Articulating Ankle-Shock/Torque Pylons summary

Articulating Ankle-Shock/Torque Pylons summary

These are some of the posts I have received so far concerning the following
post. They also include responses i received from the AMP-L list serve

>Colleagues,
>
>Can anyone tell me if any studies have been, or are currently being
conducted
>to establish the benfits of ankle motion in prosthetic feet?
>
>This seems intuitively to be a benefit since it mimicks natural
biomechanics.
>Adding a dynamic response characteristic would be an additional benefit for
>the more active amputee. Am I right about this?
>
>Should we be prescribing feet with ankle motion whenever possible?
>Are you doing this in your practice?
>
>Mark Benveniste CP
>VA Medical Center
>Houston,TX

Dear Mr Benveniste

In response to your posting of 24/08/99 can I suggest that you pay a visit
to the RECAL Information Services website – <URL Redacted>.

RECAL Information services specialises in the provision of guides to the
literature in prosthetics, orthotics, physical medicine and rehabilitation.
Our services aim to keep the clinician, research worker and rehabilitation
professional in touch with the published literature in a variety of easy to
use and convenient formats.

Thank you for your time.

Heather Smart
Information Officer
National Centre for Training and Education in Prosthetics and Orthotics
University of Strathclyde
--------------------------------

Dear Colleagues,
A recent message posted by Mark Benveniste CP, raised the issue of ankle
articulation and the prescription criteria for such componentry.
This topic is one that could be expanded upon to include a new range of
components, ie. Vertical shock pylon, T/T Pylon etc. collectively I will
refer to them as Pogo Sticks.
As you may surmise from the description used above, my opinion of the Pogo
Stick range is one of scepticism. I would dearly like to encourage a list
discussion about this subject to gauge experience and opinions other than my
own, (my own being limited).
There is no doubt that in nearly all cases of a Pogo Stick upgrade the
response is a positive one, with comfort being the big C word. It worries
me however that we have provided a vertical compression that can only be
returned in one way - vertically. I know that during my studies in P&O, that
an important Biomechanics principle was to minimise the vertical displacement
of the centre of mass during gait. A vertical displacement followed by
subsequent vertical replacement that is provided by the Pogo Sticks is
surely forming a tangent away from these principles.
The more normalised gait pattern incorporating an articulated ankle provides
not only compression qualities but at the same time dissipates these via a
further progression into the gait cycle, (plantarflexion). This is achievable
now-a-days with a range of feet, from the simple single axis with bumper
design to energy storage systems present at the heel component.
It would be interesting to hear from anyone with research into this area, ie.
Centre of mass differentials with and without Pogo Sticks; Energy
expenditure comparisons; Long term effects of vertical displacement on the
spine?
I look forward to reading your responses on this topic, it is I believe the
main reason for this list - Information exchange leading to professional
development of the Prosthetist/Orthotist

I eagerly await,
Mark Raabe
Division Manager
Technical Orthopaedics
Otto Bock (A/Asia)
Ph. +61 2 9319 6852
Fax. +61 2 9699 1459
Mob. 0414 682 301
<Email Address Redacted>
-------------------------------
Dear M.Benveniste CP
 I have carefully read your mail and have practically done self research,
using my own designed soft to the required level to mimic and function
to the natural foot action.
My stump is free from socket abrasion and has gained more strength
and hair for the last three years in self use.I can now be called a normal
person
where earlier no prosthetist had recommended instead I was advised surgery
which I have overcome completely, It is highly recommended for experienced
amputees.
Best Regards,
Rabinder Singh Sahni (lbk 9/55 congenital, deformed fingers both
hands)
Chennai INDIA ISPO member 060.2.0084
--------------------------------------------

>Your thinking on the issue is spot on. As a user of both solid keel feet
over the years and anatomic anologs, motion is king. In the arena of
anatomic motion with durability and not uncontrolled motion, I believe we
are the kings. Please check us out.

As for the studies, contact James Breaky, PhD and CP at (408) 723-0883 in
California. He can tell you the why of the matter better than I can.

Chris Johnson
<Email Address Redacted> (personal address)
Scorpa 250 EZ Fun/Gas-Gas 160/Fantic 305/Yamaha Virago 1,100/XV920RH Euro
<Email Address Redacted> as Director of Engineering at College Park
see www.college-park.com
------------------------------
Mark,

I never think that motion (especially plantar flexion) is a bad idea.
However, keep in mind that increased complexity equals increased maintenance.
If you can find a solid ankle type foot (including Springlite or FlexFoot)
that allows for greater motion, you get the best of both worlds.

