Noisy Endo Component Tips
Chris L Johnson
Description
Collection
Title:
Noisy Endo Component Tips
Creator:
Chris L Johnson
Date:
1/30/2000
Text:
On Sat, 29 Jan 2000 20:53:47 -0500 Rheinstein < <Email Address Redacted> >
writes:
> Chris,
>
> I would be interested in your other findings. I am working on a
> female TT whose prosthesis started (after about a year) to make a
little click
> as she goes from HS through MS. I took the entire leg apart and found
> nothing wrong (no locktite was used, just a torque wrench). Do you
think the
> order in which you tighten the screw has any effect on noise? Do you
think
> being at the far end of the alignment range makes for more possible
> problems? Thanks for raising this subject.
>
> John
John and List:
Here are some of my findings of the last 4 years. These are my opinions
and I welcome other contributions to this subject. I'm just going to
stream here and not spend a lot of time editing. Please forgive any
redundancy, errors, or excessive length. As Ben Franklin once said to a
friend, I would have written you a shorter letter, but I did not have
the time.
The number one problem I've found with endo components is flexing of the
system. They look like they don't move, but they do with every step.
Repeat this often enough, and the tubes gall, the set screw tips polish,
and pretty soon you have the infamous click or tinking at heel strike.
Why mostly at heel strike?
The components flex the most and the slowest late in the stance phase due
to reaction from the toe lever being loaded at push-off. The foot then
gently lifts during the swing phase with the endo components having take
a slight set in the direction of the toe lever. At heel strike, the load
is not only reverse, but heel strike sends a shock wave though the endo
components. This load reversal plus the shock wave will reset the
flexing of the components in the opposite direction. The movement is
rapid enough for the set screws to skip (microscopically) across the
pyramid facets, and to break an adhesion set up between the tube adapters
and the tubes. Once the set screws have micro polished, and the anodize
is breached on the aluminum tubes, and adhesion initiates, you can get
noise.
So you have the noise interfaces of the set screws and the pyramid
facets, and between the tube clamp adapter and the tube. Another is
between the tube and a bonded tube adapter.
I have found this interface can break down over time. The adhesive agent
is pummeled so much it begins to break down. It can still look OK, but
the tube is flexing and taking a set in the tube adapter, with some
percentage of the bond line being compromised. Same noise scenario of
clicking at heel strike, mostly.
If you really have a noise maker, you can get noise both at heel strike
and during push off, really anywhere in the stance phase. An example of
this is when prosthetists do the no-no is using a piece of cut tube to
space the limb longer, and the bare ends of the tube are sliding (again
microscopically) across each other. there is more flexing in that case
because the rigidity of a continuous tube has been broken.
I did mention how uncured Locktite getting between flexing interfaces can
make noise in the last e-mail on this subject.
How have I dealt with endo component noise? I have some solutions.
These are mine and other may have others. All I know is the following
works for me.
In my opinion, the #1 no-no is endo components is design related. It is
the use of relatively thin-wall tubes, which allow too much flexing in
the tube and tube clamp adapters. Most tube is 2mm wall. I have found
some components which have less tendency to loosen and make noise than
any others, in part, because the tube is 3mm wall. These are the Ortho
Enterprises (Ortho Europe) System 2000 Gold Award Series. These are
all-aluminum endo components. They are very well made and have the 3mm
wall tube. They are gold. Personally, I think gold is cheezy, like
those `60s gold house shoes those housewives wore in advertisements
worshipping their home appliances. I wish that beautiful green they have
with the 2mm wall tubes was in the 3mm! The aluminum tube clamps and
tube adapters are the same across the whole product line, regardless of
color. Anyway, silly anality aside, I love these components. With the
3mm wall tube, I have found titanium tube and tube adapters to be
unnecessary. They even resist rotation better than any other brand I've
tried. This is good stuff, folks. My guess is, it may be cheaper too
being all aluminum. No, I will not profit (God forbid) from any Ortho
Enterprises sales. If you want to flame me for this, please take it out
on your hamburgers the next time you grill. Their stuff is simple great,
and since they are little known, I thought it good to pass on solutions I
have found valuable.
One thing to check for in endo components is manufacturing tolerances. A
correctly toleranced set-up will have the tube clamp adapter (with
clamping screw backed off) with a slight drag fit on the tube. Ideally,
the tube clamp can be slid on the tube, the tube positioned such that the
tube clamp adapter hangs, and gravity does not pull it off. If it does
fall off, it's OK if there is no slop and it just slides off. Some
unnamed manufacturers will make things so sloppy that the tube clamp
adapters have to be mongo tightened to not slip under the normal torque
of walking. The sloppier the tube clamp adapter is on the tube to start
with, the more point contact stresses there will be between the tube and
the bore of the tube clamp adapter upon tightening. More point contact
stresses mean shorter time to noise generation.
