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When does a 3/4 length FFO stop working?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Phil Wells, Jul 31, 2009.

  1. Phil Wells

    Phil Wells Active Member


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    Dear all

    I had a discussion with a colleague yesterday regarding treating an unstable/flexible midfoot with a flexible/less stiff forefoot valgus.
    He beleived that if an orthoses was supportive enough under the navicular that propulsive phase posting and rear foot posting was not needed.
    I believe that a bit of everything was more appropriate i.e. a medial skive to reduce calc plantarflexion, arch 'support' and 2-5 sulcus posting.
    My question is when does a 3/4 device actually stop working?
    Is it enough to apply ORF to 70% of the gait cycle and not the final 30%?

    Any thoughts would be great.

    Cheers

    Phil
     
  2. david3679

    david3679 Active Member

    Hey Phil

    Is that not the purpose of propulsive phase posting?

    Dave MCk
    Stepeasy
     
  3. Phil:

    Rearfoot posting is critical to optimizing foot orthosis function in those patients that need to have their foot orthoses significantly alter their subtalar joint pronation/supination moments. Anyone who tells you differently probably either has a financial interest in an orthosis lab that doesn't use rearfoot posts (e.g. Ed Glaser/Sole Supports) or simply doesn't understand the mechanics of the foot.

    Many patients also need forefoot extensions, past the 3/4 length of the standard orthosis shell, to optimize their gait function and get maximum therapeutic response from their foot orthoses. I use forefoot extensions in approximately 1/3rd of the custom orthoses I dispense to my patients.
     
  4. Phil Wells

    Phil Wells Active Member

    Dear Mr Mcketchup

    I may already know the answer to this question, I think, but how do you decide when to post the forefoot i.e. the rearfoot and midfoot control needs additional help?

    Cheers

    Fluff
     
    Last edited: Jul 31, 2009
  5. Phil Wells

    Phil Wells Active Member

    Kevin

    I assume by rearfoot posting you mean an extrinsic post and medial/lateral skives?
    If a rearfoot post is so critical, why do you think this is?
    Possible methods of action include a sagittal plane component, strengthening of the shell (although with CAD technology this need not be the case) frontal plane deceleration via moments etc.

    Just for fun, I would like your gut feeling based on your experience rather than research based opinion.
    I think it may open up new thought patterns as people can hypothesis without being interrogated by the more picky members of the forum.

    This is just a polite request/thought experiment with no agenda on my part.

    Here's hoping

    Phil
     
  6. david3679

    david3679 Active Member

    Hi Phil
    I would start off with the level of description of the problem is limited to part of the foot problem with explanation of the pathology being minimal.
    The first issue being that the adequate support suggests no corrective element in the orthotic but more " physical bulk". Now my understanding is that the change in pressures and moments achieved with orthotics is aimed at the reduction of excessive dysfunction not the elementation of normal function. The other view point is if you have a hypermobile and unstable midfoot then why? what is the cause of the hypo hypermobility imbalance. what do we have to achieve to make the midfoot stable the use of cuboid skives etc.

    ultimately when do we forefoot post. Whats the patient going to use the device for, does it involve propulsive phase mechanics exclusively. how severe are the symptoms of the patient. I would say that the use of optimal control would involve as close to 100% control that is tollerable by the patient.

    more info would be nice Phil

    HAlf a story again

    Dave:drinks
     
  7. Phil:

    When I refer to rearfoot posts, I am referring to the external addition added to an orthosis plate in the rearfoot of the orthosis on the plantar shell, not heel skives.

    Rearfoot posts are an important part of the orthosis in many patients since it greatly increases the surface area of contact of the rear section of the foot orthosis with the sole of the shoe. This increased surface area of contact then better allows the orthosis to exert strong orthosis reaction forces on the plantar rearfoot during the first half of stance phase to either increase the external subtalar joint (STJ) pronation moments or increase the external STJ supination moments acting on the foot during that phase of gait.

    Rearfoot posts also will increase stiffness of the orthosis shell to frontal plane and sagittal plane bending forces from the foot which can then be used by the prescribing clinician to "tune" the flexibility of the orthosis to the desired orthosis shell stiffness for the patient. Rearfoot posts can also be used as platforms for the addition of unilateral or bilateral heel lifts which can be a critical part of effective therapeutic foot orthosis design.

