Choosing appropriate prosthetic ankle work to reduce the metabolic cost of individuals with transtibial amputation

Kimberly A Ingraham,Deanna H Gates,Hwan Choi,Emily S Gardinier,C David Remy

doi:10.1038/s41598-018-33569-7

Kimberly A Ingraham, Deanna H Gates + Show 3 more

Open Access

https://doi.org/10.1038/s41598-018-33569-7

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Journal: Scientific Reports	Publication Date: Oct 17, 2018
Citations: 20	License type: open-access

Affiliation: University of Michigan–Ann Arbor

Abstract

Powered ankle prostheses have been designed to reduce the energetic burden that individuals with transtibial amputation experience during ambulation. There is an open question regarding how much power the prosthesis should provide, and whether approximating biological ankle kinetics is optimal to reduce the metabolic cost of users. We tested 10 individuals with transtibial amputation walking on a treadmill wearing the BiOM powered ankle prosthesis programmed with 6 different power settings (0–100%), including a prosthetist-chosen setting, chosen to approximate biological ankle kinetics. We measured subjects’ metabolic cost of transport (COT) and the BiOM’s net ankle work during each condition. Across participants, power settings greater than 50% resulted in lower COT than 0% or 25%. The relationship between power setting, COT, and net ankle work varied considerably between subjects, possibly due to individual adaptation and exploitation of the BiOM’s reflexive controller. For all subjects, the best tested power setting was higher than the prosthetist-chosen setting, resulting in a statistically significant and meaningful difference in COT between the best tested and prosthetist-chosen power settings. The results of this study demonstrate that individuals with transtibial amputation may benefit from prescribed prosthetic ankle push-off work that exceeds biological norms.

Highlights

Individuals with transtibial amputation spend 10–30% more metabolic energy when walking compared to able-bodied individuals[1,2,3]
We evaluated the influence of different prosthetic ankle power settings on users’ metabolic cost, using a commercially available powered prosthesis (BiOM)
We hypothesized that 1) to minimize their energy cost, users would require a higher power setting than the power setting chosen by the prosthetist, which approximated the work of the biological ankle, and 2) the highest power setting (100%) would not be the optimal power setting to minimize metabolic cost

Summary

Introduction

Individuals with transtibial amputation spend 10–30% more metabolic energy when walking compared to able-bodied individuals[1,2,3]. To overcome these limitations of passive devices, various types of powered ankle prostheses have been developed[10,11,12] These powered devices use actuators to deliver positive work to the user during the push-off phase, and can potentially alleviate the increased energetic demand that people with amputation experience during walking. The studies which demonstrated the largest reductions in metabolic cost were those that tested high-functioning active-duty military members[13] Another important factor when evaluating the BiOM’s impact on reducing metabolic energy expenditure is how the device is tuned; Esposito et al.[13] suggested that near-optimal tuning of the BiOM is required to positively impact an individual’s metabolic cost. These additional losses might render the power delivered to the center of mass smaller than anticipated

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