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Does Ankle Exoskeleton Assistance Impair Stability During Walking in Individuals with Cerebral Palsy?

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Abstract

Lower-limb exoskeletons have the potential to improve mobility in individuals with movement disabilities, such as cerebral palsy (CP). The goal of this study was to assess the impact of plantar-flexor assistance from an untethered ankle exoskeleton on dynamic stability during unperturbed and perturbed walking in individuals with CP. Seven participants with CP (Gross Motor Function Classification System levels I-III, ages 6–31 years) completed a treadmill walking protocol under their normal walking condition and while wearing an ankle exoskeleton that provided adaptive plantar-flexor assistance. Pseudo-randomized treadmill perturbations were delivered during stance phase by accelerating one side of a split-belt treadmill. Treadmill perturbations resulted in a significant decrease in anteroposterior minimum margin-of-stability (− 32.1%, p < 0.001), and a significant increase in contralateral limb step length (8.1%, p = 0.005), integrated soleus activity during unassisted walking (23.4%, p = 0.02), and peak biological ankle moment (9.6%, p = 0.03) during stance phase. Plantar-flexor assistance did not significantly alter margin-of-stability, step length, soleus activity, or ankle moments during both unperturbed and perturbed walking. These results indicate that adaptive plantar-flexor assistance from an untethered ankle exoskeleton does not significantly alter dynamic stability maintenance during unperturbed and perturbed walking for individuals with CP, supporting future research in real-world environments.

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Abbreviations

CP:

Cerebral palsy

GMFCS:

Gross Motor Function Classification System

EMG:

Electromyography

MoS:

Margin-of-stability

AP:

Anteroposterior

ML:

Mediolateral

CoM:

Center of mass

BoS:

Base of support

g :

Gravity

l :

Pendulum length

iEMG:

Integrated EMG

SL:

Step length

SW:

Step width

ANOVA:

Analysis of variance

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Acknowledgments

This research was supported in part by the Eunice Kennedy Shriver National Institute of Child Health & Human Development of the National Institutes of Health under Award Number R15HD099664. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. This work was also supported in part by the University of Arizona College of Medicine – Phoenix MD/PhD Program. The authors would like to thank James Babers and Leah Liebelt for their assistance with device manufacturing. The authors would also like to thank the participants and their families for their involvement in the study.

Competing interest

ZFL is a named inventor on pending utility patent applications that describe the exoskeleton utilized in the study. ZFL is a co-founder of a company seeking to commercialize the device. The other authors declare no conflict of interest.

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Authors and Affiliations

  1. Department of Mechanical Engineering, Northern Arizona University, 15600 S McConnell Drive, NAU EGR Bldg 69, Flagstaff, AZ, 86011, USA

    Taryn A. Harvey & Zachary F. Lerner

  2. College of Medicine – Phoenix, University of Arizona, Phoenix, AZ, USA

    Benjamin C. Conner & Zachary F. Lerner

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  1. Taryn A. Harvey
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Correspondence to Zachary F. Lerner.

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Associate Editor Stefan M Duma oversaw the review of this article.

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Harvey, T.A., Conner, B.C. & Lerner, Z.F. Does Ankle Exoskeleton Assistance Impair Stability During Walking in Individuals with Cerebral Palsy?. Ann Biomed Eng 49, 2522–2532 (2021). https://doi.org/10.1007/s10439-021-02822-y

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