Hi all,

At 02:27 PM 10/26/2004 -0700, Kevin Miller wrote:
>
>Given that the purpose of the windlass is to raise the COM in the
>gravitational field in order to produce potential energy for release on
>the next heel strike, and given that the purpose of this action is to
>produce an impulse which results in spinal rotation, thus hip rotation, it
>should follow that hip stabilization in the form of an abductory moment
>and an external rotation moment through toe-off should exist.  There is a
>timing issue, as Eric suggests, but I would question the placement of FHL
>as suggested.  (Unless I misunderstand Eric.)  Here is why....

I don't necessarily agree with your "givens".  Ankle plantar flexion will
raise the COM a whole lot better that winding the windlass.  Now I would
agree that the windlass is important for maintaining foot rigidity so that
the ankle plantar flexors could lift the leg.  (It may not lift the trunk,
because there may be knee and hip flexion.)  When you refer to potential
energy are you referring to the lift of pre swing leg as it becomes the
swing leg?

>
>At heel strike and through toe-off, the external rotators, supinators, and
>invertors must act in an eccentric fashion to maintain timing in gait.  No
>help out of these groups results in a step that progresses too fast.  The
>opposite side must counter or the individual will walk in a circle.  There
>are other effects, but the main idea is that gait becomes inefficient even
>if it appears relatively normal.  (This is a neurological parlor trick
>produced by the cerebellum as a "fail-safe" mechanism for gait.)  If the
>step begins to progress too quickly, but the cuboidonavicular articulation
>fails or is plastic, the aforementioned mechanisms dorsiflex and supinate
>the medial column before ground force reactions can affect it.  That is,
>the mechanism for FHL occurs because of medial/lateral column instability
>and presents prior to the normal initiation of the windlass.  The halux is
>then "limited" because it is already at the end of its physi! ologic
>limits before ground force reaction occurs.  Add to this the hypotonia
>that results in muscles which move pathomechanical joints, and it appears
>that many gait anomalies are simply normal, required actions which occur
>out of a normal timing sequence.  This effect does not rest on force
>transfer through knee ligaments alone as Eric suggests.  The TFL extends
>past the knee joint medial to the tibial tubercle.  Tension of the TFL
>produces both a rotary and abductory force on the lower leg.....enhanced
>if tibial internal rotation is greater than normal.
>

TFL?  Tensor fascia Latta?  The fascia is oriented vertically  and is
ideally positioned to prevent adduction of the tibia on the femur and the
femur on the hip.  Any twist in the tibia would just twist the fascia
latta.  Fascia has very little torsional stiffness.


Cheers,

Eric Fuller

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