Oxford Foot Model Kinetic Analysis During the Stance Phase in Gait

Abstract

The objective in the present paper was to obtain the forces and moments present in the joint formed by the Forefoot and Hindfoot segments in the Oxford Foot Model (OFM) via an inverse kinetic approach. The starting point of the work is a number of experimental data gathered using a set of retroreflective markers and a stereophotogrammetry camera, as well as the information collected by a Ground Reaction Force Plate (GRF). With the markers' data, we are able to know the position and orientation at all times of the different segments that comprise the OFM multi-segment model. After that, the velocities and accelerations, both linear and angular, are obtained using the finite difference method for calculating derivatives. An estimation of the masses, centers of gravity and moments of inertia were needed in order to calculate our desired outcome. An analysis of the different forces and moments that affect our system was conducted: the gravitational force, the ones derived from the Force Plate and the ones in the inter-segment area were found, as well as the inertial summands of the equations. And so, it was a closed problem that would be resolved using the Newton-Euler equations, the output of which are the three components of the inter-segment forces and moments. These results were later on compared to those obtained by Dixon et al. (2012), with the main difference between the two studies found in the age group of the subjects employed by each study; in the case of Philippe Dixon, he studied the gait in a set of young, healthy adolescents, while this paper's experimental data is collected using a male adult subject. The findings were an increase in peak values in the moments and power, with a similar progression in the shape of the three graphs in this study. This was thought to be caused by the increased weight and size of the individual in this study. Also, an analysis was done to see the relative importance of each of the summands of the equations used, finding that the inertial ones play a negligible role in them, and thus could be not taken into account for further studies, at least when pursuing a first result with less precision required. Finally, the results could be improved if further information regarding centers of gravity and moments of inertia was available, in stead of having to estimate them using limited information, and if more trials with the same subject and with other subjects of a similar age and weight group in order to eliminate repeatability issues.