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View Full Version : Re: Measure of tibio-femoral rotation



achaudhari96
09-10-2007, 03:11 AM
Hi Stephane,

You may have missed it, but there was a long and animated discussion about
the feasibility of measuring values such as internal-external rotation on
Biomch-L about a month or so ago. That thread had the subject
heading "Marker-set independent gait analysis" if you'd like to look back
through the archives. My experience in Tom Andriacchi's group and his
experience over the last 30 years makes us believe that it is possible to
measure internal-external rotation with reasonable accuracy with a
technical marker set such as the point-cluster technique (Andriacchi TP,
J. Biomechanical Engineering, 1998). That paper includes a validation
using simulated noise (both random and systematic). This technique was
also validated for the tibia in a subject wearing an Elizarov device
(Alexander EJ, J. Biomechanics, 2001), and the results for another subject
with a femoral Elizarov device were similar. I would point you to our
contribution to the Biomch-L thread on August 2, 2007. Based on these
validations, we are confident that the point-cluster gives us data
accurate enough to make meaningful observations of the internal-external
rotation of normal and ACL-deficient patients during walking (Dyrby CO, J
Orthopaedic Research,2004, Andriacchi TP, J. Biomechanics, 2005).

As we and others discussed in the Biomch-L thread, there are limitations
to using any motion capture system, whether it uses skin markers, a
clamped-on external fixation, x-rays, bone pins, etc. So it is important
to understand your specific tool, its limitations, and the way it was
validated well enough to be able to interpret its results properly.

In the near future, I intend to begin using the point-cluster technique
with a Vicon MX system and functional joint center determination, just as
you are considering. While identifying the functional joint center for
the knee does not change your absolute accuracy, it gives another relevant
baseline to judge the motion from in addition to a standing reference.
And accurately estimating hip joint moments depends on identifying the hip
joint center accurately, so using a functional approach for that joint
also seems prudent. If you are interested, I think it might be a good
plan to work together to implement this approach within the Vicon software
pipeline.

Ajit M.W. Chaudhari, PhD
Department of Orthopaedics
The Ohio State University
http://www.ortho.ohio-state.edu