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How to Calculate the STJN and the Corrective Degree of Rearfoot Wedge

Discussion in 'Biomechanics, Sports and Foot orthoses' started by JULIE SMITH, Sep 24, 2006.


    JULIE SMITH Member

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    What is the STJ neutral compensation and how to calculate it?

    My understanding is if a rearfoot has the following details:
    1. 24 degs Inversion
    2. 4 degs Eversion
    3. NCSP 6 degs
    4. RCSP 5 degs
    5. Tibia 4 degs varum

    The STJ ROM =28 degs and the STJ NEUT = 6 degs. Therefore is the RCSP the foot compensation to be controlled with a rearfoot wedge? And if so would this patient need a 4 degs or 5 degs rearfoot wedge? Where does the tibia degs come into the calculation?

    My misunderstanding is after doing the STJ measurement I am not sure what is the corrective degree of rearfoot posting to compensate the foot mal-alignment.

    I would appreciate any help

    Many thanks
  2. Craig Payne

    Craig Payne Moderator

    I did not know anyone still did things that way as it does not work ... we got over it last century.

    BUT, wedging is generally used depending on the amount of force needed to get it to the position wanted. If we were in last century, I would have said a rearfoot post would be added to hold foot in its STJ neutral, ie 6 deg post .... but we now know that in reality it does not work.

    Why are you asking?
  3. Cause somebody somewhere still teaching it.
  4. Craig Payne

    Craig Payne Moderator

    Try this as an experiment

    1) Measure someones STJN
    2) Make a wedge of the same angle to invert the foot
    3) Have patient/subject stand on wedge and measure angle of rearfoot
    4) Notice the lack of relationship between angles

    We published data in 2002 that shows on average a wedge inverts the foot, but it was not systematic and some people actually evert more when standing on a medial wedge.

    Try second experiment:
    1) take cast of foot
    2) ask lab to make orthotic to hold foot in STJN
    3) ask lab for cast back
    4) place cast on orthotic and measure calc angle
    5) congratulate yourself as the orthotic holds the cast in the STJN position
    6) have patient stand on orthotic and measure calc angle
    7) scratch head as the foot does not go to neutral
    8) scratch head again two weeks later when patient gets better

    We got paper coming up in JAPMA that shows no relationship between rearfoot motion changes with foot orthoses and symptomatic changes

    We over it ....

    JULIE SMITH Member

    I am asking out of interest because recently my mind has been thinking where is the compensation of a foot mal-alignment occuring ie., is it from the STJ (deviation from its neutral position?) or tissue stress / strain syndrome of the foot structure? Because of not understanding the STJ calculation. Why is it that the STJ motion, RCSP, NCSP and tibia measurements not so importment these days? When you read biomechanic books and it emphasis the importance to do a clinical STJ measurement etc to issue a functional orthotic with a rearfoot wedge. If this is not the correct way to calculate then how do you clinical measure an abnormal foot with excessive pronation to issue an orthotic with the means to stabilise the foot during gait etc..........
  6. Craig Payne

    Craig Payne Moderator

    What are the dates that those books were published? We learnt a lot since then.

    There is plenty of information in the threads recommended for students on where most of the work is heading.

    Essentially, ... the angle of the rearfoot post is probably less irrelevant now, so much so that many do not use them anymore. I tend to go for a vertical post. The angle of rearfoot wedging does seem to be important ... ie the more wedging needed if supination resistance is high (see the discussion on the DC wedge).
  7. Less relevant or more relevant?

    I'm not sure what you mean here, do you mean balancing the forefoot posting to achieve heel vertical? If not, what is a vertical rearfoot post?

    And this is what is confusing. When trying to grasp orthotic prescription and fabrication the student is told that "old school angles" are meaningless. But we still post in angles and cannot give a relationship between angle and orthotic reaction force position and magnitude. If we are not careful here we will find ourselves in the realms of Morgan's meat pie theory. If we are to move forward we must rationalise why we use a fifteen degree medial heel skive as oppose to a 14 degree, 13, 12, 11, 10, 9 etc. etc.

    To an outsider looking in- this is guess work at the moment. Ed is right calibration (or orthotic tuning) is key, just that nobody seems to have achieved this.

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