Simon, you asked Craig:
>Given that you did not see significant change in rearfoot position in your
study, can you postulate on how the orthotics might have produced the
reduction in force required for dorsiflexion.<

The frontal plane position and the direction of motion of the posterior
surface of the calcaneus are only one indicator of the position or direction
of motion of the STJ.  Although more difficult to observe or measure without
x-ray, the transverse and sagittal plane position of the talus is also an
indicator of STJ position.  When you dorsiflex the hallux during the
Hubschere maneuver the arch height increases.  How does arch height
increase?  Probably a combination of closed chain MTJ supination and STJ
supination.  This requires talar dorsiflexion and abduction or forefoot
adduction and plantarflexion.

To some degree, an orthosis supports the medial arch of the foot, thereby
reducing the extent of adduction and plantarflexion of the talar head during
relaxed stance.  When wearing an orthosis the medial arch of the orthosis is
under load.  The higher the arch of the orthosis, the greater the supination
moment created by the device.  This is obvious if you imagine a highly
exaggerated arch shape within an orthosis (forefoot plantarflexes and
rearfoot inverts-not necessarily comfortably though).

So one question is, how much of the force need to dorsiflex the hallux is
necessary to supinate the MTJ in a closed chain condition?  Can we really
differentiate STJ and MTJ motion or the forces necessary to produce motion
in a closed chain situation?  Perhaps the orthosis reduces the force
necessary to dorsiflex the hallux because it influences the position of
and/or moments at the MTJ!

Respectfully,

Jeff Root

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