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mtwiste33
07-24-2006, 10:59 PM
Dear Rabinder

When the alignment of a residuum in the frontal plane is being considered, and in
particular a varus angulation, then it is important to precisely define what is meant by
a "varus residuum". As you know, genu varus referrs to bowlegs. So, when you talk
about a varus residuum, there are two ways of looking at this.

1) Do you mean that, like in bowlegs, the knee deviates away form the body's midline,
so that the distal end of the residuum is turned towards to the body's midline, and is
hence adducted?

or

2) Do you mean that, like in knock knees, the knee turns towards the body's midline,
so that the distal end of the residuum deviates away from the body's midline, and is
hence abducted?

Let's assume scenario 1) is present, then the pylon would need to be turned, so that
its distal end is moved laterally, thereby adduction the socket, or abducting the pylon.
The goal during this alignment procedure is to ensure that the pylon is vertical during
mid stance. If this was achieved, then the inversion / eversion alignment of the foot
should be in neutral, so that the foot is flat on the ground during mid stance.

However, although the pylon may be vertical and the foot flat on the ground, the fact
that the socket was adducted to follow the adduction angle of the residuum means
that the distal end of the socket is closer to the body's midline, so that the pylon, even
though it is vertical, is now also closer to the body's midline. Consequently, the pylon
would have to be linearly shifted laterally (equal amount of translation at its distal and
proximal end), or the socket linearly shifted medially, in order to restore an
acceptable walking base (or width).

I hope that this clarifies matters.

Cheers.

Martin

Dr Martin Twiste BSc, PgCert, MSc, PhD
Lecturer
Directorate of Prosthetics & Orthotics
University of Salford
Manchester M5 4WT, England
Tel: 0161 295 7029
http://www.healthcare.salford.ac.uk/prosthetic/
http://www.healthcare.salford.ac.uk/crhpr/



Date sent: Mon, 24 Jul 2006 03:02:07 -0700
Send reply to: Rabinder Sahni
From: Rabinder Sahni
Subject: Re: [BIOMCH-L] Prosthetic foot alignment
To: BIOMCH-L@NIC.SURFNET.NL

Dear Martin Twiste

I am glad to read your response to Chi Wei TAN of NUS
however when it comes to actual practical evaluation
it all depends on background experience.

How would you describe theoretical Prosthetic foot alignment,
when the the subject a unilateral bk amputee has
a severe varus stump.

Best Regards
Mr.Rabinder Sahni
Prosthetics R&D,Designer lower limbs,Self user
INDIA

Martin Twiste wrote:
Dear Chi

If you are looking for a relationship between socket angle and foot
angle, then you need to distinguish between the following two aspects:

1) Changes in socket angle that occur during gait due to motion of the
residuum (i.e. the changes from backward to forward leaning of the
residuum / socket from heel strike to push off, respectively) - in
this case the angle between the socket and shank (often also referred
to as pylon) remains the same.

2) Changes in socket angle that occur during alignment changes (i.e.
the changes from backward to forward leaning of the residuum / socket
from extension to flexion of the socket, respectively) - in this case
the angle between the socket and pylon changes.


When you refer to any changes in socket angle (may that be due to
aspect 1) or aspect 2)), then it is import to distinguish between:

a) Changes in socket angle and the resultant foot angle (without
sufficient force applied through the pylon to passivley move the
foot).

b) Changes in socket angle and the compensatory changes in foot angle
that are required in order to leave the foot flat on the ground.


In my explanations that follow, I will assume that we are dealing with
situation a) (from which you can obviously derive situation b)). Also,
I just want to reinforce what certain angle changes mean: backward
leaning of the socket / residuum / pylon implies that their proximal
end is posterior to their distal end, whereby forward leaning of the
socket / residuum / pylon implies that their proximal end is anterior
to their distal end.


Regarding aspect 1):

If the residuum / socket is leaning backward at heel strike, then the
foot would appear to be dorsiflexed. The reason why the foot would
only appear to be dorsiflexed is because its angle relative to the
pylon has not changed (unless sufficient force is applied through the
pylon to passivley plantarflex the foot). The toe part of the foot is
up in the air (and heel on the ground) simply due to the backward
leaning pylon.

