Eric, you wrote:
> The nutcracker's arms are both touching the nut.  There is little force
> applied to the nut.  Then the brain sends the signal to the muscle to
> increase contraction.  There is increased tension in the muscles the
> fingers push harder on the nutcracker and there is increased stress on the
> nut.  This all occurs without motion.

Then as muscle create more force the nut reaches a point where it deforms
and then cracks.  The nut cracker then moves because there was a force
applied to it by the fingers.  The brain rapidly reduces the signal to the
muscles so that there is some nut left to eat and the brain can make it to
the next day without starving.

So, if we just look at the motion we miss the first paragraph.  If you just
look at the second paragraph you may still get the nut, but you get a better
picture of what's going on if you look at both paragraphs.<

Eric, you could use the development of halluxabductovalgus (HAV) to
illustrate your point.  In the early stages, there may be abnormal STJ
pronation occurring without any evidence of deformity or abnormal forces at
the 1st MPJ (although we know through experience that HAV may occur in this
patient with abnormal pronation).  The forces (moments) that create osseous
compression and separation leading to osteoclastic and osteoblastic activity
can be likened to the pressure on the nut and the imperceptible deformation
that occurs prior to the shell cracking.  It is much easier for us to
observe the nut actively breaking or the evidence that it has occurred after
the fact, than it is to appreciate the forces leading up to the event.

In podiatry, we have seen the broken nut enough times to realize that if we
wish to prevent it, we need to block the nut cracker or stop squeezing the
handles, or if the shell has started to crack, we need to stop the forces to
prevent the shell from cracking further.  The key is finding the tools to
allow us to see the forces before they result in deformity or in progression
of the deformity when deformity has occurred.  Since we are dealing with a
pathological population, we obviously haven't arrived at the stage of
preventative biomechanics.  Understand forces better may help us get there.

Respectfully,
Jeff Root

-----------------------------------------------------------------
This message was distributed by the Podiatry JISCmail list server

All opinions and assertions contained in this message are those of
the original author. The listowner(s) and the JISCmail service take
no responsibility for the content.

to leave the Podiatry email list send a message containing the text
leave podiatry
to [log in to unmask]

Please visit http://www.jiscmail.ac.uk for any further information
-----------------------------------------------------------------