The Ortho Enterprises stuff does not use fancy barrel nuts on the
clamping system, just a simple screw. But they hold better than anything
I've tried yet (yes, I've used just about everything available), even in
aluminum. The simple setup works because of good tolerance control and
great design in the details. Yes, in aluminum. In my most humble
opinion, the expense of titanium is not justified for the vast majority.
When design right, the aluminum components can match or out perform the
titanium stuff. I'm not exactly sure all the reasons why, yet.
One thing I have not tried is the 34mm systems. Those might actually be
more suited to my activity level. But, why use 34mm tube if the 30mm
tube systems, if done correctly, work fine? After all, the size of the
pyramid adapters is the same on the 34mm tube systems as the 30mm. I am
interested in the slimmest, lightest setup possible that will not give me
problems. I do pound stuff too. I have even bent the tube (only 4.5
long on me) on certain unnamed systems.
Another thing to be aware of is that if tight is good, tighter is not
always better. Over tightening of sets screws actually increases noise
propensity. One diagnostic I use to find noise in the set screws of a
tube clamp adapter is to back off the screws to where they are just
barely tight enough to walk on. If the noise is in that interface, I
will often hear a loud click separate form un tightening as I back off
the screw. If the noise goes away, I suspect either Locktite is between
the set screws and pyramid facets, or the set screws have become
polished. So I remove them and sand the flat surfaces of the set screw
tips to break polished surfaces. Reassemble them dry, with only enough
Locktite to gum up the threads and not run down the tips. I don't use
torque wrenches, but I do not over tighten. If one has the tendency to
tighten things a bunch, a torque wrench is best. With Locktite to
prevent runaway loosening of the set screws, and with the thicket tubes,
I do not have problems with loosening, even though my set screws are
probably looser than most would feel comfortable with.
Some info on set screws: They should be the black type and not stainless
steel, which is a real noise maker, or the zinc chromate clear (silver
looking) or zinc chromate gold-tinted type. Zinc chromate is the plating
found on the vast majority of steel fasteners. Unfortunately, it is not
the best for endo components, as it can cause seizing of the set screws
on the threads and noise. Just the plain, black set screws are best.
They should be flat tipped (not easy to find) and not the standard cup
point. If you want spares, you can buy these from McMaster-Carr:
www.mcmaster.com (630) 833-0300. They are DIN 913 Alloy Steel Black
Finish Flat Point Metric Set Screws, M8 X 16 part number 93245A143 $14.03
for a box of 100. The best overall length is 14mm, but the next size
down available from the 16mm above is 12mm. the 16mm are a smidge long
but work very well.
Over tightening of the tube clamp screw poses similar problems. If you
are using poor-quality components, or components that flex too much
(those thin tubes), then you can get noise between the tube and tube
clamp. If I suspect noise there, Ioosen the screw to where I can just
walk on it without the foot wanting to toe in. If there is a problem
there, I will usually hear a clicking noise as I release the screw.
I do not Locktite the tube clamp screw, but rather grease the thread to
prevent sticking and false torque reading. I tighten them only as much
as is necessary to prevent rotation under rigorous activity, no more.
I've never had one loosen.
Now more about tubes. If you remove a tube and find that nice smile
corresponding to the exit edge of the bore of the tube clamp, where the
anodize has worn though, or you find areas, particularly near the tube
clamp screw, where the anodize is worn off, you should replace that tube.
The worst area for wear is the anterior proximal edge of the distal tube
clamp adapter. If you don't have another one you can rotate the tube 180
degrees so the high wear spots are refreshed. Once the thin anodize is
breached, a noise generating site is created. Anodize is only .0002
(,005mm) thick. Again, I've had the best luck so far with the Ortho
stuff at preventing breeches of anodize. Some manufactures make the
mistake of having a sharp edge on the tube clamp bore. Usually, if they
have that, either the tube is undersized or the bore of the tube clamp is
over sized, so the problem is worse.
The key contributor to this is the use of thin tubes. I am active, but
only 170 pounds (77kg). If I use the normal, 2mm-wall aluminum tubing, I
will shortly have noise, no matter whose tube adapters I use. In my
humble opinion, it pays to use thicker-wall tubing. Thin wall tubing
allows the tube adapters and tube clamp adapters to flex too much,
setting up micro movements between the tube and tube clamp adapters, and
between the set screws and the pyramid facets.
I have tried advanced composite tubes, and even amorphous polymer tubes.
I have not had good luck with them. The main failing has usually been
the inability to keep them from rotating. The low relative compressive
strength of these materials makes clamp retention a real pain. My
current favorite is plain aluminum (when it is thick enough).
I'm tapped out for now. There is more, but I can get into that later.