Larry Lange CPO

-------------------
<< That was to be my next post (Benefits of shock and torque absorbing
 pylons-should we be using more of them) >>

With this renewed interest is shock absorbing systems does anyone know why
systems like the Winkley Slip Socket dating from the Civil War stopped being
used?
Is this renewed interest a case of old ideas with new materials? Is anyone
looked at updating this old technology? I heard that someone on the West
coast was making a hammock type socket.

Al Pike, CP
<URL Redacted>

There is an article directly related to your question in the Fall
97 edition of the AAOPJournal.
-------------------------------
Mark,

I appreciate and share your concern about this particular technology. I'm
responding off the cuff, as it were, so I don't know if you're an Academy
member. Regardless, this is the perfect venue for the Academy Societies,
especially Lower Limb Prosthetics, to organize such a study. While they may
not be capable of producing laboratory quality statistics as would a
university, they could certainly provide organized clinical field evaluations
in great numbers within a relatively short time frame that would have as much
merit as any outcomes study. I am interested in reading the responses you
receive. Best regards, Bill Schumann, CPO

-----------------------------------
an R Fothergill@OSSUR
25.08.99 09:13

Hi Mark.

One of the most surpassing examples of extreme ankle motion providing
extremely
good function was on a short clip of video footage about a foot called the
Jaipur foot.
Although the details are a little scechy in my mind, it was a foot made in
Jaipur (India) from local materials and by local craftsmen.
It was in a large part made from old car tyres layered and bonded, a very,
very
short wood keel provided the attachment.
The video featured very well rehabilitated users performing their ADL´s, and
the
image that sticks in my mind is of one user climbing a tree by gripping the
trunk and walking foot over foot up the near vertical surface. This required
(I estimate) some 50°+ doriflexion to grip sufficiently to the bark, barefoot.

This prompted many questions in my mind, firstly how can such a foot ever
provide enough stability for normal ambulation, these questions were soon in
the
back of my mind as the fellow jumped from the first branch of the tree, a
height
of some 2-3 metres and walked off with a very natural gait.

Having said all this the users in my clinic walk just as well, but would not
dream of climbing trees.

This brief exposure has left me questioning of prosthetic feet. To cut a long
story short are all the feet we see in our workshops not too stiff and
immobile.
Or does extreme ankle flexion only help with trees in our way?


Ian Fothergill (CPO)

---------------------------------

Greetings from Downunder,
I am very interested in the responses that you receive and would appreciate
a copy of your results when available - a worthwhile topic.

We believe the disadvantages of TT pylons (ie increased pelvic sway)
outweigh the benefits. In a couple of TF cases who were heavy heel walkers
they did provide good visual feedback when retraining out of this bad gait
pattern. When gait was normalised the amount of pylon pistoning was minimal
and there was no longer any need for this feature. Are we using these
things to mask poor gait training and less than optimal alignment???

Allan Wicks
Director Orthotics and Prosthetics
Royal Adelaide Hospital
email <Email Address Redacted>
--------------------------------------
Dear Mr. Benveniste,

Thank you for your interest in our work with the vertical shock-absorbing
pylons. The mechanical characterization of the three shock-absorbing
pylons that you saw on our Web site was performed to see how the
stiffnesses and damping characteristics of the devices compared with one
another. For clinical application, I believe that the shock-absorbing
pylons we tested have similar characteristics, and that the basis for
choosing one over another would relate to other factors such as cost,
weight, mechanism for shock absorption, etc.

We are about to begin clinical studies of unilateral transtibial amputees
walking with and without a shock-absorbing pylon. I don't believe the
particular type of pylon is important; instead, I think that all lower-limb
amputees will benefit from added prosthetic compliance. All of the shock
pylons that we tested, and that are currently on the market, are
functionally similar-- they shorten telescopically in response to an
applied axial load, providing shock absorption by lengthening the loading
time of the prosthetic limb. The unit that we will be using for our
clinical studies is the Endolite TT Pylon, which I like because of the
helical spring design. The torque absorption feature complicates our study
of vertical shock absorption to some degree, but I have heard some amputees
say that is what they like best about the Endolite unit. After thinking
further on the issue, I'm now at the point that I also want to study the
torque absorption of the Endolite TT Pylon in addition to the vertical
shock absorption. Hopefully, we will begin clinical studies within the
next month or so.

Please contact me if you have additional questions.

