Hi all,  Kevin M wrote in response to my comments:

At 05:34 PM 12/16/2004 -0800, you wrote:
>
>You wrote: Looking at the location of the center of pressure, in a static
>situation,
>with no muscles acting does take into account all the joints and ligaments
>and can be used relatively simply to explain what happens in the foot.
>
>I respectfully submit that COM represents little more than the sum of
>forces acting through the kinetic chain.  It does not describe nor predict
>specific joint kinematics or force transfer.


I'll assume that you meant center of pressure and not center of
mass.  (These are different things.)  The center of pressure can be used to
calculate moment about joints.  A patient is seated in a chair with their
foot pointed toward you.  They have an average STJ axis location.  You
push, with your finger, dorsally on their 5th metatarsal head.  The center
of pressure acting on this foot is at the 5th metatarsal head and is distal
to MTJ.  This force will cause the subtalar joint to pronate.  The center
of pressure does allow you to calculate the effect of forces on joints of
the foot.

>  This is of no consequence if you assume that the midfoot acts as a unit
> as Kevin K. suggested.  However, if you subscribe to the hypothesis, as I
> do, that the midfoot is mobile, malleable, and adaptable to surface
> topography until such time during gait that its joints reach their
> endpoint, then their function becomes paramount.

How often, in weight bearing do the joints of the foot not reach their most
dorsiflexed position.

>
>So, there are a myriad of ways to change the course of my COM, just as
>there is an infinite (practically) number of permutations in summing
>31variables to reach the same value.  (31 is the number of articulations
>from the talocrural joint distal...... depending on how you count.... if
>you were wondering where pulled that from.)  The question then becomes,
>"Do I alter COM by correcting joint kinematics or by wedging the entire
>foot?"

Kevin, I don't understand your question.  Are you referring to COM or COP?


Cheers,

Eric Fuller

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