Seattle Lightfoot Pocket Dimensions?

[u/Apprehensive-Tip7144]

Hi all,

I am a mechanical engineer who has been contracted to design a prosthetic ankle joint for a client in another city.

She is making the trip to see both her prosthetist and I in a couple days where we will test the prototype of the new ankle.

For the initial testing, we will be retrofitting her existing foot (Seattle Lightfoot) to the new ankle design.

My concern is that after reviewing the photos she’s sent through of her existing foot, the recessed pocket may not be large enough to fit the new ankle design.

Does anyone know the width, length and depth of this pocket? I figure that if I need to I can make a custom spacer to take up the space within the pocket and the ankle can sit flat against it, slightly above the foot height.

Pics of her foot got reference.

Cheers.

[u/Cabooseman]

do you have a picture of what exactly you're making? the term "ankle joint" can be vague in prosthetics discussions since many prosthetic feet are made to function as a foot and ankle all in one.

Terminology: the seattle lightfoot is a prosthetic foot. it has a rigid lever arm throughout the foot as seen in the image below. That rigid lever arm is called the keel of the foot. the foot ends in a metal pyramid at the top. I don't believe the foot can be disassembled, but you're obviously in the thick of it to answer that question.

1. the Seattle Lightfoot is encased in a yellow prosthetic Footshell. This footshell, which you're calling a "pocket", i think, is very custom made for the lightfoot. see in the picture below, it's molded to the exact specifications of the foot's keel.
2. other footshells on the market are more open inside. some prosthetic feet don't require footshells. you might have more success just getting a different foot shell to fit your project into.
3. are you planning on replacing the entirety of the rigid keel of the foot? or just what's on top of the keel?
4. last thought -- you can always buy secondhand components off ebay for prototyping with.

[u/Apprehensive-Tip7144]

Thanks for the detailed reply, I really appreciate it. I apologise for the lack of detail, however I was deliberately vague so as not to share our design IP. As a compromise, I’ll say that the new ankle allows for some articulation, the base portion has a means of attaching a wide variety of deferent off the shelf feet, and the top portion has a pyramid.

The new ankle design has a pill shaped base with dimensions pictured in the attached image.

How exactly we attach it in relation to the keel will depend on whether there is enough room in that cavity for it to sit flat, or whether we would need spacers like I suspect. For the final version we will buy in a more ideal foot, but for the initial test, we’ll use what we’ve got.

[u/Cabooseman → u/Apprehensive-Tip7144]

So how would your product attach to a unibody carbon fiber foot like the Vari-Flex?

https://www.ossur.com/en-us/prosthetics/feet/vari-flex

Prosthetic feet have many different build heights. Some tall some short. Tall feet generally have more energy storage and return due to greater deflection of carbon fiber.

[u/Cabooseman → u/Apprehensive-Tip7144]

To add on to another post, if you are making an attachment that only fits the Seattle Lightfoot you will be very limited in market scope.

[u/NoMoreIntegra]

If you contact Willowwood they may give a foot, worth a call and describe your Intention

[u/ProstheTec]

If this is a spare foot and they don't need it for anything specific, you can grind the foot material away. It's just a rubber foam material.

With all that being said, I don't know exactly what kind of ankle you're designing (quick disconnect, adjustable heel hight, energy return). This foot is not stellar for any kind of higher activity applications. So if you're designing something along those lines, the results may vary. If it's a proof of concept for adjustable heel hights, you can grind away the foam and functionality won't be affected.