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schwartz69
07-05-2007, 09:37 PM
I don't usually get entangled in these debates; however, the recent post by
Thomas Greiner really hit the mark and motivated me to chime in.

What I wanted to add is that there is no need to rely on the HH marker set,
or *any* marker set for that matter. It is entirely possible and practical
to obtain functional joint parameters (Hip Center, Knee Center, and
Effective Knee Axis) in a manner that doesn't depend on marker placement
(within reason; markers need to be visible and reasonably well spaced,
etc.).

We have been doing this at Gillette Children's Specialty Healthcare Center
for Gait and Motion Analysis since Jan 1 2004 on EVERY patient that we see.
That covers over 2000 patient visits and a wide range of ages, diagnoses,
levels of involvement. We use a method developed in our lab (Schwartz &
Rozumalski, J Biomech, 38:107-116, wherein the marker independence is
demonstrated among other things), but there are lots of good functional
methods available (a quick survey of the literature will reveal many
options) and most/all work well if properly implemented.

One thing worth noting is that because the functional methods don't rely on
a specific marker set, they can be run *simultaneously* with any of the
commercial models. This is what we do at our center - we run functional and
PIG models simultaneously. In addition to providing a "second opinion" (the
two models are largely independent) this approach also allows us to acquire
concurrent validity data on the functional method.

Finally, I think it's worth pointing out that the functional approach is
compatible with the kinematic fitting method (championed in this thread by
my esteemed colleague, a great scientist, great humanitarian, and my
dearest, dearest friend for nearly a decade...Richard Baker). Rather than
starting out the kinematic fitter with regression/alignment-jig based
parameters, you can start out with subject-specific functional joint
parameters. You can also use the ROM trials (collected in order to define
the functional parameters) as input for the kinematic fitter.

_______________________
Michael H. Schwartz, Ph.D.

Director of Bioengineering Research
Gillette Children's Specialty Healthcare

Associate Professor - Orthopaedic Surgery
University of Minnesota

Graduate Faculty - Biomedical Engineering
University of Minnesota