions. However, despite the progresses realized in computational analyses, it remains difficult to assess in a patient specific manner the loading conditions at the BII due to the complexity of the implant geometry and of the bone material properties. Different biomechanical techniques have been developed to assess implant stability. For example, percussion test methods based on the measurement of the contact duration between the implant and the impacting device have been developed in the context of dental 19 and orthopedic surgery 20,21. The most commonly used biome-chanical technique is the resonance frequency analysis (RFA) 22 , which consists in measuring the first bendin

A time-domain method to solve transient elastic wave propagation in a multilayer medium with a hybrid spectral-finite element space approximation

International audienceThis paper introduces a new numerical hybrid method to simulate transient wave propagation in a multilayer semi-infinite medium, which can be fluid or solid, subjected to given transient loads. The medium is constituted of a finite number of unbounded layers with finite thicknesses. The method has a low numerical cost and is relatively straightforward to implement, as opposed to most available numerical techniques devoted to similar problems. The proposed method is based on a time-domain formulation associated with a 2D-space Fourier transform for the variables associated with the two infinite dimensions and uses a finite element approximation in the direction perpendicular to the layers. An illustration of the method is given for an elasto-acoustic wave propagation problem: a three-layer medium constituted of an elastic layer sandwiched between two acoustic fluid layers and excited by an acoustic line source located in one fluid layer

Reflection of an ultrasonic wave on the bone-implant interface: Effect of the roughness parameters

Quantitative ultrasound can be used to characterize the evolution of the bone-implant interface (BII), which is a complex system due to the implant surface roughness and to partial contact between bone and the implant. The aim of this study is to derive the main determinants of the ultrasonic response of the BII during osseointegration phenomena. The influence of (i) the surface roughness parameters and (ii) the thickness W of a soft tissue layer on the reflection coefficient r of the BII was investigated using a two-dimensional finite element model. When W increases from 0 to 150 μm, r increases from values in the range [0.45; 0.55] to values in the range [0.75; 0.88] according to the roughness parameters. An optimization method was developed to determine the sinusoidal roughness profile leading to the most similar ultrasonic response for all values of W compared to the original profile. The results show that the difference between the ultrasonic responses of the optimal sinusoidal profile and of the original profile was lower to typical experimental errors. This approach provides a better understanding of the ultrasonic response of the BII, which may be used in future numerical simulation realized at the scale of an implant

PEG-asparaginase induced severe hypertriglyceridemia

Asparaginase (ASP) is an effective chemotherapy agent extensively used in children with acute lymphocytic leukemia (ALL). There has been a recent interest in using ASP in adults with ALL, particularly the less toxic pegylated (PEG) formulation. Hypertriglyceridemia (HTG) is a rare complication of PEG-ASP therapy. We report two cases of obese patients who developed severe HTG after receiving PEG for ALL. Both patients were incidentally found to have severe HTG (TG of 4,330 and 4,420 mg/dL). In both patients, there was no personal or family history of dyslipidemia or hypothyroidism. There was no evidence of pancreatitis or skin manifestations of HTG. Both patients were treated with PEG cessation, low-fat diet and pharmacotherapy. Both patients were re-challenged with PEG, with subsequent increase in TG but no associated complications. TG returned to baseline after discontinuing PEG and while on therapy for HTG. A literature review of PEG-induced HTG in adults demonstrated similar results: asymptomatic presentation despite very severe HTG. HTG is a rare but clinically important adverse effect of PEG. Underlying obesity and/or diabetes may represent risk factors. Clinicians should monitor TG levels during PEG therapy to avoid TG-induced pancreatitis

Computational multiple scattering analysis of elastic waves in unidirectional composites

A numerical procedure is presented in this paper for the two-dimensional, time-harmonic elastodynamic multiple scattering problems for unidirectional fiber-reinforced composites. The proposed procedure is based on the eigenfunction expansion of the displacement potentials and the numerical collocation method to solve the expansion coefficients, and is capable of modeling arbitrary fiber arrangements. To demonstrate the applicability of the procedure, the P and SV wave propagation characteristics in unidirectional fiber-reinforced composites are analyzed for different fiber arrangements and fiber volume fractions. The simulated results are shown to capture the detailed features of the local wave fields in the composites accompanying the mode conversion. From the computed wave fields, the effective phase velocities of the composites are identified as functions of the frequency, and found to be in good agreement with the predictions of a micromechanical model for random composites. The energy transmission spectra of the P and SV waves are also demonstrated, which exhibit the stop-band formation for the composites with regular fiber arrangements

Étude d'une méthode d'inversion basée sur la simulation pour la caractérisation de fissures détectées par ultrasons dans un composant revêtu

Jury : M. Pierre CALMON, Ingénieur de Recherche CEA,Saclay M. Frédéric COHEN-TENOUDJI, Professeur M. Gilles CORNELOUP, Professeur M. Jean-François DE BELLEVAL, Professeur M. Frédéric LASSERRE, Ingénieur Intercontrôle M. Daniel ROYER, ProfesseurThis work deals with the inversion of ultrasonic data. The industrial context of the study in the non destructive evaluation of the internal walls of French reactor pressure vessels. Those inspections aim at detecting and characterizing cracks. Ultrasonic data correspond to echographic responses obtained with a transducer acting in pulse echo mode. Cracks are detected by crack tip diffraction effect. The analysis of measured data can become difficult because of the presence of a cladding, which surface is irregular. Moreover, its constituting material differs from the one of the reactor vessel. A model-based inverse method uses simulation of propagation and of diffraction of ultrasound taking into account the irregular properties of the cladding surface, as well as the heterogeneous nature of the component. The method developed was implemented and tested on a set of representative cases. Its performances were evaluated by the analysis of experimental results. The precision obtained in the laboratory on experimental cases treated is conform with industrial expectations motivating this study.Le travail effectué au cours de cette thèse porte sur l'inversion de données ultrasonores. Le contexte industriel en est le contrôle non destructif des cuves de réacteurs à eau pressurisée. Ces contrôles visent à détecter et caractériser des fissures. Les données ultrasonores se présentent sous la forme d'échographies obtenues à l'aide d'un capteur fonctionnant en émission-réception. Les fissures sont détectées par diffraction de leurs arêtes. L'analyse des données obtenues est rendue difficile du fait de l'existence d'un revêtement dont la surface est irrégulière et dont le matériau diffère du matériau constitutif de la cuve. Une méthode est ici proposée pour localiser avec précision les arêtes diffractantes et donc permettre un dimensionnement des fissures à partir des échographies ultrasonores obtenues. Cette méthode s'appuie sur l'application d'outils de modélisation de la propagation et de la diffraction des ultrasons prenant en compte à la fois le caractère irrégulier de la surface et la nature hétérogène du composant. La méthode développée a fait l'objet d'une implémentation informatique et a pu être testée sur un ensemble de cas représentatifs. En particulier, ses performances ont été évaluées à partir de l'analyse de résultats expérimentaux. La précision obtenue en laboratoire sur les cas expérimentaux traités est conforme à la demande industrielle qui a motivé cette étude

Dysfonction autonome cardiaque chez les obèses non diabétiques (influence des nutriments sur la balance vagosympathique)

PARIS7-Xavier Bichat (751182101) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Étude d'une méthode d'inversion basée sur la simulation pour la caractérisation de fissures détectées par ultrasons dans un composant revêtu

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF