Are there Prosthetic Arms that Move?

There are all sorts of prosthetic arms on the market today. Many function in slightly different ways, but can be sorted into groups based on their controls. The range of movement these prosthetics have depends on where the amputation or congenital limb difference is positioned. For example, as they have fewer joints to manipulate, prosthetics designed to fit below elbow arm amputees will have more controls dedicated to grip patterns.

Get ready to explore some of the different ways prosthetic arms can move!

Body powered prosthetics

Body powered prosthetic arms use a harness and cables to move the arm. They can be controlled by the same arm or the opposite shoulder, depending on the user's limb difference. This is the function-over-form option, which people who use their prosthetic in wet or otherwise rough environments tend to pick. The absence of electronics makes them a bit more durable and hard-wearing.

As you learn how to use your body powered prosthetic, you start to get used to the levels of tension on the cable. Over time you begin to understand the prosthetic's relative position, giving you a great level of control. Plus, being mechanical, there is a greater level of customizability available. Many users swap out the hand (or terminal device) for a hook or other tool suited to the task they need to complete. You can also adjust the grip strength by adding or removing rubber bands, or swap out the cables for finer or more durable options depending on your needs.

While body powered prosthetics are incredibly functional, they can be uncomfortable and initially unwieldy. If using your opposite limb, the control method requiring a harness to use makes wearing the prosthetics for long periods of time uncomfortable. They're not the best fit for every individual.

Depending on the person's interests, the utility offered by body powered prosthetics can range from essential to inadequate. Their mechanical design and basic level of function can make them useful for jobs or hobbies like woodworking and other workshop environments, but they're less practical for tasks like typing.

Myoelectric prosthetics

Still a relatively new technology, myoelectric prosthetics are powered by electric motors. There are electrode sensors fitted into the socket of the prosthesis, which read electrical impulses generated by muscles in the residual limb. This signal corresponds to a particular movement, allowing for finer motor control.

A myoelectric device can be incredibly useful in your daily life. Their controls are intuitive and improvements in modern designs allow users to move the hand in more natural ways. Scientists are still iterating on myoelectric designs, making them more lightweight, durable and user friendly all the time! If you're living in the UK there are some myoelectric models available through the NHS, too.

One of the more common problems with myoelectric prosthetics is the socket slipping, which can interrupt the surface connection. Some myoelectric arms try to make the controls more accurate by surgically implanting the electrode sensors into the muscles of the patient (rather than relying on surface contact in the socket). This makes the electrical signals made by muscles in the residual limb much stronger.

Some users dislike the lack of feedback offered by myoelectric prosthetics. A suggested workaround for this is vibration in the prosthetic that the wearer can use to determine their relative grip strength, for example.

Another recent innovation in myoelectric design is the implementation of AI. The idea here is that the controls for myoelectric prostheses are set up by the prosthetist when you get them. As you use the prosthetic in your everyday life you may want to change these controls, for example making different muscle movements correspond to different grips. Some of the commands can be close together, the result being the arm not behaving exactly as you want it.

By including a small computer in the arm, an AI can try to adapt to how you want to use your arm. Measuring your commands and desired outcomes, the machine learns which muscle movements you want to make to, for example, make the hand grasp an object. Over time the AI can start to suggest movements increasingly intuitively, making it easier to use over time.