京都大学 / 新制・課程博士 / 博士(医学) / 甲第24527号 / 医博第4969号 / 新制||医||1065(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 黒田 知宏, 教授 大森 孝一, 教授 森本 尚樹 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

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The total knee arthroplasty (TKA) has become one of the most successful procedures in all of medicine, with an average of over 966,000 operations performed a year. Since its introduction in 1968, the TKA’s surgical process and implant designs have continuously been improved to increase survivability. However, the need for a revision TKA – due to aseptic loosening – continues to be a problematic aspect of the procedure. Stress shielding induced by different design parameters of the implant has generated controversy in the determination of an ideal configuration. The purpose of this study is to investigate how implant design parameters – fixation technique, stem geometry, cement stiffness, and interface condition – affect the stress shielding within the tibia, and to find an optimal combination of designs that mitigates stress shielding. A CT scan of a tibia was used to simulate multiple configurations of TKAs for finite element analysis in ABAQUS. Stress shielding was assessed by taking the average minimum principal stress of different regions at interval cuts along the depth of the tibia. The results concluded a short, full-cement stem to be the ideal combination of stem length and fixation technique, high-stiffness cement to be ideal for hybrid cements, low-stiffness cement to be ideal for full cements, and a sliding friction interface to be ideal for all models.

First devised over half a century ago, metal-on-polyethylene (MoP) hip prostheses have become the gold standard for total hip arthroplasty (THA), a surgical intervention for degenerative hip joint conditions. The accumulation of polyethylene wear debris after long-term, in vivo articulations, can induce adverse cellular reactions, osteolysis and aseptic loosening of the implant – ultimately resulting in the failure of the THA. Despite the distinct differences between the biotribology of MoP and MoM prostheses, there is a lack of congruent high resolution research investigating the biotribological interactions and surface structures of MoP hip prosthesis components. This study characterized the surface and subsurface microstructural changes in failed MoP hip prosthesis retrievals using advanced electron microscopy techniques. The samples were comprised of retrieved metallic cobalt-chromium-molybdenum (CoCrMo) alloy femoral head components, one ultra-high molecular weight polyethylene (UHMWPE) acetabular cup component, and unused CoCrMo reference samples. The surface of the reference samples contained linear, parallel, uniform scratches as a result of the manufacturing process; whereas the surface of the retrieval samples were covered in an abundance of scratches and a layer of residual deposits, attributable to in vivo articulation of the implant. Characteristic hard phases were observed and examined on the surface and from the cross-sectional preparation of the cast CoCrMo samples. The multiphasic hard phases on the cast samples can strengthen the material but also be sites of crack propagation and material detachment, contributing to the generation of wear particles. Lastly, a nanocrystalline layer, 20 to 400 nm in thickness was observed in the subsurface microstructure of all samples (including references). Previous MoM studies suggest that the nanocrystalline layer is a result of dynamic crystallization in response to multidirectional, chronic loading in vivo, however, the presence of the layer in the unimplanted references suggest that the nanocrystalline layer can be formed during the production of the prosthesis component and therefore, pre-exists implantation. The imperfections on new, unused implants can have protective effects (e.g. troughs from scratches can be a reservoir for wear debris) but may influence in vivo wear processes after implantation (e.g. scratches may be a source of wear debris). Higher resolution analyses on more retrieval and reference samples are required to pinpoint the exact mechanism of failure in MoP hip prostheses and extend the longevity and efficacy of THA. / Thesis / Master of Applied Science (MASc)

