Numerical Modeling of the Adhesive Contact at the Bone-implant Interface PDF Download

Author: Katharina Immel
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Languages : en
Pages : 0

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Book Description
Cementless implants have become more and more common for joint replacement anddental surgery. Initial stability is obtained during the surgery through a press fit processin the host bone, while long-term stability is obtained by bone growing around and intothe porous surface of the implant, a process called osseointegration. As debonding ofthe bone-implant interface due to aseptic loosening and insufficient osseointegration stilloccur and may have dramatic consequences, predicting implant stability and failure isone of the major goals in modern implant research.This work presents different 3D FE modeling approaches to model contact and initialand long-term stability of cementless implants using the example of a cylindrical implantand an acetabular cup implant (ACI).First, an approach to assess the initial stability of an ACI considering a realisticgeometry of a patient's hip, based on Coulomb's friction contact and standard FE, ispresented. The influence of different patient and implant-specific parameters is analyzedin order to determine optimal stability for different configurations and thus obtain theoptimal combination of the implant's surface roughness and the press-fit, based on apatient's bone quality.Second, a phenomenological model for the frictional contact behavior of debondingosseointegrated implants is developed. The classical Coulomb's law is extended froma constant to a varying friction coefficient, that models the transition from an unbroken(osseointegrated) to a broken (debonded) state, based on a state variable depending on thedeformation of the bone-implant interface. Thus, this model can account for the highertangential forces observed in osseointegrated implants compared to unbonded implants. Inaddition, a NURBS-enrichment approach for 3D contact elements is used for an efficientmodeling of the geometries and their contact. This model is applied to the torsionaldebonding of CSI and the results are compared to experimental data and to a previousanalytical model.Third, the modified Coulomb's law model is extended in normal direction consideringa cohesive zone model, to account for debonding in normal direction and allow for adhesivefriction. This model is applied to simulate secondary stability and debonding ofan ACI in different removal tests, and to determine the relevance of osseointegration andbiomechanical factors for long-term stability. The results are compared with the purelytangential model to identify the relevance of normal adhesion in the debonding of ACI.Last, two simple evolution laws for osseointegration based on initial stability is presentedto account for realistic and time-dependent osseointegration.Due to their generality, all models presented herein can be applied to all kinds of endosseousimplants or imperfectly bonded interfaces in general. Furthermore, the modelscan be coupled with remodeling algorithms or realistic loading data, to make simulationsand prognoses for the whole life cycle of an implant from the surgery, through bone remodelingand osseointegration, to long-term stability under cyclic loading.