Hello Eric,

I am really glad the actual discussion about the influence of the
peroneus longus on 1st ray plantar flexion seem bit by bit  to clear
up the last remaining stumbling blocs for a complete and unambiguous
understanding of this important biomechanical phenomenon.
So lets move on till the end.

Eric, you said below:

>
>When using force couples you are less likely to make the mistake
>that Root et al did in their analysis on the change in function of
>peroneus longus as the STJ changes position.  If you look at the
>downward component of force, from peroneus longus, at the base of
>the metatarsal, you must have a counter force to create a plantar
>flexion moment.  (If there is no counter force you will get
>translation, downward, of the base and not rotation.)  This counter
>force has to be proximal to the force from the tendon.  There is
>just not a structure, or enough bone proximal to attachment of the
>tendon to create a significant force to create a force couple that
>would create a plantar flexion moment.  Therefore, you have to look
>for some other reason to explain the motion that is seen when you
>pull on the tendon.


Just to refine my anatomical knowledge. It was my believe that the
insertion of the peroneus longus was *distal* to the center of the
joint connecting the 1st metatarsal and the 1st cuneiform. I know the
distance between both not to be large, though significant enough to
enable the *perpendicular* (downward) component of the peroneal
tensile force  to create some plantar flexion of the 1st metatarsal.
If this distance between joint center and insertion point is really
that small as you seem to imply, than I can agree with you rationale
above.
However, if we talk about the plantar flexion, not of the 1st
metatarsal, but of the 1st ray (which includes the 1st cuneiform),
then I think the joint center  between cuneiform and the navicular is
posterior or proximal enough compared to the insertion of the
peroneus tendon to allow the *perpendicular* (or downward) tensile
component of the peroneus to achieve  a very significant plantar
flexion moment. And, here again I need the assistance of anatomy
experts, I believe that, in that case, the lever arm of the
*perpendicular* (or downward) force component for an inverted foot
may be quite larger that the one associated with the *longitudinal*
(or backward) force component of the peroneus. This would imply that,
in contradiction with what I said in my former mail, the
perpendicular  and not the longitudinal force component may create
the dominant plantiflexion moment, especially wiyh the foot in an
inverted angular position. In this case, this would give Root's
theory (still incomplete though)  a greater edge.

Well the discussion gets really interesting now. If we all continue
to clear up the discussion as it is going now, the new revised
chapter on the function of the peroneus with respect to the 1st ray
stabilization may be born and finalized before the end of the weekend.
Who voiced the idea in the past to edit and publish all interesting
and rejuvenating mailbase stuff into a new book ?  Something like
"The new frontiers of biomechanical podiatry" sounds quite attractive
to me. But I am afraid the editing job required to get the book done
is not attractive at all. Too bad or is there  any hope for a miracle
?

A nice weekend to all,
Bart


--
*******************************************************************
  Bart Van Gheluwe
Laboratory of Biomechanics
Vrije Universiteit Brussel -Fac. LK
Vakgroep BIOM
Pleinlaan 2, 1050 Brussel, Belgium
Tel.: 02/629.27.33 (31)
Fax: 02/629.27.36
*******************************************************************

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