2 liners summary

2 liners summary

Gary M. Berke

3/19/1999

The following is a summary of the two liners techniques that are available.
It is clear that no matter which method you use, the exactness is variable
and the technique complex. I will repost any future responses to this
issue. Thank you all for your comments and time. gb
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What I have done in this situation is to make two inserts (one at a time).
When forming each insert I would use indirect vacuum - heating and pulling
the
liner over the cast and then pulling a heavy weight plastic bag over the
liner
and evacuate the air, using a vacuum pump- to mold each Liner to the same
cast. I then use a latex balloon ( a lubricated condom works well) over the
liner and then do a bi-valved impression of the liner on the cast. Pouring
and smoothing this impression form over the cast does two things: it allows
you to laminate/vacuum a definitive socket or check socket; it also allows
you
to have the original model for doing future inserts.
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We just replaced soft interface liners on an existing bilateral
B/K Transtibial today and all of our B/K's are designed with thermoplastics.
Therefor the liners thermoformed into there final state with the
simultaneous
application of heat a pressure at the same time. (Not like laminates where
heat occurs after the resin begins to set.) In our case we find it
necessary
to waste a sheet of thermoplastic to duplicate the liners more
appropriately.

If you are using thermoplastic rigid interfaces I would suspect you would
have
to do the same if making 2 sets and your goal were to have the best
possible
match.

It has been 25 yrs. + since we have used a laminate for a rigid B/K
interface.
The technique we used then for the duplication of liners was to apply vacuum
with a heavy plastic bag over the pelite liner and positive model. I never
had a problem with this approach either.
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Skive a distal end pad and skive a pelite cone. Cut the cone 2 above the
socket. Heat the distal end pad and set it in the socket. Use a bag with a
stockinette (end sewn) over it, put into socket and add compressed air(allow
some air to leak out top:) to expand the bag forming the distal end pad. Do
the same for the pelite cone and glue the two pieces together. You may have
to reheat for the posterior wall. Takes about 20 minutes. Let me know how
it works if you try it.
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Most of the time it is the VA who requests 2 liners, I personally find this
a
waste of money as that by the time the first one wears out the prosthesis
does
not fit any more. I try to only fab 1 liner when presenting my quote but
they always ask for 2. No one wants to listen to lowly me. In response to
2
liners. The change in liners occurs because the original is compacted by
heat
and pressure. I don't disagree with Bob's recommendation I just take it one
step more and use scrap plastic to pull over the 2nd liner. This works well
for us. I'm curious to see other suggestions.
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his may be something you already tried. When you cut the socket off the
cast, leave the trimlines long. After breaking up the cast, use vaseline to
coat the inside of the liner. Fill the liner with plaster while holding the
liner in a bucket or sink filled with water. The water pressure keeps the
plaster from distorting the shape of the liner. Add a mandrel to the
plaster
and then use an air hose under the liner to blow it off the new cast. Fab a
new liner over this cast. Blow the new liner off and cut both liners to
trimlines. Hope this helps.
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What I have done in the past was to try to make every piece, every glue line
exact right down to the finished liner, prior to laminating or forming.
Once
at this point, which you are probably already doing, place the liners, one
at
a time, on the cast as if you are about to laminate or form over them. I,
then, apply a PVA bag and cap and introduce vacuum. Then, using a heat gun,
heat the liner carefully and evenly. Remove the liner you will be issuing
as
a spare and do the same to the next. Proceed to either laminate or form
over
the second liner.
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Using prefabricated pelite cones can help reduce the inconsistencies but
isn't the entire answer.
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Gary M. Berke MS, CP
Clinical Instructor, Orthopaedic Surgery
University of Oklahoma
<Email Address Redacted>