Development of mechanical polycentric knee prosthesis: Introducing a methodological approach
Book Chapter
Amador, BT, Torrealba, RR, Müller-Karger, CM. (2015). Development of mechanical polycentric knee prosthesis: Introducing a methodological approach
. 41-77.
Amador, BT, Torrealba, RR, Müller-Karger, CM. (2015). Development of mechanical polycentric knee prosthesis: Introducing a methodological approach
. 41-77.
According to a survey done in the literature on the field until 2010, design of 4-bar mechanisms for polycentric knee prostheses was performed heuristically. Therefore, the main motivation of this work was to determine aspects of the design process on this kind of prosthetic devices suitable of a technical approach, which could go far beyond from a simple empirical point of view. Knee prostheses must comply several basic characteristics in order to provide a safe and biomechanical performance to its user during walking, these are: 1. stability during load response, 2. easy flexion during late stance and pre-swing, 3. recover of extension during late swing before next contact, and 4. proper resistance to critical loading. From these, 1 and 2 might be related to the location of the instantaneous center of rotation (ICR) of the prosthesis with regard to the ground reaction force (GRF) line during the stance phase of gait cycle [1]. The third aspect requires the proper analysis of forces and moments of the assistant extension mechanism (AEM) respect to the ICR and the latter requires a detailed structural stress analysis of the device. For proper kinematical functioning, dimensions of the 4 linkages of the mechanism must be set, as well as the angular position of the prosthesis on the leg. This renders a multi-dimensional search problem that is complex to solve. Nonetheless, artificial intelligence techniques have emerged as a very good alternative to carry out this kind of searches. In particular, genetic algorithms (GAs) perform a search with bias in a multi-dimensional space of solutions. In this work, the aforementioned dimensions of the mechanism, targeting a specific trajectory of the ICR, were gauged by a particularly programmed GA integrated with gait analysis data on a computing platform. Later, a structural analysis of the prosthesis was performed via finite element method [2,3], according to the requirements of the standard ISO 10328 [4]. And finally, a functional prototype was manufactured and adapted to two unilateral transfemoral amputees, which allowed assessing the performance of the design qualitatively, using questionnaire, and quantitatively, via gait analysis. This work is based on a series of articles published by the co-authors on this matter, but at the same time, it is a new text never published before as a whole, as this presents all the content brought out by this project up-to-now for the first time.
