Introduction to Myoelectric Prostheses
by Amber Henson, on Jan 18, 2021
Myoelectric prostheses have motors and batteries on board to power the movement of the devices that are ultimately controlled by input from electrical signals generated by muscles in the residual limb. When muscles are contracted, they give off an electrical signal. In prosthetics, electrodes sitting on the skin inside the socket detect these muscle signals and send them to a controller, which triggers movement to correspond to what the user intends. When you want to close the hand, you squeeze your muscles that correspond to closing and the hand will close. Technologies now exist to make this even more intuitive for individuals to control multiple features in an arm such as grasping patterns in a hand, wrist rotators, elbows and even shoulders.
The advantages of myoelectric prostheses over body-powered devices include a reduction of harnessing, access to effortless strength and multiple grip patterns, more natural hand movements and, with the help of TMR surgery (see below), a more intuitive control of the prosthesis. People also enjoy the “cool, robotic look” they can offer when not covered by a cosmetic glove. An often-stated limitation of myoelectrics is that they cannot get wet. That too has been overcome with recent advancements in waterproofing technologies for some terminal devices and elbows (though, in general, they still cannot be submerged in water).
Myoelectric technologies are available for all levels of upper limb loss. We discuss some options below:
Electric finger solutions for those with finger amputations consist of individually powered prosthetic fingers that can bend, touch, pick up and point. Electric finger solutions are designed to replicate natural finger movement and are available to replace complete missing fingers. You can see some at work in the gif below.
There are two types of myoelectric hands: single-motor hands and multi-articulating hands. Single-motor hands open and close — that's all they can do. But they can be covered by a realistic-looking glove so that, at a cursory glance, other people may not know you are missing your hand.
Multi-articulating myoelectric hands are available from a variety of manufacturers in multiple sizes and configurations. Some of the most popular devices are:
- The Taska Hand (featured in the gif below)
- The bebionic
- The i-limb
- The Michelangelo Hand
At times, an electric hook may be exactly the tool you need for fine, precision tip pinch, high pinch strength, durability and all electric hooks are waterproof. There are a few electric hook options available such as:
You can read more about them in our article, “Introduction to Electric Terminal Devices.”
Elbows have the job of helping to pre-position the terminal device in space. When a person does not have the strength or ability required to operate a body powered elbow, an electric elbow can be used because they still just need electrodes on the surface of the skin to control the movement of the elbow. Some elbows are even capable of lifting quite heavy loads and holding them to make carrying things over the forearm much easier. Each elbow has specific features that may be important to you and needed to maximize your outcome potential. You can learn more in our article, "Accomplishing More with Prosthetic Elbows." There are several elbows on the market including:
- UtahArm 3+ (pictured below)
For those whose amputation level is above their elbow or at the shoulder level, a look into targeted muscle reinnervation surgery may be warranted. In that surgery, the surgeon “reassigns” nerves that once controlled hand or arm muscles on the residual limb or chest. This allows the individual to improve their control of a myoelectric device, and helps to prevent painful neuromas, which are bundles at the ends of cut nerves that are there because of an amputation. Learn more in our “Introduction to Targeted Muscle Reinnervation (TMR)” article.
Would you like to learn more about myoelectric devices and what they can do to make your life easier? Please contact us and let us know you’re interested in a complimentary consultation. We will discuss all available options for you. If you currently use a myoelectric device, please tell your fellow amputees in the comments about how you like your device!
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