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Van Den Bogert, Ton
09-06-2007, 12:45 AM
If you want to measure internal-external rotation, this is defined as a rotation about the long axis of the tibia, according to the standard knee joint coordinate system. So defining knee and ankle joint centers will be necessary, either using anatomical landmarks or a functional method. I don't think this part of the method is terribly critical, because the skin movement is a much more important sources of error.

Internal-external rotation of the femur can occur without much involvement of the skin and markers on the femur. You can expect errors (in walking) of about 5 degrees, and the real skeletal axial rotation is also about 5 degrees so you will not get good information (Reinschmidt et al, Gait & Posture 1997, Figure 4, middle row of plots).

There is a nice paper by Jeff Houck (Gait & Posture 2004) on a femoral tracking device which seeems to eliminate most of the skin movement problem for axial rotation, even in running. The device carries reflective markers and is clamped onto the epicondyles of the femur.

Another way to solve the problem is to choose a different variable to measure, if you can find one that has clinical relevance and is easier to measure. Axial tibia rotation relative to the foot, or relative to the ground, is a much more reliable measurement because it is not using any skin markers on the femur (e.g. Bellchamber & van den Bogert, J Biomech 2000). But then you are no longer measuring tibiofemoral kinematics, so the relevance to ACL deficiency is not as strong.

--

Ton van den Bogert
Department of Biomedical Engineering
Cleveland Clinic Foundation
http://www.lerner.ccf.org/bme/bogert/


> -----Original Message-----
> From: * Biomechanics and Movement Science listserver
> [mailto:BIOMCH-L@NIC.SURFNET.NL] On Behalf Of Stéphane Bouilland
> Sent: Wednesday, September 05, 2007 5:26 AM
> To: BIOMCH-L@NIC.SURFNET.NL
> Subject: [BIOMCH-L] Measure of tibio-femoral rotation
>
> Hi,
>
> We would like to use our optoelectronic system (Vicon MX) to
> measure axial rotation of the knee (tibio-femoral rotation)
> in young patients with ACL.
> For the moment, I think to use the following protocol :
> functional method to identify the hip, knee and ankle centres
> and axis of rotation, and technical marker set in order to
> take account for skin artefact.
> My wish would be to share experience with someone on the
> following points :
> - What accuracy and repeatability can I expect ?
> - Is that protocol the best one for my purpose ?
>
> Many thanks by advance,
>
> Stéphane BOUILLAND
> Chargé de mission R&D
> Fondation Hopale - Centre Calvé
> 72 Esplanade Parmentier
> 62608 Berck sur mer
> France
> tel : 03-21-89-31-99
> fax : 03-21-89-33-18
> email : sbouilland@hopale.com
> http://www.hopale.com
> Site Perso : http://www.stephane-bouilland.com/
> ---------------------------------------------------------------
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