Sincerely,

Steven Gard

--------------------------
Mark, in regard to your topic and other inquiries by other list members I
offer the following: I am 40 years old. In May of 98 I was involved in a
train accident to took my left leg just below the knee. I work for a
railroad in Maine. The injury left me with only 3 inches of bone and muscle
and tissue below that, giving me about 5 inches in all. My stump is 90%
skin grafted. I use a Tech liner with the IceX pin lock, the TT pylon by
Endolite and the Cirus foot. The combination of these components provides
maximum shock absorption to protect the grafted skin, and so far it has
worked very well. I am very active. I walk very comfortably, exercise on a
Stairmaster and a stationary bike. I also play golf among other things.
The TT pylon also features a swiveling action which works well, especially
when golfing. With such a short stump, the liner extends over my knee
restricting some movement but I am very happy with this set-up. I am
fortunate to be at the hands of two excellent prosthetist in Bill Velicky
and Molly Pitcher. I know this doesn't answer all your questions or
concerns, but I how this will be helpful.

Bradley

---------------------------
Dear Mark,
I have been an amputee for 24 years now.. I was a sportsperson when I was
younger and I represened my country [ Australia] in the 1980 Olympics for
the disabled, in track and field. The Appliance and Limb Centre had me
testing new products for them. A couple were moveable ankles. This is only
my opinion but I personally found no extra benefit in any of these. The
extra weight factor was a major deterant to my using one. Even were they to
be lighter I still feel with a good fitting leg this is not necessary.
People I have casually know for years are totally surprised if they find out
that I am an amputee. I was even called the 'Bionic Mum' by one newspaper. I
have four sons and lead a very active life. I have many able bodied friends
who can't keep up with me. It is wonderful to know that you prothetists are
enquiring what is good for the client but please go to the source and
enquire there you might find some valuable information. Keep up the good
work.


Charmaine.
------------------------------
Mark,

I've forwarded your message to the engineers in the research department.
They have been looking at prosthetic feet for some time now. I don't know
if they have analyzed articulated feet.

Either Dr. Steve Gard or Laura Miller will be in touch with you.

I hope this information will stir some quality conversations on the list.

Thanks,

Mark

Mark Edwards phone 312-908-8006
Director, Prosthetics Education fax 312-503-6803
Northwestern University web address
<Email Address Redacted> <URL Redacted>
------------------------
> mark,
i am an ak, bk, and have tried several feet.
unfortunately i have never gotten the full potential out of any of them, due
to poor socket fit.
i had the vsp for awhile, and i really did like them, for as much as i got to
use them.
i had no problem with either bk, or ak. when i wore the vsp, i was also
wearing the black max SNS knee.
i am now weraing seattle lite feet with endolite ankle, and again, the black
max knee.
i found the edolite ankle to be a bit wobbly on the ak side, and we used as
many bumpers as possible, without defeating the purpose of the ankle. i have
no problem walking on it.
i did try the college park tru-step, and found it to be glitchy. there was
no way to achieve a smooth roll over on this foot. (for me)
have also tried spring lite feet, and carbon copy lll. i have no opinion of
them , as i said, i never got full potential from them.

 In addition I am looking for testimony from amputees favorable or
unfavorable
 about their experience with shock and torque absorbing pylons (trans femoral
 and trans tibial)

a> have tried on several occassions to get someone to let me try the shock
pylon(s), but to no avail. maybe it's because i'm ak,bk?

a> hope this helps a bit.
:)
anita
--------------------------
What follows is the inclusion of Mark Raabe's compilation because I thought
it would be helpful as a body of Information to have together

Dear Colleagues,
Below is my original message followed by the responses received.
Comfort seems to indicate prescription criteria in most cases.
Thank you to all that responded, I hope this topic is researched further.
Cheers
Mark Raabe

