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Waterproof Prosthesis??? Answered

Hello Everyone, I just recently became a below elbow amputee. I don't even have my prothetic yet! But I was wondering if anyone knows of how I could make a body powered hook waterproof. I thought I could just replace all the parts with stainless steel (or any waterproof metal), but my prothetist says that none of the arm companies make those little components (at the end of the arm) in anything but steel. I even popped a question to a representative at Ossur to ask if their suspension sleeve came with stainless steel parts. He said only water 'resistant'. Anyway, I was wondering if I could get a metal shop to make the parts or if you guys knew of anyone who has tried a similar endeavour. If I was to take my soon to be prosthesis into water, I know it would rust and seize. I would have to return to the shop every few weeks. An idea I had was just to make a passive hook (captain hook style) but it would lose most of it's function. Any ideas??? Getting the parts in another metal seemed like a good idea to me, but I don't know what kind of shop would make custom metal pieces. P.S. If you're wondering what it is for, I use to kiteboard and sail and want to do it again.



11 years ago

I've been hoping for an arm that I wouldn't have to take off to get through airline security. That rules out myo, since no one has come up with those non-metallic wires yet, but I think the rest is doable. Conveniently enough, such an arm would also do well in water.

I've been looking at the hardware , and I think that the most of the metal in a body-powered prosthesis could be replaced with plastic or a composite. The arms are mostly made of those materials already.

Spectra cable (http://www.anglerscenter.com/spectra_powerpro.htm, and teflon-coated spectra spiderwire http://www.spiderwire.com/) is lower-friction than steel cable, and is already extensively used in prosthetics.

I think that a stiff hose (maybe without the same liner that is used with the spectra) like http://www.mcmaster.com/ part 5394K13 or 5439K19 might work the second might be lower friction.

The low-profile t-nuts that are used to hold the socket to the frame could be replaced with plastic rivets and drilled out for maintenance. I haven't seen any low-profile plastic fasteners that look like good alternatives. These are the sort used on the inside:
With low profile screws on the outside.
They are called barrel screws, and mcmaster actually has a couple in plastic: 90249A225 and 90249A190. Maybe they would work.

Cable fittings could be replaced with knots in the spectra.

That brings us to the last major components, the wrist and terminal device. I think that a very strong hosmer 5x-type hook could be made of glass-filled nylon, delrin, or even carbon fiber. I think that the wrist connection would have to be a little beefier to suit the material, but there's no reason that the terminal device to wrist attachment couldn't be almost as thick as the wrist.

Crapfinger has a good point, too. A task-specific arm might be completely different. Do you need to push as well as pull when you kitesurf? I would guess not. If all you have to do is pull, you could design some strapping or a harness (not even an arm really) that attached to your arm above the condiles of your humerous (the bony protrusions at the sides of your elbow), and then it wouldn't be as bad an experience to get smacked in the face with it when you bit it (have a friend who cut his face snowboarding with a hook).

I still want a Glock arm for the security line, though.

In my experiance ,steel doesn't rust if you oil it often and dry it after it gets wet. To get all the water out of the joints I suggest using a hair dryer. The high temperature and air speed drives the water out as well as heating the metal to evaporate trapped water.

Thanks everyone for the suggestions, I'm planning to use an aluminum design while trying to be very finicky about cleaning and oiling it. One idea was to clean it with alcohol, so it evaporates quicker. I'll just have to wait and see if a combination of the two works. I'll leave comments once I try it (probably early May).

I don't think oil does anything for aluminum. P.S when you mix metals(alum and steel), it makes corrosion and rust worse, due to the battery effect when two metals touch.

oh yeah if the water was clorinated or salt water, rinse the metal with fresh tap water before heating it up with a hair dryer, as the chemicals might react with the metal+heat.

Um, my animatronics professor made the aliens in The Abyss with Lexan gear joints. It worked for what they needed, but I have no idea how strong the joints would be. I think they used Lexan primarily to have the joints become invisible underwater, but it is pretty strong plastic.

I don't remember aliens other than CGI in the abyss. There are certainly strong plastics but I'd suppose that the problem lies in fabrication.

I think he machined the gears himself. Yeah, there were aliens at the end of the movie with butterfly wings and glowing parts--they were animatronic.

i wonder if it would be more prudent to make a modified prosthesis instead of making an exact copy of the current hook? i would imagine that for kiteboarding etc... you wouldn't need quite the dexterity correct? just enough strenght to hold on to...well whatever it is you're holding on to...correct? maybe something like replacing the hook with a stainless quick release..that could then be actuated by the same method as the hook...which i assume is the standard "back strap" type deal? something kite boarding specific..instead of a complete stainless reproduction...cuz in normal day to day..you wouldn't need it to always be stainless right?

sounds like salt water would be your biggest problem. a machine shop should be able to copy the function (if not the look) of the pieces, but there would be a question about how much stress you are going to put on each piece-i don't imagine that the regular prosthesis would be built to take the strain of kiteboarding (hanging your weight off the hook). you might need your prothetist to make an extra sleeve? that was for work not looks. if you can't find a machine shop nearby, you might try the local collage or vo-tech. maybe one of the welding or machining students (or faculty) would be willing to help.