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Scott M. Colby
06-29-1997, 11:22 PM
Thank you to the following persons who responded to my question about
foot pressure measurement systems:

Robert Abramczyk
Paul Fiolkowski
Michael Mueller
Raymond Brodeur
Mark Cornwall
Elizabeth Higbie
Tom Kernozek
Rami Abboud
Michael Torry
Stephanie Jasper
Valeri Drobyshevsky
Peter Seitz

My original posting, as well as a synopsis of the responses follows.
Thanks again.

Scott Colby
Duke University Medical Center
scolby@acpub.duke.edu

Our laboratory is trying to decide which foot pressure system to buy: the
Novel Pedar system or the F-Scan system. I realize that there are
publications out there which suggest that the Novel is much more accurate
than F-Scan, and I also realize that there has been discussion on the
BIOMCH-L about this topic in the past. I understand that recently F-Scan
has claimed to solve its accuracy problems. I would like to know what
the current thinking is on which system is better in terms of accuracy,
repeatability, etc. Is it still widely believed that the Novel system is
the more superior product? Thank you.

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have you looked at the Parotec system (Paromed GmBH, germany).
We use it inm the biomechanics labe here at UF. It collects up to 250 Hz,
and is very reliable with respect to temperature and humidity.

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I don't think its a black-white issue. Like any testing device, the main
point is that one works within the limits of the testing device. There is
data to indicate that absolute accuracy of the Emed is better than that of
F-Scan. Therefore, if the absolute value of the pressure is important, Emed
is better. The benefits of the F-scan compared to the Emed include its
resolution and
the thickness of the sensor. We have found thats its reliability is
adequate for rank ordering (Mueller and Strube, Clin Biomechanics,
11:159-164, 1996). Rank ordering is useful for clinical measures and for
repeated measures type research designs. One also has to be careful to do
things like allow the sensor to warm up in the shoe and load repeatedly (ie
walk for several steps) before calibration.

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We have an F-Scan system which we use for insole evaluations. Initially we
expected to use the F-scan only to study relative pressure distributions.
However, we were pleasantly surprised to find the total force from all
pressure
cells is within 5% of the Z-force measured on a force platform. This
requires
that the mats be calibrated only after thermal equilibrium has been reached.

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We have used both systems in our laboratory and are one of the groups which
have published a comparison between the two (Lower Extremity 2:95-103,
1995). There are serious accuracy problems with the F-Scan. In addition,
reliability is very poor except under extremely strict controls, making it
impractical for many studies investigating "real-world" situations. As far
as F-Scan's claim to have fixed their problems, make sure you see the
actual data. They have made this claim at least three different times over
the last several years.

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You need to get the EMED. The FSCAN has a design flaw in its calibration
process. The FSCAN cannot be used for repeated measures. The EMED is much
more expensive but worth it in the long run.

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Novel is by far better than F-Scan.

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Look at this month's Clinical Biomechanics Journal (April, 1997 Vol. 12:
NO. 3)
There are several abstract detailing relibility and some compare
Tech-Scan and Novel.

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We have the Tekscan F-Scan system. I have found it to be accurate and
useful.
I have not actually worked with the Novel Pedar system, but we do have the
Novel Pliance system for seating. In comparison of the Tekscan and Novel
seating systems I have found that the Tekscan is more accurate.

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Our laboratory employs various pressure measurement systems in clinical
orthopaedics since 1991. Some of my former colleagues have become
authors of orthopaedic software produced by NOVEL company.
I would recommend that you read the article "Distribution of
Pressure-Motion
Analysis - It's High Time" in the German magazine "Orthopadia Technik"
10\1996,
pp. 782-788.
This article provides an objective comparison of EMED-pedlar, Fast-Scan,
ACP, Medi Capteur PEL38, Ormes, Ortho-Tronic, Parotec System by F.W. Kraemer
according to 22 points: precision, price, software, type of sensors, etc.

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Talking of accuracy in PDM means first of all talking about the accuracy
of EACH INDIVIDUAL SENSOR.
TOTAL FORCES collected from a high number of sensors and compared to
results from a Kistler Force Plate ARE NOT SUFFICIANT, because
underestimating sensors could be compensated by overestimating sensors.
In PDM you look for LOCAL accuracy.
Theoretically you can approximate a total force from a high number of
switches (hysteresis 100 %).
One needs to prove the ACCURACY and REPEATABILITY of each individual
sensor curve.
Another big factor is the COMPLIANCE of the sensor array.
Only ELASTIC sensors allow the adaptation to 3-d deformed surfaces.
Unelastic sensors wrinkle and at the location of the wrinkels they either
brake or show wrong pressures.
All force or pressure transducers need A CLEARLY DEFINED RESTORING FORCE
that can act like a spring balance. The quality of the spring balance
defines the quality of the sensor.

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The consensus is that Novel was much more accurate & repeatable that
F-Scan. F-scan is
OK for podiatrists (a main customer base for them), but inadequate for
any serious research where results count. At a gait conference
a paper was presented looking at the accuracy of F-Scan. They
said that with a person just standing still on the insoles, the measured
force was off by around 25% (I think). A paper by Peter Cavanaugh at
Penn State also showed problems with the F-scan system. At the time of
our purchase, I have no doubt that Novel was far better than F-scan,
although it costs about 5 times as much. However, F-scan claimed to have
solved its problems shortly after our purchase, so maybe things have
changed. If you have the money, I'd suggest Novel.

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