Validation d'un modèle par éléments finis de tige fémorale biomimétique en matériau composite et optimisation du matériau

Physiologie de l'os -- Procédé de fabrication de la prothèse biomimétique -- Le modèle initial de la prothèse -- Problématique et objectifs du projet -- Optimisation du matériau biomimétique -- Statistiques -- Validation du modèle par éléments finis -- Techniques de mesures -- Optimisation du matériau composite biomimétique -- Validation de la modélisation -- Modifications à la modélisation

Design d’une prothèse de resurfaçage de hanche en matériau composite biomimétique : mise au point d’outils d’évaluation numérique

Hip resurfacing arthroplasty (HRA) is proposed as an alternative to total hip arthroplasty for patients suffering from osteoarthritis or degenerative arthrosis. HRA consist in removing the articular surface of the femoral head and replacing it with a spherical metallic implant that has a thin straight stem used as an alignment aid during implantation. HRA cannot be offered to all patients due to surgical contraindications related to bone quality in the femoral head. To overcome some of those problems, it has been suggested in the literature to cement the alignment stem of the femoral component. However, this could generate stress shielding (understressed bone tends to resorb, thus destabilizing the implant and causing aseptic loosening) in the femoral head, which could compromise the implant long term stability. The use of a biomimetic composite material with bone-matching properties could be a means of using the stem to optimize load transfer to the femoral bone. This optimisation would aim at minimizing stress shielding in the femoral head for an implant with a fixed stem, benefiting from the same stability as cemented stem implants without the increased stress shielding. The current thesis objective was to evaluate this solution by developing a finite element model of a hip resurfacing femoral component with a stem made of biomimetic composite material, and to evaluate its potential in terms of stress shielding reduction and biomechanical performance. Numerical results from a first study showed reduction of stress shielding for the implant with a fixed biomimetic stem when compared with a cemented metallic stem, but the biomimetic stem was still stress shielded when compared with an unfixed metallic stem or healthy femur. A second study examined modeling methods for bone-cement and bone-implant load-bearing interfaces for different fixation scenarios. It showed that traditional methods (bonded /frictional contact elements) created under certain circumstances unrealistic results such as complete absence of micromotions at bone-stem interface. A new interface element was developed to address some of the limitations observed on traditional interface modeling methods. This new interface element aimed at simulating the progressive degradation of bone-cement interfaces and osseointegration of bone-implant interfaces. Numerical results obtained with the biomimetic implant using the new element showed a partial osseointegration pattern on the stem surface, with the presence of “spot-welds” (localised points of perfect osseointegration). The new implant with its biomimetic stem allows reduction of stress shielding when compared with current metallic implants. Recommendations following this thesis include optimisation of the geometrical shape of the biomimetic stem, in order to further improve load transfer to the femoral proximal bone

Secondary stability of a composite biomimetic cementless hip stem

Peer reviewed: YesNRC publication: Ye

Stabilit\ue9 primaire et secondaire d\u2019une proth\ue8se totale de hanche non-ciment\ue9e en mat\ue9riau composite biomim\ue9tique

Peer reviewed: YesNRC publication: Ye

Validation of the finite element model of a biomimetic hip prosthesis

Peer reviewed: NoNRC publication: Ye

Global postural re-education in pediatric idiopathic scoliosis: a biomechanical modeling and analysis of curve reduction during active and assisted self-correction

Abstract Background Global postural re-education (GPR) is a physiotherapy treatment approach for pediatric idiopathic scoliosis (IS), where the physiotherapist qualitatively assesses scoliotic curvature reduction potential (with a manual correction) and patient’s ability to self-correct (self-correction). To the author’s knowledge, there are no studies regarding GPR applied to IS, hence there is a need to better understand the biomechanics of GPR curve reduction postures. The objective was to biomechanically and quantitatively evaluate those two re-education corrections using a computer model combined with experimental testing. Methods Finite elements models of 16 patients with IS (10.5–15.4 years old, average Cobb angle of 33°) where built from surface scans and 3D radiographic reconstructions taken in normal standing and self-corrected postures. The forces applied with the therapist’s hands over the trunk during manual correction were recorded and used in the FEM to simulate this posture. Self-correction was simulated by moving the thoracic and lumbar apical vertebrae from their presenting position to their self-corrected position as seen on radiographs. A stiffness index was defined for each posture as the global force required to stay in the posture divided by the thoracic curve reduction (force/Cobb angle reduction). Results The average force applied by the therapist during manual correction was 31 N and resulted in a simulated average reduction of 26% (p < 0.05), while kyphosis slightly increased and lordosis remained unchanged. The actual self-correction reduced the thoracic curve by an average of 33% (p < 0.05), while the lumbar curve remained unchanged. The thoracic kyphosis and lumbar lordosis were reduced on average by 6° and 5° (p < 0.05). Self-correction simulations correlated with actual self-correction (r = 0.9). Conclusions This study allowed quantification of thoracic curve reducibility obtained by external forces applications as well as patient’s capacity to self-correct their posture, two corrections commonly used in the GPR approach

Finite Element Modeling of a Composite Biomimetic Hip Stem

Peer reviewed: NoNRC publication: Ye

A new interface element with progressive damage and osseointegration for modeling of interfaces in hip resurfacing

Finite element models of orthopedic implants such as hip resurfacing femoral components usually rely on contact elements to model the load-bearing interfaces that connect bone, cement and implant. However, contact elements cannot simulate progressive degradation of bone\u2013cement interfaces or osseointegration. A new interface element is developed to alleviate these shortcomings. This element is capable of simulating the nonlinear progression of bone\u2013cement interface debonding or bone\u2013implant interface osseointegration, based on mechanical stimuli in normal and tangential directions. The new element is applied to a hip resurfacing femoral component with a stem made of a novel biomimetic composite material. Three load cases are applied sequentially to simulate the 6-month period required for osseointegration of the stem. The effect of interdigitation depth of the bone\u2013cement interface is found to be negligible, with only minor variations of micromotions. Numerical results show that the biomimetic stem progressively osseointegrates (\u3b1 averages 0.7 on the stem surface, with spot-welds) and that bone\u2013stem micromotions decrease below 10\u2009\ub5m. Osseointegration also changes the load path within the femoral bone: a decrease of 300\u2009\ub5\u3b5 was observed in the femoral head, and the inferomedial part of the femoral neck showed a slight increase of 165\u2009\ub5\u3b5. There was also increased stress in the implant stem (from 7 to 11\u2009MPa after osseointegration), indicating that part of the load is supported through the stem. The use of the new osseointegratable interface element has shown the osseointegration potential of the biomimetic stem. Its ability to model partially osseointegrated interfaces based on the mechanical conditions at the interface means that the new element could be used to study load transfer and osseointegration patterns on other models of uncemented hip resurfacing femoral components.Peer reviewed: YesNRC publication: Ye