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. 2016 Jan 25;11(1):e0147661.
doi: 10.1371/journal.pone.0147661. eCollection 2016.

Assessing the Relative Contributions of Active Ankle and Knee Assistance to the Walking Mechanics of Transfemoral Amputees Using a Powered Prosthesis

Kimberly A Ingraham  1 , Nicholas P Fey  1   2 , Ann M Simon  1   2 , Levi J Hargrove  1   2
Affiliations

Assessing the Relative Contributions of Active Ankle and Knee Assistance to the Walking Mechanics of Transfemoral Amputees Using a Powered Prosthesis

Kimberly A Ingraham et al. PLoS One. .

Abstract

Powered knee-ankle prostheses are capable of providing net-positive mechanical energy to amputees. Yet, there are limitless ways to deliver this energy throughout the gait cycle. It remains largely unknown how different combinations of active knee and ankle assistance affect the walking mechanics of transfemoral amputees. This study assessed the relative contributions of stance phase knee swing initiation, increasing ankle stiffness and powered plantarflexion as three unilateral transfemoral amputees walked overground at their self-selected walking speed. Five combinations of knee and ankle conditions were evaluated regarding the kinematics and kinetics of the amputated and intact legs using repeated measures analyses of variance. We found eliminating active knee swing initiation or powered plantarflexion was linked to increased compensations of the ipsilateral hip joint during the subsequent swing phase. The elimination of knee swing initiation or powered plantarflexion also led to reduced braking ground reaction forces of the amputated and intact legs, and influenced both sagittal and frontal plane loading of the intact knee joint. Gradually increasing prosthetic ankle stiffness influenced the shape of the prosthetic ankle plantarflexion moment, more closely mirroring the intact ankle moment. Increasing ankle stiffness also corresponded to increased prosthetic ankle power generation (despite a similar maximum stiffness value across conditions) and increased braking ground reaction forces of the amputated leg. These findings further our understanding of how to deliver assistance with powered knee-ankle prostheses and the compensations that occur when specific aspects of assistance are added/removed.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Transfemoral amputee subjects wearing the powered knee and ankle prosthesis.
Fig 2
Fig 2. Design of experiments.
A partial factorial design was used to evaluate the contributions of three factors: powered plantarflexion, increasing ankle stiffness and knee swing initiation.
Fig 3
Fig 3. Diagram of the finite state machine used to control walking.
Fig 4
Fig 4. Impedance parameters modified across conditions.
A) Knee equilibrium angle, B) ankle equilibrium angle, and C) ankle stiffness were modified in early to mid-stance and late stance. Increasing ankle stiffness was initiated in early to mid-stance when the ankle angle (solid black line) began to dorsiflex. Swing initiation and powered plantarflexion were initiated in late stance when the vertical load (dashed black line) began to decrease.
Fig 5
Fig 5. Anterior/posterior (A/P) GRF for amputated and intact limbs.
Average positive and negative A/P GRF values are shown. Main significant effects of swing initiation (▲), powered plantarflexion (†), and increasing ankle stiffness (§) are denoted. Significant pairwise t-test results are indicated with brackets.
Fig 6
Fig 6. Kinematics for hip, knee, and ankle joints of the amputated and intact limbs.
Group average results shown. Main significant effects of swing initiation (▲) and powered plantarflexion (†) are denoted.
Fig 7
Fig 7. Stance phase joint moments for hip, knee, and ankle of the amputated and intact limbs.
Group average traces and average positive and negative values of joint moments are shown. Significant main effects of swing initiation (▲), powered plantarflexion (†), and significant interaction effects of powered plantar flexion and increasing stiffness (†*§) are denoted. Significant pairwise t-test results are indicated with brackets.
Fig 8
Fig 8. Stance phase joint power for hip, knee, and ankle of the amputated and intact limbs.
Group average traces and average positive and negative values of joint power are shown. Significant main effects of powered plantarflexion (†) and significant interaction effects of powered plantar flexion and increasing stiffness (†*§) are denoted. Significant pairwise t-test results are indicated with brackets.
Fig 9
Fig 9. Swing phase hip moment and power of the amputated and intact limbs.
Group average traces and average positive and negative values of hip moment and power are shown. Significant main effects of swing initiation (▲), powered plantarflexion (†), and increasing ankle stiffness (§), and significant interaction effects of powered plantar flexion and increasing stiffness (†*§) are denoted. Significant pairwise t-test results are indicated with brackets.
Fig 10
Fig 10. Stance phase intact knee abduction moment.
Group average traces and average positive values of knee abduction moment are shown. Significant interaction effects of powered plantar flexion and increasing stiffness (†*§) are denoted. Significant pairwise t-test results are indicated with brackets.
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