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New VO Prosthesis Designs

Updated: Jul 18, 2019

We have added some exciting new variations to our prosthesis systems. Read about the new voluntary-open (VO) hand, how it works, and why it is important in Part 1.

When the Victoria Hand Project began, the first prosthesis system tested and deployed in developing countries was a voluntary-close (VC) design. This means that the hand remains open until the user extends their arm or flexes their shoulders, causing it to close. After working with many amputees to develop and test the design, we received feedback stating that while the VC hand works well for certain tasks, there are others that would be much better suited to a voluntary-open(VO) hand. Opposite to a VC hand, a VO hand will remain closed until the user extends their arm or protracts their shoulders. This is how a split-hook mechanism is normally operated, and therefore requires less training for amputees.



The appeal of the voluntary-open hand is that the amputee can grab onto an object and hold onto it without consciously needing to think about extending their arm. The voluntary-close hand does have a back-lock mechanism that allows the hand to stay closed, but the user is required to turn it on and off when grasping and releasing an object. The downside to the voluntary-open hand is that the force required to open the hand is equal to the force that the hand grabs an object with, meaning the hand can only squeeze as hard as the springs can pull. With the voluntary-close hand the user can continue pulling on the cable to squeeze harder.


Inside a VO hand, there are springs or elastics which hold the hand closed until it is used. Initially, we used elastics which are also used in traditional split-hook prosthesis, however these elastics were not available in Kathmandu, Nepal. As a result, the new VO hands have been designed to use extension springs rather than elastic bands. These same springs are used in the VC hands and are therefore more easily accessible.

The initial designs for the voluntary-open hand began in the summer of 2015 as an engineering student’s design project, but following this, priority was placed on improving the design of the voluntary-close hand to prepare for our first deployment outside of trials. The first voluntary-open hands were deployed to amputees in Guatemala in the Spring of 2016 to test the design and to receive valuable feedback. Design updates to the voluntary-close hand have been implemented into the voluntary-open hand, and the hand was deployed again in Nepal in the Summer of 2016. Following this, minor design updates have occurred and multiple amputees, including amputees in Ecuador and Victoria, have received the voluntary open hand.



An amputee in Nepal was able to use the VO hand to write his name on a piece of paper with a pen, and hold onto objects even when swinging his arm around. A construction worker in Ecuador was able to hold a nail with the VO hand and hit it with a hammer. As we further develop our line of prosthesis systems we look forward to more experiences like these! Thanks for your support!

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