Summary: Transtibial casting techniques, Part 1

Summary: Transtibial casting techniques, Part 1

Ben Lucas

7/17/2007

Dear list,

Thank you for all the great responses to my question on TT casting
techniques. I received a lot of great feedback regarding this topic. Below
are summaries of the responses given to me about this subject. Some of the
emails have been edited due to personal comments or requests to be not be
published. To keep this down to manageable size, you will be getting two
volumes.

Thanks for all of your help,

Ben Lucas, MS, CO, prosthetic resident


As an amputee with a long, mature (not fleshy) residual; I have found what
works best for me is the 2 stage method over the liner I will be using. We
use an anterior panel to capture to boney prominences followed by a
circumferential wrap. By the way, I use a sealing seal and one way valve for
suspension.

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Our office has used the gamut of casting techniques over the years and not
one stands out as the only way to go with transtibial impressions. My
personal favorite though is the old Fillauer 2-stage impression technique
whereby the anterior layer is applied and set prior to wrapping the
remaining part of the limb. Now, for vacuum sockets and
when laid on plaster impressions are used, we use this same technique with
vacuum applied, as per Carl Casper's instructions. This makes the most sense
to me, although there are prosthetists who believe that molding the shape as
you go is a valid and useful technique. Personally, I think this is more old
school technology and one that is more
difficult to teach, much like the MAS transfemoral socket that Marlo Ortiz
teaches. It is also very subjective as to where pressure should and should
not be applied. We rarely use supracondylar sockets anymore so the
techniques above do not include those, but I suppose they would work. Also,
with exception of Symes, these techniques do not use any
weight bearing while taking the impression. Finally, I do not use elastic
plaster for any molding technique except for those transfemoral cases that
require a hand impression and then it is only the most proximal section. To
use elastic plaster as it was designed, the water needs to be warm enough to
shrink the wet plaster roll prior to starting a wrap. This is what gives it
the elastic stretch. I have seen many prosthetists who do not do this and
it then basically becomes a more flexible roll of plaster, albeit much
weaker than the non-elastic type. Properly rolled, a non-elastic roll of
plaster can capture virtually any shape or undercut that is required. Hope
this helps with your project.


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elastic. reason being, it shrinks some when it hardens, thus giving a tad
snugger impression. no panels, no two stage. i was shown how to do it
canadian way (it is described in CAPO book on lower extremity prosthetics)
and since then i have no trouble with casts. all i do differently is to have
palms of my hands really snug on condyles, to approximate ML as much as i
can, as it is very hard to modify in positive. that results in extra soft
tissue squeezed out in the popletial, but that does not matter as it's being
shaved off to get AP anyways and there's no bony anatomy to violate. i'll do
fiberglass only on really large transtibials, when anatomy is vague and
pretty much is carved in into the positive. otherwise, fiberglass is just
not pliable enough. i have seen very, very nice impressions done over
casting balloon.


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My casting technique depends on the type of prosthesis I'm making (TSB vs.
PTB vs. VASS, etc.). In general, I do an anterior panel, then a wrap of
elastic, followed by a wrap
of rigid plaster when hand casting. I do not use fiberglass to cast BKs.
 If I am doing a Vaccuum or pressure cast things are different because my
hands are not in contact with the plaster. With patients who get
significant elongation when wearing a gel liner, I cast with the limb
distracted by pulling at the pin site with between 6 and 8 lbs of force.
Measurements are taken in this state as well. There is a wide range of
casting methods that may work for the same patient. It would be interesting
to see how widely varied casting techniques are across practitioners, and
how much of a role their length of practice, place of schooling, and place
of clinical training influences their choice of technique.

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You can pick up a complete fingerprint, hold body parts in the same position
or patella indentation by compressing it with your fingers and then the
vacuum will hold it, and
its much faster because the excess water is vacuumed out which causes it to
cure faster. Also you can apply the plaster wetter to get a more conforming
cast and still get a faster cure because the water is vacuumed leaving the
plaster cream. You will want to use the filmiest plastic you can find for
bagging it like a dry-cleaning bag. The entire problem with casting is not
the technique but the practitioners personality and hands. Take a piece of
round foam and see how each person compresses it differently. The
thagomizers squeeze the hell out of it. The deformed, twist the hell out of
it. The big hands strangle it. The little hands elongate it. To be an
accurate caster you need to get yourself out of the loop. Vacuum does the
best so far because the vacuum provides uniform pressure everywhere,
naturally, if you simply lay the bandages on and let it do its own thing.
 As a new practitioner you will be more successful and others more
frustrated. In prosthetics, people learn through trial and error by person
A taking a perfectly round cylinder and making it oblong and then adding
plaster later to make the almost round shape, while person B makes it into a
square and then adds plaster to make it almost round
again. Why bother? The practitioners who learned it this way may,
possibly, unlikely, will still add their personality to a vacuum cast and
still try to corrected it back to the original shape. Or they will take a
pure vacuum cast without their personality in it and try to modify it the
way they would do their old casts. A set in their way practitioner would do
well to use vacuum without personality, make a check socket and compare that
to a regular personality cast with clear check socket and think about the
differences or let the patient decide.


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I hand cast, usually with one roll of elastic bandage and then one or two of
rigid. If the limb is atrophied and boney, I will use more than one stage,
but otherwise just the one wrap has given me successful results.

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On casting my eval. leads me to the type of design of socket, and cast
technique. On manufacturers liners I will try to abide by suggested use
guidelines to not void any warranties. On fleshy limbs with no bony
prominences I will use a wrap cast synthetic or plaster. On all other types
I will use vacuum and at least a two stage using plaster bandage. For my
prosthetic casts I always use plaster. It is interesting that new patients
whom have had prostheses before ask me why I take measurements over the
limb, and also the limb liner. I am always surprised by their statements.
It tells me that most people just take a cast without measurements and they
trust the cast. I would like you to include the question in your survey of;
Do you cast and proceed without measurements trusting your cast?, and if
yes to the first question then ask, When do you decide it is important to
take circumference,linear, M-L andA-P measurements?. Like I said, patients
who have been elsewhere seem to think the other prosthetist's should have
recorded this valuable information after they have observed me doing so.