Dear Colleagues,
A recent message posted by Mark Benveniste CP, raised the issue of ankle
articulation and the prescription criteria for such componentry.
This topic is one that could be expanded upon to include a new range of
components, ie. Vertical shock pylon, T/T Pylon etc. collectively I will
refer to them as Pogo Sticks.
As you may surmise from the description used above, my opinion of the Pogo
Stick range is one of scepticism. I would dearly like to encourage a list
discussion about this subject to gauge experience and opinions other than my
own, (my own being limited).
There is no doubt that in nearly all cases of a Pogo Stick upgrade the
response is a positive one, with comfort being the big C word. It worries
me however that we have provided a vertical compression that can only be
returned in one way - vertically. I know that during my studies in P&O, that
an important Biomechanics principle was to minimise the vertical displacement
of the centre of mass during gait. A vertical displacement followed by
subsequent vertical replacement that is provided by the Pogo Sticks is
surely forming a tangent away from these principles.
The more normalised gait pattern incorporating an articulated ankle provides
not only compression qualities but at the same time dissipates these via a
further progression into the gait cycle, (plantarflexion). This is achievable
now-a-days with a range of feet, from the simple single axis with bumper
design to energy storage systems present at the heel component.
It would be interesting to hear from anyone with research into this area, ie.
Centre of mass differentials with and without Pogo Sticks; Energy
expenditure comparisons; Long term effects of vertical displacement on the
spine?
I look forward to reading your responses on this topic, it is I believe the
main reason for this list - Information exchange leading to professional
development of the Prosthetist/Orthotist

REPLIES
______________________________________________________________________________
_________________________________
Mark Raabe submitted a post about shock pylons.
That was to be my next post (Benefits of shock and torque absorbing
pylons-should we be using more of them)so I am glad that others are thinking
that these are important concerns in modern prosthetics and also look forward
to hearing responses.
I am aware of limited studies on a few of the older shock pylons and have
asked people at Northwestern University if there were more studies on the
way. I have asked a similar question about ankle motion. Of course, I would
like to be aware of ongoing studies worldwide.
These are two subjects where research/and observed clinical
results/individual pt experience, would be valuable to share with the whole
professional community
Mark Benveniste CP
With this renewed interest is shock absorbing systems does anyone know why
systems like the Winkley Slip Socket dating from the Civil War stopped being
used?
Is this renewed interest a case of old ideas with new materials? Is anyone
looked at updating this old technology? I heard that someone on the West
coast was making a hammock type socket.
Al Pike, CP
It is my opinion that there is only one foot that really mimics the
anatomical ankle in function, and that is the TruStep by College Park. Dr,
Jim Breakey has done some excellent research into the normal gait vs. an
amputee with a TruStep Foot. The use of active planter and dorsiflexion ,
rotation , and vertical displacement at the correct time during the gait
cycle and how this is key in generating normal gait and at the same time
eliminating unnecessary wear and tear on the amputee. The vertical
displacement is not the same as that received with the use of a shock pylon
that takes length away at the wrong time and does not give it back until
it's to late. Vertical displacement is only achieved through the use of the
two independent axis of the TruStep. The displacement takes place during
early stance and is returned prior to swing through where it is needed.
Michael Link BOCP
Mark:
I can't direct you to any professional studies - but from 25 years of using
prosthetic limbs ranging from post WWII Blatchford models to Otto Bock
modular types - I have to say the Flex Foot Re-Flex is by far the greatest
thing I have had on the end of my socket.
The energy return it gives, the added spring to the step is incredible.
Comfort is increased due to the shock absorbing capability - I tried going to
a shock free set up and it was terrible. Some form of shock absorbtion with
some degree of rotation is the only way to go especially for an aK like me.
Hope this opinion helps.
Ian Gregson
Mark:

Here are some thoughts on vertical shock and torque absorbing units (pogo
stick) from my limited perspective.

I am the Engineering Director for College Park Industries, Inc. in Michigan,
USA (see www.college-park.com). Your thoughts on the issue of pogo sticks
accord with what I have found experientially. I have a lot of experience
testing all kinds of feet, with and without vertical shock pylons.

As a long-time user of College Park feet in particular, I can attest to the
benefits of vertical displacement analogous to the human body minimizing
deviations in center of mass. In street talk, it just plain hurts less.
I recently tested a new foot that does not have vertical deflection or
transverse rotation. I walked, and played frisbee and volley ball on it.
It was a pretty good design, but the lack of any foot-flat vertical
deflection or transverse plane rotation was very noticeable and a definite
negative.

I have one of my legs currently set up with a vertical shock and torque
absorbing pylon, the Century 22 Total Shock. I like this unit for its
simplicity and superior bearing overlap.
I find a pogo stick with significan vertical excursion does detract from
gait symmetry. I can walk with close to no noticeable gait deviation. One
would be hard pressed to see deviation even with the pogo stick installed.
Nevertheless, sighting on a spot on a wall and walking toward it, I can see
my center of mass varyies more on the prosthetic side with one of these
units installed. However, there is a perspective that must not be
overlooked, the comfort issue you have identified.

