Comparison of body-powered voluntary opening and voluntary closing prehensor for activities of daily life

Abstract

Abstract-Persons with an upper-limb amputation who use a body-powered prosthesis typically control the prehensor through contralateral shoulder movement, which is transmitted through a Bowden cable. Increased cable tension either opens or closes the prehensor; when tension is released, some passive element, such as a spring, returns the prehensor to the default state (closed or open). In this study, we used the Southampton Hand Assessment Procedure to examine functional differences between these two types of prehensors in 29 nondisabled subjects (who used a body-powered bypass prosthesis) and 2 persons with unilateral transradial amputations (who used a conventional body-powered device). We also administered a survey to determine whether subjects preferred one prehensor or the other for specific tasks, with a long-term goal of assessing whether a prehensor that could switch between both modes would be advantageous. We found that using the voluntary closing prehensor was 1.3 s faster (p = 0.02) than using the voluntary opening prehensor, across tasks, and that there was consensus among subjects on which types of tasks they preferred to do with each prehensor type. Twenty-five subjects wanted a device that could switch between the two modes in order to perform particular tasks.

Design and evaluation of voluntary opening and voluntary closing prosthetic terminal device

“…Subjects did not have a substantial improvement in the fourth trial, in which they used their nonpreferred mode, which is consistent with previous studies that indicate that learning does not occur across trials [21]. Average (± standard deviation) IOF scores for VO (50.2 ± 7.3) and VC (53.8 ± 11.0) were similar but slightly lower than IOF scores in a previous study that used commercially available VO and VC TDs (53.6 ± 10.9 for VO and 55.4 ± 11.5 for VC) [21], although not enough subjects took part in this pilot study to determine whether that difference is significant.…”

“…In a recent study that supports this finding, we found that the majority of subjects with an intact arm performing the Southampton Hand Assessment Procedure (SHAP) [20] with both VO and VC TDs expressed a desire to switch between modes on a task-by-task basis [21]. Thus, a strong need exists for a TD that can switch between modes, but clinical viability requires that it must be the same size and weight as conventional TDs, it must maintain the same default Bowden cable attachment position in both modes, the lateral tong must be the moveable tong in both modes, and the mechanism must be simple enough to allow manufacturers to fabricate the TD for a reimbursable cost.…”

“…When asked to compare the TD with others with which they had experience, five subjects reported that it was simple and easy to switch between modes, which seemed an advantageous feature, although one subject clarified that he would need to find more tasks that required VO mode to make the VO/VC TD more useful than a VC TD. Another subject reiterated that it was difficult to maintain cable tension when holding an object in VC mode while moving the elbow or shoulder (e.g., rotating a screwdriver), which is a known issue for VC TDs [21].…”

“…In contrast with our previous study [21], subjects completed each self-timed task four times before moving on to the next task. For the first repetition, subjects used VO or VC modes (assigned in random order).…”

“…This experiment used the same methods presented in Berning et al [21], except where otherwise noted.…”