plastic responses

plastic responses

nathan keepers

5/17/2006

Hello,
   
  Following my initial question are the responses I received. (Quite a few, so I pared them down in their content) The situation that I proposed is actually more complex than a simple leaf spring for drop foot. The patient has an undiagnosed nervous disorder that causes a tone response of rapid plantar flexion and inversion, as well as knee flexion when stimulated. Normal walking without an AFO stimulates the response. It seems that knee extension and plantar flexion are the triggers. Therefore, we are asking a lot from a PLS design. This is her choice, as she does not like the idea of a hinged AFO, and the possibilities that the posterior stop may make noise. Also limited by patient's lack of insurance, so not inclined to try too extravagant styles without knowing their longevity in her situation. We have tried a Toe-Off, that did not provide the knee extension control desired. We have experimented with different designs, and found the PLS, with reinforcement of
 the entire posterior strut to be most accepted by her and a good compromise that allows her some dorsiflexion, which is not a problem for her. This is why the AFO's have been fracturing in the posterior arch, because the reinforcement has forced all the stress to be directed here. They have been breaking every 6 months on average. She does have a solid ankle design that has given no indication of breaking for some time, but she prefers the dorsiflexion our design allows. We did try HDPE this time, and found it to be more flexible than the Polypro. This was too flexible and looked to be a failure until we added Dacron straps across the curve between the posterior strut and the sides of the footplate. This is providing the proper plantar flexion resistance and knee control, but allowing dorsiflexion. Hopefully this will result in a longer term solution due to the HDPE being less brittle than PP. We have previously tried copoly, with a Polypro strut, but had problems
 with the two bonding to each other, and the copoly was too flexibe. The strap solution may have helped with that, but didn't think of it at the time.
  ----------

  Are there any plastics that are of similar rigidity to polypro, but

not as brittle. I have a patient that has a PLS AFO that continues to

break at the posterior arch area. We have tried Copoly, which is too

flexible for her problem. She is not interested in hinged AFO's.

 Nathan Keepers, CPO

You might try using high density polyethylene
    I use a two peice AFO in cases that require rigidity in a small package. This is a difficult manner of fabrication to become efficient with. I take the copoly sheet(full size for an AFO) and lay it onto the oven tray. Cut a piece of 3/32 poly pro to extend from effected area to proximal ankle . Say if the AFO sheet is 18x24 then your polypro peice would be about 7x24. Place copoly in the oven then put the polypro directly on top of the coppoly in the area best estimated to fall around your affected area. As the plastic heats up ,it will bond together. Pull the plastic with the poly side against the cast. This insures the bonding a little better. Trim to normal and you should have a strong AFO without the problems with craking. Hope this helps.


Try Subortholen... it's tough to pull but tough to break.

-------

Put graphite ankle reinforcement in the AFO on each side
    You might want to try using a Chevron reinforcement with either PP or CP. A Chevron is an upside down Y extra piece of plastic, you chose the thickness. The upside down part of the Y goes on either side of the heel while the single piece obviously goes up the back - usually about 2/3 the OAL. It helps to skive the edges. Apply it just after the vacuum is successful. After the negative AFO is removed from the mold, you can grind it to blend very well, almost impossible to see. Here is a link to a movie. The blue is the Chevron or Chevy, they add a reinforcement to the foot section as well for a very hvy duty (armed forces running young man's drop foot) use. This was presented by a group of three Canadian COs at the best Orthotic seminar I ever attended - but I never saw it advertised again.


Have you considered laminating a poly pro PLS piece to (or inside) a

colene shell? Don Weber (Chedoke Hosp. in Hamilton Ontario) and Gord

Ruder

(Clinical Orthotic Consultants of Mississauga) have been using this

technique for several years now. Gord calls his the chevron AFO

because the

poly pro piece looks like a chevron inside the AFO. Don calls his the

Plastic reinforced AFO. - they both teach at George Brown College in Toronto.


    Nathan, you could always try HDPE. I have used it for years for various applications. Hard to say if your PLS is failing b/c of the plastic...it may be the design or maybe your pt is a very hard user. Hope this helps

    i might try a thicker poly pro, like 1/4 vs 3/16 as most of us use, just a suggestion

  You can use the 3 OR 4MM SupOrtholeen it comes of sheets 4X2 and you can order it from any Vender who sells Plastic.I use it for Soccer players and have a great result.
  
    Nathan, not sure about any plastics out there as we don't use plastic much. However we do central fabricate a pre preg carbon fiber energy return orthosis.

