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

Abstract

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.

An ankle-foot prosthesis emulator with control of plantarflexion and inversion-eversion torque

“…The end-effector was lightweight, having about 60% of the mass of a typical human foot [33] and about a third of the mass of other tethered [3,14,15] and untethered [2,34] robotic ankle-foot prostheses. The device produced large torques in both plantarflexion and inversioneversion directions, with peak measured plantarflexion and inversion-eversion torques that were 50% and 230% greater, respectively, than observed at the ankle joint during normal walking among typical male humans [19,35] and similar to those in other devices with powered plantarflexion [2,3,34] or inversion-eversion [14].…”

“…The device has a mass of 2.9 kg, can produce torques of up to 34 N·m, and has a 90% rise time of 0.180 s. A plantarflexion degree of freedom is provided using a passive spring. Ficanha et al [15] describe a prototype device intended to provide both plantarflexion and inversion-eversion control using two motors and a gimbal joint. The device has a mass of 3.0 kg.…”

Anthropomorphic Robotic Ankle-Foot Prosthesis With Active Dorsiflexion- Plantarflexion and Inversion-Eversion

“…This was significantly different from straight step that started at 1.7° eversion at heel strike and transitioned to 1.4° inversion at push off. These results indicated that the change in ankle angle in the IE direction at the step turn is significantly larger and different from straight step (19). The ankle inversion is required for generating a ground reaction force during the step turn as reported in (18,36).…”

“…Such differences in gait strategies lead to a different biomechanics of turn and increased risk of secondary complications. During a turn, ground reaction forces are modulated to accelerate the center of mass of the body along the path; thus, during a step turn, lateral and propulsive impulses are larger compared to a straight step (18); also, preliminary studies have shown an increase in inversion during a step turn, leaning the body toward the inside of the turn, when compared to a straight step (19). These evidences suggest that turning may not be considered a passive mechanism and requires modulation of ankle impedance in both sagittal and frontal planes.…”

Estimation of Multi-Directional Ankle Impedance as a Function of Lower Extremity Muscle Activation

“…The ankle modulates about multiple degrees of freedom during ADLs [27]- [29]. Active transtibial prostheses that are capable of generating motion in the frontal and transverse planes are currently being researched and can contribute to a more natural ankle function.…”