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The Potentailly Injurious Effects of Forefoot Varus Posting

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Craig Payne, Nov 28, 2010.

  1. Craig Payne

    Craig Payne Moderator


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    I made some comments at recent Boot Camps on the potentially injurious effects of forefoot varus posting on foot orthotics; we have had a number of threads in the past on forefoot varus. I have had a couple of emails about what I said, so it’s easier to post a generic reply here:

    Forefoot varus is very rare, but when it is present, the rearfoot has to pronate to bring the medial side of the forefoot down to the ground. The traditional approach to dealing with forefoot varus is to use a foot orthotic with a medial forefoot post to bring the ground up to the foot so the rearfoot does not have to pronate.

    The point I tried to make was that a forefoot varus post will have two very different effects depending if the foot orthotic was a rigid plastic or a semi-rigid/flexible material:

    Semi-rigid/flexible orthotic:
    For the forefoot varus posting to work, it is going to have to dorsiflex the first ray to end range of motion and then supinate the mid-foot joints to end range of motion before it can have any effect on the rearfoot pronation --> potentially injurious due to jamming at end range of motion

    Rigid orthotic:
    The effect of the forefoot varus posts is immediately transferred to the rearfoot to stop it pronating via the rigidity of the plastic --> does not have to move joints to end range of motion to effect rearfoot pronation.

    Conclusion:
    Using a forefoot varus post on anything other than a rigid plastic orthotic to treat forefoot varus induced rearfoot pronation is theoretically and potentially injurious

    NB:
    There are also effects of the medial forefoot posting on the windlass mechanism
    There may be other indications for medial forefoot posting when its use is warranted.
     
  2. Craig:

    I use varus forefoot extensions in shank-dependent plastazote #3 orthoses for runners without any first ray symptoms. These work great for treating medial tibial stress syndrome and patello-femoral syndrome in runners. In fact, the injury may persist without proper use of the varus forefoot extension added to the orthosis. I really don't think it makes the orthosis plate material makes much difference. However, I rarely used varus forefoot extensions on foot orthoses for non-runners.
     
  3. Craig Payne

    Craig Payne Moderator

    So do I, but I see that as a different 'kettle of fish' to the above scenario due to the so-called 'runners varus'.

    Would you agree, that if forefoot varus was present that the effect of a forefoot varus post would be very different on rearfoot pronation depending on the rigidity of the orthotic shell?
     
  4. Craig:

    I think a better way to put it (especially considering that many shank-dependent orthoses have very low "rigidity" but deform very little inside the shoe) is to say that the biomechanical effect of a forefoot varus post would be dependent both on the congruity and the amount of deformation of the orthosis under weightbearing loads.
     
  5. pod29

    pod29 Active Member

    Craig



    I am not one too use a forefoot varus post very often, and yes I do agree that forefoot varus is a rare beast.

    However, I have a few questions/ideas...

    Do you think that your statement regarding Flexible orthoses may be paying too little attention to the properties of the shoe (as Kevin has eluded too) in which the orthosis is placed. A flexible orthosis in a shoe with a stiff shank should still allow transfer of forces from the FFVR post to the rearfoot. As we have all discussed in the shank dependancy thread. Additionally transfer of forces to the reafoot would also be promoted via the stiffness characteristics of the plantar fascia, spring ligament and potentially stretch reflexes in the plantar intrinsic foot muscles. I do agree that a rigid device will be more effective at transferring force, however I'm just not too sure about the statement re-flexible orthoses.

    Additionally, Do you think that this argument leans a little bit too much in the direction of "position/motion", rather than tissue stress/ force alteration, and may be a little too simplistic? For example... When we are trying to reduce pronation about the STJ axis, we don't try to maximally supinate the rearfoot to stop pronation. We aim to apply enough force to the medial side of the joint axis to reduce excessive pronation FORCE. With this in mind, why do we have to maximally dorsiflex the first ray and maximally supinate the midfoot to effect any changes on pronation? . Correct me if I'm wrong, but it is my belief that force transmssion/alteration can happen before we see any changes in kinematics. Is this any different in FF varus?In a true forefoot varus, where the foot pronates to get ground ground contact under the medial forefoot, any pathogy will be caused by the forces encountered whilst getting to the endpoint of pronation, rather than being caused by the end pronated position itself. By adding a FF Varus post, you are essentially bringing the ground/shoe up to the medial forefoot. A forefoot varus post should enable earlier contact of the medial forefoot with the shoe/ground, thus reducing STJ pronatory acceleration and force. This may not change the total rearfoot excursion but would significantly alter the loading rate.

