Dear Eric and other courageous still awake,

Glad that there is some agreement now butEricin his last posting  said
about late stance pronation:

>I agree that it is possible for a pronation moment to create enough momentum
>for the STJ (Not MTJ, long axis is not a good hinge) to evert and load the
>medial forefoot.  First, there has to be range of motion of both the STJ and
>MTJ to do this.  A forefoot valgus wedge could, if high enough use up all the
>available range of motion in the direction of eversion.  Secondly, in some
>feet, with slow motion video, you see a rapid initial pronation and then a
>slowing or stopping of pronation and then just around heel off additional
>pronation occurring.  This acceleration-deceleration-acceleration of
>pronation velocity must be accompanied by changes in STJ moment.  So, it
>seems that there is some other source of moment that causes pronation that
>causes this additional pronation.  The point here is that momentum of the STJ
>seems to be an unlikely explanation of additional "late stance phase"
>pronation.
>

Bart replies:

This two-phase pronation  (what Eric calls
acceleration-decelaration-acceleration pronation velocity)does happen but
is rather rare.  Most of  the time  you see subtalar pronation smoothly
evolving in so called midtarsal pronation, or in what I prefer to call
midtarsal collapse (the subtalar pronation unlocks the midfoot joints and
by so doing destabilizes the midfoot forcing  it into  collapse).
So, the classical concept of  "unlocking"  the midfoot structure through
subtalar pronation, especially if the STJ is medially displaced, offers a
simple explanation for late stance phase pronation.

Regards 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
*******************************************************************




%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%