Powered ankle-foot orthoses: the effects of the assistance on healthy and impaired users while walking

Abstract

In the last two decades, numerous powered ankle-foot orthoses have been developed. Despite similar designs and control strategies being shared by some of these devices, their performance in terms of achieving a comparable goal varies. It has been shown that the effect of powered ankle-foot orthoses on healthy users is altered by some factors of the testing protocol. This paper provides an overview of the effect of powered walking on healthy and weakened users. It identifies a set of key factors influencing the performance of powered ankle-foot orthoses, and it presents the effects of these factors on healthy subjects, highlighting the similarities and differences of the results obtained in different works. Furthermore, the outcomes of studies performed on elderly and impaired subjects walking with powered ankle-foot orthoses are compared, to outline the effects of powered walking on these users. This article shows that several factors mutually influence the performance of powered ankle-foot orthoses on their users and, for this reason, the determination of their effects on the user is not straightforward. One of the key factors is the adaptation of users to provided assistance. This factor is very important for the assessment of the effects of powered ankle-foot orthoses on users, however, it is not always reported by studies. Moreover, future works should report, together with the results, the list of influencing factors used in the protocol, to facilitate the comparison of the obtained results. This article also underlines the need for a standardized method to benchmark the actuators of powered ankle-foot orthoses, which would ease the comparison of results between the performed studies. In this paper, the lack of studies on elderly and impaired subjects is highlighted. The insufficiency of these studies makes it difficult to assess the effects of powered ankle-foot orthoses on these users.To summarize, this article provides a detailed overview of the work performed on powered ankle-foot orthoses, presenting and analyzing the results obtained, but also emphasizing topics on which more research is still required.

Actuation system of the ankle exoskeleton T-FLEX: first use experimental validation in people with stroke

“…Spatial-temporal parameters allow measuring the device's effects on the user [19,35]. Mainly, orthotic devices should improve the subjects' parameters to enhance their mobility in the execution of ADLs [36].…”

“…In this context, and based on promising results in the inclusion of robotic devices in therapy [15,16,17], rehabilitation programs are motivating the development of Active Ankle-Foot Orthoses (AAFOs) [18]. Currently, novel control strategies and different actuation principles are applied in robotic orthoses [19,18], which are looking for improving the human-robot interaction, and thus the user gait patterns.…”

A Review on the Control of the Mechanical Properties of Ankle Foot Orthosis for Gait Assistance

“…Moreover, the participants in the AFO experiment were mostly healthy subjects, if not younger patients with some disabilities. Therefore, the lack of participation by the elderly in the AFO experiment should be addressed in a future assessment of the AFO effects [97].…”

Experimental comparisons of passive and powered ankle-foot orthoses in individuals with limb reconstruction

“…There have been numerous important advancements in the design of passive ankle assistive devices over recent years [ 14 ]. However, in response to the limitations of passive AFOs, powered AFOs were first introduced into the literature in 2005 as a proof-of-concept [ 15 ] and numerous models have been developed over the past 12 years [ 16 – 21 ]. Generally, a powered AFO addresses the inherent limitations of passive devices by providing a tunable assistive torque about the ankle joint [ 22 – 24 ].…”

“…Advances in untethered designs are an important step towards the clinical incorporation of these devices. The vast majority of powered AFOs and exoskeletons have been tested on able-bodied individuals [ 15 , 19 , 27 – 33 ], and there have been ongoing efforts to introduce these designs clinically [ 17 , 20 , 34 – 36 ], but more research is still needed to better understand how different clinical populations interact with these devices [ 21 ]. For example, various designs have been tested in stroke patients, in whom plantar flexor weakness is common [ 36 ], but there are additional opportunities to explore the efficacy of these designs in patients with lower limb reconstruction whose weakness stems from traumatic injury.…”