Bionic arms. How do amputees with bionic arms control the fingers and wrists to do things like picking up a cup and drinking so smoothly?

Question

This was asked a few years ago on here, but things have apparently improved a lot since then.

The top answer from before was describing a process that was a little cumbersome, but there’s videos of folks with new arms moving them and using their new hands much more smoothly than I would have thought possible using the older method described.

In: 100

Answer 1

First, there are different types of prosthesis that correspond to the location of the amputation. Prosthesis is a term for man-made limbs used in place of limbs that are missing. I’ll assume that because you said “bionic arms” you mean something above the wrist.

There are two primary ways to control prosthetic arms, body-powered and myoelectric. Body powered means that movements of the body control (such as moving your shoulder down and away from the body) result in actions of the prosthetic, like closing the hand. Muscles generate small amounts of electricity when they contract [for adults: also at “rest” most people have muscle activation, we call that ”tone”]. Myoelectric is a word that means muscle electricity. So these types of prosthesis have sensors that can detect the muscle electricity and signal motors in the bionic arm to move. This explains how the person can control the machine.

The muscles used depends on the level of amputation. Muscles are attached to bone, so if part of a bone is removed, the muscle is no longer attached. This means the muscle can’t work because it is only attached on one end. Doctors will either screw the muscle into what is left of the bone [adults: myodesis] or tie the muscles on one side of the arm to the muscles on the other side [adults: myoplasty]. Now this explains how we can get working muscles with amputation of the bones they attach to.

So normally I contract muscles in my forearm to flex or extend my wrist, but if I am missing my wrist and hand, these muscles can be attached to sensors of a myoelectric prosthesis. The trick is you need to learn to control these muscles individually. In order to close your bionic hand, you need to relax muscles on one side of your arm and contract the muscles on the other side. This is something that often physical therapists do to help the person learn to use the prosthetic correctly.

Source: physical therapy student who just took a prosthetic class.