Prosthetic Knee Choices RESPONSES

Prosthetic Knee Choices RESPONSES

Roland van Peppen

10/18/1999

These are the responses I had on the question:
I like to hear your ideas about the choice of a prosthetic knee for a
TF-amputee.
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Your question is excellent, and one I have raised and will continue to
discuss in this and other forums. In fact, I am hoping to eventually
catalyze
a Knee Seminar for examining our choices for knees.

I have also approached manufacturers for various design ideas and
improvements. I believe we need better choices.

With respect to you example of the Teh Lin vs Total knee. You need to
specify
which 4 bar Teh Lin. The same with the Total knee.
(friction,pneumatic,hydraulic, adjustable.etc. There are differences in
the
centroid (path of the instantaneous center of rotation), height and
position
of the ICR, effective toe clearance differences, weight of unit,
smoothness
of knee action, ease of mounting, assessed value of the locking feature
of
the total knee.

All that said, many of these factors are not considered by prosthetists.
In addition, if the patient is a cadidate for a single axis knee, we may
opt
for one that has a hydraulic unit that will allow for stumble recovery.

Sincerely,
Mark Benveniste CP
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I will try to respond to your question as best I can. Since you
mentioned two polycentric knees and no single axis knees I will limit my
response to choices of which polycentric knee to choose. First you
should evaluate the capabilities of the patient including the range of
motion, strength in all planes, length of the residuum, activity level
and amount of stability needed in the knee joint. For example: if the
patient has a long residuum with good strength in all planes and an
active lifestyle it would be optimal to have some type of fluid control
and a stance/flexion feature. Compare that to lets say a geriatric
patient with adequate length but only moderate strength but has the
potential to ambulate with a single point cane for short distances at a
single speed. Clearly the choices would be different for these two
scenarios. Another factor is the alignability of the knees. Some
knees have a tube clamp adapter at the distal end which will limit the
alignability compared to a pyramid connection. Some knees allow for
slide adjustments to the proximal connection which helps a lot to
achieve a good outcome because the alignment can be a critical factor
towards the success of a prosthesis. In a temporary/preparitory
prosthesis I try to find a very adjustable knee so I can keep on top of
the alignment of the prosthesis as the patient progresses through
therapy. I may set the knee up very stable at delivery and as the
patient learns the motions necessary to control the knee I will
progressively adjust the alignment to optimize the gait. I feel there
is no one knee that is the best for all amputees or even one knee that
is necessarily better or worse than another knee as long as durability
is not in question. I use a variety of knees in my practice simply
because they all have little subtle advantages and/or disadvantages to
them that can sometimes become evident at the best and/or worst times.
Finally, another consideration is any special needs that need to be
met. Some people like to garden and will need to kneel or sit on the
ground. Will the knee have enough available flexion? Some knees only
flex to 115' and some have no limit and the shin can flex fully behind
the socket. How heavy is the unit? Is cosmesis a concern? Some units
are a nightmare to cosmetically finish in a continuous cover and need to
be finished with a two piece cover. Some units are so big you can
almost never get the finished size down to match the sound leg. Will
that be acceptable? Obviously there are many factors other than the
mechanics of the knee that can play important roles in the success of a
prosthesis. But for what it is worth, I hope this will help.

Kevin Warner CP
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Roland,
This is a good Question? One that I believe
all of us should ask. There are many that offer the
same. Is price , warrenty ,speed of delivery (service),
the difference? Weight? Cost? There are many questions
associated with this question. I would like to talk more.

Hal
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>why do you choose a Teh Lin knee and not a Total Knee?

In our several year experience with both the Teh-Lin requires less
servicing than the Total Knee, which seems to require work every 6
months
or so. Aside from general maintenance, lubricating and so on, as a
general rule, I think pneumatic systems are less prone to leakage than
hydraulics, can continue to function despite them, and aren't as messy
when they occur.

Aryeh
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Is the question How do Physicians,Physical Therapists and Prosthetists
make
knee choices for pts?

 I personally believe that well informed Prosthetists SHOULD be making
the
decision based on what they think will work best for the pt with the
input
from the rehab staff.
This conclusion may happen by trying a few knees to see what works best.
Until we have better choices, we are often choosing the best of what is
available.

Dedicated physicians and therapists can be somewhat familiar with
componentry
but they are specialists in their area, not in prosthetics.

In all fairness, there are not always clear guidelines. There are
principles
that are followed such as choosing a 4 bar knee when toe clearance is
desired
, but sometimes these are theoretical and in practice you may find the
pt is
more concerned about falling in the beginning and may not be ready for
that
until later, if at all. Weight is an important consideration as well.
Activities and activity level play an important part.
If the pt is capable of a variable cadence (walking at different speeds)
then in the USA, we are justified in using a hydraulic or pneumatic
knees.
Although, not all hydraulic & pneumatic knees give variable cadence.

Again, we don't necessarily have optimal choices, but I believe the
manufacturing industry is trying to provide better choices.

Decisions are often made based on familiarity with the component, or
choosing
the best options. In some cases it is much more clear cut. for a knee
disarticulation we generally see 4 bar knees. However, some prosthetists
make
think the single axis SNS hydraulic function will be more useful to the
pt
and so they try for that and make a compromise on knee center. When a
good 4
bar knee with SNS hydraulic function is available, that should be the
optimal
choice. However, weight and maintenance might be another determining
factor.

Once again, my personal opinion is that we need more choices. I would
like to
see a 4 bar knee with a weight activated stance control feature.
The Geoflex is a new knee from an American manufacturer that may be an
improvement over the standard weight activated stance control knee.
I am not familiar enough with it to determine that yet.

CP means Certified Prosthetist which in most countries (I believe) means
that
you have undergone formalized education, participated in a residency
program,
and passed extensive exams. A prosthetic technician
is one who specialises in the fabrication of a prostheses under the
direction
of a prosthetist.

I suggest you visit some prosthetists and ask how they make their knee
component selections. This field is rapidly evolving and better choices
are
being offered to the patients/clients by informed prosthetists.

-Mark
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<< We try to make a 'decision-tree'. Some decisions are in our opinion
quit
clear (locked/not-locked). But what we like to know is, for example, why
do
you choose a Teh Lin knee and not a Total Knee? >>

Sound like you are trying to over simply the prescription process. The
difference in some knee systems is the brand name. What is lacking
currently
is a database of outcomes with the various systems and then in this day
and
age a virtual realty program not an anarchic decision tree

Al Pike, CP
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The best knee component out there is the Total Knee on all levels.

In order of usefulness to a TF amputee - which I am - twice in fact

Total Knee - stable and helps ensure proper posture and swing through
because the toe actually lifts off the ground and doesn't drag. The
unlocking sweet spot can be set for each individuals preferences, mine
is
set to disengage on toe off - but I can also break the lock (to sit etc)
by
turning the toes in slightly (less than 10 degrees) and tapping a very
bit
of weight on it.

Otto Bock 3R60 - slightly lighter - the locking works but disengaging
the
lock when you aren't walking is difficult to accomplish as you have to
use
a severe hip hike.

I have used practically every knee out there and as a DAK amputee of
over
33 years, all my life in fact, I always recommend the Total Knee because
of
the way it has worked for me.

I hope it helps to have an opinion that is not influenced by money.
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THANKS YOU FOR THE RESPONSES,
ROLAND