RESPONSES: Transtibial Modification Question
Lindsey Jastrzab
Description
Collection
Title:
RESPONSES: Transtibial Modification Question
Creator:
Lindsey Jastrzab
Date:
2/11/2013
Text:
QUESTION:
Hi List-
I've been experimenting with socket modification techniques and am curious
to see what others typically do to reduce the fit of a check socket. I'm
interested in knowing what percentage you reduce your mold by per sock ply.
For instance, if someone fits into a check socket in a 3-ply sock, how much
do you reduce the mold?
I'm curious to see what other people have found to be most successful for
an accurate fit. Any information is appreciated. Thank you in advance.
RESPONSES:
***I know this sounds silly, but I use .75% as a ply. I got that number
from a tech at Ottobock, a few years ago, and it's always worked well for
me.
***In this case, I would add the 3ply sock to the cast, take
circumferential measurements (as you would on the patient's limb), then
measure without the sock and reduce the cast the difference at each
measurement. If anything go a little shy of those numbers due to
compression of soft tissue.
***I would reduce the interface by placing the same or similar 3 ply sock
inside and using a bag or rubber/latex casting balloon, seal off the
trimline, insert a vacuum barb in the interface, pull vacuum, and then pour
w/ plaster. That way you know for sure you are getting a true 3 ply
reduction (at least for the type of sock that you used for the fitting).
***That's an interesting question and I think you should share the
responses with the list. I usually reduce the plaster model with a sureform
and it's just by a sense of feel. I find taking three passes with the
sureform, avoiding boney areas will ususally reduce it 3 ply. I put the
check socket back on as a method to check it. Of course, the best
method isusing a CAD system.
***Yes it works, and of course the idea is to provide the correct sized
sock so the user doesn’t have to pull or stretch resulting in a thinner
sock. I do use this technique if the test interface is too large. I am
almost exclusively doing passive suction or elevated vacuum TSB sockets w/
liners only, no socks. I very rarely have to use a sock in the test
interface as I hand cast under vacuum over the liner only, digitize the
interior with our TracerCad black box, modify by software and reduce
circumferentially by 4%-5% depending on tissue density. Sometimes though,
the interface comes out too big and that’s when I use my described process
to reduce.
***I've found that 2mm off each perimeter per ply for a typical TTA mold
works well. For TFA I use 3mm per perimeter per ply.
*****We will spray glue in a sock then pour to reduce the socket uniformly
while maintaining the same contours. A 3 ply sock will typically reduce the
socket to equivalent of a 5 ply after smooth it up and 1 ply will reduce 2
ply essentially after smoothing. Works really well and quick, just make
sure there is no gapping between sock and socket
***For my socket design I find that a 3-5 mm (depending on limb or tissue
type) reduction equals a one ply sock ply reduction. Good luck.
***I have put socks into the diagnostic socket and lined that with latex
ballon, then evacuated the air with brake bleeder and then filled that with
plaster.
***This may appear to make things overly complicated, but I am kind of a
precise socket fit geek, so I will share in a somewhat simplified form what
I do. As a disclaimer, although I fit them, I am not a great fan of
TSB/hydrostatic sockets, and it seems that relatively few clinicians are
doing specifically distributed pressure socket designs anymore. In my
opinion, too many prosthetists have become very lazy about socket design,
and it is too easy to hand someone a 6mm gel liner, create a generic,
reduced-by-the-numbers shape, and call it good. The patient may be
comfortable, and ambulatory, but I would like to think that we can do
better than that. I would love to do a study of this sometime, because I
believe that there are some meaningful inefficiencies with doing sockets
that way, mostly in the realm of increased energy consumption, but also
regarding balance and fine motor control. If nothing else, there is
unnecessary weight in the thicker liner, the main reason I rarely use 6mm
liners. I don't mean this as any kind of insult to you, or anyone else, but
I think that percentage reductions, which take no account of shape or
functional pressure distribution, are an inherently imprecise way of
designing a socket. They are obviously functional for a lot of amputees,
but they also rest on the assumption that all tissues are not only equally
pressure tolerant but also equally functional when loaded. If they really
believed that, there would be no reason to use the thicker liners. They are
counting on the distortion of the gel and its thickness to address socket
fit issues, and if anyone is paying attention to the functional variations,
not just patient preference and comfort, they are not publishing on it or
talking about it.
