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research-article

Evaluating the Effects of Ankle Foot Orthosis Mechanical Property Assumptions on Gait Simulation Muscle Force Results

[+] Author and Article Information
Amy K. Hegarty

Department of Mechanical Engineering Colorado School of Mines Golden, CO 80401
ahegarty@mymail.mines.edu

Anthony J. Petrella

Department of Mechanical Engineering Colorado School of Mines Golden, CO 80401
apetrell@mines.edu

Max J. Kurz

Department of Physical Therapy Munroe-Meyer Institute for Genetics and Rehabilitation, University of Nebraska Medical Center Omaha, NE 68198
mkurz@unmc.edu

Anne K. Silverman

Department of Mechanical Engineering Colorado School of Mines Golden, CO 80401
asilverm@mines.edu

1Corresponding author.

ASME doi:10.1115/1.4035472 History: Received July 21, 2016; Revised November 21, 2016

Abstract

Musculoskeletal modeling and simulation techniques have been used to gain insights into movement disabilities for many populations, such as ambulatory children with cerebral palsy (CP). The individuals who can benefit from these techniques are often limited to those who can walk without assistive devices, due to challenges in accurately modeling these devices. Specifically, many children with CP require the use of ankle-foot orthoses (AFOs) to improve their walking ability, and modeling these devices is important to understand their role in walking mechanics. The purpose of this study was to quantify the effects of AFO mechanical property assumptions, including rotational stiffness, damping and equilibrium angle of the ankle and subtalar joints, on the estimation of lower-limb muscle forces during stance for children with CP. We analyzed two walking gait cycles for two children with CP while they were wearing their own prescribed AFOs. We generated 1000-trial Monte Carlo simulations for each of the walking gait cycles, resulting in a total of 4000 walking simulations. We found AFO mechanical property assumptions influenced the force estimates for all muscles, with the ankle muscles having the largest resulting variability. Muscle forces were most sensitive to assumptions of AFO ankle and subtalar stiffness, which should therefore be measured when possible. Muscle force estimates were less sensitive to estimates of damping and equilibrium angle. When stiffness measurements are not available, limitations on the accuracy of muscle force estimates for all muscles in the model, especially the ankle muscles, should be acknowledged.

Copyright (c) 2016 by ASME
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