Basic Prosthesis (Very Beginner, not complex at all) opinions

chaitanya_gupta · January 21

So I started making a simple prosthesis that has a few dimensions that are taken and can easily act as a sort of "peg leg." It's very basic, but a friend told me that there are a bunch of below-the-knee amputations, and since prosthetics can be super expensive, it might be worth making a quick, temporary solution for people. So I made this.

https://cad.onshape.com/documents/93730c50683e58555a7f3fee/w/8526e0da4661786f82d9d057/e/974d4346d723961dd1a43404?renderMode=0&uiState=697017f670a05d357f25ff41

Here, the 1-part prosthesis is really what I'm looking at. There's a bunch of overhangs, and so the build won't be very clean, but it seemed to be a quick solution for someone who is limbless, so they can get a temporary fix (either because they can't get an actual prosthesis or if their order is backlogged to some degree).

The way it works is I simply take a few dimensions; I take the Cs (the stump circumference around 0.7 inches from the bottom of the stump), the Cu (the upper-stump circumference, or the circumference of the stump in inches, which is Df_s inches from the ground), and Du_s dimensions (the maximum clearance for the stump on the prosthesis). I understand that this approach is limited (not everyone has the same leg shape), there is, of course, the calves (hence the breathing room being afforded as the opening on the side, which can allow the calf muscle to rest outside), and it cannot be a simple one-size-fits-all.

But the hope is, if a filament like TPU (which is strong and flexible) is used, the cavities on the side of the stump (the slots for an elastic band) can serve to tighten the stump's upper features, whilst a sock can be used to properly connect the prosthetic's stump and the 3D printed stump. From what I understand, some moderate soft filling (perhaps some sort of light fabric) can be used to fill the bottom of the stump, potentially making it tighter.

Again, this is a very temporary and basic fix (I am not very talented at Onshape). But I have run a few calculations and have found that this build can be printed for >$100, and does not have assembly (again, it is a one-print part, although it may require significant touch-up if someone wants to remove supports, despite this being unnecessary).

Does anyone have any recommendations as to where I should move from here? I understand I am in deep waters and way over my head here, but this seems like a somewhat decent solution if it can be durable enough.

martin_kopplow · January 21

Hi @chaitanya_gupta , it looks like you already included a big deal of answers in your question. If I were tasked with this, I'd try to get much more organic, and that is for two reasons: I'd want to make it easier on the printer, and faster as a side effect, and I'd want to reduce the volume of material required, thus saving on time and money again.

What is the reason for the 4 separate profiles in the shin region? I guess that might use a lot of dense material for the shell, where a unified body with only one shell, maybe a sandwich with low denisty infill, would be preferable?

Also the transition from the foot spring to the leg at the ankle might be prone to stress peaks and could also benefit from a more organic approach? There's quite some material to be saved there, too.

So, I guess your next step will be learning surface modeling. ;0)

EvanReese · January 21

Have you checked out O+P Digital Designer? It's a whole site dedicated to education on prothetic modeling. There are tutorials for a number of softwares, but I know Arthur is a skilled Onshape user and pro in the prosthetics space.

Basic Prosthesis (Very Beginner, not complex at all) opinions

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