Electromyographically controlled prosthetic wrist improves dexterity and reduces compensatory movements without added cognitive load

Abstract

Wrist function is a top priority for transradial amputees. However, the combined functional, biomechanical, and cognitive impact of using a powered prosthetic wrist is unclear. Here, we quantify task performance, compensatory movements, and cognitive load while three transradial amputees performed a modified Clothespin Relocation Task using two myoelectric prostheses with and without the wrists. The two myoelectric prostheses include a commercial prosthesis with a built-in powered wrist, and a newly developed inexpensive prosthetic wrist for research purposes, called the "Utah wrist", that can be adapted to work with various sockets and prostheses. For these three participants, task failure rate decreased significantly from 66% ± 12% without the wrist to 39% ± 9% with the Utah wrist. Compensatory forward leaning movements also decreased significantly, from 24.2° ± 2.5 without the wrist to 12.6° ± 1.0 with the Utah wrist, and from 23.6° ± 7.6 to 15.3° ± 7.2 with the commercial prosthesis with an integrated wrist. Compensatory leftward bending movements also significantly decreased, from 20.8° ± 8.6 to 12.3° ± 5.3, for the commercial with an integrated wrist. Importantly, simultaneous myoelectric control of either prosthetic wrist had no significant impact on cognitive load, as assessed by the NASA Task Load Index survey and a secondary detection response task. This work suggests that functional prosthetic wrists can improve dexterity and reduce compensation without significantly increasing cognitive effort. These results, and the introduction of a new inexpensive prosthetic wrist for research purposes, can aid future research and development and guide the prescription of upper-limb prostheses.

Keywords: Cognitive load; Compensation; Prosthesis; Wrist.

Fig. 1

Design of the Utah wrist. a Exploded view of the Utah wrist. The red and green arrows correspond to the motors associated with pronation/supination and flexion/extension (or ulnar/radial deviation), respectively. b Photo and dimensions of the assembled wrist with the attachments to connect to a bypass socket. c The wrist can adapt to various terminal devices by printing a new interface part such as the two shown here. d Expanded view of the rotary joint mechanism, as highlighted in part b. e The wrist can connect to various sockets by printing a new interface part, such as the one shown here.

Fig. 2

Methods a The amputee participants were instructed to pick up a clothespin and move it from a horizontal beginning position to a vertical end position. b The Utah wrist was attached to the amputee participants using a multi-user functional check socket. c IMUs were attached to the amputee participant’s chest and bicep to measure the compensatory motions when attempting to complete the task. The white blocks represent the placement of the IMUs and their change in orientation while the participant performed the task. See Supplementary Figure S1 for a photograph of one participant completing the task.

Fig. 3

Experiment results. a Compensatory movement for forward lean was significantly reduced with the wrist compared to without the wrist. b Compensatory movement for leftward bend at the hip (i.e., the maximum angle deviation) was significantly reduced with the wrist compared to without the wrist while using the commercial prosthesis configuration only. c Failure rate for the clothespin relocation task (CRT) using the research prosthesis configuration decreased when the task was performed with the Utah wrist. d Average number of attempted movements under each condition. e Participants preferred to use the prostheses with the wrist enabled compared to without the wrist enabled. Note that the error bars are not present in the commercial condition, because every participant ranked the commercial condition the same. No variance between participant response is seen for the C+W and C-W condition. f No significant differences were seen in the subjective workload with the wrist vs. without. g No significant differences were seen in the DRT miss rate with the wrist vs. without. h No significant differences were seen in the DRT response time with the wrist vs. without. Data show mean ± standard error. Bars show aggregate data across all participants and all sessions, and lines show individual participant performance averaged across their own sessions. * p < 0.05. Generalized linear model with binomial distribution and log link used for Failure Rate and Secondary Task Response Accuracy. Linear model with robust or sandwich estimator of variance used for Leftward Bend, Forward Lean and Secondary Task Response Time. Permutation test of mean differences with 10,000 Monte Carlo simulations used for Subjective Workload. (N = 3).