System training and assessment in simultaneous proportional myoelectric prosthesis control.

BACKGROUND: Pattern recognition control of prosthetic hands take inputs from one or more myoelectric sensors and controls one or more degrees of freedom. However, most systems created allow only sequential control of one motion class at a time. Additionally, only recently have researchers demonstrated proportional myoelectric control in such systems, an option that is believed to make fine control easier for the user. Recent developments suggest improved reliability if the user follows a so-called prosthesis guided training (PGT) scheme. METHODS: In this study, a system for simultaneous proportional myoelectric control has been developed for a hand prosthesis with two motor functions (hand open/close, and wrist pro-/supination). The prosthesis has been used with a prosthesis socket equivalent designed for normally-limbed subjects. An extended version of PGT was developed for use with proportional control. The control system's performance was tested for two subjects in the Clothespin Relocation Task and the Southampton Hand Assessment Procedure (SHAP). Simultaneous proportional control was compared with three other control strategies implemented on the same prosthesis: mutex proportional control (the same system but with simultaneous control disabled), mutex on-off control, and a more traditional, sequential proportional control system with co-contractions for state switching. RESULTS: The practical tests indicate that the simultaneous proportional control strategy and the two mutex-based pattern recognition strategies performed equally well, and superiorly to the more traditional sequential strategy according to the chosen outcome measures. CONCLUSIONS: This is the first simultaneous proportional myoelectric control system demonstrated on a prosthesis affixed to the forearm of a subject. The study illustrates that PGT is a promising system training method for proportional control. Due to the limited number of subjects in this study, no definite conclusions can be drawn.

The influence of passive wrist joints on the functionality of prosthetic hands.

BACKGROUND: The addition of a passive wrist to a single degree of freedom prosthesis has an effect on its functionality. The amount of impact is undetermined. OBJECTIVES: To measure the grasping function of a commercial single degree of freedom hands with and without two forms of passive wrist flexor. STUDY DESIGN: Form-board and timed tasks. METHOD: Repeated measures with a single subject using a validated assessment tool. The test measured the function of one conventional, single axis, powered hand controlled by the same myocontroller format. It was used in conjunction with a passive three position wrist flexor, a wrist with compliance in the flex/extend and radial/ulnar deviation and compared with a hand without these axes. RESULTS: The overall functional score of the hand alone was 80 out of 100. The use of a wrist flexion unit resulted in a higher score (83) and the compliant wrist achieved a score of 79. The addition of a wrist allowed improved performance in Power, Lateral and Tips grips for both wrist designs, in addition the Extension grip was improved with the compliant wrist. CONCLUSION: Wrist flexion had a positive impact on the functional score. It enabled some tasks to be performed quicker and with less difficulty.

The influence of control format and hand design in single axis myoelectric hands: assessment of functionality of prosthetic hands using the Southampton Hand Assessment Procedure.

BACKGROUND: It is important to measure the functional capabilities of a prosthesis in order to make informed decisions when prescribing a limb. OBJECTIVES: To measure the functional of a range of commercial single degree of freedom hands to act as baseline comparisons for the newer multi-axis hands. STUDY DESIGN: Form-board and self-timed tasks. METHOD: Repeated measures with a single subject using a validated assessment tool. The test measured the function of three conventional, single axis, powered hands, controlled by five different myocontroller formats. One transcarpal device was also tested. RESULTS: When controlled by the same type of two channel myoelectric controllers (proportional voluntary opening, voluntary closing) the overall functional scores were similar for all similar types of hand, with a maximum score of 94 out of 100. The smaller transcarpel hand had a score of 84. Only when a more limited single channel three state controller was used was the score much lower (81). CONCLUSION: All of the hands were of a similar design and were set in a precision grip, but the precision grip did not achieve the highest individual grip score. Additionally, while the Southampton Hand Assessment Procedure (SHAP) score is dependent on the speed of execution of the task, the speed of the prosthesis did not have as great an impact on the score as the other variables. CLINICAL RELEVANCE: This study provides comparative data between similar designs of commercial hands. This will allow clinicians to be better informed when they prescribe a device for a user.

Establishing a standardized clinical assessment tool of pathologic and prosthetic hand function: normative data, reliability, and validity.

OBJECTIVE: To develop a new assessment procedure, the Southampton Hand Assessment Procedure (SHAP), that allows contextual results of hand function to be obtained readily in a clinical environment. DESIGN: Reliability (test-retest, interrater) and validity (criterion, content) of new assessment procedure against standard medical outcome measure techniques. SETTING: Normative data collected in a university laboratory. PARTICIPANTS: Twenty-four volunteers selected on the basis of optimum hand function using these criteria: age (range, 18-25 y), and no adverse hand trauma, neurologic condition, or disabling effects of the upper limb. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: The normative control group was assessed for variability, and the procedure measured in terms of interrater and test-retest reliability. The absence of a direct comparison prevents a criterion standard from being established; however, content validity was shown by expert peer review. RESULTS: The control group data were shown to be multivariate gaussian; test-retest and interrater reliability were demonstrated at the 95% confidence level. The content validity was demonstrated by peer panel approval. CONCLUSIONS: Results of the control group established the statistical integrity of SHAP. Clinical trials are underway, although more extensive use of the procedure is advocated in primary care and rehabilitation centers where physiotherapy and occupational therapy are actively used in hand rehabilitation.