Background: Lower limb amputees face many challenges, and most of them prefer to use prosthetics for daily tasks and activities. The prosthesis is usually a combination of connected prosthetic components, and their spatial orientation is called the prosthetic alignment. Proper alignment is essential, as it substantially affects the quality and comfort of a prosthesis.   Objective: The aim of this study was to create a method that could accurately and effectively quantify the alignment of a transtibial and transfemoral prostheses using Vicon optical motion capture system.   Methods: Two experimental series were conducted. The first one was to test the repeatability of the measurement. Three analysts placed retroreflective markers on the prostheses three times, and five measurements were recorded each time. Alignment parameters were calculated in Vicon ProCalc for each measurement, and a standard error of measurement was found for each alignment parameter. The standard error of measurement was calculated from three variance components, between-analyst, within-analyst, and between-trial variability. The second experimental series was conducted to understand the relationship between alignment adjustments and the outcome parameters. The socket height, internal rotation, flexion, adduction, and translation were modified and measured. The socket translation was calculated in three coordinate systems to study how they affect the outcome.   Results: For the first experimental series, the standard error of measurement for every alignment parameter was below 3° and 6 mm. The between-analyst variability was the most prominent, and the parameters calculated in the sagittal plane were more reliable than those calculated in the frontal and transverse plane. In the second experimental series, there was a linear relationship between the modifications and the measured outcome. When a connection between two prosthetic components was changed by turning the screws one round, the average change in angle between them was 2°, and the average translation change was 4.4 mm. Of the three coordinate systems, the translation calculated in ankle coordinates was more reliable than in global coordinates and describe the translation more effectively than in socket coordinates.   Conclusion: The reliability of the measurements was considered good. The standard error of measurement was low, and the main variability resulted from differences in marker placement between the analysts. The results from the measured alignment changes were as expected. All the parameters could be effectively interpreted, and the ankle coordinates were considered advantageous in describing the socket translation.

L’objectif de ce travail de thèse est de caractériser, chez les amputés unilatéraux du membre inférieur, les modalités posturales qui interviennent dans la régulation de l’équilibre orthostatique et d’étudier l’impact de l’amputation sur la production de force à la cheville physiologique. Une première étude a révélé la présence de trois modalités posturales afin de réguler le contrôle postural : les amputés transfémoraux adoptent une modalité posturale basée sur les paramètres de stabilité, les amputés transtibiaux optent pour une modalité posturale mixte et les non amputés se réfèrent aux paramètres de l’attitude posturale. Etant donné que l’articulation de la cheville joue un rôle essentiel dans la régulation de l’équilibre postural, il était alors pertinent d’investiguer la production de force à la cheville physiologique. Toutefois, les ergomètres permettant d’étudier l’articulation de la cheville présentent des biais de mesure majeurs. Dans ce cadre, une deuxième étude a été menée afin de développer et valider un nouvel ergomètre pour cheville : le B.O.T.T.E. Parallèlement, la mise en place d’une méthode de mesure basée sur le retour visuel permettant une quantification fiable du couple de force a fait l’objet d’une troisième étude. Ensuite, une quatrième étude visait à utiliser le B.O.T.T.E. pour investiguer l’impact de l’amputation sur la production de force à la cheville physiologique. Les résultats de cette étude confirment la présence d’un déficit au niveau du couple de force généré en flexion plantaire (conditions maximale et sous maximale) chez les amputés transfémoraux. Enfin, ce travail de thèse vise à aider les rééducateurs et les cliniciens à optimiser la prise en charge des patients amputés. / This Ph.D. thesis aims to evaluate the standing posture modalities and the ankle joint torque in the intact limb in unilateral lower limb amputees. A first study shows the presence of three posture modalities: the non-amputee group relied on standing erect, the transfemoral amputees’ stance depended on balance control and the transtibial amputees exhibited a mixed modality of simultaneously maintaining an upright stance and standing balance. Since the ankle muscles have a functional importance in standing posture modalities, it is imperative to investigate the ankle joint torque in the intact limb. However, the current devices used to assess the ankle joint present substantial limitations for the measurement. Thus, a second study was designed to develop and to validate a new ankle ergometer B.O.T.T.E. Moreover, a third study was achieved in order to estimate the effect of visual feedback on enhancing isometric maximal voluntary contractions. A fourth study was realized to investigate the ankle joint torque in the intact leg of unilateral lower limb amputees. The results show that transfemoral amputees produce less torque and are less steady compared to transtibial amputees and able-bodied individuals. Overall, the present findings of this Ph.D. thesis could have implications for clinical practice and for rehabilitation of patients with a lower limb amputation.

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