This page contains information about Bracing.
Subject: Carbon fibre braces??
From: Steve's Account
Many new braces are being made of carbon fibre.. It's got a number of advantages...
1) It's about 3 times as strong on a pound for pound basis than steel.
2) It can be both light and rigid.
3) it can be molded into complex shapes.
As a material for making braces, it has lots of advantages over "metal and leather" or "plastic" (polypropylene).
The metal and leather versions are heavy, bulky, and since they contact the leg in just a few places, the loads at each of those points when providing an effective "counter force" can be quite high.. (compared to the same load spread over the total contact area of the inside surface of carbon fiber molded brace.)
Polypropylene will "creep" over time, trying to return to it's original "flat" shape meaning that the fit will change over time.. This is worse on tight curves or at high temperatures.
It's caused by the way braces are made. The plastic comes in large sheets. Those sheets are cut to the approximate size, heated in a large oven, (like a pizza oven) and then the hot, saggy plastic is quickly draped over a plaster mold of your leg. The technician quickly wraps the plastic around the mold, seals the edges together, and opens a vacuum valve to pull the plastic closer to the plaster mold. As the plastic touches the mold, it cools quickly, and "freezes". The inside of the plastic, nearest the mold, cools first, and then the outside. This leaves internal stresses in the plastic, which over time, will cause the plastic to try to return to "flat".
This effect is slow.. but it will cause a snug fitting brace to become "loose" over time, loosing it's ability to maintain your leg in it's correct possition.
Since carbon fibre is a "fabric" which is soaked with epoxy resin, none of the internal stresses are manufactured in a carbon fibre brace when it's made.. It's high rigidity also helps maintain it's shape under load.
Polypropylene has some advantages, though.. it can be adjusted with a heat gun.. once the expoxy in a carbon fiber brace hardens there is no "adjusting it".. if it's not perfect, you must either grind some away or re-make it. If you grind some away, you make it weaker... and it only works if it was too tight.. not too loose!
http://www.beckeroregoncatalog.com/pg0009im.jpg
Here's an example of some of the types of braces that can be made from carbon fiber with metal joints laminated in.
Here's some polypropylene versions.. Notice the gray area around the ankle of the one in the middle.. That's a laminated in strip of carbon fiber to make the ankle stiffer and more resistant to cracking.
http://www.beckeroregoncatalog.com/pg0016im.jpg
Because the carbon fiber version is so thin and strong, you can often get away with just a "dr. sholls" type cushion in the oppsite shoe to equalize the length. You also have a wider selection of shoes since they don't have to be so much wider to accomodate the brace insert in your shoe.
If you don't need the "total contact" to control the position of your leg in the brace.. they can be VERY light and thin..
http://www.beckeroregoncatalog.com/pg0013im.jpg
Another down side of carbon fiber is... if you ever do succeed in overstressing the shell (VERY HARD to do..!!!) it will "fail" suddenly as opposed to "bending out of shape more slowly" like polypropylene will... Carbon fiber "splinters" like a shattered piece of wood if you manage to over stress it.. but.. because of it's immense strength you'd have to do something VERY DRASTIC to ever get it to fail.
Notice that in the laminated carbon fiber versions, there are no rivits attaching the "plastic" to the metal uprights.. Rivits have almost always been the cause of my brace failures.. either by weakening the metal side bar at the rivit hole.. or by the rivit itself breaking..
Steve
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Subject Re- KAFO Brace Alternatives
From Gillian Thomas
Hi
I thought that those interested in this topic might like to read some
articles published in our newsletter, Network News, over the last few
years.
I have extracted the relevant pages and uploaded them to our website
(PDF format). Just click on the links below to download them.
http://www.post-polionetwork.org.au/news/NN_58_pp3-10.pdf
http://www.post-polionetwork.org.au/news/NN_73_pp9-18.pdf
http://www.post-polionetwork.org.au/news/NN_78_pp6-7.pdf
Cheers
Gillian
Gillian Thomas
President
Post-Polio Network (NSW) Inc
Sydney, Australia
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