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Depuis les dernières années, la prévalence de personnes souffrant de dégénérescence des cartilages articulaires, communément appelée ostéoarthrite (OA), ne cesse d’augmenter. Les douleurs articulaires et les raideurs musculaires associées à cette pathologie mènent à des limitations des capacités fonctionnelles, à une perte de mobilité et d’autonomie affectant grandement la qualité de vie de ces personnes. Afin de soulager les personnes souffrant de cette pathologie, l’arthroplastie de la hanche est une procédure chirurgicale fréquemment utilisée. À la suite de cette chirurgie, une amélioration de la qualité de vie et une reprise des capacités fonctionnelles sont souvent observées. Cependant, comparativement à des sujets sains, la vitesse de marche est diminuée, une faiblesse des muscles abducteurs de la hanche est constatée et des mouvements compensatoires au niveau du tronc sont persistants. L’objectif de cette thèse est d’évaluer le patron locomoteur chez des patients qui subiront une arthroplastie de la hanche. Plus spécifiquement, les adaptations locomotrices pré et post-opératoires seront quantifiées dans le but d’apporter des modifications aux programmes de réhabilitation pour ainsi favoriser un patron locomoteur sans déficit. Afin de répondre à cet objectif, trois études distinctes ont été effectuées. Dans le cadre de la première étude, l’impact de l’implantation d’une prothèse totale de la hanche avec une tête fémorale de large diamètre et une prothèse de resurfaçage a été évalué par rapport aux sujets sains lors de la locomotion. Au cours de cette étude, le contrôle du tronc a été analysé en utilisant la distance entre le centre de masse corporel et le centre articulaire de la hanche opérée. Suite aux résultats obtenus, aucune différence majeure n’existe entre les deux types de prothèses en ce qui a trait au contrôle du tronc et ce, à un an post-opératoire. Lors de la deuxième étude, la symétrie des paramètres biomécaniques des membres inférieurs lors de la locomotion chez des patients ayant bénéficié de l’implantation d’une prothèse de la hanche a été caractérisée suite à un programme d’exercices péri-opératoires (pré et post-opératoire). Lors de cette étude, le programme d’exercices péri-opératoires était complémentaire au protocole de réadaptation du centre hospitalier. D’après les résultats obtenus lors de cette étude exploratoire, ce programme d’exercices péri-opératoires semble permettre d’améliorer la symétrie de la puissance et du travail musculaire au niveau de la hanche, du genou et de la cheville favorisant ainsi un patron de marche avec de minimes compensations. Finalement, dans le cadre de la troisième étude, l’approche prédictive et l’approche fonctionnelle, utilisées pour localiser le centre articulaire de la hanche, ont été comparées aux mesures radiographiques, chez des patients à la suite d’un remplacement articulaire de la hanche. À la suite de cette étude, les résultats démontrent que l’utilisation de l’approche fonctionnelle est plus appropriée chez des patients ayant bénéficié d’une arthroplastie de la hanche. En effet, cette approche individualisée est plus précise ce qui, par conséquent, permettra d’obtenir des résultats de plus grande qualité lors d’analyses biomécaniques de la locomotion. / In recent years, the prevalence of people suffering from joint cartilage degeneration, called osteoarthritis (OA), still increases. The joint pain and muscle stiffness related to this pathology have an impact on patients’ quality of life by limiting their functional capacities, mobility and autonomy. In order to relieve these patients, hip arthroplasty is a frequently used surgical procedure. Even if there is an improvement in quality of life and a restoration of functional capacities in these patients, some impairment seem to persist during the post-operative period. The walking velocity is slower when compared to healthy subjects, a hip abductor muscle weakness is observed and trunk compensations lasted during the post-operative period. The aim of this thesis is to evaluate patients undergoing hip arthroplasty during locomotion. More specifically, gait pattern adaptations will be quantified pre and post-operatively to revise rehabilitation programs in order to promote a healthy gait pattern. Three separate studies were conducted to meet this objective. The first study compared the effect of a large femoral head hip prosthesis and a hip resurfacing prosthesis to healthy subjects. During this study, the trunk control was analyzed using the distance between the body center of mass and the hip prosthetic joint center. The results obtained show no major difference between the two types of prosthesis and the healthy control one year post-operatively. During the second study, biomechanics parameter symmetry of the lower limb of gait pattern in patients undergoing hip arthroplasty was characterized following a peri-operative (pre and post-operatively) exercise program. The exercise program was complementary to the medical center standard rehabilitation program. Based on the results of this exploratory study, the peri-operative exercise program seems to improve the symmetry of the muscular power and work of the hip, knee and ankle which promote a healthy gait pattern without compensations. Finally, for the third study, the predictive and the functional approaches, used to locate the hip joint center, were compared to radiographic measurements in patients undergoing hip arthroplasty. The results of this study demonstrated that the functional approach was more appropriate for these patients. This individualized approach is more accurate which leads to quality improvement during biomechanical analysis of gait pattern.