Conversely, if the residuum / socket is leaning forward at push off,
then the foot would appear to be plantarflexed. The reason why the
foot would only appear to be plantarflexed is because its angle
relative to the pylon has not changed (unless sufficient force is
applied through the pylon to passivley dorsiflex the foot). The toe
part of the foot is on the ground (and heel and in the air) simply due
to the forward leaning pylon.


Regarding aspect 2):

If the residuum / socket is leaning backward or forward due to
extension or flexion of the socket relative to the pylon,
respectively, then the main reason for making adjustments in this way
is because of the natural angle of the residuum relative to the thigh.
Extending or flexing the socket to maintain the natural angle of the
residuum relative to the thigh is aimed at keeping the pylon vertical
during standing and during mid stance phase for amputees with a
hyperextended knee or flexion contractures, respetively. As the pylon
is supposed to stay vertical during standing and during mid stance
phase, the foot would therefore be in a plantigrade position (no
dorsiflexion or plantarflexion).

However, if the socket is, say, extended relative to the pylon and the
socket is held straight relative to (or in line with) the thigh, then
the pylon would be leaning forward, and the foot would appear to be
plantarflexed. Like in the explanation regarding aspect 1), the reason
why the foot would only appear to be plantarflexed is because its
angle relative to the pylon has not changed (unless sufficient force
is applied through the pylon to passivley dorsiflex the foot), but in
order to achieve foot flat, the foot would need to be dorsiflexed.

Conversely, if the socket is, say, flexed relative to the pylon and
the socket is held straight relative to (or in line with) the thigh,
then the pylon would be leaning backward, and the foot would appear to
be dorsiflexed. Like in the explanation regarding aspect 1), the
reason why the foot would only appear to be dorsiflexed is because its
angle relative to the pylon has not changed (unless sufficient force
is applied through the pylon to passivley plantarflex the foot), but
in order to achieve foot flat, the foot would need to be
plantarflexed.


Finally, while the socket is held straight relative to (or in line
with) the thigh, as extension and flexion of the socket relative to
the pylon makes the pylon lean backward and forward, respectively,
this therefore not only changes the angle of the foot relative to the
ground, but it also changes its position on the ground, and therefore
relative to the centre of mass (COM) of the amputee. Positional
changes of the foot consequently change the location of the centre of
pressure, which, in turn, affects the ground reaction forces (GRFs) as
these also change position relative to the COM. In addition,
positional changes of the GRFs can affect the stability of lower limb
joints, and in particular the knee joint.

Conclusively, angle changes of the socket should not be considered an
equivalent to angle changes of the foot.

I hope this helps.

Cheers.

Martin

Dr Martin Twiste BSc, PgCert, MSc, PhD
Lecturer
Directorate of Porsthetics & Orthotics
University of Salford
Manchester M5 4WT, England
http://www.healthcare.salford.ac.uk/prosthetic/
http://www.healthcare.salford.ac.uk/crhpr/



----- Original Message -----
From: "Tan Chi Wei"
To:
Sent: Thursday, July 20, 2006 4:04 PM
Subject: [BIOMCH-L] Prosthetic foot alignment


Hi All :



I am a student and am new here. I learnt about Biomch-L after one of
my professors sent me an email regarding a topic of interest.



I am writing in today to find out how many people would agree with me
in the following:



In the alignment of the prosthetic foot, dorsiflexion was the most
important alignment change (ref: Fridman, Ona and Isakov; P&O
International 2003, 27. 17-22)

Would you agree if I say extension of a BK socket is actually
equivalent to dorsiflexion of the prosthetic foot and that flexion of
the BK socket is equal to plantar flexion of the prosthetic foot? I
say this because during mid stance, the shank is to be perpendicular (
or close to) to the floor. Therefore, if a BK socket is flexed, shank
perpendicular to the floor, then the foot will have to be plantar
flexed. Vice versa.



Open for comments.



Thanks

Chi Wei TAN

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