Enough pontification, and back to your question. First, the amount that I
modify out changes depending on what kind of tissue the modification is
over, and my answer assumes that there is in fact a uniform, total contact
fit. A sock compresses more over boney tissue than it does over soft
tissue, so I will modify less in the boney areas and more over soft tissue.
Using your 3 ply example, and assuming that you want to reduce to a no-sock
fit, on an otherwise average limb, I would reduce by about 2mm radially
over boney tissue and about 3mm over soft tissue to maintain the same
pressure distribution. Because of those variations I usually don't think in
terms of circumference, but if you were looking for an equivalent
circumference number, that would be 8-10mm. Another consideration is limb
size. My modification numbers will increase somewhat as the limb size
increases to obtain the same quality of fit.
As a general number, I use .8-.9mm per ply, but even that may depend on
other considerations. For instance, two 3-ply socks do not fit the same as
one 6-ply sock, but are somewhat thicker, so if I was trying to reduce a
socket from two 6 ply socks, I would reduce it slightly more than I would
for a single 6-ply sock. In this case I would remove the equivalent of
about 1 additional ply.
This may seem overly complex, and it may be, but that is my approach,
refined over the past 22 years. I have spent a considerable amount of time
with any number of new socket designs, and have incorporated various
features that seemed to be efficacious. Very few of the new designs in the
past 20 years have any kind of scientific validation to them, which does
not make them bad designs, but it doesn't give me anything even
approximately objective to compare to, and the amount of experimentation I
am going to do on my patients is limited.
Hope that this is helpful.
***5 ply equals 1/4 in reduction. 3 ply equals 1/8
***Fill the check socket with the #ply you wish to reduce it - eg if you
want to reduce fit by three ply, place aa three ply sock in empty socket
and fill sock with plaster of paris making sure sock conforms to check
socket when filled with plaster.
***I have used CAD for 20 years
Currently we use Tracer and carve models on an Art Carver
it is repeatably accurate
Just mark sure to use the minus
(-) symbol, example -3
To indicate a negative reduction of 3 ply
Each ply is valued at 0.4 mm in thickness (this is based on the Sterling
sock thickness manufactured by Knit Rite) different brands may or may not
have the same value per ply or be consistent through the range of socks
offered
Therefore -3 ply is equal to 1.2 mm in radial reduction
Using this value has proven to be successful as long as the pt was wearing
a Knit Rite 3 ply
If not, you may find the socket slightly loose or tighter but it should be
Slight one way or the other
Measure twice cut once
Be consistent with the brand of sock and apply a consistent logic
You will get a consistent result
***If you fit with a three ply sock take a .bottle can or jar about the
same size as your residual limb and measure the circ. then slide the sock
over that same bottle can or jar and measure the circ. at the same level if
the increase in circ is 3/8 of an inch then that is generally what you need
to reduce your model by. I have been using this a a guideline for 30+ years
and it hasn't failed me.
***My understanding is 1 ply=1/8 in circumference.
So I shoot for 3/8 reduction in my measurements.
***Bonding a 2 or 3 ply sock to the inner socket and casting it. Additional
proportional rectifications over the flat broad expanse of the medial tibial
flare, lateral compartment, and slight fibular shaft for stabilization are
usually required to provide optimal fit.
***In the case of a test fitting I usually measure over the sock and then
the
liner to determine the difference at several levels. That is the amount
that I remove from the model. This is all guess work anyway. I think this
method removes any formula and replaces real numbers.
***So far I've been having decent luck(?) removing the difference from a
circumference measurement with an old 3-ply on the mold. Please post your
responses as I'm very interested in what the field has to say. Thanks!
***i take a scotchcast impression not under vacuum and reduce it 4%
usually. if the patient has minimal soft tissue and small residual limb i
will reduce that number to 3% and if they are larger with excessive soft
tissue i will increase to 5%. usually ends up in a 3 ply fit. i do most
modifying by hand.
Thank you for all your responses! The variation of responses proves how
much we all differ! I appreciated the variations and ideas! Thank you!!!!
--
Lindsey Jastrzab, CPO
Prosthetic Orthotic Associates
3303 N. 75th Street
Scottsdale, AZ 85251
480-946-2286 - Scottsdale Phone
623-209-0109 - West Valley Phone
480-946-9942 - FAX
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Public commercial postings are forbidden. Responses to inquiries
should not be sent to the entire oandp-l list. Professional credentials
or affiliations should be used in all communications.
Hi List-
I've been experimenting with socket modification techniques and am curious
to see what others typically do to reduce the fit of a check socket. I'm
interested in knowing what percentage you reduce your mold by per sock ply.
