This thesis presents an engineering approach to the modeling and analysis of custom foot orthotics. Although orthotics are widely used and accepted as devices for the prevention of and recovery from injuries, the design process continues to be based on empirical means. There have been many clinical studies investigating the various effects that the orthotics can have on the kinematics and kinetics of human locomotion. The results from these studies are not always consistent, primarily due to subject variability and experimental nature of the design. Alternatively, a better understanding of the therapeutic effects of custom foot orthotics, as well as designing for optimal performance, can be achieved through simulation-based engineering modeling and analysis studies. Such an approach will pave the way to clarify some of the ambiguous findings found in the clinical studies-based literature. Towards this goal, this research presents a methodical process for the replication of the orthotics’ complex three-dimensional geometry and for the construction of finite element analysis models using estimated nonlinear material properties. As part of this research, laser scanning techniques are used to capture the objects’ details and geometry through generation of point cloud surface images by taking multiple scans from all angles. Material testing and Mooney-Rivlin equations were used to construct the hyperelastic nonlinear material properties. Using the mid-stance phase of gait for loading conditions, the ANSYS finite element package was utilized to run analyses on three different load classifications and the corresponding maximum stresses and deflection results were generated. The results indicate that the simulated models can augment and validate the use of empirical tables for designing custom foot orthotics. They can also provide the basis for the optimal design thicknesses of custom foot orthotics based on an end-users’ weight and activities. From a practical perspective, they can also be useful in further exploring different orthotics, loading conditions, material properties, as well as the effectiveness of orthotics for different foot and lower extremity deformities.

This research details a procedure for the systematic design of custom foot orthotics based on simulation models and their validation through experimental and clinical studies. These models may ultimately be able to replace the use of empirical tables for designing custom foot orthotics and enable optimal design thicknesses based on the body weight and activities of end-users. Similarly, they may facilitate effortless simulation of various orthotic and loading conditions, changes in material properties, and foot deformities by simply altering model parameters. Finally, these models and the corresponding results may also form the basis for subsequent design of a new generation of custom foot orthotics. Two studies were carried out, the first involving a methodical approach to development of engineering analysis models using the FEA technique. Subsequently, for model verification and validation purposes, detailed investigations were executed through experimental and clinical studies. The results were within 15% difference for the experimental studies and 26% for the clinical studies, and most of the probability values were greater than α= 0.05 accepting our null hypothesis that the FEA model data versus clinical trial data are not significantly different. The accuracy of the FEA model was further enhanced when the uniform loading condition was replaced with a more realistic pressure distribution of 70% of the weight in the heel and the rest in the front portion of the orthotic. This alteration brought the values down to within 22% difference of the clinical studies, with the P-values once again showed no significant difference between the modified FEA model and the clinical studies for most of the scenarios. The second study dealt with the development of surrogate models from FEA results, which can then be used in lieu of the computationally intensive FEA-based analysis models in the engineering design of CFO. Four techniques were studied, including the second-order polynomial response surface, Kriging, non-parametric regression and neural networking. All four techniques were found to be computationally efficient with an average of over 200% savings in time, and the Kriging technique was found to be the most accurate with an average % difference of below 0.30 for each of the loading conditions (light, medium and heavy). The two studies clearly indicate that engineering modeling, analysis and design using FEA techniques coupled with surrogate modeling methods offer a consistent, accurate and reliable alternative to empirical clinical studies. This powerful alternative simulation-based design framework can be a viable and valuable tool in the custom design of orthotics based on an individual's unique needs and foot characteristics. With these capabilities, the CFO prescriber would be able to design and develop the best-fit CFO with the optimal design characteristics for each individual customer without relying upon extensive and expensive trial and error ad hoc approaches. Such a model could also facilitate the inspection of robustness of resulting designs, as well as enable visual inspection of the impact of even small changes on the overall performance of the CFO. By adding the results from these studies to the CFO community, the prescription process may become more efficient and therefore more affordable and accessible to all populations and groups.

La connaissance des effets biomécaniques induits par les orthèses plantaires représente un enjeu important afin de faire reconnaitre le rôle du podologue dans le traitement des pathologies ostéo-articulaires et musculo-tendineuses de l'appareil locomoteur. Ainsi, ce travail de thèse consiste à modéliser, par la biomécanique, l'appareil locomoteur afin d'évaluer les effets du port des orthèses plantaires durant la marche. Avant toute chose, une étude méthodologique a été menée afin de vérifier la reproductibilité des données biomécaniques de la marche. Les principaux résultats montrent que ces données biomécaniques peuvent présenter une variabilité importante, principalement causée par des erreurs de positionnement des capteurs sur le sujet, rendant parfois difficile l'interprétation clinique. Toutefois, la deuxième partie de cette étude a montré que l'utilisation d'une méthodologie de correction segmentaire à partir d'une position statique imposée permettait de réduire cette variabilité. Une étude clinique a donc été menée sur les répercussions de l'utilisation d'une orthèse plantaire de supination sur la correction instantanée du pied valgus. Les principales conclusions montrent que les données cinématiques et dynamiques, notamment du pied et de la cheville, sont impactées. Enfin, afin de démontrer l'intérêt d'utiliser la méthodologie de correction segmentaire pour l'interprétation des effets biomécaniques du traitement par orthèses plantaires à plus ou moins long terme, deux cas cliniques ont été analysés, l'un concernait un patient atteint d'un syndrome de loge de la jambe et l'autre d'une gonarthrose. Les principales conclusions indiquent que les orthèses plantaires ont une action sur des pathologies de la cheville et du genou mais que l'interprétation de cette action peut être erronée si la variabilité des données biomécaniques de la marche n'est pas prise en considération / The knowledge of the biomechanical effects induced by foot orthotics is an important issue in order to recognize the role of the podiatrist in the treatment of osteoarticular and musculotendinous disorders of the musculoskeletal system. So, this work consists in modeling, by the biomechanics, the musculoskeletal system to assess the effects of wearing foot orthotics during walking. A first study was conducted to check the reproducibility of gait biomechanical data through two different sessions. The results show that these biomechanical data may show significant variability, mainly caused by errors in the positioning of sensors on the subject, making it difficult clinical interpretation. However, the second part of this study showed that the use of a methodology for segmental correction, from a static position imposed, allowed reducing this variability. Thus, a study was conducted on the impact of the use of supinated foot orthotics on immediate correction of valgus foot. The main findings show that the kinematic and dynamic data, notably the foot and ankle, are impacted. Before being able to estimate if this correction lasts over time, a second study was conducted. Thus, to demonstrate the benefits of using this methodology for the interpretation of the biomechanical effects of treatment with foot orthotic in the longer term, two clinical cases were analyzed, one involved a patient with compartment syndrome of the leg and the other with knee osteoarthritis. The main findings indicate that the insoles have an impact on diseases of the ankle and knee but that the interpretation of these actions may be wrong if the variability of gait biomechanical data is not considered