Ankle mechanics during sidestep cutting implicates need for 2-degrees of freedom powered ankle-foot prostheses

Abstract

Abstract-The ankle joint of currently available powered prostheses is capable of controlling one degree of freedom (DOF), focusing on improved mobility in the sagittal plane. To increase agility, the requirements of turning in prosthesis design need to be considered. Ankle kinematics and kinetics were studied during sidestep cutting and straight walking. There were no significant differences between the ankle sagittal plane mechanics when comparing sidestep cutting and straight walking; however, significant differences were observed in ankle frontal plane mechanics. During straight walking, the inversion-eversion (IE) angles were smaller than with sidestep cutting. The ankle that initiated the sidestep cutting showed progressively increasing inversion from 2 to 13 degrees while the following contralateral step showed progressively decreasing inversion from 8 to 4 degrees during normal walking speed. The changes in IE kinematics were the most significant during sidestep cutting compared with straight walking. The IE moments of the step that initiated the sidestep cutting were always in eversion, acting as a braking moment opposing the inverting motion. This suggests that an ankle-foot prosthesis with active DOFs in the sagittal and frontal planes will increase the agility of gait for patients with limb loss.

Mechanical Impedance of the Non-loaded Lower Leg with Relaxed Muscles in the Transverse Plane

“…Currently, available powered ankle–foot prostheses focus on improving mobility by powering the ankle joint in the sagittal plane; however, there is substantial ankle function in all anatomical planes, even during straight walk on level ground (Weyand et al, 2000 ; Taylor et al, 2005 ; Ficanha et al, 2015b ). Ankle–foot prostheses with anthropomorphic characteristics may improve the metabolic cost while generating a more comfortable gait and decreasing the secondary injuries due to overuse or misuse of other joints.…”

“…The ankle and lower leg kinetics and kinematics show significant variability when comparing the angles and torques during straight walking and sidesteps cutting (a step where the leading leg pushes the body sideways near or at 45° to avoid an obstacle on the ground while walking forward) in both external–internal (EI) and inversion–eversion (IE). It has been shown that during a sidestep cutting maneuver at normal walking speed, the ankle torque in the lateral direction at the push off phase increased more than six times compared to walking on a straight path (Ficanha et al, 2015b ). This result indicated that a torque in the transverse plane is transferred from the human body to the ground through the ankle during walking on a straight path.…”

Cable-Driven Two Degrees-of-Freedom Ankle–Foot Prosthesis1

“…Turning steps require the ankle functions in inversion-eversion (IE) and in dorsiflexion-plantarflexion (DP). In IE, ankle torques are required for walking in a straight line, and larger torques are required for turning [3,4]; this requirement can be addressed by designing two degrees-of-freedom (DOF) ankle-foot prostheses. Bellman et al designed an ankle-foot robot with 2DOF [5]; however, a prototype had not been developed.…”

Validation of an Instrumented Walkway Designed for Estimation of the Ankle Impedance in Sagittal and Frontal Planes

“…Impedance controllers are often used in prosthesis, as it allows the device to mimic the mechanical properties of the human limb. For an ankle-foot prosthesis, the quasi-static impedance of the ankle in the sagittal plane has been used [2][3][4]; however, for proper control of the prosthesis, there is strong evidence that time-varying and task-dependent impedance modulation of the ankle is necessary [5,6]. Activities of daily living (ADLs) include gait scenarios that require significant modulation of the ankle impedance in all anatomical planes, mainly in Inversion-Eversion (IE) and Dorsiflexion-Plantarflexion (DP) [5,6].…”

“…Copyright © 2016 by ASME To calculate the torque applied to the mockup's ankle, the moment arms between the ankle center of rotation and the foot center of pressure, and the reaction forces measured with force plate are required. The ankle center of rotation was calculated based on the average position of the two reflective markers placed symmetrically on both sides of the spherical joint, averaged at each sample time as described in [16]. The center of pressure on the mockups foot can be obtained from the force plate readings, and the moment arm is the vector from the center of pressure to the spherical joint's center.…”