Eric/ Ray et al

On Thursday, 12 October 2000 18:25, [log in to unmask] 
[SMTP:[log in to unmask]] wrote:
> I am sure that we can all agree that forefoot to rearfoot deviations and
> rearfoot to leg deviations do exist when the foot is examined in TN 
congrency
> and with the forefoot fully pronated.  What we cannot agree on is if 
these
> morphological variations are pathomechanically significant and if they 
create
> predictable abnormal compensation. What appears to have been exposed in
> recent years, especially with the development of plantar pressure 
systems, is
> that what we see by way of abnormal foot function is not always linked to 
the
> 'foot types'  as desribed by Dr. Root.

I have recently been involved in a study using the Pedar system to 
investigate the relationship between standing foot posture and dynamic 
function (N=30 people, 60 limbs). Much of the literature has reported 
coefficients of determination (the amount of variation in the dynamic 
measures which is predicted by the static measure ) of the order of 20-30% 
depending on the precise choice of static and dynamic measures, this still 
leaves >60% of the variation in dynamic functional measures either 
unexplained, or explained by factors other than the underlying structure. 
Using a multiple set of  8 measures to statically evaluate the foot in all 
three planes and in rearfoot and mid/forefoot segments we have been able to 
explain 35-50% of the dynamic variation, an improvement on the existing 
literature but still suggesting strongly that there is far more to the 
dynamic story than the standing (or non-weightbearing) structure.

Of particular interest is that prior to the mathematical analysis, as part 
of the preliminary process for trying to identify where the predictors 
might lie, we laid out all the pressure maps in order on a large walkway 
with a continuum from left to right set out by foot type (with the patterns 
from the most pronated feet on the left and the most supinated feet on the 
right.) We then got 6 experienced practitioners from the department to try 
to identify patterns which might be consistent with foot type.  In the 
event the relationship was pretty sketchy to the naked eye. Some features 
 such as high 1ipj joint pressures in the more pronated feet more fairly 
obvious (although not 100% consistent), but the classic expected 'Rootian' 
patterns of high mpj  2-4 pressures in pronated feet and high mpj 1/5 
pressures in supinated feet were *NOT* clearly evident across the 
continuum. While there were visible 'trends', even at the real extremes 
(and these were fairly extreme) there were pressure patterns which, for 
example according to the 'Root" model would be expected to be associated 
with excessively pronated feet - that were actually obtained from quite 
supinated feet and vice versa. There were 'consistencies' in the patterns, 
but they were *not* complete, as there were also individuals who's pressure 
pattern definitely did not conform to the expected foot type.

For the record, the best predictor was the capacity of the overall group of 
measures (all 3 planes), in combination, to predict 1st ipj pressures - 
which were consistently higher in more pronated individuals. The rearfoot 
measures were almost useless at predicting the 1st ipj pressure. Rearfoot 
measures were reasonable predictors of mpj pressures , the data suggesting 
that supinated feet generally had higher pressures in the forefoot. However 
the (widely used) rearfoot frontal plane measures were fairly weak 
predictors of anything other than a moderate relationship with 5th mpj 
pressure. We will probably be recommending in the paper that rearfoot 
measures alone are inadequate descriptors of pronated/supinated foot 
structure or function.

>. This
> is where your Pedar or F-Scan analysis may give added information on the
> type and degree of compensation present.

In spite of the above we must be careful not to overstate the case. 
Pressure measures, in whatever form, only give us the external resultant of 
all of the internal machinations of the foot. Like trying to decipher the 
detailed workings of an engine only by looking at it from the outside and 
analysing its power output curves. The experienced mechanic could have good 
go at working out what was going on inside but it would be no more than 
educated guesswork. Pedar etc tell us the ultimate effect of what happens 
in the foot but not the mechanism by which the effects are brought about.

The relationship between structure and function is incomplete (although 
improving) and the current statically based, theories are only moderate 
predictors of the dynamic variability. We must keep that in mind when 
confronted by patients in whom we identify what appear to be structural 
abnormalities.

The paper on which this message is based should be written up in the coming 
months and will be published in an industry journal somewhere to be 
decided.

Tony



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