    Therefore, clinicians that never use rearfoot posts in their orthoses (just to save on orthosis costs??!!) are, in many cases, not giving their patients the full benefit of the many therapeutic benefits of custom foot orthoses.
     
  8. Phil Wells

    Phil Wells Active Member

    Dave

    No further info as the practitioner in question treats ALL his patients this way. Tissue stress does not come into it. He believes that in this type of patient he only needs to cast the foot with the Hicks windlass fully engaged (inverted heel, high arch etc), no arch fill to the casts, 1st ray additions to allow for pf of the 1st ray and any forevalgus/varus balanced with a small extrinsic post to behind the mets.
    The reason for the conversation is that he has a high degree of patients non compliance of FFO's due to lateral heel cup irritation.
    Is it my manufacturing process or his casting technique - I will hopefully have a definitive answers.

    As an aside, would you elaborate on your use of Mortons extensions for short 1st rays as I think you have got a good prescription approach that other people may find useful - I definitely have used it successfully.

    Cheers
    Phil
     
  9. pgcarter

    pgcarter Well-Known Member

    If the foot has a large and rigid forefoot valgus there is going to be a significant lateral shift/tilt of the whole foot in late stance/propulsion phase as the previously elevated lateral forefoot proceeds to make contact with the ground. The transition to this position will tend to push the foot out onto whatever lateral cup may be there, a good way of causing irritation I would have thought.. You could get rid of the heel cup, but that is failing to address the cause, Personally I think forefoot mechanics and it's effect on rear foot and lower limb torsion issues have been under done so far in research and teaching. The whole idea of the talus as being a torque converter begs for further investigation.
    I always use forefoot extensions in situations where there is likely to be additional torques generated by existing forefoot/rearfoot anomalies. These forces are likely to be higher in feet that have high ligamentous tone.
    regards Phill Carter
     
  10. pgcarter

    pgcarter Well-Known Member

    And to flog a dead horse....maybe he should be making his own and he would learn how to avoid more of his tolerance and return issues. It's not you making them that's the problem, you've never seen the foot, it's the fact that he's not making them.
    regards Phill
     
  11. Phil:

    Tell your colleague that since he is using high-arched orthoses, then it would be expected, as one of he problems inherent with these types of orthoses, is that the foot will tend to slide laterally harder against the lateral heel cup, thus causing increased potential for lateral heel cup irritation. To remedy the problem your colleague will either have to do one or a combination of orthosis modifications to his current "favorite orthosis prescription protocol" to improve patient compliance and increase patient comfort:

    1. Increase lateral heel cup height and/or add lateral clip to heel.
    2. Evert device to add more intrinsic forefoot valgus correction.
    3. Add valgus forefoot extension to orthosis.
    4. Add a thicker layer of medial expansion to cast (i.e. lower medial arch height).
     
  12. Phil Wells

    Phil Wells Active Member

    Phil and Kevin

    Thanks for the advice.
    I couldn't agree more about the cause and effect of his FFO approach and it is good to hear others saying the same.
    I also couldn't agree more re forefoot mechanics teaching, especially how to assess and treat.

    Cheers to all.

    Phil
     
  13. david3679

    david3679 Active Member

    Phil
    Tissue stress does not come into it. He believes that in this type of patient he only needs to cast the foot with the Hicks windlass fully engaged (inverted heel, high arch etc), no arch fill to the casts, 1st ray additions to allow for pf of the 1st ray and any forevalgus/varus balanced with a small extrinsic post to behind the mets.
    The reason for the conversation is that he has a high degree of patients non compliance of FFO's due to lateral heel cup irritation.
    Is it my manufacturing process or his casting technique - I will hopefully have a definitive answers.


    I would look for the answer in your own reply on that. I have used differing companies that you have worked for and you occassional drop some manufactor clangers. I think Its more to do with the practitioners model of biomechanical practice that would seem more at fault. If I follow my particular route of practice his orthosis model would create an artificial hypomobility in the talar navicular and navicular cuniform complex. The foot would be forced as Kevin stated to irritate on the lateral edge of the orthosis. The creation of an artificial hypomobility would require incresed movement and this would tend to occur at the calc/cuboid. I would see this create an issue of congruence to the orthosis.

    I would see the compliance issue being trying to create an abnormal joint movement and blocking a more normalised function. As a manufactorer you only make whats instructed do you have an obligation if the prescription or biomechanical approach is off the planet maybe but not my call

    Dave

    Dave
     
  14. 5. Increase co-efficient of friction of top-cover material
     
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