Chris Johnson
<Email Address Redacted> (personal address)
<Email Address Redacted> as Director of Engineering at College Park
writes:
> Chris,
>
> I would be interested in your other findings. I am working on a
> female TT whose prosthesis started (after about a year) to make a
little click
> as she goes from HS through MS. I took the entire leg apart and found
> nothing wrong (no locktite was used, just a torque wrench). Do you
think the
> order in which you tighten the screw has any effect on noise? Do you
think
> being at the far end of the alignment range makes for more possible
> problems? Thanks for raising this subject.
>
> John
John and List:
Here are some of my findings of the last 4 years. These are my opinions
and I welcome other contributions to this subject. I'm just going to
stream here and not spend a lot of time editing. Please forgive any
redundancy, errors, or excessive length. As Ben Franklin once said to a
friend, I would have written you a shorter letter, but I did not have
the time.
The number one problem I've found with endo components is flexing of the
system. They look like they don't move, but they do with every step.
Repeat this often enough, and the tubes gall, the set screw tips polish,
and pretty soon you have the infamous click or tinking at heel strike.
Why mostly at heel strike?
The components flex the most and the slowest late in the stance phase due
to reaction from the toe lever being loaded at push-off. The foot then
gently lifts during the swing phase with the endo components having take
a slight set in the direction of the toe lever. At heel strike, the load
is not only reverse, but heel strike sends a shock wave though the endo
components. This load reversal plus the shock wave will reset the
flexing of the components in the opposite direction. The movement is
rapid enough for the set screws to skip (microscopically) across the
pyramid facets, and to break an adhesion set up between the tube adapters
and the tubes. Once the set screws have micro polished, and the anodize
is breached on the aluminum tubes, and adhesion initiates, you can get
noise.
So you have the noise interfaces of the set screws and the pyramid
facets, and between the tube clamp adapter and the tube. Another is
between the tube and a bonded tube adapter.
I have found this interface can break down over time. The adhesive agent
is pummeled so much it begins to break down. It can still look OK, but
the tube is flexing and taking a set in the tube adapter, with some
percentage of the bond line being compromised. Same noise scenario of
clicking at heel strike, mostly.
If you really have a noise maker, you can get noise both at heel strike
and during push off, really anywhere in the stance phase. An example of
this is when prosthetists do the no-no is using a piece of cut tube to
space the limb longer, and the bare ends of the tube are sliding (again
microscopically) across each other. there is more flexing in that case
because the rigidity of a continuous tube has been broken.
I did mention how uncured Locktite getting between flexing interfaces can
make noise in the last e-mail on this subject.
How have I dealt with endo component noise? I have some solutions.
These are mine and other may have others. All I know is the following
works for me.
In my opinion, the #1 no-no is endo components is design related. It is
the use of relatively thin-wall tubes, which allow too much flexing in
the tube and tube clamp adapters. Most tube is 2mm wall. I have found
some components which have less tendency to loosen and make noise than
any others, in part, because the tube is 3mm wall. These are the Ortho
Enterprises (Ortho Europe) System 2000 Gold Award Series. These are
all-aluminum endo components. They are very well made and have the 3mm
wall tube. They are gold. Personally, I think gold is cheezy, like
those `60s gold house shoes those housewives wore in advertisements
worshipping their home appliances. I wish that beautiful green they have
with the 2mm wall tubes was in the 3mm! The aluminum tube clamps and
tube adapters are the same across the whole product line, regardless of
color. Anyway, silly anality aside, I love these components. With the
3mm wall tube, I have found titanium tube and tube adapters to be
unnecessary. They even resist rotation better than any other brand I've
tried. This is good stuff, folks. My guess is, it may be cheaper too
being all aluminum. No, I will not profit (God forbid) from any Ortho
Enterprises sales. If you want to flame me for this, please take it out
on your hamburgers the next time you grill. Their stuff is simple great,
and since they are little known, I thought it good to pass on solutions I
have found valuable.
One thing to check for in endo components is manufacturing tolerances. A
correctly toleranced set-up will have the tube clamp adapter (with
clamping screw backed off) with a slight drag fit on the tube. Ideally,
the tube clamp can be slid on the tube, the tube positioned such that the
tube clamp adapter hangs, and gravity does not pull it off. If it does
fall off, it's OK if there is no slop and it just slides off. Some
unnamed manufacturers will make things so sloppy that the tube clamp
adapters have to be mongo tightened to not slip under the normal torque
of walking. The sloppier the tube clamp adapter is on the tube to start
with, the more point contact stresses there will be between the tube and
the bore of the tube clamp adapter upon tightening. More point contact
stresses mean shorter time to noise generation.
The Ortho Enterprises stuff does not use fancy barrel nuts on the
clamping system, just a simple screw. But they hold better than anything
I've tried yet (yes, I've used just about everything available), even in
aluminum. The simple setup works because of good tolerance control and
great design in the details. Yes, in aluminum. In my most humble
opinion, the expense of titanium is not justified for the vast majority.
