Myoelectric Forearm Prostheses: State of the Art from a User-Centered Perspective

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INTRODUCTION

The loss of a hand from amputation or congenital defects causes disability. Prostheses have been developed throughout history to restore some of the hand's original functionality and appearance. Though a variety of forearm prostheses are presently available, such as purely cosmetic hands and body-powered prostheses, modern prosthesis research is mainly focused on myoelectric (ME) prostheses [1]. A major problem for the development of new ME prostheses is that despite significant technological advancements, a large number of amputees choose not to use them [1]. The issues associated with acceptance of ME forearm prostheses have been investigated in the literature [1-3]. In these investigations, three main problems were mentioned as reasons that amputees stop using their ME prostheses: nonintuitive control, lack of sufficient feedback, and insufficient functionality. However, these studies only considered prostheses that were commercially available at the time, and their information was mostly collected through questionnaires, which offer no opportunity for discussion or patient feedback.

Recent research projects have implemented new technologies in an attempt to overcome the shortcomings outlined by Atkins et al. and others [1-3]. However, the effect of these new technologies on user acceptance is currently unknown, because most of these systems are still in the prototype stage. Though several commercial ME forearm prostheses have recently been developed [4-6] that have greater functionality than those evaluated by Atkins et al. and others [1-3], their control systems do not yet take advantage of the recent improvements in sensing, control, and feedback research.

Klopsteg and Wilson recommend a user-centered approach for improving prosthesis performance and acceptance [7]. Therefore, we investigated the state of the art in ME forearm prosthesis research by determining a set of requirements for user acceptance and using these requirements to evaluate recent technological developments.

The structure of the prosthesis should result in intuitive control to improve user acceptance. This can be accomplished by making the signal flow between the prosthesis and the user resemble that of the nondisabled body. The signal flow can be divided into three parts: user intent, motion control, and sensory feedback. A prosthesis should contain subsystems that account for each of these parts; such a desired system is shown in Figure 1. The subsystems are described as follows: electromyographic (EMG) sensing, which determines user intent by detecting the activity of residual muscles through electrodes on the skin; control system, which actuates the prosthesis according to control signals received from EMG sensing; and feedback system, which provides the user with artificial sensory information. The combination of these three subsystems gives the user a noninvasive way to control an electronic prosthesis with the residual limb.

In the "Needs Assessment Method" section, we describe the process of assessing the needs for ME forearm prostheses. A workshop with participants from various relevant fields was arranged to establish these needs. We discuss the workshop results and formulate functional requirements for user acceptance in the section "Needs Assessment Results." In the "Literature Survey" section, we investigate the state of the art in ME prosthesis research with a literature review covering the aforementioned requirements. In the "Discussion," we discuss the applicability of the needs assessment method. We then combine the results of the preceding two sections, evaluating the research state of the art using the functional requirements for user acceptance. Finally, we make recommendations for future research.

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NEEDS ASSESSMENT METHOD

In this section, we describe the method used to determine user-centered needs. A workshop was organized in which the functional and nonfunctional needs of the ideal forearm prosthesis with regard to the EMG sensing, control, and feedback subsystems were discussed. …