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Alexander Schmidt (neenah/wi)
03-20-1996, 05:59 AM
Hello subscribers,

I posted last week requesting the following about the Tekscan pressure
system:

After spending several days with the Tekscan pressure system, I am
somehow sceptical about the capabilities of the system. Our original
euphoria to use this equipment to measure absolut pressures and
pressure distribution between two deformable medias/surfaces is over
now and we are just at the beginning of a long learning curve regarding
sensor calibration, best sensor shape (no bending influence on pressure
output), interpreting the huge data output and many other things. I
realised that this equipment has been successfully used in the past to
determne pressures, where the sensor is placed between a deformable and
a more or less nondeformable surface.
Does anyone has some experience in the area described above?
Has anyone ever quantyfied the influence of the sensor bending to the
pressure output?


Here comes a summary of all the response:
(Thanks to all who contributed)


From: Claus Willemer

Dear Mr Schmidt,
I know two groups in Germany working with pressure distribution on soft
surfaces. Prof Dr Nicol (University Muenster) developed the
Novel-analyzing medhod. Another method is used in Koeln (deutsche
Sporthochschule), may be Tekscan.


From: "Michael J. Mueller"

I have been using the Tekscan pressure system (FScan) to measure
pressures
inside the shoe for patients with DM and peripheral neuropathy. We
performed reliability testing in an applied situation, ie having
subjects
use the sensor and comparing across trials with same sensor, across
sensors,
and across days (ie 4 different days) with calibration as recommended
by
manufacturer and with additional calibration from a force platform. We
found acceptable reliability (generalizability coefficients=.75) for
"relative measures" ie comparing the rank. We also calculated the
index of
dependability which assesses the ability to take absolute measures. To
obtain adequate reliability for absolute measures, we found the need to
"adjust" with a calibration from a force platform. The manuscript has
been
accepted in Clinical Biomechanics and should be published soon.
Overall, I
have been pleased with the system - but like all measuring devices, one
has
to work within the limits of the system. Other suggestions found in
the
literatuare are to repeatedly load the sensor before calibration and
then
to collect data immediately after calibration. Several references
referring
to reliability of the system in footwear applications are listed below.


1. Birke JA, Foto JG, Deepak S, Watson J: Measurement of
pressure walking in footwear used in leprosy. Lepr Rev:
1994; 65:262-271.

2. Mueller MJ, Sinacore DR, Hoogstrate S, Daly L: Hip and
ankle walking strategies: Effect on peak plantar pressures
and implications for neuropathic ulceration. Arch Phys Med
Rehabil, 1994;75:1996-2000.

3. Koch M: Measuring plantar pressure in conventional shoes
with the TEKSCAN sensory system. {German} Biomedizinische
Technik 1993; 38:243-248.

4. Rose NE, Feiwell LA, Cracchiolo A: A method of measuring
foot pressures using a high resolution, computerized insole
sensor: The effect of heel wedges on plantar pressure
distribution and center of force. Foot & Ankle 1992; 13:263-
270.



From: Thomas W Kernozek

Dear Alexander,

Unfortunately, I do not have a solution for your problems with the
Teckscan measurement system. There are published papers indicating
similar problems with this system so you are not alone. Work by Xia,
Garbalosa, & Cavanaugh Error Analysis of Two Systems to Measure In-shoe

Pressures (American Society of Biomechanics, 1994 - Ohio State),
Cavanaugh, Letter to the Editor of Foot and Ankle (1995), Werner,
Green,
Fortino, Mann and Short, Evaluation of a Dynamic Intra-articular
Contact
Pressure Sensing System (41st Annual Meeting ORS, 1995 Orlando),
McPoil,
Cornwall and Yamada, A Comparison of Two In-shoe Plantar Pressure
Measurement Systems (The Lower Extremity, 1995) have shown similar
problems. The majority of the work expresses poor sensor
characteristics
such as drift (creep), linearity, temp. sensitivity, & hysteresis. Not

something that can be easily remedied, if at all.

I would suggest trying Novel Inc. (612) 332-8605 as an alternative
system. They market pressure measurement systems for various
applications. The sensor characteristics are much better and are
calibrated by homogeneous air pressure enable measurements within 5%.
The contact name is Susan Diekrager.

If you have any further questions, contact me via e-mail.

Sincerely,

Tom Kernozek, Ph.D.
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Thomas W. Kernozek, Ph.D. [ ] [ ]
University of Minnesota / /\ \ / /\ \ GO--------
Division of Kinesiology / / \ / \ \ GOPHERS!!!
Human Movement Research Lab [ ] [ ] [ ] ----------
e-mail: kerno001@maroon.tc.umn.edu
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Alexander Schmidt

Neenah, WI (USA)
Tel.: 414-721-6481, Fax.: 414-721-5459
Email: aschmidt@kcc.com