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Idiot's guide to foot mechanics and tissue stress pathology

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Raphael1974, Jul 1, 2015.

  1. Raphael1974

    Raphael1974 Member

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    Hi all,

    I'm new to this site and firstly want to thank the contributors for their generosity of sharing expertise and knowledge. I recognise that in our culture the temptation to 'everyone being an expert' is rife and I encounter this in my own field too, so I find myself advancing where Angels fear to tread.....

    From my own knowledge base, but also from what I can discern from what has been shared by podiatrists here, is it correct to state:


    The foot is an incredibly complex structure which has to respond and adapt to multiple, varying Forces acting on it through it's interaction with surfaces ('floor') it encounters.

    It is 'designed' to provide BOTH stability during Force loading and propulsion AND flexibility to adapt to loading Forces and altering foot-surface interfaces. There is a sequence of dynamic flux between these aspects depending on the loading, activity, surface and point in the stance/gait cycle.

    Pathology arises when tissues are loaded outside their functional range (either acutely or chronically). Although a simple thing to say, there is a complex interplay of structure type/quality and nature of loading (Force vectors, levers, moments, sudden or repetitive). Thus an aged and 'worn' tissue will have a lower range of functional response to stress meaning lower level kinetic changes are more likely to cause pathology, whereas healthier tissue may require a higher load to cause pathology (Force vectors are key here as a tissue in alignment to respond better to stresses will take a higher magnitude of Force than a tissue which is in a sub-optimally aligned position).

    Therefore foot motion-postural (kinematic) changes may be due to:

    - Intrinsic structural changes (malformation/rotation, structural damage) - causing 'misalignment' to respond to loading stresses
    - Compensatory due to structural/pathological issues both within the foot as well as higher up in the kinetic chain
    - Changes in external Force vectors (activity, surfaces, footwear)

    And likely a combination of all 3 of the above.

    Expert biomechanical analysis and treatment involves:

    - Detecting site of pathology and the kinetic and kinematic factors causing and arising from this pathology (which requires assessment of the dynamic response of the foot in motion and loading applicable to the patient's lifestyle/sport)
    - Deduce what is needed to address these factors (and what kinematic shifts need to occur to achieve this)
    - Advice/Rx to effect these changes
    - Monitor outcome and reassess/change input as needed

    The above aim is to restore Force loading through the affected tissue which fits with it's functional range (dependent on tissue quality and loading nature) and thus prevents recurrence (although initial input may be to offload this tissue altogether to allow the healing response to occur).

    Changes which can be applied at the level of the foot itself are:

    - Extrinsic (Orthotics, taping, bracing) - these alter the Force vectors occurring through the foot by providing an altered alignment for the 'surface' to react against (considering Newton's 'equal and opposite Force' law)
    - Intrinsic (recruitment of associated contractile units and/or alteration of kinematic sequencing) - again, this will change the Force vectors but by bringing the foot alignment into an altered position so that surface 'equal and opposite Forces' act on different parts of the foot

    Extrinsic interventions will also change intrinsic factors, hence there is a complex interplay here as well!

    Because of all the above, no two patients will ever be identical and clinical input needs to account for:

    - Age, tissue quality, healing capacity
    - Activity/Sport (both desired and possible)
    - Detection of tissue pathology in response to abnormal loading
    - Management of the tissue injury (through promoting healing)
    - Correcting Force vectors passing through the foot to allow the affected tissue to work within the best possible functional range possible for it
    - Reassessing response and tailoring input to ensure maximum benefit obtained

    Would this be a far summary of what I've read so far?

  2. Craig Payne

    Craig Payne Moderator

    Good understanding!

    I have a even briefer version:
    If tissue hurts, you either/or/and decrease the load in that tissue and increase the ability of that tissue to take the load.
  3. Raphael1974

    Raphael1974 Member

    Thanks Craig, I prefer your version ;)

    I'm doing a talk to a bunch of GPs in the autumn and I'm thinking of talking about common foot conditions and approaching it from a pathological (especially as seen on US) and biomechanical perspective. I'll cover what I said above in broad strokes but will quote you (with attribution of course) as a summary statement!!

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