Fatigue-free operation of most body-powered prostheses not feasible for majority of users with trans-radial deficiency

Mona Hichert, Alistair N Vardy, Dick Plettenburg, Mona Hichert, Alistair N Vardy, Dick Plettenburg

Abstract

Background: Body-powered prostheses require cable operation forces between 33 and 131 N. The accepted upper limit for fatigue-free long-duration operation is 20% of a users' maximum cable operation force. However, no information is available on users' maximum force.

Objectives: To quantify users' maximum cable operation force and to relate this to the fatigue-free force range for the use of body-powered prostheses.

Study design: Experimental trial.

Methods: In total, 23 subjects with trans-radial deficiencies used a bypass prosthesis to exert maximum cable force three times during 3 s and reported discomfort or pain on a body map. Additionally, subjects' anthropometric measures were taken to relate to maximum force.

Results: Subjects generated forces ranging from 87 to 538 N. Of the 23 subjects, 12 generated insufficient maximum cable force to operate 8 of the 10 body-powered prostheses fatigue free. Discomfort or pain did not correlate with the magnitude of maximum force achieved by the subjects. Nine subjects indicated discomfort or pain. No relationships between anthropometry and maximal forces were found except for maximum cable forces and the affected upper-arm circumference for females.

Conclusion: For a majority of subjects, the maximal cable force was lower than acceptable for fatigue-free prosthesis use. Discomfort or pain occurred in ~40% of the subjects, suggesting a suboptimal force transmission mechanism. Clinical relevance The physical strength of users determines whether a body-powered prosthesis is suitable for comfortable, fatigue-free long-duration use on a daily basis. High cable operation forces can provoke discomfort and pain for some users, mainly in the armpit. Prediction of the users' strength by anthropometric measures might assist the choice of a suitable prosthesis.

Keywords: Upper-limb prosthetics; body-powered prosthesis; cable operation force.

Conflict of interest statement

Declaration of conflicting interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Figures

Figure 1.
Figure 1.
Measurement setup for maximum force measurements: (a) the “figure-of-nine” harness and (b) thermoplastic shell are connected through a (c) Bowden cable, which is interrupted by a (d) force sensor. In this setup, cable excursions are disabled.
Figure 2.
Figure 2.
Body map colored by one subject indicating pain in the right armpit, irritation at the back of the left elbow, and touchiness on a stripe of his back.
Figure 3.
Figure 3.
Male subjects attained significantly higher forces than female subjects (t(22) = 9.89, p < 0.001). Subjects created cable forces of 257 (124) N (mean (standard deviation)). The maximum attained forces range from 87 to 360 N (188 (87) N) and 199 to 538 N (332 (117) N) for female and male subjects, respectively.
Figure 4.
Figure 4.
Pinching 15 N repetitively with five voluntary closing prostheses fatigue free is impossible for 26%–100% of prosthesis users. Fatigue-free operation is considered at 20% of users’ maximum cable force and is desired for ADL. Cable forces required to pinch 15 N with five voluntary closing prostheses vary between 33 and 131 N. The maximum strength of 13% of prosthesis users is insufficient to pinch 15 N with the Hosmer Soft Hand.
Figure 5.
Figure 5.
Achieving a 50-mm prehensor opening repetitively with five voluntary opening prostheses fatigue free is impossible for 52%–91% of prosthesis users. Fatigue-free operation is considered at 20% of users’ maximum cable force and is desired for ADL. Voluntary opening prostheses, which are able to pinch at least 15 N, require between 50 and 94 N cable force to achieve a 50-mm prehensor opening. The maximum strength of 4% of prosthesis users is insufficient to open the Otto Bock Hook.

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Source: PubMed

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