Pediatric knee - Responses
ana medeiros
Description
Collection
Title:
Pediatric knee - Responses
Creator:
ana medeiros
Date:
9/20/1999
Text:
Thank you all who replied me. I'm sorry for taking so long to post a
summary, but here it goes.
-----Mensagem original-----
De: ana medeiros < <Email Address Redacted> >
Para: <Email Address Redacted> < <Email Address Redacted> >
Data: Quinta-feira, 2 de Setembro de 1999 00:21
Assunto: Pediatric knees
Hello,
My name is Ana Medeiros, I'm graduate student in Chiba University
(Faculty of Engineering) - Japan, studying about materials applied in
pediatric prosthetic knees. I read some articles which explained this
subject, but I still have some big doubts on polycentric knees. So if
possible could anyone give me a little help? I would be forever
grateful.
1- It is advocated that polycentric knee is a good choice for a
child with knee disarticulation. Which are the most important points in
the polycentric design that influence this choice?
a) The ability to support the body weight in flexioned position?
(center of rotation - in full extension- not elevated and between
superimposed heel contact and push off lines)
b) The stability during stance-phase? (elevated instant center,
or hyper-stabilized center)
c) Flexion is not restricted until at least 130 degrees?
d) Mechanical knee center is better located (closer to the
anatomical center in sound limb) than in single-axis knees?
2- For a young child, who walk with flexionated knees in a wide
base, a flexionated prostheses is used? If so, (for knee disart.)that is
the polycentric #1 a) (writen above), or which other?
3- Which available pediatric knee would you use for a knee
disarticulation prostheses for a young child (for the instance suppose
the ideal one: average weight, height, motor development) who is
receiving the first articulated knee? Why?
Well, I may have asked redundant, wrong questions. If you think
so, please correct me and save a soul from the eternal ignorance.
Thank you very much for your attention and help.
Sincerely,
Ana
------------------------------------------------------------------------------------
Ana,
This is a good topic for discussion in general. The advantages of 4 bar
knees.
Typically the advantages are stated as follows.
1)Higher center of virtual rotation-which presumably makes it easier
to
flex the knee because of a shorter lever arm.
2)Virtual center of rotation is more posterior to weight line making
knee
more stable
3) Toe clearance is improved because of knee geometry
I know this doesn't answer all your questions and in fact I am trying to
find
out more about the stated and true advantages of 4 bar geometry as well.
I am
sure other people will give you more detailed answers.
Mark Benveniste CP
<Email Address Redacted>
------------------------------------------------------------------------------------
======== Fwd by: John Stephens ========
My name is John Stephenson and I am a Certified Prosthetist at the Texas
Scottish Rite Hospital for children in Dallas, Texas. We routinely use a
couple different types of polycentric knees here for the pediatric
amputees.
For a couple of reasons that you mentioned. One is because of the knees
design with the instaneous center of rotation being posterior to the
weight
line, there is inherent stability built into the knee. Much more than
with a
single axis knee. Also the design of the knee allows less of a
discrepancy
in the knee centers because it allows you to get the prosthetic socket
lower
to the knee axis. this allows it to be more cosmetic. there also is a
knee
designed by Century XXII which actually has a stance phase mechanism
built
into which makes for better stability during gait, this is especially
helpful with bilateral patients.
We definitely use many more polycentric knees compared to single axis
knees.
It would certainly be the knee of choice for me. The two knees that we
use
the most are the pediatric Total Knee from Century XXII and the TK-40C
four
bar knee from DAW industries. Hope this helps.
John W. Stephenson, C.P.
<Email Address Redacted>
------------------------------------------------------------------------------------
Hello Ana,
First, to answer some of your questions:
a) The ability to support the body weight in flexioned position?
(center of rotation - in full extension- not elevated and between
superimposed heel contact and push off lines)
Seems like a poly-centric knee would not do better than a
single-axis, since flexing the knee results in a shift forward of the
rotation center, which makes the leg instable.
b) The stability during stance-phase? (elevated instant center, or
hyper-stabilized center)
No more stable than a posteriorly placed single-axis
c) Flexion is not restricted until at least 130 degrees?
That would be a big one, since kids like to sit on the ground when
playing, and move around a lot. A leg which bends no further than 100
degrees would be more restrictive than one which goes up to 130
d) Mechanical knee center is better located (closer to the
anatomical center in sound limb) than in single-axis knees?
It is not always. Only in the later phase of flexion does it approach
the anatomical center. Anyway, the anatomical center of a healthy knee
is not fixed. It can be approximated by a four-bar knee, but probably
not as well as with a well-placed single axis. Disadvantages of the
single-axis are then that the stump must be relatively short (otherwise
there is no room for the hinge) and that the prosthesis is less stable
during stance.
I think one of the main advantages of a four-bar is that people with a
long stump (for instance knee exarticulation) do not get an extended
upper leg when sitting down. A single axis can be applied, but then it
needs to be placed 'in the hollow of the knee', meaning 'up' and 'back'.
