The great electric vs. manual arms debate is one that divides many ardent upper extremity amputees into one of two camps.

Harold Sears, a bioengineer with Motion Control, a leader in the field of electric arms manufacturing and design, is always willing to share his expertise, putting aside any professional biases one may expect from him.

Sears addressed some of the questions we at Active Living are often asked… and he needed no strong-arming!

Q. Just how do electric arms work? How are they controlled by the amputee? What’s the learning curve for a new amputee? Is this rocket science?!

myoelectric prosthesis

Sears: Electric arms for prostheses are generally controlled by myoelectric inputs from the wearer’s remnant muscles. That’s the beauty of this concept – muscles which cannot move the missing limb are now dedicated to controlling the prosthetic arm’s functions. If no muscles are available (due to nerve damage, for instance) then cable motion can be used, but amplified by a Force Sensor, or Linear “slider”, which works a lot like power steering in our vehicles.

New amputees can usually learn the basic function within a week or two – and we always recommend training with the help of a therapist. In fact, at Motion Control, we even offer a training course by video for therapists, so they’ll know how to work with an electric arm. It’s not rocket science.

Q. Are there particular types of users who are better suited to using electric rather than manually controlled arms?

Sears: It’s more the type of usage, than the type of person that determines which arms will work best. The same person, for instance, might use a body-powered arm for tasks in a wet or dirty environment (such as a farm or cottage), where the electrical components might be at risk. Body-powered hooks can usually stand up better to staining and scratching than the cosmetic covers of prosthetic hands; however, these rules are beginning to change. There are now highly water-resistant electric hooks (the ETD), and some cosmetic gloves are much more stain-resistant (the MicroCoated glove) than their predecessors.

From a clinical point of view, there are some people who can’t pull a cable at all comfortably, so they are only candidates for an electric hand, or a purely passive arm.
Q. What are some of the most common problems faced by electric arm users? How do you help your clients to meet these challenges?

Sears: A good fit of the socket is absolutely critical, so we help prosthetists to achieve this by providing support such as courses, and other educational materials on our website. Usually an electric arm is a little heavier than a body-powered or a passive arm so that places even more importance on the fit of the socket – a well fitting socket just “feels” lighter.

The wearer’s problems, beyond fit, might be the learning involved in controlling the EMG signals for myoelectric control. There are training exercises provided to help with the learning process. These are usually available through the prosthetist, but they are also available on the Motion Control website for anyone who needs them.
I’m sorry to say that the biggest challenge faced by electric arm users is reimbursement! A set of reimbursement guidelines is also available on the website.

Q. How would an amputee benefit from a switch from a manual to an electric arm? And what would be considered drawbacks?

Sears: The positive things that users notice are often the greater comfort they achieve from having eliminated the control cables and some of the harness materials. They also feel a greater range of motion of the shoulder and (if remaining) the elbow.

Hook prosthesis

One drawback to electric arms can sometimes be the weight – although many people feel the additional weight helps them to balance side-to-side. Electric arms demand more care as well. An electric arm requires daily maintenance, which involves charging the battery and cleaning the electrodes. A point to remember: all arm wearers – electric or manual – should clean their socket daily.

Q. What is the cost difference between the two types of arms? Are there ‘upgrades’ to the standard robotic arms that can be made to improve their effectiveness for users and if so, what are the costs involved with these?

Sears: There is variation, of course, but electric arms are typically five to 10 times more expensive than body- powered or passive arms. Upgrades to electric arms can be made when the prosthesis is replaced or refitted, which should happen every two to eight years: sockets should be refitted every two years and arms should be replaced every four to eight years.

Electronic control units are evolving rapidly, as are the Terminal Devices – such as hands with more motions (faster hands, hands with flexion wrists, and water resistant hands are all now available). The Terminal Devices are the easiest to upgrade because of their modularity – nearly all adult TDs use the quick disconnect system developed by Otto Bock, so they can be replaced with a new upgrade without remaking the entire prosthesis.

Q. As an experienced bioengineer, what advice would you offer to electric arm designers to increase the usefulness of their products?

Sears: Prosthetic arms improve by being more useful to our clients, the prosthesis wearers, so I would advise anyone who wants to improve prosthetic devices to talk to the wearers! Find out the pros and cons of what they use now, and what their real needs are. Sometimes providing what a wearer truly wants – to replace the natural arm – is beyond our capabilities, but anyone who listens will quickly learn the priorities of comfort, reliability, and affordability. We have a long way to go on those areas, just for a start.

Q. One of the major trends in prosthetic development is toward lighter materials and motors. Are there any other significant trends you see in electric arms?

Sears: Certainly, there is widespread use of higher quality silicone and vinyl covers, which are less susceptible to staining, and better looking. Higher performance is big too – faster, higher grip forces, water resistance, more motions (e.g., flexion at the wrist, wrist rotation, etc.).

Q. A word about cosmesis. How difficult is it to create arms that match the wearer’s skin tone, etc.? Is this an involved process and is this an important issue for users?

Sears: It is important for nearly everyone, but with wide variation in the priority relative to other things. The bilateral amputee often says, “give me function, function, function”, though that doesn’t mean they don’t care about appearance. Sometimes, appearance just has to take a back seat.

My friend John Michael, a columnist with OandP.com says succinctly, “the clients will adjust their expectations to match what is available to them.” The point is, if we could offer more realistic prostheses, affordably, all our clients would love to have the best they could get. Because we have historically offered disappointing results, their expectations are lowered.

The nicest covers, usually silicone, are expensive, but there are more and more vendors for them, so it doesn’t take as long as it used to, and you don’t always have to travel to the vendor to give them the first hand to look at while painting the covers.

The microcoating of vinyl gloves will make keeping an off-the-shelf glove clean an easier task, once they are in common use. Those are simply chosen from about 18 different colors, from the prosthetists’ color swatches.

Note: Visit the Motion Control website at www.utaharm.com to learn more.