VO-VC

Project

Novel Body-Powered Prehensor

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Persons with upper-limb amputations comprises many thousands of people in the United States, including many combat-injured military service personnel. Most people experience arm amputation because of an accident or other trauma, and are overwhelmingly young and active.

Despite the emergence of advanced robotic prostheses, many amputees still prefer using body-powered devices, in which movement of the users’ body (typically shoulder movement) is transmitted through a harness and cable system to operate the prosthesis. Body-powered prosthesis users typically chose to use a prehensor (e.g., a split hook), rather than a hand, as they are generally light, durable, and functional.

Currently, two types of body-powered prehensor are available: voluntary open (VO) devices, in which the user exerts force through the cable system to open the device; and voluntary close (VC) devices, in which pulling on the cable closes the device. VO devices only provide a weak grasp force (e.g., for holding light objects), but are easy to use. VC devices enable the user to apply large grasp forces but require the user to maintain tension in the cable to hold an object.

With previous funding from the National Institute on Disability, Independent Living, and Rehabilitation Research (NIDILRR), we developed an innovative prehensor that provide both VO and VC modes through a simple manual switching system. This VO/VC device can be used in the VO mode for manipulating light objects and switched to VC mode to provide a high grasp force, when needed.

The goal of this project was to evaluate the clinical utility of the VO/VC prehensor by objectively quantifying whether people choose to use both modes while performing in their home environments.

We integrated force sensors into subjects’ harnesses so that we could record use of the prehensor at home—forces exerted, time worn, and number of times used—in individuals with transradial amputations who were VO or VC users. Then we prompted them to switch the device for different tasks at home. Finally, we stopped prompting and just monitored usage, to see if they continued to use both modes of the device. We also asked them about the device using a questionnaire.

Many users found that the VO/VC was not strong enough in both modes, which was due to design limitations that we addressed in our final design. Several participants also found the device heavy compared to the lightweight Hosmer hooks.

Despite these limitations, all study participants chose to switch device modes while completing in-lab assessments. At home, 3 out of 4 study participants switched the device at least 5% of the time, and all switched a minimum of 7 times/day without prompting, suggesting that having two modes was useful.

All subjects were enthusiastic about the concept and indicated they would be interested in such a device if commercially available.

Another issue raised by users was that switching between modes using a mechanical switch was cumbersome. Switching would also likely be especially difficult for individuals with bilateral amputations. To address this issue, we have begun development of a myoelectrically-controlled switch that would be more intuitive to use and would not interrupt task performance. The electrode(s) would be placed in the prosthetic socket, as in a conventional myoelectric device.

Related Publications

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Papers

Sensinger JW, Lipsey J, Thomas A, and Turner K. Design and Evaluation of Voluntary Opening and Voluntary Closing Prosthetic Terminal DeviceJ Rehabil Res Dev, 52(1): 63-76, 2015.

Conference Presentations

Sensinger J, Lipsey J, Thomas A. VOVC Body-powered hand with multiple grasp patterns. ISPO June 22-25, Lyon, France.

Swartz A, Turner K, Jayaraman A, Sensinger J. Evaluation of daily use and function of conventional body-powered prostheses and custom VO/VC terminal device. Accepted Podium presentation Myelectric Controls Symposium (MEC) ‘17, August 2017, Fredericton, NB, Canada.

Patents

Gripping device with switchable opening modes. Sensinger, J. Application #14/030,095. Filed 9/18/13.

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The contents of this webpage were developed under a grant from the National Institute on Disability, Independent Living, and Rehabilitation Research (NIDILRR grant number 90RE5014-02-00). NIDILRR is a Center within the Administration for Community Living (ACL), Department of Health and Human Services (HHS). The contents of this webpage do not necessarily represent the policy of NIDILRR, ACL, HHS, and you should not assume endorsement by the Federal Government.

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