How Do Prosthetic Arms Work?

If you're looking for the first prosthetic arm for your child, you've certainly run into all sorts of different prosthetic options, ranging from expensive bionics to passive cosmetic options, as well as everything in between. If you haven't had a prosthetic fitted before, you may be asking yourself "how do prosthetic arms work?". That's a great question - and as with any good question, the answer is "it depends"!

Prostheses are customised to suit the needs of each patient, but you can generalise prosthetic options into two camps, to match varying levels of limb loss: trans-humeral, meaning the separation is above the elbow; and trans-radial, meaning it’s below the elbow. Regardless of whether the limb difference is congenital (existing at birth) or acquired (due to amputation or injury), it is possible to find a prosthetic option that works for you.

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So what type of prosthetic should you get? That depends on a few factors. Primary should be the goals of the person using the prosthetic. Ask your child what they want out of a prosthetic - do they want it just for appearance, or to play sports with? The needs associated with these goals will help you determine the kind of prosthetic arm would be most suitable for those applications.

 

For example, if the young person with a limb difference wants to improve their art skills, the ability to move their hand and wrist with increased accuracy will be more important. Or, if it's for regular daily chores like lifting things from shelves, grip and pull strength would factor more into the design.

 

You'll generally find each prosthetic product strikes a balance between aesthetics and function - the more realistic a prosthetic looks, the more likely it is to have reduced practicality or movement capability. Equally, the more function a prosthetic offers the more likely it is to be uncomfortable to wear for an extended period of time, due to the increased weight.
 

While research and innovation in the field of prosthetics is constantly moving the dial, this triangle spectrum of utility, appearance and comfort has held true and is a useful means to narrow your options down and make the right choice.

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Okay but, really, how do prosthetic arms work?

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For this article we're excluding passive prosthetic options. As the name implies they offer limited function, focusing instead on appearance. While they can still be useful and appropriate for certain tasks, there isn’t much to explain when it comes to their mechanics.

 

Modern prosthetics focused on function fall into three categories, differentiated by the means of control - these are body powered, motor powered and myoelectric prosthetics.

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Body Powered

 

Body Powered prosthetics are fully mechanical arms, meaning they are unpowered. They are controlled with cables, allowing for an extensive range of motion. Depending on the limb difference, these cables attach to different parts of the body. The ExpHand, for example, is designed to work for young people with below-the-elbow limb difference, which means there is enough muscle for the hand to be controlled with the corresponding upper arm.

 

Of the functional prosthetic options available, body powered prosthetics are generally the least expensive options on the market. This doesn't include the time investment required to learn to use the prosthetic though, which can be done at home or with the help of a physiotherapist.

 

Motor Powered

 

Motor powered prosthetics function similarly to body powered ones, but instead of cables they are controlled by switches or buttons - each performing a different function. These prosthetics are electric, and are powered by a battery which needs to be recharged regularly.

 

This is the middle-ground technology, and comes at a corresponding medium price point. Motor powered prosthetics can be difficult to use initially, requiring some therapy or practice exercises to get started. They can also be pretty heavy, and so can be taxing for young people to use for extended periods of time.

 

Myoelectric 

A myoelectric (or bionic) prosthesis is the most advanced prosthetic technology that is widely available. A myoelectric device uses electrode sensors placed on the skin to read muscle contractions, generating an electrical signal. This signal then causes the limb to move. Like motor powered arms myoelectric prosthetics use a battery (which will be integrated or removable, depending on the product), and require a decent amount of practice or therapy to use effectively.

 

Being a relatively recent innovation in prosthetic engineering, myoelectric options can be comparatively expensive. While they can be a good fit for adult patients, this price point means they may not be recommended for young people - they're likely to rapidly outgrow the device, making it necessary to update or replace the prosthetic frequently.

 

For more information you should consult a prosthetist, which you can do through the NHS in the UK. As well as answering any further questions you have, the prosthetist can offer support and guidance as to what style of prosthetic would best suit your child.

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Some children, especially those with congenital limb difference, may not initially see the benefits of a prosthetic. As their parents, however, it's your job to do the long term thinking - they will almost certainly value the functionality provided by a prosthetic when they're older. As discussed by the Amputee Coalition, some adults born with limb difference advocate for the use of a prosthetic to be encouraged by parents as much as possible. It is best to seek a middle-ground between your child's initial reaction and the recommendations of the prosthetist.

 

On the other hand, prosthetics aren't solely in the realm of medical application. There is a lot of room for personal preference and expression with modern prosthetic options, and the process of choosing a new prosthetic should be a fun one! It's important to communicate with your child and make sure they want to use the prosthetic, as this will encourage them through the stages of learning how to use it.

 

While research is of course important, there's no substitute for your child trying these options for themselves. It's important to experiment with the different types of arms that are available, learning which is most suitable for their day-to-day life. It's not uncommon for prosthetic users to have multiple different types of prosthetic, in order to participate in different activities. There are no right or wrong answers when it comes to your child's prosthetic!
 

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