Reduction Values Responses Part I

Reduction Values Responses Part I

LEOPOLDO FUENTES, CPO

10/26/2011

Hi to all, thanks for the responses I received regarding the post on
reduction values. Seems like there is no formula but some sent interesting
and useful information. Here is the original post followed by the answers.

 

QUESTION:

 

What would be the circumferential reduction on an transtibial mold in terms
of % to reduce the thickness of a 3 ply sock or a any other number of plies?

Is there any formula that we can use?

 

RESPONSES:

 

________________________________________________________

 

1 ply equals 1/8

 

_______________________________________________________

 

That is really hard to say. If the person is soft then I start with 6% at
at 1 inch under MTP down to 0. If not soft then start with 5%. That
produces a socket without any socks or only a fitting sock. Not exactly
what you asked, I know.

Generally a single ply value is considered to be roughly .015 inches or
metric 0.380 mm.

Looking at a diameter it would be divided in half circumferentially to
achieve the desired change.

_______________________________________________________

 

2mil per ply as far as I understand

 

_______________________________________________________

 

I would think the percent would change depending on size of limb. I do think
it would stay constant. ?

_______________________________________________________

 

Eddy,

 

If you assume the socket is a circle and the limb is a solid cylinder of
non-compressible material and the sock is also the sameŠ it is pretty
simple.

The circumference is the diameter multiplied by 3.14 so if you changed the
diameter by adding a sock (the thickness of the sock X2) you can take the
current circumference divide by 3.14 to get the current diameter, reduce
that by the sock thickness (x2) then multiply the new diameter by 3.14 to
get the new circumference.

 

Example:

 

Current circumference 10

Current diameter 3.18 (10/3.14)

Sock thickness .04 (X2 = .08)

New diameter 3.10

New socket circumference 9.75 (3.10 X 3.14)

 

The issue with this is the assumptions of the circle are not true and the
limb and the sock are not solid.

It can still give you a point of reference though.

 

_________________________________________________________

I would recommend you visit 'oandptech.com'. Under the prosthetic tab,
scroll down to the 'suction reduction' thread. Hope this helps. If you need
clarification, e-mail me at <Email Address Redacted>

_____________________________________________________

 

There is no formula that I know of that relates sock ply to percentage
reduction because a sock ply is a constant thickness whereas its relative
percentage of total thickness in relationship to overall volume is based on
the circumferences of the residual limb. I.E. a 3% reduction on a
circumference that is 100 cm is quite different from a 3% reduction on a
circumference of 200 cm. It is generally accepted that 1 ply of sock is
about 1/8, so if you were reducing 3 ply you would reduce your
circumferential measurements by 3/8 globally.

 

____________________________________________________

 

Mr Fuentes,

 

I have looked into this very complicated question and this is what I found.

 

I my opinion a % reduction is not adequate in that a % is relative to the
size of the model and a sock is consistent*

 

I use a radial reduction value. I am using CADCAM so its consistent.

 

Interestingly, not all socks are the same. A 3ply from company X might
measure .99mm per ply while a 3 ply from company Y might measure 1.2mm. I
measured two different manufactures 3 and 5 ply socks and got different
values. I used calipers to measure the thickness of ply for different socks.
for example I measured .33mm per ply for a Comfort AG Brand so 3ply would be
.99mm radial reduction on the model. I have found this to be quite accurate
clinically as I can easily do a global reduction with CAD and fit a new
socket.

 

Its my opinion each sock model must be measured because they vary.

 

*There are other variables to consider as the tighter the sock the more it
thins out..

 

I hope this helps...

 

 

Eddy Leopoldo Fuentes, C.P.O.

CLINICAL DIRECTOR

Diabetic Solutions, Corp.

Urb. Flamboyan Calle 3 D9

Manati, PR 00674

 

Office Phone: 1-787-884-3382

Fax: 1-787-854-2000

Cel. 1-787-317-7525

 

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<Email Address Redacted>

 

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