# Aron Ralston's prosthetic hand **URL:** \ **Category:** Factual Questions\ **Created:** [July 29, 2003, 10:03am UTC](https://boards.straightdope.com/t/aron-ralstons-prosthetic-hand/191615 "2003-07-29T10:03:21Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Dunderman](https://avatars.discourse-cdn.com/v4/letter/d/ecb155/32.png) [@Dunderman](https://boards.straightdope.com/u/Dunderman)\ **Post date:** [July 29, 2003, 10:03am UTC](https://boards.straightdope.com/t/aron-ralstons-prosthetic-hand/191615/1 "2003-07-29T10:03:21Z")
I was watching Letterman last night, and Aron Ralston, the guy who got his arm trapped under an 800-pound boulder while rock-climbing and proceeded to cut it off with his knife and then walk six miles, was there. He had a prosthetic hand. At one point during the interview, he says he wants to show Letterman a trick. He holds an empty coffee cup in his prosthetic hand. The hand spins around 360 degrees without him touching it. How did he do that? How did he make it spin? In a comic book they’d just hook up his nerves to the hand so he could, say, try to close his fist and that would make the hand spin, but I thought we were a long way away from doing that in reality. How was it done? In case anyone’s wondering, I’m in Sweden where Letterman’s show is shown with a one-week delay. ---
**Author:** ![Dijon\_Warlock](https://avatars.discourse-cdn.com/v4/letter/d/a9a28c/32.png) [@Dijon\_Warlock](https://boards.straightdope.com/u/Dijon_Warlock)\ **Post date:** [July 29, 2003, 10:17am UTC](https://boards.straightdope.com/t/aron-ralstons-prosthetic-hand/191615/2 "2003-07-29T10:17:27Z")
Presumably someone who knows the ins and outs of it better than I will come along, but I believe it’s done by means of sensors which pick up the electrical signals in his remaining muscles which then activate a small motor in the prosthesis. Very much like your comic book. We’ve been doing this for a while now, I think. ---
**Author:** ![Larry\_Mudd](https://avatars.discourse-cdn.com/v4/letter/l/f14d63/32.png) [@Larry\_Mudd](https://boards.straightdope.com/u/Larry_Mudd)\ **Post date:** [July 29, 2003, 10:21am UTC](https://boards.straightdope.com/t/aron-ralstons-prosthetic-hand/191615/3 "2003-07-29T10:21:09Z")
If it’s substantially like other artificial limbs I’ve seen, there are simple sensors positioned near the muscles further up the forearm. Feel the underside of your forearm with your opposite hand. Now, move your wrist side to side. Note you can feel pressure at two distinct places depending on which way you move your wrist. Not _too_ hard to exploit that sort of thing for articulation. Modern engineering is pretty amazing and inspiring, what? I’ve seen artificial limbs that work like this to provide a gripping action, but I’ve never seen anything quite like Mr. Ralston’s. Ordinarily, I think it horrible to even think about making a “rotator cuff injury” joke, but since Aaron seems to be the most well-adjusted young man _on the planet_, I won’t beat myself up too much. preview: too slow. ---
**Author:** ![Phlosphr](https://avatars.discourse-cdn.com/v4/letter/p/c68b51/32.png) [@Phlosphr](https://boards.straightdope.com/u/Phlosphr)\ **Post date:** [July 29, 2003, 12:20pm UTC](https://boards.straightdope.com/t/aron-ralstons-prosthetic-hand/191615/4 "2003-07-29T12:20:28Z")
I believe the man’s got a [Utah Arm](http://www.utaharm.com/products.htm#u2) . A specialized prosthetic. They call them Smart Limbs. They are even coming out or already have all digit movement and bionic type grip. No feeling of course. But you could flip someone off - allbeit slowly.