Ankle Angles during Step Turn and Straight Walk: Implications for the Design of a Steerable Ankle-foot Prosthetic Robot


This article compares the three-dimensional angles of the ankle during step turn and straight walking. We used an infrared camera system (Qualisys Oqus ®) to track the trajectories and angles of the foot and leg at different stages of the gait. The range of motion (ROM) of the ankle during stance periods was estimated for both straight step and step turn. The duration of combined phases of heel strike and loading response, mid stance, and terminal stance and pre-swing were determined and used to measure the average angles at each combined phase. The ROM in Inversion/Eversion (IE) increased during turning while Medial/Lateral (ML) rotation decreased and Dorsiflexion/Plantarflexion (DP) changed the least. During the turning step, ankle displacement in DP started with similar angles to straight walk (-9.68° of dorsiflexion) and progressively showed less plantarflexion (1.37° at toe off). In IE, the ankle showed increased inversion leaning the body toward the inside of the turn (angles from 5.90° to 13.61°). ML rotation initiated with an increased medial rotation of 5.68° relative to the straight walk transitioning to 12.06° of increased lateral rotation at the toe off. A novel tendon driven transtibial ankle-foot prosthetic robot with active controls in DP and IE directions was fabricated. It is shown that the robot was capable of mimicking the recorded angles of the human ankle in both straight walk and step turn. INTRODUCTION Straight walk requires a complex sequence of muscle activation to modulate the ground reaction forces to keep stability and produce forward motion. Similarly, modulation of the reaction forces to steer the body is required for turning [1]. Two different strategies are commonly used for turning. The spin turn consists of turning the body around the leading leg (e.g. turning right with the right leg in front). The step turn consists of shifting the weight to the leading leg and stepping in the opposite leg while still shifting the body (e.g. turning left with the right leg in front). The step turn is more stable since the base of support is wider [2] and for this reason it was used in this study. It has been shown that the step turn velocity, length, and width are considerably different than the straight walk with higher turning reaction forces [3]. Three-dimensional measurement of the ankle angles during step and spin turn have been previously studied [4]; however, it is of interest to study the ankle angles during heel strike, flat foot, and toe off during the step turn stages of the gait and also compare these results to the ankle angles during straight steps. Different approaches have been used to measure ankle angles such as using flexible electro-goniometer, electromagnetic tracking devices, and motion capturing cameras [2-6]. We used a motion capture camera system in this study. Much research has focused on straight walk and the dorsiplantarflexion of the ankle, while less attention has been given to the turning mechanism, although it plays a major role in locomotion [6]. As an example, amputees use their hip mainly in the sagittal plane to turn in such a way that the outside step length is longer than the inside step length, causing the body to rotate without the need to lean the body. Non-amputees rely mainly on ankle rotations in the sagittal plane and hip rotations in the coronal plane to tilt the body towards the inside of the turn [1]. It is estimated that the different strategies are required to compensate for the lack of propulsion in the passive prostheses to increase stability and maneuverability [1]. This evidence suggests that an ankle-foot prosthesis controllable in both dorsi-plantarflexion and inversion-eversion directions may provide more assistance in conforming the foot to the ground profile and uneven surfaces, walking in arbitrary directions on 1 Copyright © 2013 by ASME Proceedings of the ASME 2013 Dynamic Systems and Control Conference DSCC2013 October 21-23, 2013, Palo Alto, California, USA

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@inproceedings{Ficanha2013AnkleAD, title={Ankle Angles during Step Turn and Straight Walk: Implications for the Design of a Steerable Ankle-foot Prosthetic Robot}, author={Evandro M. Ficanha and Mohammad Rastgaar and Barzin Moridian and Nina Mahmoudian}, year={2013} }