3D-printed custom-designed prostheses for partial hand amputation: Mechanical challenges still exist

STUDY DESIGN

This is a technical report involving evaluation of two 3D-printed custom-designed prosthetic prototypes for an adult male with partial amputation of his dominant hand.

INTRODUCTION

Prosthetic solutions for partial hand amputations have progressed modestly in comparison with advances in full hands for transradial and higher amputations. 3D-printing technology allows Bespoke prosthetic design and rapid prototyping, but evidence regarding functional performance and consumer ratings of devices is lacking.

PURPOSE OF THE STUDY

The purpose of this study was to compare grip strength, dexterity, and consumer perceptions for two novel 3D-printed devices with a myoelectric prosthesis.

METHODS

This study involves a 2-year iterative design process with an input from the participant, engineers, a prosthetist, and a hand therapist. The evaluation involved standardized tests of grip/pinch strength and dexterity and participant ratings of key criteria.

RESULTS

Both 3D-printed devices had very poor grip and pinch strength but comparable dexterity with the myoelectric prosthesis. The participant was more satisfied with the weight and thermal attributes of the 3D-printed devices.

DISCUSSION

Aspects of both 3D-printed designs showed the potential for future refinements; however, the mechanical solutions to minimize force required at the wrist to activate grip are still required.

CONCLUSION(S)

Future design efforts should be client-centered and involve professionals with specialist prosthetic and engineering knowledge.

A Cable-actuated Prosthetic Emulator for Transradial Amputees

Upper limb prosthesis has a high abandonment rate due to the low function and heavyweight. These two factors are coupled because higher function leads to additional motors, batteries, and other electronics which makes the device heavier. Robotic emulators have been used for lower limb studies to decouple the device weight and high functionality in order to explore human-centered designs and controllers featuring off-board motors. In this study, we designed a prosthetic emulator for transradial (below elbow) prosthesis to identify the optimal design and control of the user. The device only weighs half of the physiological arm which features two active wrist movements with active power grasping. The detailed design of the prosthetic arm and the performance of the system is presented in this study. We envision this emulator can be used as a test-bed to identify the desired specification of transradial prosthesis, human-robot interaction, and human-in-the-loop control.

Getting a Grip on the Impact of Incidental Feedback From Body-Powered and Myoelectric Prostheses

Sensory feedback from body-powered and myoelectric prostheses are limited, but in different ways. Currently, there are no empirical studies on how incidental feedback differs between body-powered and myoelectric prostheses, or how these differences impact grasping. Thus, the purpose of this study was to quantify differences in grasping performance between body-powered and myoelectric prosthesis users when presented with different forms of feedback. Nine adults with upper limb loss and nine without (acting as controls) completed two tasks in a virtual environment. In the first task, participants used visual, vibration, or force feedback to assist in matching target grasp apertures. In the second task, participants used either visual or force feedback to identify the stiffness of a virtual object. Participants using either prosthesis type improved their accuracy and reduced their variability compared to the no feedback condition when provided with any form of feedback (p < 0.001). However, participants using body-powered prostheses were significantly more accurate and less variable at matching grasp apertures than those using myoelectric prostheses across all feedback conditions. When identifying stiffness, body-powered prosthesis users were more accurate using force feedback (64% compared to myoelectric users' 39%) while myoelectric users were more accurate using visual feedback (65% compared to body-powered users' 53%). This study supports previous findings that body-powered prosthesis users receive limited force and proprioceptive feedback, while myoelectric prosthesis users receive almost no force or proprioceptive feedback from their device. This work can inform future supplemental feedback that enhances rather than reproduces existing incidental feedback.