In a message dated 4/2/00 8:06:33 PM Eastern Daylight Time, [log in to unmask] 
writes:

<<  Whether we say that the foot pushes the body forward or the body 
 uses the foot to push the body forward, I believe, is semantics;  just two 
 ways of saying the same thing.  >>

Kevin,

I actually do not believe that this is semantics.  It is truely at the crux 
of understanding sagittal plane biomechanics.  If the model depicts the foot 
as active (foot pushing the body), then the concept of motion control makes 
sense.  If the model insteads regards the foot as passive, then the goal is 
to permit the normal amount of sagittal plane motion to occur at the time it 
is designed to occur.  This will dictate orthotic Rx design, and prehaps this 
can be another discussion.  

With regard to the MTP joint influencing the RF, Kevin wrote,

>>Otherwise, people with hallux rigidus or patients who have 1st mpj fusion 
surgeries would all have maximally pronated feet, which is definitely not the 
case.  In fact, in the feet which I have done first mpj fusions on, they all 
seem to walk more 
supinated and less pronated than they did before surgery.>>

And I am quite sure you did these procedures correctly with the hallux 
slightly dorsiflexed on the 1st metatarsal.   This is like keeping the 
Windlass active permanently and I am not the least bit surprised as to the 
enhanced stability they acheived.  During single support phase, only 15-20 
degrees of 1st MTP joint dorsiflexion is really required.  If that is 
basically built into the fusion, then it stands to reason that these patients 
can do reasonably well.  The trouble they run into is through toeoff and 
swing phase initiation, but would clearly not pronate in late midstance.  

Hallux rigidus, on the other hand, is a different situation.  These patients 
often have many other pathologies related to DJD in the mid and rear foot, 
and they are not really comparable to patients with dorsiflexed, fused MTP 
joints.  In a handful of cases I have seen of patients S/P hallux fusion when 
the toe and MTP joints are fused rectus rather than dorsiflexed, they have 
horrendous postural pain symptoms.  

Kevin wrote:

>>I am in agreement with most of what you say above.  The BK amputee can walk 
with a peg leg, but not as smoothly as a person who has control of their 
ankle joint plantarflexors during late midstance and propulsion. >>

It is a well known phenomena in O&P that patients with BK (or even AK for 
that matter) amputations, extend the hip far greater on the amputated side 
then on the viable side.  The only explanation I can see for this is the 
ability for the viable side to pull the body over the prosthesis far more 
effectively than can the prosthetic side pulls the body over the viable side. 
 This exception proving the rule concept is something to which most theories 
should be subject.  

Kevin concluded:  
<<Now, that doesn't mean that I will 
ever agree with you 100%.  Then we wouldn't have anything to argue, uh, I 
mean, discuss about.>>

Rx Labs BBS 2000 this August in London should be quite interesting for those 
attending.  (Kevin and I are both on the program.)  Even if we see things 99% 
the same, that last 1% should make for a very exciting discussion!  

Regards, 
Howard Dananberg


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