Simon,
How does talar plantarflexion/adduction take place during closed chain STJ
pronation?  How does the talus actually move?  If the calcaneus simply
inverted and everted during STJ motion and the calcaneal inclination angle
remained unchanged, could the talus become lower at the level of the talar
trochlea?  When we say that the talus adducts and plantarflexes, isn't most
of the motion occurring at distally at the talar head?  If so, then how does
the trochlea become lower?  Wouldn't the STJ unit have to move vertically in
response to the position of the MTJ?

It seems to me that for the leg to functionally shorten, compensation has to
occur at both the STJ and MTJ.  The STJ contributes by everting the
calcaneus which lowers the entire STJ.  As the STJ pronates, the MTJ allows
the forefoot to dorsiflex on the rearfoot which decreased both the medial
and lateral longitudinal arch heights (closed chain MTJ pronation).  Or put
another way, the foot flattens which lowers the trochlea!

Regards,
Jeff

> > Closed chain STJ pronation increases the ROM of the MTJ and produces
> > relative dorsiflexion of the forefoot on the rearfoot in many
individuals.
> > This enables a unilateral decrease in the calcaneal inclination angle
> which
> > contributes to lowering of the rearfoot (and therefore the entire limb),
> as
> > a component of the compensatory process.
>
> Interesting, but I believe the ability to gain a reduction in limb length
> via this mechanism would be dependent upon the radius of curvature of the
> medial calcaneal tubercle in the sagittal plane and clearly the spatial
> orientation of the STJ axis. Can you suggest how much declination would be
> required to bring about a reduction of 1cm in limb length via this
> mechanism?
>
> Best wishes,
> Simon

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