For instance, if someone fits into a check socket in a 3-ply sock, how much
do you reduce the mold?
I'm curious to see what other people have found to be most successful for
an accurate fit. Any information is appreciated. Thank you in advance.
RESPONSES:
***I know this sounds silly, but I use .75% as a ply. I got that number
from a tech at Ottobock, a few years ago, and it's always worked well for
me.
***In this case, I would add the 3ply sock to the cast, take
circumferential measurements (as you would on the patient's limb), then
measure without the sock and reduce the cast the difference at each
measurement. If anything go a little shy of those numbers due to
compression of soft tissue.
***I would reduce the interface by placing the same or similar 3 ply sock
inside and using a bag or rubber/latex casting balloon, seal off the
trimline, insert a vacuum barb in the interface, pull vacuum, and then pour
w/ plaster. That way you know for sure you are getting a true 3 ply
reduction (at least for the type of sock that you used for the fitting).
***That's an interesting question and I think you should share the
responses with the list. I usually reduce the plaster model with a sureform
and it's just by a sense of feel. I find taking three passes with the
sureform, avoiding boney areas will ususally reduce it 3 ply. I put the
check socket back on as a method to check it. Of course, the best
method isusing a CAD system.
***Yes it works, and of course the idea is to provide the correct sized
sock so the user doesn’t have to pull or stretch resulting in a thinner
sock. I do use this technique if the test interface is too large. I am
almost exclusively doing passive suction or elevated vacuum TSB sockets w/
liners only, no socks. I very rarely have to use a sock in the test
interface as I hand cast under vacuum over the liner only, digitize the
interior with our TracerCad black box, modify by software and reduce
circumferentially by 4%-5% depending on tissue density. Sometimes though,
the interface comes out too big and that’s when I use my described process
to reduce.
***I've found that 2mm off each perimeter per ply for a typical TTA mold
works well. For TFA I use 3mm per perimeter per ply.
*****We will spray glue in a sock then pour to reduce the socket uniformly
while maintaining the same contours. A 3 ply sock will typically reduce the
socket to equivalent of a 5 ply after smooth it up and 1 ply will reduce 2
ply essentially after smoothing. Works really well and quick, just make
sure there is no gapping between sock and socket
***For my socket design I find that a 3-5 mm (depending on limb or tissue
type) reduction equals a one ply sock ply reduction. Good luck.
***I have put socks into the diagnostic socket and lined that with latex
ballon, then evacuated the air with brake bleeder and then filled that with
plaster.
***This may appear to make things overly complicated, but I am kind of a
precise socket fit geek, so I will share in a somewhat simplified form what
I do. As a disclaimer, although I fit them, I am not a great fan of
TSB/hydrostatic sockets, and it seems that relatively few clinicians are
doing specifically distributed pressure socket designs anymore. In my
opinion, too many prosthetists have become very lazy about socket design,
and it is too easy to hand someone a 6mm gel liner, create a generic,
reduced-by-the-numbers shape, and call it good. The patient may be
comfortable, and ambulatory, but I would like to think that we can do
better than that. I would love to do a study of this sometime, because I
believe that there are some meaningful inefficiencies with doing sockets
that way, mostly in the realm of increased energy consumption, but also
regarding balance and fine motor control. If nothing else, there is
unnecessary weight in the thicker liner, the main reason I rarely use 6mm
liners. I don't mean this as any kind of insult to you, or anyone else, but
I think that percentage reductions, which take no account of shape or
functional pressure distribution, are an inherently imprecise way of
designing a socket. They are obviously functional for a lot of amputees,
but they also rest on the assumption that all tissues are not only equally
pressure tolerant but also equally functional when loaded. If they really
believed that, there would be no reason to use the thicker liners. They are
counting on the distortion of the gel and its thickness to address socket
fit issues, and if anyone is paying attention to the functional variations,
not just patient preference and comfort, they are not publishing on it or
talking about it.
Enough pontification, and back to your question. First, the amount that I
modify out changes depending on what kind of tissue the modification is
over, and my answer assumes that there is in fact a uniform, total contact
fit. A sock compresses more over boney tissue than it does over soft
tissue, so I will modify less in the boney areas and more over soft tissue.
Using your 3 ply example, and assuming that you want to reduce to a no-sock
fit, on an otherwise average limb, I would reduce by about 2mm radially
over boney tissue and about 3mm over soft tissue to maintain the same
pressure distribution. Because of those variations I usually don't think in
terms of circumference, but if you were looking for an equivalent
circumference number, that would be 8-10mm. Another consideration is limb
size. My modification numbers will increase somewhat as the limb size
increases to obtain the same quality of fit.
