New Prosthetic Hands

[makattak]

http://www.popsci.com/article/technology/video-marine-prosthetic-hand-controlled-his-own-muscles

Now, I'm sure many of you have read (or seen the videos) about the marine with a prosthetic limb controlled internally.

It's pretty cool and wonderful to see the advances we have made in prosthetics.

I'm wondering one thing: if the hand is completely autonomous from the actual muscles (other than as signals), why are the designers making them like human hands?

Shouldn't they be upgrading them? Why not make a hand that can spin like a drill? Fingers that can close in a fist on either side of the hand?

If your body has to learn how to control it, it is no more difficult for the recipient to learn the new features in addition to learning normal features.

Maybe someone is working on those, but all the new ones are attempting to replicate human capabilities, not expand them.

(Now I realize we aren't at the point where a prosthetic is better than a normal limb, but I don't see how expanding the capabilities should be at all difficult.)

For example, we have the running blades that are (arguably) better than human legs for the task they were designed. Why are hands/arms not going that route?

[fifth_column]

I imagine they will.  How about a thumb on both sides of the palm?

Why are hands/arms not going that route?

I imagine they will.  Maybe an opposable digit on each side of the palm.  Or make them all opposable.

[geronimotwo]

inspector gadget!

[AZRedhawk44]

I guess it's probably because they are queuing on the nervous impulses or muscle remnants that performed the conventional motions.  None of us have nerves or muscles that allow our fingers to make a fist on the backs of our palms, or rotate the wrist more than +/- 90 degrees.

Your choices for enhanced range of motion would be to compound existing nervous impulse instructions into multiple simultaneous or a series of movements... or to grow new nervous tissue that are completely new instructions for the body to learn.

If we could grow new tissue, then we could just regenerate the hand to OEM configuration.

Compounding instructions to build a new instruction runs into difficulties, because there are already compound instructions that the OEM body follows.  You have to find a series of compound instructions (for rotating the wrist backwards 180 degrees from normal, for instance) that don't conflict with different instructions.  A compound instruction might be confused or misinterpreted as a dextrous operation while applying force to a different task.  Did you really want to rotate your wrist 180 degrees while tying your shoes, or did you just want to tug upwards and maintain pressure on the bunny ears while the other hand went around and up?

[Gewehr98]

[MechAg94]

A guy I used to work with had an in-law relative that does make tool attachments that fit in place of prosthetic hands.  I think they are pretty expensive though.  I don't think they were powered or anything, it just allowed a bit more usefulness. 

[Perd Hapley]

Probably because amputees don't see the prosthetic as a chance to "upgrade." They want normal hands, not weird Dr. Strangelove hands.

And cost.

[TommyGunn]

I imagine some of the difficulties involved in doing what the OP suggests ("Why not make a hand that can spin like a drill? Fingers that can close in a fist on either side of the hand?")  could be overcome.   The nervous impulses that apply the extensor muscles to open the hand probably still exist as even the human fingers reach their mechanical limit.   It would be a matter of training.  
Having a hand that spins like a drill depends upon how it is connected to the body and how the data is transmited into the prosthetic.
People who are familiar with the popular 1970s TV series The Six Million Dollar Man recall that Colonel Austin was rebuilt after a horrific crash using the science of bionics, giving him extra strength & speed.  How did THAT work?  
That series was based on a Martin Caidin novel called Cyborg.  In Caidin's novel the bionics limbs had some abilities the TV show lacked (while also "lacking" something the TV show added).  The bionics hand in the novel had a tiny CO2 powered dart gun hidden in one finger.   With this Austin could kill with a poison dart from a distance.  Hidden in secret compartments in the legs was a tiny bottle of compressed air for underwater use, and a tiny radio transceiver.  Small collapsable swim fins were fitted into the soles of his bionics feet, so all sorts of cool stuff might be imagined.  In the 1970s the TV series' budget prohibited the employment of above devices, so the TV hero lacked them.  He did, however, have an actual working bionic eye with nightvision plus a handydandy zoom, something the book character didn't have.

Probably because amputees don't see the prosthetic as a chance to "upgrade." They want normal hands, not weird Dr. Strangelove hands.

And cost.

You know, in the end, I think Fistful pretty much nailed it.