Cette thèse, née d’une collaboration entre le laboratoire LEMTA et l’entreprise Novastep, a pour but de concevoir une prothèse de resurfaçage des têtes métatarsiennes des rayons latéraux (2ème, 3ème et 4ème orteils). Ces rayons sont touchés par de nombreuses pathologies (arthrose, maladie de Freiberg, …) pouvant engendrer des douleurs et être handicapantes au quotidien. Bien que de nombreuses solutions prothétiques pour le resurfaçage des têtes métatarsiennes soient disponibles sur le marché, elles sont en majorité conçues pour le resurfaçage du 1ier rayon. La prothèse de Novastep est donc prévue pour offrir une solution viable pour le traitement de ces pathologies. Le développement de la prothèse passe par plusieurs étapes qui sont : • La recherche des exigences médicales et mécaniques à respecter ; • La conception de la prothèse ; • La mise au point de la technique opératoire (instrument pour la pose) ; • La réalisation des essais (vérification des performances de la prothèse). Ce cycle de conception permet de justifier les performances de la prothèse dans l’optique d’obtenir l’autorisation de mise sur le marché. En parallèle de la conception de la prothèse de resurfaçage, une étude de remodelage des métatarsiens après implantation a été effectuée. Cette étude a pour but, dans un premier temps, de présenter et valider un protocole pour la préparation des modèles EF de remodelage osseux à partir de données tomodensitométriques spécifiques au patient. Dans un deuxième temps, cette étude a permis d’analyser l’impact de la prothèse de Novastep sur l’os et de comparer ces résultats avec ceux obtenus pour une prothèse concurrente (LMHI de Wright Medical). Dans un dernier temps, l’influence de différents paramètres de la loi de remodelage et du modèle a été étudiée. A notre connaissance, ce travail est le premier portant sur le remodelage osseux d’un métatarsien prothésé. A terme, ce travail pourra aboutir à la création d’un outil d’aide à la décision destiné aux concepteurs pour les choix technologiques de design des prothèses et aux chirurgiens pour sélectionner la technique chirurgicale la plus adaptée à chaque patient. Pour ce faire, il sera nécessaire de valider les résultats issus des prévisions numériques de remodelage avec des résultats cliniques post-opératoires / This doctoral thesis, the result of a collaboration between LEMTA laboratory and Novastep company, explains the design of a metatarsal head resurfacing prosthesis of the lateral toes (2nd, 3rd and 4th toes). These toes can be affected by several pathologies, including arthritis and Freiberg’s disease, which are painful and can bec ripping in everyday life. Although many prosthetic solutions for the resurfacing of the metatarsal heads are available on the market, they are often developed for the first toe only. Novastep’s prosthesis was developed to afford a viable solution for the treatment of those pathologies in other toes as well. The development of this prosthesis requires several steps which are: • The definition of medical and mechanical requirements which must been taken into account ; • The design of the prosthesis ; • The development of the surgical technique, that is, the instrumentation for setting up the prosthesis ; • Mechanical and clinical testing to verify the performance of the prosthesis. This design cycle permits justification of the device’s performance necessary to obtain the market approval. In parallel with the resurfacing prosthesis, a study of metatarsal bone remodeling after implantation was realized. This study aimed to present and validate a protocol for the preparation of finite element models of bone remodeling from patient specific computed-tomography data. It also permitted analysis of the impact of the Novastep’s prosthesis on the metatarsal and comparison of those resuts with results obtained with a competitor’s equivalent prosthesis (LMHI of Wright Medical). To our knowledge, this study was the first on the bone remodeling of a prosthetic metatarsal. In the long term, this work could lead to the creation of a decision-making tool for designers for the technological choices of prosthesis design

Rheumatoid arthritis (RA) is an inflammatory autoimmune disease that affects the feet in up to 90% of patients, and can result in bone erosions. Little is known about disease activity at the metatarsophalangeal joints (MTPJs). Magnetic resonance imaging is used to visualize erosions, but does not provide quantification. Quantitative computed tomography (QCT) allows for differentiation between bone layers and quantifies volumetric bone mineral density (vBMD). We used a peripheral QCT (pQCT) scanner in MTPJs 2-5 in RA patients to determine reliability of a pQCT protocol, and then we determined the variability in vBMD between RA patients and controls. Patients (n=25) diagnosed with RA (2010 ACR criteria) were recruited from an academic Rheumatology clinic. Controls (n=27) were also recruited and matched for sex, age and ethnicity. Baseline MR data demonstrated that 80%, 64%, 40% and 20% of patients had erosions at MTPJs 2-5, respectively. One year later, MTPJs 2-5 were scanned using pQCT (XCT 2000); 2 transaxial slices were acquired per joint. A trained pQCT operator acquired 2 scans per participant with repositioning. Test-retest, intra- and inter-rater reliability were assessed blindly for total and cortical subcortical densities (mg/cm3). Reliability was reported as root mean square coefficients of variation (%RMSCV) and RMS standard deviation (RMSSD). The mean (SD) age and disease duration were 57.8 (10.2) years and 5.0 (0.9) years, respectively. Test-retest reliability was better for MTPJs 2 and 3, than MTPJs 4 and 5. Inter- and intra-rater reliability demonstrated high reproducibility. Total and cortical subcortical vBMD appeared lower in RA patients than controls. We have reliably determined vBMD using pQCT in MTPJs 2 and 3 in RA patients. The lower vBMD in MTPJ 3 suggests that RA patients may have true erosions at this joint. This research is in the early phases, but we hope to explore the correspondence between pQCT and other RA assessment tools. / Thesis / Master of Science (MSc) / Rheumatoid arthritis (RA) affects joints in the hands and feet. The bones of these joints are affected by periarticular bone loss leading to bone erosions. Magnetic resonance imaging (MRI) and X-ray are used to visualize erosions. Since erosions are characterized by a decrease in bone mineral density (BMD) leading to holes in the bone, we tested the reliability of a peripheral quantitative computed tomography (pQCT) scanner, to measure volumetric BMD (vBMD) in 25 RA patients and compared vBMD to healthy controls. The vBMD measures appeared lower in RA patients than healthy individuals in some joints. As well, there was agreement between bone erosions detected by MRI and reduced vBMD measured by pQCT. Although we could not monitor the change over time, we are hopeful that this scanner will be able to better characterize RA disease activity, with vBMD as a surrogate marker for erosion presence.