From hook to bionic jack-of-all-trades

Some people want their prosthetic hands to look as natural as possible; others want hands that can do nearly everything; and yet others may wish to have bodies that are intact to the maximum extent possible. To each his own. This is as true for prostheses as it is for anything else. That said, the bionic prosthetic arm really is revolutionary. Arie Rommers, who has used the arm, and EMC researcher/lecturer Ruud Selles will tell students all about it at a lunchtime lecture given on 17 October.

“All fingers can move, and on top of that, each finger has two bending points – two phalanges, if you will,” says Vera van Heijningen, an occupational therapist specialising in hand therapy and a colleague of Selles’ at Erasmus MC. “Which really is unique, because so far, all other myoelectric prosthetic arms (conventional myoelectric prostheses) have only had one point at which they could move, without any phalanges.”

As a result, the thumb and index finger, along with the middle finger, can bend towards each other so as to pick things up. “Using the bionic hand, you can grip things more tightly and hold on to them without their slipping from your fingers,” Van Heijningen explains. “Electrodes on the muscles in your arm will transmit signals that provide motor innervation to the bionic arm.”

In future, the brain may be able to transmit such signals. “Research on this is currently being conducted in the United States,” says Van Heijningen. “I definitely expect something like that to become available to Dutch patients at some point. Which would be absolutely wonderful.”

For what it’s worth, Van Heijningen is not saying that conventional prostheses and traditional hooks will no longer be used when this happens. “It depends on what you want your prosthesis to do for you,” she explains.

Basically, there are three types of prostheses: passive, body-powered and myoelectric prostheses. Passive prostheses are hands or hooks that cannot be opened or closed. “They make your limbs longer, and as far as arms are concerned, they can look quite real,” says Van Heijningen. “Silicone hands, in particular, look so real it’s hard to tell them from the real thing. They are covered by very tight skin-coloured gloves which make the hands look like they’re real. We could also put something like that on bionic hands, but due to the moveability of such hands, softer silicone gloves would be required, which would break much sooner.”

Body-powered prostheses can be moved, using the power of your own muscles. As Van Heijningen explains, “Such prostheses are firmly attached to the body, generally by means of a corset of sorts, thus allowing you to get them to move by using the power of your muscles in your good arm, or in another body part on the other side of your body.”

Then there are myoelectric prostheses, such as the bionic arm. But there are also more conventional myoelectric prostheses, which can be charged by putting a plug into an electric wall socket. Van Heijningen explains how these work: “Electrodes placed on the muscles of your arm or a different body part will transmit signals that will set the [bionic] arm in motion.”