Jeff, Kevin,



The device in question should apply not a resultant force, but forces over the full plantar surface as per in walking. I would add video here, and correlate-sync motion with the forces. These forces can be obtained by doing in-shoe or floor mat recordings, and having the device apply these same forces with same timing. Yes, every foot and gait is different, but you can collect with x numbers of non-pathological feet and gait, get average, and have a baseline, and call it non-pathological or non-symptomatic base line (but not normal). With this, you now collect with symptomatic feet and/or gait (pending foot problem to investigate), and start making comparisons.



To get ideal number (number of subjects), do a power-analysis. Stats textbooks will inform and show how to do a power-analysis, and determine sample size needed to make results (study) significant.



Norman



	-----Original Message----- 

	From: A group for the academic discussion of current issues in podiatry on behalf of Jeff Root 

	Sent: Wed 9/22/2004 12:35 PM 

	To: [log in to unmask] 

	Cc: 

	Subject: Re: GRF on Forefoot, What Moves?

	

	

	Kevin, you wrote:

	

	To measure midtarsal joint (MTJ) compliance in a live subject, I would have the subject laying supine on a table with three dimensional markers on their tibia, lateral calcaneus and 5th metatarsal.  A force sensing device could be used to press on the plantar forefoot of the individual and could simultaneously measure force on the forefoot.  For every 2 mm of forefoot dorsiflexion relative to the tibia that the device applied to the forefoot, the force under the forefoot would be registered.  In addition, at every 2 mm of forefoot movement, the MTJ and ankle/rearfoot joints motions would be noted so that an approximation of MTJ stiffness could be made (stiffness of MTJ= force under forefoot/displacement of forefoot to rearfoot.  This experiment would demonstrate differences in MTJ stiffness (or compliance) in a live subject.  However, this experiment would be greatly improved if bone markers could be used in the talus, navicular, calcaneus and cuboid.  I agree it would not be an easy task to perform the experiment (without bone pins, unless you're in Sweden then we could use bone pins), but it could be done by many biomechanics laboratories around the world.

	 

	What about the transverse plane component of MTJ motion?  You can apply a dorsiflexion force to the forefoot and sometimes get more forefoot abduction motion than forefoot dorsiflexion motion.  Or it may appear that the forefoot is dorsiflexing when in actuality, the rearfoot is adducting and the forefoot is everting.  So I suppose that in the above experiment you would be measuring sagittal plane compliance of the MTJ.  In a sense, this is like using frontal plane motion of the calcaneus to demonstrate relative motion at the STJ in that it is not a triplane measurement.  In order to measure true MTJ compliance, wouldn't it be necessary to have a triplane measurement?

	 

	Respectfully,

	Jeff Root

	p.s. I commend you for thinking outside the box even if the answers aren't easy.  Of course, neither are the questions!  But they do make for some interesting discussion.



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