The biomechanical effect of different spring extension assist mechanisms in mechanical 4-bar polycentric prosthetic knees for unilateral above/through-knee amputees
File(s)
Published online version
Author(s)
Type
Journal Article
Abstract
Background:
Passive prosthetic knees incorporate extension assist mechanisms to enhance the swing phase of the gait cycle for persons with above/through-knee amputations. In conventional polycentric knees using a 4-bar linkage, the extension assist mechanism connects one of the bars to the body of the prosthesis. However, this design introduces a singularity in the spring action delivery, causing the spring to push the knee into flexion beyond a certain angle. In contrast, polycentric prosthetic knees with an extension assist mechanism that links the upper and lower parts of the knee eliminate the singularity feature, ensuring that the knee is pushed toward extension throughout the full range of motion.
Objective:
This study aims to investigate the effects of different spring extension assist mechanisms in polycentric knees on the walking capacity of unilateral above/through-knee amputees.
Study Design:
Repeated measures.
Methods:
Gait data were collected at self-selected and fast speeds from 8 unilateral above/through-knee traumatic amputees using a 10-camera motion capture system. Participants trialed 2 different polycentric prosthetic knees with and without the singularity feature, both coupled with a solid-ankle-cushioned-heel prosthetic foot. They underwent gait analysis with both prosthetic knees, and a comparison analysis was conducted to examine the trial conditions.
Results:
The symmetry between the prosthetic and intact knee flexion angles was higher for the design without singularity by 5.2% (p = 0.025) at self-selected speeds and by 7.7% (p = 0.003) at fast speeds. Also, peak prosthetic knee flexion angles were lower for the design without singularity by 9.4° (p < 0.001) at self-selected speeds and by 9.6° (p = 0.012) at fast speeds.
Conclusions:
The extension assist mechanism without singularity improved the symmetry between the intact and prosthetic knee flexion angles by preventing excessive prosthetic knee flexion in the swing phase of the gait cycle.
Passive prosthetic knees incorporate extension assist mechanisms to enhance the swing phase of the gait cycle for persons with above/through-knee amputations. In conventional polycentric knees using a 4-bar linkage, the extension assist mechanism connects one of the bars to the body of the prosthesis. However, this design introduces a singularity in the spring action delivery, causing the spring to push the knee into flexion beyond a certain angle. In contrast, polycentric prosthetic knees with an extension assist mechanism that links the upper and lower parts of the knee eliminate the singularity feature, ensuring that the knee is pushed toward extension throughout the full range of motion.
Objective:
This study aims to investigate the effects of different spring extension assist mechanisms in polycentric knees on the walking capacity of unilateral above/through-knee amputees.
Study Design:
Repeated measures.
Methods:
Gait data were collected at self-selected and fast speeds from 8 unilateral above/through-knee traumatic amputees using a 10-camera motion capture system. Participants trialed 2 different polycentric prosthetic knees with and without the singularity feature, both coupled with a solid-ankle-cushioned-heel prosthetic foot. They underwent gait analysis with both prosthetic knees, and a comparison analysis was conducted to examine the trial conditions.
Results:
The symmetry between the prosthetic and intact knee flexion angles was higher for the design without singularity by 5.2% (p = 0.025) at self-selected speeds and by 7.7% (p = 0.003) at fast speeds. Also, peak prosthetic knee flexion angles were lower for the design without singularity by 9.4° (p < 0.001) at self-selected speeds and by 9.6° (p = 0.012) at fast speeds.
Conclusions:
The extension assist mechanism without singularity improved the symmetry between the intact and prosthetic knee flexion angles by preventing excessive prosthetic knee flexion in the swing phase of the gait cycle.
Date Issued
2025-04-09
Date Acceptance
2025-02-22
Citation
Prosthetics and Orthotics International, 2025
ISSN
0309-3646
Publisher
Lippincott, Williams & Wilkins
Journal / Book Title
Prosthetics and Orthotics International
Copyright Statement
© 2025 The Authors. Published by Wolters Kluwer incorporated on behalf of The International Society for Prosthetics and Orthotics. This is an open access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal
Identifier
10.1097/PXR.0000000000000448
Subjects
lower limb amputee
transfemoral
knee disarticulation
prosthetic design
4-bar knee joint
extension assist mechanism
low-tomiddle-income countries
Publication Status
Published online
Date Publish Online
2025-04-09