Impact of an Ankle Foot Orthosis on Reactive Stepping in Healthy Young Adults Using a Lean-and-Release Paradigm

Date of Award

2020

Degree Name

M.S. in Mechanical Engineering

Department

Department of Mechanical and Aerospace Engineering and Renewable and Clean Energy

Advisor/Chair

Advisor: Kimberly Bigelow

Abstract

Ankle-foot orthoses (AFOs) are commonly prescribed to individuals with conditions such as stroke and multiple sclerosis (MS) to assist with foot drop and other gait deficits. While AFOs have obvious benefits, there is still a high fall rate among wearers. This is likely due to the rigidity and support provided by AFOs, restricting ankle movements, which could be helpful for recovery upon a slip or trip. While there are numerous studies that utilize a lean-and-release mechanism to examine reactive stepping in order to better understand fall mechanisms and fall recovery strategies, no study has used this mechanism to understand the impact of an AFO. The goal of this study was to examine, first in healthy young adults, differences in step recovery with and without an AFO using a lean-and-release paradigm. Twenty healthy, young adults completed a total of 30 reactive stepping trials (10 no AFO and 10 wearing the AFO on each leg) in a lean-and-release system. The forward lean angle was set to a 15║. To determine release, two retro-reflective markers were attached to the harness, which would separate upon release. Each participant had retro-reflective markers placed on anatomical locations of the back, hips, thighs, shank, and feet. Study participants were instructed to do whatever was necessary to regain their balance. All trials were recorded with a VICON motion capture system linked to two Bertec in-ground force plates, one for each foot. Temporal and kinematic variables were calculated, as well as stepping foot preference. Differences between conditions were determined by running a one-way ANOVA with a Tukey post-hoc in SPSS to compare. Participants, on average, stepped 1.4 times more frequently with the leg not wearing the AFO. Step length was significantly shorter (p<0.001) in the stepping leg AFO condition (0.56 ▒ 0.12 m), as compared to the no AFO condition (0.63 ▒ 0.09 m). However, step duration remained the same across all conditions, indicating changes in average step velocity. As expected, the maximum joint angle of the ankle was significantly less plantarflexed (p<0.001) when the AFO was on the stepping leg (No AFO: 20.86░ ▒ 3.47░, AFO Stepping: 18.01░ ▒ 3.04░). Changes were noted along the kinematic chain, with significant differences at the knee and hip as well.This shows that in addition to influencing stepping foot preference to favor keeping the AFO leg in stance, wearing an AFO influences the kinematics of a reactive step. Motivation for these adjustments could be due to a preference for landing flat footed, as a shorter step is needed to minimize ankle extension. These results might be exacerbated when studying those prescribed an AFO, since they typically will have underlying limb weakness. Clinically, those prescribing AFOs should train reactive stepping responses and restrict the limb without the AFO to ensure practice stepping with both limbs. This will allow patients to develop new fall recovery strategies that account for the presence of an AFO in a safe and controlled environment before any real-world slips or trips.

Keywords

Mechanical Engineering, Biomechanics, Biomechanics, Reactive Stepping, Ankle Foot Orthosis, Joint Kinematics, Fall Recovery

Rights Statement

Copyright © 2020, author

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