This gives good cosmesis (equal leg lengths when standing and sitting)
and stable stance, but I am not sure how well the active walker can walk
with it. I think one of the main disadvantages of the four-bar is that
the rotation center moves forward, which results in shortening of the
leg during swing.
2- For a young child, who walk with flexionated knees in a wide
base, a flexionated prostheses is used? If so, (for knee
disart.)that is the polycentric #1 a) (writen above), or which other?
I do not know if all young children walk with flexed knees. A flexed
knee can hardly be made stable except with a polycentric knee which has
been designed for that purpose. Wether they exist I do not know. For a
person with a knee-exarticulation one would either need a polycentric
hinge or a posteriorly and proximally placed single-axis.
Well, I may have asked redundant, wrong questions. If you think so,
please correct me and save a soul from the eternal ignorance.
I don't know. You may also be getting a lot of wrong answers (including
mine?), so maybe that balances the scales?
Regards,
Edsko Hekman
..........................................................
.Edsko Hekman .
.Laboratory of Biomechanical Engineering .
.Twente University .
.PO box 217 tel. 31-53-4893173 .
.7500AE Enschede fax. 31-53-4893471 .
.e-mail <Email Address Redacted> .
...........................................................
------------------------------------------------------------------------------------
Dear Ana,
A company in Russia called OIME produce an excellent polycentric knee
joint
usable for children from the age of 2 years. I know that this joint is
unique and has been used in Germany.
Their Fax is 007 095 5160560
Regards Michael Mais
German Technical Cooperation (GTZ)
China College for Orthopaedic Technologists (CHICOT)
25 Xue Yuan Jie,
101601 Yan Jiao, Beijing Dong
China V.R.
<Email Address Redacted>
------------------------------------------------------------------------------------
Hi,
As far as what I understand, POlycentric knees are lighter in wt. than
single axis knees, they require less training, so that is why it is
used.
Please will you forward the replies you get to me.
Thanks,
Srivatsa
<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 of a
commercial nature should not be sent to the entire oandp-l list. Responses
should be collected and reposted by the person asking the question.
Send a message to the list by sending to: <Email Address Redacted> To unsubscribe,
send a message to: <Email Address Redacted> with the words UNSUB OANDP-L in the body of the
message. All postings related to US-politics must use a subject line
starting with US-Politics:
Any questions should be directed to Paul E. Prusakowski, CPO at
<Email Address Redacted>
summary, but here it goes.
-----Mensagem original-----
De: ana medeiros < <Email Address Redacted> >
Para: <Email Address Redacted> < <Email Address Redacted> >
Data: Quinta-feira, 2 de Setembro de 1999 00:21
Assunto: Pediatric knees
Hello,
My name is Ana Medeiros, I'm graduate student in Chiba University
(Faculty of Engineering) - Japan, studying about materials applied in
pediatric prosthetic knees. I read some articles which explained this
subject, but I still have some big doubts on polycentric knees. So if
possible could anyone give me a little help? I would be forever
grateful.
1- It is advocated that polycentric knee is a good choice for a
child with knee disarticulation. Which are the most important points in
the polycentric design that influence this choice?
a) The ability to support the body weight in flexioned position?
(center of rotation - in full extension- not elevated and between
superimposed heel contact and push off lines)
b) The stability during stance-phase? (elevated instant center,
or hyper-stabilized center)
c) Flexion is not restricted until at least 130 degrees?
d) Mechanical knee center is better located (closer to the
anatomical center in sound limb) than in single-axis knees?
2- For a young child, who walk with flexionated knees in a wide
base, a flexionated prostheses is used? If so, (for knee disart.)that is
the polycentric #1 a) (writen above), or which other?
3- Which available pediatric knee would you use for a knee
disarticulation prostheses for a young child (for the instance suppose
the ideal one: average weight, height, motor development) who is
receiving the first articulated knee? Why?
Well, I may have asked redundant, wrong questions. If you think
so, please correct me and save a soul from the eternal ignorance.
Thank you very much for your attention and help.
Sincerely,
Ana
------------------------------------------------------------------------------------
Ana,
This is a good topic for discussion in general. The advantages of 4 bar
knees.
Typically the advantages are stated as follows.
1)Higher center of virtual rotation-which presumably makes it easier
to
flex the knee because of a shorter lever arm.
2)Virtual center of rotation is more posterior to weight line making
knee
more stable
3) Toe clearance is improved because of knee geometry
I know this doesn't answer all your questions and in fact I am trying to
find
out more about the stated and true advantages of 4 bar geometry as well.
I am
sure other people will give you more detailed answers.
Mark Benveniste CP
<Email Address Redacted>
------------------------------------------------------------------------------------
======== Fwd by: John Stephens ========
My name is John Stephenson and I am a Certified Prosthetist at the Texas
Scottish Rite Hospital for children in Dallas, Texas. We routinely use a
couple different types of polycentric knees here for the pediatric
amputees.
