Bharti Rajput wrote:

> Was wondering whether anyone has some ideas on what effect
> frontal/transverse plane crosstalk can have on Sagittal plane
> kinematic and kinetic data. e.g. the effect of knee abduction
> and adduction on ankle dorsiflexion and plantarflexion.

It depends on whether you do a 3D or 2D analysis.

In a 3D analysis, the ankle should have its own coordinate system in which the kinematic and kinematic variables are reported. So rotating the leg out of the sagittal plane should have no effect on the results.

In a 2D analysis (which is becoming rare these days), joint moments and angles are expressed with respect to a medio-lateral axis that is fixed in the global reference frame. So there is a potential for error if the actual movement is not in the sagittal plane. The good news is that these errors are usually small. Considering that you are projecting a 3D vector onto a plane, you can see that the error is only about (1-cos(a)) where a is the ab-adduction or internal-external rotation. If a = 10 degrees, the error is only (1-cos(10)) = 1.5%. Even at 20 degrees, the error is only 6%. In CP patients, as suggested by Dave Smith, the error may be larger.

In 3D analysis there is a problem with crosstalk from large sagittal plane variables influencing the smaller transverse and coronal plane variables (Ramakrishnan & Kadaba, 1991; Woltring, 1994). This is an entirely different problem, due to the fact that joint coordinate systems are not well defined. However, there still would be no effect of knee motion on ankle joint variables.


Ton van den Bogert


A.J. (Ton) van den Bogert, PhD
Department of Biomedical Engineering
Cleveland Clinic Foundation

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