A third arm — Design of a bypass prosthesis enabling incorporation

Abstract

A variety of factors affect the performance of a person using a myoelectric prosthesis, including increased control noise, reduced sensory feedback, and muscle fatigue. Many studies use able-bodied subjects to control a myoelectric prosthesis using a bypass socket in order to make comparisons to movements made with intact limbs. Depending on the goals of the study, this approach can also allow for greater subject numbers and more statistical power in the analysis of the results. As we develop assessment tools and techniques to evaluate how peripheral nerve interfaces impact prosthesis incorporation, involving normally limbed subjects in the studies becomes challenging. We have designed a novel bypass prosthesis to allow for the assessment of prosthesis incorporation in able-bodied subjects. Incorporation of a prosthetic hand worn by a normally limbed subject requires that the prosthesis is a convincing, functional extension of their own body. We present the design and development of the bypass prosthesis with special attention to mounting position and angle of the prosthetic hand, the quality of the control system and the responsiveness of the feedback. The bypass prosthesis has been fitted with a myoelectrically-controlled hand that has been instrumented to measure the forces applied to the thumb, index, and middle fingers. The prosthetic hand was mounted on the bypass socket such that it is the same length as the subject's intact limb but at a medial rotation angle of 20° to prevent visual occlusion of the prosthetic hand. Force feedback is provided in the form of electrical stimulation, vibration, or force applied to the intact limb with milliseconds of delay. Preliminary data results from a cross-modal congruency task are included showing evidence of prosthesis incorporation in able-bodied subjects. This bypass will allow able-bodied subjects to participate in research studies that require the use of a prosthetic limb while also allowing the subjects to sense that the prosthesis is an extension of the body.

Assessing the quality of supplementary sensory feedback using the crossmodal congruency task

“…To determine if different modalities of feedback provided to a person could be incorporated, we measured the CCE score 25 , 35 of 60 able-bodied individuals after training with a bypass prosthesis 36 (Fig. 2 ).…”

“…2 ). Participants trained using the bypass prosthesis to move mechanical eggs with one of three feedback modalities: vibration, electrical stimulation or skin deformation 36 . Training duration (short vs. extended) and spatial separation between the expected feedback on the fingertip contact point and the perceived feedback (matched on fingertip vs. >12 cm away) were also varied (see Supplementary Table S1 for all experimental conditions).…”

Improving Fine Control of Grasping Force during Hand–Object Interactions for a Soft Synergy-Inspired Myoelectric Prosthetic Hand

“…To overcome these drawbacks, we built a gravity compensation system that offsets the gravitational force created by wearing the prosthetic hand (Figure 1 A). This system is functionally similar to the one developed in Wilson et al ( 2017 ). Specifically, we use a light cable and a series of pulleys to connect the wrist part of the prosthesis to a counter-weight.…”

“…Additionally, these tasks typically do not assess subjects’ ability to control grasp force, which plays an important role in ADL. Researchers have recently started to incorporate motion capture and force sensors to quantify and standardize the evaluation of the hand–object interactions during use of prosthetic hands (Hebert and Lewicke, 2012 ; Engeberg and Meek, 2013 ; Fani et al, 2016 ; Godfrey et al, 2016 ; Wilson et al, 2017 ). Such quantitative assessment can identify potential bottlenecks and issues within the complex integration among hardware, control, and human user input, therefore helping to validate and optimize the prosthetic systems.…”

Mechanotactile Sensory Feedback Improves Embodiment of a Prosthetic Hand During Active Use

“…Simulated upper-limb prosthesis systems are commonly used as an approximation to prostheses used by persons with upper-limb amputation, as a method of allowing able-bodied participants to actively control a prosthetic hand in a situation more similar to actual prosthesis use. Researchers have used various versions of simulated prostheses to investigate the performance of commercial prosthetic hands (Kyberd, 2011), performance of novel control strategies (Johansen et al, 2016;Shehata et al, 2018a), kinematic movement trajectories when using prosthetic hands (Williams et al, 2019), and, recently, the effect of providing sensory feedback to users on performance in functional tasks (Wilson et al, 2017;Engels et al, 2019). In this work, we used a sensorized simulated prosthesis to investigate the contribution of sensory feedback to the embodiment phenomenon during active motor control of the prosthesis, utilizing a common methodology in the literature, namely the RHI (Longo et al, 2008).…”