For a couple of reasons that you mentioned. One is because of the knees
design with the instaneous center of rotation being posterior to the
weight
line, there is inherent stability built into the knee. Much more than
with a
single axis knee. Also the design of the knee allows less of a
discrepancy
in the knee centers because it allows you to get the prosthetic socket
lower
to the knee axis. this allows it to be more cosmetic. there also is a
knee
designed by Century XXII which actually has a stance phase mechanism
built
into which makes for better stability during gait, this is especially
helpful with bilateral patients.
We definitely use many more polycentric knees compared to single axis
knees.
It would certainly be the knee of choice for me. The two knees that we
use
the most are the pediatric Total Knee from Century XXII and the TK-40C
four
bar knee from DAW industries. Hope this helps.
John W. Stephenson, C.P.
<Email Address Redacted>
------------------------------------------------------------------------------------
Hello Ana,
First, to answer some of your questions:
a) The ability to support the body weight in flexioned position?
(center of rotation - in full extension- not elevated and between
superimposed heel contact and push off lines)
Seems like a poly-centric knee would not do better than a
single-axis, since flexing the knee results in a shift forward of the
rotation center, which makes the leg instable.
b) The stability during stance-phase? (elevated instant center, or
hyper-stabilized center)
No more stable than a posteriorly placed single-axis
c) Flexion is not restricted until at least 130 degrees?
That would be a big one, since kids like to sit on the ground when
playing, and move around a lot. A leg which bends no further than 100
degrees would be more restrictive than one which goes up to 130
d) Mechanical knee center is better located (closer to the
anatomical center in sound limb) than in single-axis knees?
It is not always. Only in the later phase of flexion does it approach
the anatomical center. Anyway, the anatomical center of a healthy knee
is not fixed. It can be approximated by a four-bar knee, but probably
not as well as with a well-placed single axis. Disadvantages of the
single-axis are then that the stump must be relatively short (otherwise
there is no room for the hinge) and that the prosthesis is less stable
during stance.
I think one of the main advantages of a four-bar is that people with a
long stump (for instance knee exarticulation) do not get an extended
upper leg when sitting down. A single axis can be applied, but then it
needs to be placed 'in the hollow of the knee', meaning 'up' and 'back'.
This gives good cosmesis (equal leg lengths when standing and sitting)
and stable stance, but I am not sure how well the active walker can walk
with it. I think one of the main disadvantages of the four-bar is that
the rotation center moves forward, which results in shortening of the
leg during swing.
2- For a young child, who walk with flexionated knees in a wide
base, a flexionated prostheses is used? If so, (for knee
disart.)that is the polycentric #1 a) (writen above), or which other?
I do not know if all young children walk with flexed knees. A flexed
knee can hardly be made stable except with a polycentric knee which has
been designed for that purpose. Wether they exist I do not know. For a
person with a knee-exarticulation one would either need a polycentric
hinge or a posteriorly and proximally placed single-axis.
Well, I may have asked redundant, wrong questions. If you think so,
please correct me and save a soul from the eternal ignorance.
I don't know. You may also be getting a lot of wrong answers (including
mine?), so maybe that balances the scales?
Regards,
Edsko Hekman
..........................................................
.Edsko Hekman .
.Laboratory of Biomechanical Engineering .
.Twente University .
.PO box 217 tel. 31-53-4893173 .
.7500AE Enschede fax. 31-53-4893471 .
.e-mail <Email Address Redacted> .
...........................................................
------------------------------------------------------------------------------------
Dear Ana,
A company in Russia called OIME produce an excellent polycentric knee
joint
usable for children from the age of 2 years. I know that this joint is
unique and has been used in Germany.
Their Fax is 007 095 5160560
Regards Michael Mais
German Technical Cooperation (GTZ)
China College for Orthopaedic Technologists (CHICOT)
25 Xue Yuan Jie,
101601 Yan Jiao, Beijing Dong
China V.R.
<Email Address Redacted>
------------------------------------------------------------------------------------
Hi,
As far as what I understand, POlycentric knees are lighter in wt. than
single axis knees, they require less training, so that is why it is
used.
Please will you forward the replies you get to me.
Thanks,
Srivatsa
<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 of a
commercial nature should not be sent to the entire oandp-l list. Responses
should be collected and reposted by the person asking the question.
Send a message to the list by sending to: <Email Address Redacted> To unsubscribe,
send a message to: <Email Address Redacted> with the words UNSUB OANDP-L in the body of the
message. All postings related to US-politics must use a subject line
starting with US-Politics:
Any questions should be directed to Paul E. Prusakowski, CPO at
<Email Address Redacted>
Citation
ana medeiros, “Pediatric knee - Responses,” Digital Resource Foundation for Orthotics and Prosthetics, accessed November 24, 2024, https://library.drfop.org/items/show/213033.
