Nov 122018

One of our Instagram followers asks:

Anybody got any experience with prosthetics for tool-use?

I have two students with hypermobility that means using a tenon saw is ~70-80% chance of dislocating a thumb.

I am thinking of some sort of brace, similar to those used for carpel tunnel syndrome, but with the metal bar extended somehow, with some sort of bracket to transfer the forces to their forearms.

The two pictures here are as far as I have gotten.

Problem: this feels like a job for 3d printing, but I lack access to a printer.

Is it possible I am reinventing the wheel – does such a device already exist? (Feel free to share this with anybody that might help)

Thanks all!


  7 Responses to “Prosthetics for tool use”

  1. Thanks everyone! I’ve passed your suggestions on and we’ll see if they get back to us…

  2. Hello,
    I recently modified a Wolf Garten garden tool handle for a lady in without any muscle control in her hand who wanted to garden again. It allowed here to click in different tools and release them with the button in the handle. The modified handle sat below her arm with a hand grip at the front (hand wrapped around with a 2.5 inch elastic held in place with hook and loop tape). The rear was an arm support rescued from an old standard aluminium crutch. Photos available – just can’t work out how to insert them.

    • Andrew, this sounds like something that should be in Remapedia, or the soon-to-be-ready MakeAbility. Have you thought about uploading it?

  3. I used a medical wrist brace some years back in the way you are thinking, for a young man who had lost most of his left hand in an accident.

    The (thin) aluminium support strip you get on those things is in a pocket, and can be removed. I replaced it with a thicker strip with a couple of screw holes tapped into it. That enabled me to secure a longer 1/4 inch x 1 inch strip outside of the brace bolted through the fabric into the two tapped holes. On the end of the outer strip, I made a custom clamp out of aluminium to hold spanners and the like.

    My only reservation in your case is holding a spanner is one thing, but trying to saw with such an implement will be a different proposition. The thumb goes through the brace – so when you try and use it to saw, there could be enough movement in the brace to still pull at the base of the thumb as you can only tighten it so much around the wrist. Not sure you’ll get the stability of grip either.

    But if you ping me an email (Harrogate and Ripon group), I’ll dig out my photos and you can at least see how it was done.

    There is a power tool alternative to a tenon saw (an oscillating cutter, aka multi-tool, multi-cutter). I use mine a lot but it has some downsides that might make it unsuitable to even consider in this case – namely students would have to be safe and confident enough to use power hand tools, the cutters are noisy, the vibration levels can be high, and the blades are expensive and blunt quite quickly which can lead to kick back and even higher vibration.

  4. Hi Could they not use Japanese hand saws which have a different handle shape. If tenon saws are a problem so will be smoothing planes some hacksaws so I suppose a universal support could be a better bet.

    • These saws also work on the pull stroke which would help.

      Otherwise polymorph could be put to good use.


  5. You could try to find a local OT from a hand therapy service. They will be using thermoplastics for bespoke hand splinting. As a (now retired) OT I have in the past made several splints for occupational use, similar to what you are describing.

 Leave a Reply