How Do Prosthetic Arms Move?

Prosthetic limbs have come a long way since their inception. The answer to ‘how do prosthetic arms move?’ used to be ‘They don’t’ - but today we’re happy to say that arm prostheses are now sophisticated and versatile tools that can be used to achieve a huge range of functions, including helping individuals who have gone through upper limb amputation or who have upper limb differences regain the ability to perform everyday tasks like eating and dressing themselves.

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Prosthetists are also working to develop things like new construction technology (which would enable lighter-weight prosthetics), new interface methods and new components with more mobility than ever before. But that's technology for the prosthetics of tomorrow - how do prosthetic arms move in the here and now? ExpHand explains in the paragraphs below...

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So, how do prosthetic arms move?
Traditional methods of achieving prosthetic limb movement

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There are traditionally two ways of articulating or moving a prosthetic joint. One option is to use cables, but it should be noted that any cable-powered solution also requires the use of motors, or requires the wearer to be able to physically move or hold the cable. Alternatively, electric motors can be used to adjust positioning and articulate a prosthetic limb. Electrically powered joints have the plus point that they do not necessarily require physical input from the wearer, because they can also be controlled myoelectrically (where sensor technology reads each electrical signal sent to the relevant muscles in your body, and translates them into an accurate equivalent movement of your prosthetic).

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How do prosthetic arms move shoulder joints?

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Many prosthetic shoulder joints are essentially a ball joint. This is the same way that a fully biological shoulder moves, except that when replacing this with a prosthetic arm, the joint can be laid out in two ways. It can be laid out 'anatomically' - where the ball is attached to your arm and the socket is part of your torso, just as your skeleton does it - however It can also be done as a 'reverse' shoulder replacement where the ball is attached permanently to the torso and the socket is part of the arm section of the prosthetic.

 

How do prosthetic arms move elbow joints?

Here again, cables or electric motors can be used. Some prosthetic arms have elbow joints that are controlled by a cable harness or body movement. In these cases, the wearer has to control both parts of the arm, the elbow joint between them, and where appropriate the shoulder too. However, this is made easier by the ability to fix the elbow joint in a range of different positions through manipulation of the cable. Electrically powered elbow joints are often controlled through an array of buttons or switches within the prosthetic that the wearer can manipulate using their stump, or myoelectrically through reading brain signals as described above.

 

How do prosthetic arms move fingers and handle gripping?

 

Wrist joints can also be electronic. Where they are, they can be controlled myoelectrically or through the use of switches or pressure pads inside the prosthesis. Wrist joints don't have to be electrically powered though. They can be adjusted manually using the sound hand; or they can even be omitted - as in situations where a hand/gripping device is attached directly to the forearm in a fixed fashion.

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How do prosthetic arms move fingers and handle gripping?

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In general, the way you control your prosthetic arm is largely dictated by what kind of prosthetic you're wearing. Some will have more functional gripping devices operated by cables or myoelectrically. Others will have full prosthetic hands more akin to what you'd find with a fully bionic arm, complete with four fingers and a thumb. These digits can be controlled by flexing the muscles in the forearm that would be connected to the fingers (provided that the wearer has them), or again through using switches and pressure pads inside the prosthetic that the wearer can use to provide control inputs.

In Conclusion

Prosthetic limb research, design, construction and technology have come a long way since they were first invented. The methods that can be used to articulate them, and the precision with which they can be controlled today are just two of the benefits that these advances in science and technology have brought. For more information on how modern prosthetics work and what everyday life with an upper limb prosthetic or limb difference is like, and to answer other questions like 'how do prosthetic arms move?', including how prosthetics move through mind control and can 'feel' like real human hands or arms, why not check out the rest of our FAQ?

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However, while today prosthetics are much more lifelike in their physical appearance and are capable of movements that are more natural than ever before, we believe that there is still room for improvement. If you want to stay up to date with the latest news from the limb-different community, or simply hear some great uplifting personal stories, the ExpHand blog is the place to go - and don't forget that you can also reach us on social media too, on Facebook, Instagram, Twitter or LinkedIn!