Understanding patient preference in prosthetic ankle stiffness

Tyler R Clites,Max K Shepherd,Kimberly A Ingraham,Elliott J Rouse,Leslie Wontorcik

doi:10.1186/s12984-021-00916-1

Abstract

BackgroundUser preference has the potential to facilitate the design, control, and prescription of prostheses, but we do not yet understand which physiological factors drive preference, or if preference is associated with clinical benefits.MethodsSubjects with unilateral below-knee amputation walked on a custom variable-stiffness prosthetic ankle and manipulated a dial to determine their preferred prosthetic ankle stiffness at three walking speeds. We evaluated anthropomorphic, metabolic, biomechanical, and performance-based descriptors at stiffness levels surrounding each subject’s preferred stiffness.ResultsSubjects preferred lower stiffness values at their self-selected treadmill walking speed, and elected to walk faster overground with ankle stiffness at or above their preferred stiffness. Preferred stiffness maximized the kinematic symmetry between prosthetic and unaffected joints, but was not significantly correlated with body mass or metabolic rate.ConclusionThese results imply that some physiological factors are weighted more heavily when determining preferred stiffness, and that preference may be associated with clinically relevant improvements in gait.

Highlights

The field of assistive robotics has become remarkably adept at tailoring device design and control to maximize application-specific performance
Inter-subject mean preferred stiffness was lowest at the self-selected walking speed, compared to the fast walking speed (+ 30% self-selected) and the slow walking speed (− 30% self-selected)
Our results showed that metabolic cost was generally higher for the Variable Stiffness Prosthetic Ankle (VSPA) Foot than for the daily-use prosthesis, and 10 Meter Walk test (10MWT) speed generally slower

Summary

Introduction

The field of assistive robotics has become remarkably adept at tailoring device design and control to maximize application-specific performance. Even if resultant design biases are not intentional, the integration of knowledge from the literature and decades of shared experience inevitably drives design in the direction of historical and current measures of success. Some recent approaches, such as human-in-the-loop optimization, go as far as Meaningful efficacy criteria are especially important in the design, evaluation, and prescription of clinical assistive technologies. Despite their promise for restoration of normative gait following amputation, injury, or other limb pathologies, robotic lower-extremity prostheses and orthoses have yet to see widespread adoption. User preference has the potential to facilitate the design, control, and prescription of prostheses, but we do not yet understand which physiological factors drive preference, or if preference is associated with clinical benefits

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