Results: Socket Shape from Ball Bearings

Results: Socket Shape from Ball Bearings

Gerald Stark

7/2/2008

Dear List Serv,

Thanks to everyone who replied to my question. Below are the results
for anyone else who was interested. I kept the comments anonymous to
protect the innocent.

Regards,

Gerry Stark, CPO/L, FAAOP


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Try reading from cover to cover Human Limbs and Their Substitutes
by Klopsteg and Wilson. It should put to rest at least this old O &
P myth for you.

You may want to check with our old friend Dr Wu on the ball bearing
casting method. He developed a sand casting dilatancy casting method
and did a lot of background research.

There was just an article in a recent issue of O&P edge or business
news or one of those publications (I can't remember which one) where
a group from MIT was using a similar method in 3rd world countries.
Im not sure if that info helps, but you may be able to find it if you
have some copies laying around

There is a similar technique used for wheelchair supports, where you
place foam beads in a plastic bag and conform around patient's back.
When vacuum is applied to bag the form becomes rock hard and can be
poured with plaster as long as the vacuum is on.

I remember my Dad telling me about a electromagnetic bucket with fine
ball bearings that was used to take BK impressions by having the
amputee insert his residual limb in an electromagnetic bucket. The
prosthetist would then pour the ball bearing around the residual limb
apply current and freeze the ball bearing in place, remove residual
limb and pour a plaster mold. I think it was 1920 to 1930. I have
no documentation. You might do a patent search.

I was introduced to that one by Steve Stolberg, nothing
authoritatively, just a passing comment. Tim Staats would probably
be an excellent resource one to ask. I'll run this by some of the
folks I've been interviewing for the library.

I have not heard of ball bearing being used but I have heard of sand
being used. The patient is placed in a pillar of sand that has air
being blown into it. After the patient is in the sand the top is
sealed than a vacuum is pulled. The patient is removed but because
the sand is still under vacuum the shape is maintained.

I have not seen it for prosthetics but for foot orthotics. It was in
the old red orthotic atlas. If you can find a copy of that book you
will find it. I believe the Atlas was published in the fifties.

I remember the great Gunter Gehl telling us that the Quad socket came
from that experiment. I hope thats where I heard it, I often quote
him when talking about socket shape development, during in-services.

Is this where Dr. Woo got the sand/vacuum concept?

  I remember hearing the same thing. It apparently involved a
variation on the dilantency (spelling?) technique. There was a
development about this time from Dundee Scotland called the Dundee
Socket involving dilantency casting.

I hadn't heard of ball bearings, although it sounds theoretically
possible. I do know you can use Styrofoam balls and a vacuum. There
are seating systems using this technique to capture the body shape.
30 odd years ago we used a garbage bag with Styrofoam ball to capture
torso shapes instead of casting for TLSO. Person lays on the bean
bag and we draw a vacuum holding all the balls in place. Pt gets up
and the depression formed was filled with plaster. We then LAMINATED
TLSO, talk about stone-age. Worked okay. I would think that having
a sealed plastic bag filled with dense Styrofoam balls to which a
vacuum hose is attached is much more manageable then a container of
steel bearings and the strong electro magnet needed to capture a
shape. You should look into the companies making custom wheelchair
seats.

I also heard about a sand casting system used in elsalvador that
sounds pretty cool, I think RIC developed it?

I did hear rumors of that at one point. It was an offshoot of a
discussion about using the sand-casting method. Ever since I’ve been
daydreaming about using that magnetorheological fluid stuff (the iron
filings in silicone oil) for the same purpose. Imagine if a computer
could track the position of each particle and even shift it around a
little. You could digitally modify your negative, pour an MR positive
and laminate over that instead of plaster. Switch off the magnet and
pour it out. Some potential there.