A purist may say that gait mechanics are it, just as the purist bicyclist
may say suspension is not needed and only adds weight. The whole story
includes, however, that the amputated limb is not ideal, just as the ground
is not flat everywhere.

So I see several primary uses for pogo sticks:

- Amelioration of ground reaction forces to protect a compromised residuum
- Adding vertical deflection to feet that do not have it built in
- Adding back transverse plane rotation missing through loss of joints
- Exaggeration of motion for special purposes (e.g., golf swing)

Indeed, there are times where the extra rotation and vertical movement
detract from sound gait. I prefer heavy sports activity with the college
Park TruStep foot alone, for example. I also do not think adding a pogo
stick to make up for lack of vertical deflection in a foot is the best
tack. It is almost impossible to have friction free motion in these units.
They all will inevitably display slip-stick motion. In other words, they
get sticky and cease to move when needed. This effect does not occur in the
3-bone, 2-axis system employed in our foot.

One thing to note is the interplay betwen an articultating, multi-axial foot
and a pogo stick. A patient new to both of these should try the foot a
month without the unit, then add it. Trying both at the same time for the
first time can introduce too many variables during the alignment,
adjustment, and acclimation period.

Hope this patient/engineer perspective helps.
Chris Johnson
Mr. Raabe,

I would also like too see research on the effects of the pogo sticks as you
have so affectionately named them. I too have been somewhat skeptical of the
benefit of these devices in the past. My experience has led me to feel
otherwise. While I am not a pogo stick spokesperson I see them as
generally beneficial, particularly with the transfemoral amputee.
I think your concerns about vertical displacement should be reexamined.
During normal human locomotion the joints and muscles of the sound knee, hip
and ankle work as shock absorbers with controlled knee flexion (Quadriceps)
contributing a large component of this. The knee goes from full extension too
between 15 and 20 degrees of flexion from heel strike to foot flat
effectively preventing the rise of the center of gravity. This controlled
knee flexion is not present in the prosthesis of a transfemoral amputee that
I am aware of. (Perhaps it can be argued that the Bock 3R60 and other knees
with stance flexion features can approximate this, but that is a separate
matter.) In practice I find that few transtibial amputees actually ambulate
with a normal range of controlled knee flexion on the amputated side.
Controlled knee flexion in the sound limb occurs at the same time as weight
shift and vertical loading. This correlates with the shortening action of
the shock absorber during weight shift and vertical loading of the
prosthesis. I believe studies will show that there is less vertical
displacement (or vaulting) on the amputated side and therefore more symmetry
of gait in the transfemoral amputee (and perhaps the transtibial as well)
when utilizing a vertical shock absorbing pylon.
In my experience I have been able to lengthen the prosthesis by at least
60% of the maximum compression (~3/8 inch) and find it is easier to obtain a
level pelvis standing with equal weight on each limb.
I have long been a believer in the benefits of the torsion absorber in the
transfemoral prosthesis and find some of the new devices as light as older
torque absorbers with the added benefit of shock absorption.
I have only fitted one such device, a flex foot VSP, on a transtibial amputee
but can attest to its benefits for the highly active patient or recreational
runner.
Until there is research (gait analysis) and documentation we can argue their
theoretical effects and benefits. In the meantime I think you will find it
hard to convince those using these devices that they are more functional,
comfortable or better off without them.
Regards,
Eddie White, CP
Mark, in regard to your topic and other inquiries by other list members I
offer the following: I am 40 years old. In May of 98 I was involved in a
train accident to took my left leg just below the knee. I work for a railroad
in Maine. The injury left me with only 3 inches of bone and muscle and
tissue below that, giving me about 5 inches in all. My stump is 90% skin
grafted. I use a Tech liner with the IceX pin lock, the TT pylon by Endolite
and the Cirus foot. The combination of these components provides maximum
shock absorption to protect the grafted skin, and so far it has worked very
well. I am very active. I walk very comfortably, exercise on a Stairmaster
and a stationary bike. I also play golf among other things. The TT pylon
also features a swiveling action which works well, especially when golfing.
With such a short stump, the liner extends over my knee restricting some
movement but I am very happy with this set-up. I am fortunate to be at the
hands of two excellent prosthetist in Bill Velicky and Molly Pitcher. I
know this doesn't answer all your questions or concerns, but I how this will
be helpful.
Bradley
--------
Thank you all for responding and I hope we can have a continued dialogue at
the next Academy and/or ISPO Meeting.

Mark Benveniste CP