As a general number, I use .8-.9mm per ply, but even that may depend on
other considerations. For instance, two 3-ply socks do not fit the same as
one 6-ply sock, but are somewhat thicker, so if I was trying to reduce a
socket from two 6 ply socks, I would reduce it slightly more than I would
for a single 6-ply sock. In this case I would remove the equivalent of
about 1 additional ply.
This may seem overly complex, and it may be, but that is my approach,
refined over the past 22 years. I have spent a considerable amount of time
with any number of new socket designs, and have incorporated various
features that seemed to be efficacious. Very few of the new designs in the
past 20 years have any kind of scientific validation to them, which does
not make them bad designs, but it doesn't give me anything even
approximately objective to compare to, and the amount of experimentation I
am going to do on my patients is limited.
Hope that this is helpful.
***5 ply equals 1/4 in reduction. 3 ply equals 1/8
***Fill the check socket with the #ply you wish to reduce it - eg if you
want to reduce fit by three ply, place aa three ply sock in empty socket
and fill sock with plaster of paris making sure sock conforms to check
socket when filled with plaster.
***I have used CAD for 20 years
Currently we use Tracer and carve models on an Art Carver
it is repeatably accurate
Just mark sure to use the minus
(-) symbol, example -3
To indicate a negative reduction of 3 ply
Each ply is valued at 0.4 mm in thickness (this is based on the Sterling
sock thickness manufactured by Knit Rite) different brands may or may not
have the same value per ply or be consistent through the range of socks
offered
Therefore -3 ply is equal to 1.2 mm in radial reduction
Using this value has proven to be successful as long as the pt was wearing
a Knit Rite 3 ply
If not, you may find the socket slightly loose or tighter but it should be
Slight one way or the other
Measure twice cut once
Be consistent with the brand of sock and apply a consistent logic
You will get a consistent result
***If you fit with a three ply sock take a .bottle can or jar about the
same size as your residual limb and measure the circ. then slide the sock
over that same bottle can or jar and measure the circ. at the same level if
the increase in circ is 3/8 of an inch then that is generally what you need
to reduce your model by. I have been using this a a guideline for 30+ years
and it hasn't failed me.
***My understanding is 1 ply=1/8 in circumference.
So I shoot for 3/8 reduction in my measurements.
***Bonding a 2 or 3 ply sock to the inner socket and casting it. Additional
proportional rectifications over the flat broad expanse of the medial tibial
flare, lateral compartment, and slight fibular shaft for stabilization are
usually required to provide optimal fit.
***In the case of a test fitting I usually measure over the sock and then
the
liner to determine the difference at several levels. That is the amount
that I remove from the model. This is all guess work anyway. I think this
method removes any formula and replaces real numbers.
***So far I've been having decent luck(?) removing the difference from a
circumference measurement with an old 3-ply on the mold. Please post your
responses as I'm very interested in what the field has to say. Thanks!
***i take a scotchcast impression not under vacuum and reduce it 4%
usually. if the patient has minimal soft tissue and small residual limb i
will reduce that number to 3% and if they are larger with excessive soft
tissue i will increase to 5%. usually ends up in a 3 ply fit. i do most
modifying by hand.
Thank you for all your responses! The variation of responses proves how
much we all differ! I appreciated the variations and ideas! Thank you!!!!
--
Lindsey Jastrzab, CPO
Prosthetic Orthotic Associates
3303 N. 75th Street
Scottsdale, AZ 85251
480-946-2286 - Scottsdale Phone
623-209-0109 - West Valley Phone
480-946-9942 - FAX
********************
To unsubscribe, send a message to: <Email Address Redacted> with
the words UNSUB OANDP-L in the body of the
message.
If you have a problem unsubscribing,or have other
questions, send e-mail to the moderator
Paul E. Prusakowski,CPO at <Email Address Redacted>
OANDP-L is a forum for the discussion of topics
related to Orthotics and Prosthetics.
Public commercial postings are forbidden. Responses to inquiries
should not be sent to the entire oandp-l list. Professional credentials
or affiliations should be used in all communications.
Citation
Lindsey Jastrzab, “RESPONSES: Transtibial Modification Question,” Digital Resource Foundation for Orthotics and Prosthetics, accessed November 1, 2024, https://library.drfop.org/items/show/234742.
