Passive-Dynamic Ankle–Foot Orthoses Substitute for Ankle Strength While Causing Adaptive Gait Strategies: A Feasibility Study

Abstract

Bending stiffness of passive-dynamic ankle-foot orthoses (PD-AFOs) is a functional characteristic thought to restore lost ankle function due to weakened plantar flexors. However, lower extremity impairment profiles of patients are seldom limited to plantar flexion weakness, and PD-AFO characteristics often influence gait in other ways. Combined, all PD-AFO characteristics and patient impairments likely mask the main effect of PD-AFO bending stiffness and complicate the PD-AFO bending stiffness prescription process. In this study, we propose a biomechanical probing paradigm, where customized PD-AFOs with a range of precise stiffness values are worn by healthy subjects, to experimentally test a PD-AFO strength substitution hypothesis while simultaneously documenting gait adaptations to PD-AFO use. Two healthy subjects walked at a scaled velocity while wearing a series of three PD-AFOs that ranged in bending stiffness levels. Supporting the strength substitution hypothesis, peak ankle plantar flexion moments remained unchanged across PD-AFO stiffness conditions. Further biomechanical analyses documented a complex series of ankle related kinematic and kinetic adaptive movement strategies due to PD-AFO use. This study demonstrated the utility of the biomechanical probing paradigm to help understand the contribution of PD-AFO stiffness to ankle strength and its secondary effects on ankle biomechanics.

Paretic propulsion as a measure of walking performance and functional motor recovery post-stroke: A review

“…PD-AFO devices have been designed to supplement push-off in patients with impaired plantarflexor function by acting like a spring and storing energy at mid-stance and returning the energy to the leg during terminal stance. While the effects of PD-AFO stiffness on gait mechanics and energetics have been tested in simple models [63] and in healthy subjects [64,65] and those with musculoskeletal injuries [66,67], further research is needed to assess the effect of PD-AFOs on walking performance in post-stroke subjects.…”

A validated computational framework to evaluate the stiffness of 3D printed ankle foot orthoses

“…This way of manufacturing does not allow modification of the design parameters before the realization of the devices; therefore, it would be beneficial to quantify in advance the impact of AFO properties, such as stiffness and thickness, which are key factors for determining the amount of assistance the orthosis is able to provide (Bregman et al 2012;Esposito et al 2014;Kerkum et al 2015). Currently, different research groups have been focusing on the use of 3D printing technologies, which enable high control of design characteristics: 3D printed AFOs are manufactured for healthy subjects and patients to study their contribution to the ankle biomechanics and/or compare their performance with the commonly prescribed AFOs (Mavroidis et al 2011;Creylman et al 2013;Arch and Stanhope 2015;Harper et al 2014aHarper et al , 2014bCha et al 2017).…”

A Novel Dorsal Trimline Approach for Passive-Dynamic Ankle-Foot Orthoses

“…AFOs are exposed to external loadings from different directions during dynamic tasks, such as standing, swaying, or walking. Unlike from a solid AFO, which is typically stiff and rigid, a dynamic AFO (provides subtalar stabilization while allowing free or restricted dorsiflexion and plantarflexion) is characteristically thin, flexible and wraps around the patient's entire foot and ankle in order to provide improved sensation and alignment [14]. Due to the exposure to repetitive and excessive loadings, which create a high level of stresses concentrated over the ankle part of the AFO, dynamic AFOs undergo plastic deformation and hence, in time, they cannot satisfactorily fulfil movement restriction, which means that the patients cannot effectively benefit from the AFO [15].…”