    Try high density polyethylene. It has a similar rigidity to polypro but it’s not as brittle and as a bonus the edges polish like polyeth

  I would recommend the copoly .You can always bring the trim lines
  forward to semi-solid then trim back until desired flexibility .Polypro is
  used FOR rigidity and if you want a PLS design you have to expect it to
  flex thus the breaking. I would suggest using 3/16 copoly placing a
  piece of parachute cord (or any material) in a 4 inch long by 3/4 inch
  wide loop along the Achilles tendon and vac it in place giving you a
  gusset to shore up the flexibility . You can really use copoly for any
  design and use gussets to increase stiffness. Experiment with other
  materials like crepe or scrap carbon laminates, just about anything will work
    You could try TPE 2. It's more comparable to co-poly than poly pro but it a little more rigid than co-poly

  Did you think of making that PLS laminated? With the correct layup, it
  can
    come out just the way you want; good flexibility, and trimlines


How about a laminated carbon AFO? Might be able to handle the stress.
  
I think Ottobock and some others have PLS version.


Maybe you might have a bad batch of polypro, or it is not of good

quality. Have you ruled this out?
    Have you considered trying Northene 500? It is a high molecular weight polyethylene, similar to subortholen. This material will provide a slight degree of extra rigidity over copolymer pp with similar impact and flexural strength. Yes, it is more expensive than our copoly pp and homopoly pp, but it may prove worth it for a one off case.

    
laminated PLS
  have you tried 3/16 copolly ????
  Try a ready preg design.
  
Sounds like you need to try a PLS AFO laminated with ready-preg or Ultra-G.




We have had good results with white Polypro. I think there is a brand

called

trovidor or something like that. I found the stuff to be virtually

indestructible.

----

We've used some HDPE or UMHW PE - both are pretty bulletproof - and

probably

a bit stiffer even than the polypro. Just a thought... It's kind of

hard to

work with after molding, and shrinks like crazy in the oven, so cut a

BIG

piece, or have two people to stretch it back out over your model!!!

--------

Can't resist suggesting you reconsider thermo-plastic PLS-AFOs,

especially

in light of repeated fractures. We have largely moved to carbon AFO's

(both

pre-fabricated and custom) for majority of patients with dorsi and/or

mild

plantar-flexion weakness. Toe-off and similar products provide similar

(and

often much improved) functional characteristics to conventional

thermoplastic PLS AFOs. If patient's needs demand plastic, stick with

poly-pro, consider flattening & widening posterior strut. Prior to

fitting

make certain plastic is bending here and not fish-mouthing at arch.

Your

AFO plastic is likely cycling/bending at the curve over small area,

probably

widening/gapping as it moves into dorsi-flexion. Ideally plastic should

cycle closer to anatomical axis/bending point more posterior &

proximal,

over flatter/longer area. PLS-type AFO should bend at posterior strut

ONLY,

stiffness should vary with coronal plane width and transverse view

curve

degree of POSTERIOR STRUT (in addition to plastic type/thickness). My 2

cents.
    Try Bock's Walk On. It has worked well for our PLS patients


I would like to suggest a different approach. I don't know your

patient,

but if she is in a PLS AFO, then I assume that some degree of ankle

movement

is desired. If not, just stop reading. I would suggest using a CoPoly

spiral AFO. This is something that we are doing more and more and

having

great success with. This is very similar to some of the carbon fiber

hybrid

AFOs however, since it is made of CoPoly, delamination is not a worry.

We

normally use 5/32 copoly for the base and top layer of the strut, but

first

lay-up a 1 - 1 1/4 medial or lateral strut of 1/4 CoPoly. The strut

extends from the plantar surface of the foot right up to the proximal

trimline. Using a wider strut increases resistance to movement and

increases DF assist and deceleration assist. We have used these

primarily

with adults who are harder on the Carbon Fiber AFOs like the Toe-Off

and the

Easy Stride. Now, I am using them lieu of the off-the-shelf AFOs, just

because they are custom and I can get more control of the foot through

my

plaster mods.
    Put a long post in the posterior just as you would with a articulating afp for extra support. Can use polypro or copoly. It does make it more rigid. 1 or more wide tapered and just below the mid calf and below just past ankle access.


Have you tried high-density polyethylene?

 
    Carbon fiber inserts






Is there a chance the ToeOFF would work? It's ultra light weight and

offers dynamic response that you customize to the patient. It may give

her the support she's looking for
    How about Carbon Composite !!!

     I've had luck with co poly with a comp core inserted in the post. section of the PLS. No breakage and good toe lift.


Did you try 3/16 co poly? I've never had flexibility problems with

this thickness


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