When design right, the aluminum components can match or out perform the
titanium stuff. I'm not exactly sure all the reasons why, yet.
One thing I have not tried is the 34mm systems. Those might actually be
more suited to my activity level. But, why use 34mm tube if the 30mm
tube systems, if done correctly, work fine? After all, the size of the
pyramid adapters is the same on the 34mm tube systems as the 30mm. I am
interested in the slimmest, lightest setup possible that will not give me
problems. I do pound stuff too. I have even bent the tube (only 4.5
long on me) on certain unnamed systems.
Another thing to be aware of is that if tight is good, tighter is not
always better. Over tightening of sets screws actually increases noise
propensity. One diagnostic I use to find noise in the set screws of a
tube clamp adapter is to back off the screws to where they are just
barely tight enough to walk on. If the noise is in that interface, I
will often hear a loud click separate form un tightening as I back off
the screw. If the noise goes away, I suspect either Locktite is between
the set screws and pyramid facets, or the set screws have become
polished. So I remove them and sand the flat surfaces of the set screw
tips to break polished surfaces. Reassemble them dry, with only enough
Locktite to gum up the threads and not run down the tips. I don't use
torque wrenches, but I do not over tighten. If one has the tendency to
tighten things a bunch, a torque wrench is best. With Locktite to
prevent runaway loosening of the set screws, and with the thicket tubes,
I do not have problems with loosening, even though my set screws are
probably looser than most would feel comfortable with.
Some info on set screws: They should be the black type and not stainless
steel, which is a real noise maker, or the zinc chromate clear (silver
looking) or zinc chromate gold-tinted type. Zinc chromate is the plating
found on the vast majority of steel fasteners. Unfortunately, it is not
the best for endo components, as it can cause seizing of the set screws
on the threads and noise. Just the plain, black set screws are best.
They should be flat tipped (not easy to find) and not the standard cup
point. If you want spares, you can buy these from McMaster-Carr:
www.mcmaster.com (630) 833-0300. They are DIN 913 Alloy Steel Black
Finish Flat Point Metric Set Screws, M8 X 16 part number 93245A143 $14.03
for a box of 100. The best overall length is 14mm, but the next size
down available from the 16mm above is 12mm. the 16mm are a smidge long
but work very well.
Over tightening of the tube clamp screw poses similar problems. If you
are using poor-quality components, or components that flex too much
(those thin tubes), then you can get noise between the tube and tube
clamp. If I suspect noise there, Ioosen the screw to where I can just
walk on it without the foot wanting to toe in. If there is a problem
there, I will usually hear a clicking noise as I release the screw.
I do not Locktite the tube clamp screw, but rather grease the thread to
prevent sticking and false torque reading. I tighten them only as much
as is necessary to prevent rotation under rigorous activity, no more.
I've never had one loosen.
Now more about tubes. If you remove a tube and find that nice smile
corresponding to the exit edge of the bore of the tube clamp, where the
anodize has worn though, or you find areas, particularly near the tube
clamp screw, where the anodize is worn off, you should replace that tube.
The worst area for wear is the anterior proximal edge of the distal tube
clamp adapter. If you don't have another one you can rotate the tube 180
degrees so the high wear spots are refreshed. Once the thin anodize is
breached, a noise generating site is created. Anodize is only .0002
(,005mm) thick. Again, I've had the best luck so far with the Ortho
stuff at preventing breeches of anodize. Some manufactures make the
mistake of having a sharp edge on the tube clamp bore. Usually, if they
have that, either the tube is undersized or the bore of the tube clamp is
over sized, so the problem is worse.
The key contributor to this is the use of thin tubes. I am active, but
only 170 pounds (77kg). If I use the normal, 2mm-wall aluminum tubing, I
will shortly have noise, no matter whose tube adapters I use. In my
humble opinion, it pays to use thicker-wall tubing. Thin wall tubing
allows the tube adapters and tube clamp adapters to flex too much,
setting up micro movements between the tube and tube clamp adapters, and
between the set screws and the pyramid facets.
I have tried advanced composite tubes, and even amorphous polymer tubes.
I have not had good luck with them. The main failing has usually been
the inability to keep them from rotating. The low relative compressive
strength of these materials makes clamp retention a real pain. My
current favorite is plain aluminum (when it is thick enough).
I'm tapped out for now. There is more, but I can get into that later.
Chris Johnson
<Email Address Redacted> (personal address)
<Email Address Redacted> as Director of Engineering at College Park
Citation
Chris L Johnson, “Noisy Endo Component Tips,” Digital Resource Foundation for Orthotics and Prosthetics, accessed November 5, 2024, https://library.drfop.org/items/show/213466.