    Sorry if this is a little hard to follow, I'm just writing these down as they come to my head:morning:
     
  6. Graham

    Graham RIP

    Placing anything that dorsiflexes the first ray will inhibit first mtpj function. Again, here a varus wedge in a runner may reduce the tissue stress on the medial tibia or the pat fem but what tissues has it increased stress on?
     

    Attached Files:

  7. efuller

    efuller MVP

    As far as the STJ is concerned there is no difference between forefoot varus and rearfoot varus. It is all a matter of where the forefoot load is. If there is insufficient range of motion in the direction of eversion of the STJ to load the medial forefoot then you should use a forefoot varus wedge to increase the load on the medial forefoot. This is the old John Weed trick of trying to slide your fingers under the lateral or medial sides of the standing forefoot. If you can get your fingers under the first met, it is probably not bearing enough load.

    Terminology time out:
    Are we talking about intrinsic post or extension. Intrinsic post ends proximal to the metatarsals. Extension ends distal to the metatarsals. My discussion below is assuming extension.


    Going back to the idea of load, it doesn't matter if the device is rigid or flexible. It matters in what position the load is applied. If you had a 10 degree soft foam wedge that compressed to be effectively 5 degrees it would still be more of a wedge than a non compressible 3 degree wedge.

    I'm not sure I'm getting the difference between the rigid and flexible devices described. Whether or not the device is rigid or flexible a load will be applied to the metatarsals and they will move in response to that load. Just take a patient and seat them in a chair with the soles of their feet toward you. Take a rigid varus wedge and a flexible varus wedge and place a superiorly directed force on the met heads, is there any difference? (Do this with some "ground" under the wedges.

    I'd agree with both Kevin and Graham about forefoot varus extensions. Yes, they will tend to increase load on the first ray and they will help medial tibial stress syndrome. You shift the stress from what hurts to some other location and monitor for symptoms in other structures.
    Eric
     
  8. But this statement is the same for every orthotic device post, skive etc.

    While I don´t use FF Varus posts that much, using one and then saying what other structures has it increased stress on, this type of question should be asked of all devices not just those with FF Varus extensions.
     
  9. Graham

    Graham RIP


    I agree! However, how to we determine that the alterations in moments and force on other joints won't create secondary pathology?
     
  10. Graham at the moment I don´t think we can, but maybe we can help reduce these secondary pathology with detailed history plans. ie we can only look back not predict the future.

    eg 2 Patient present with problem that requires you to use external supination moments for the case of the example we say that they are the same even though it is impossible.

    patinet A no history of lateral ankle sprains

    patient B history of lateral ankle sprains

    so if we only consider the stressed tissue at the moment then the chance of patient B returning with lateral ankle problems is much higher than patient A.

    So just like late night Poker we play the percentages

    does that make sense

    A wise man wrote something this year that I went brilliant after reading( it was Eric) re GRF we can´t reduce it we can only move it from one place to another - maybe not in those words but that was the idea , it stuck with me, maybe I´m a few pages behind but I was of course.
     
  11. Graham

    Graham RIP

    It Does!:drinks
     
  12. Craig Payne

    Craig Payne Moderator

    I specifically had in mind the widespread practice of using an extrinsic forefoot varus post on a flexible shank dependent prefabricated foot orthotic - how is that going to have any effect on the STJ? All I can see it doing is dorsiflexing the first ray.

    Whereas an extrinsic forefoot varus post on a rigid plastic foot orthotic will have the effect of 'inverting' the plastic orthotic and affect the STJ.
     
  13. pgcarter

    pgcarter Well-Known Member

    While agree that what we call a forefoot varus seems to be rare or even extinct....what about the effect of significant tibial varum? The whole foot is shifted into varus, and when it pronates to the ground during compensation for that tibial varum a series of problems occur. If we use a rigid orthosis to limit that pronatory collapse at the rear foot via some kind of inversion prescription, then should we not also decrease the distance the metatarsal heads have to travel to reach the "ground" on the medial side of the forefoot?....ie add a flexible wedged forefoot post? so that we have in effect negated the condition of the tibial varum?
    regards Phill Carter
     
  14. Graham

    Graham RIP

    You are assuming that the pronation is an issue. I believe Craig pointed out that pronation has a poor correlation to injury. Also, if what you say is true, how do Lateral wedges in cases of Tibial Varum reduce medial knee pain?
     
  15. Craig Payne

    Craig Payne Moderator

    Traditionally, in that situation you varus post the rearfoot as well. However, even in this situation a forefoot varus post on anything less than a rigid orthotic is not going to affect the rearfoot (unless its jammed up all the medial midfoot joints).
     
  16. Bruce Williams

    Bruce Williams Well-Known Member

    For Simon;

    A study by Hall and Nester, shows that a decrease in 1st mpj dorsiflexion motion leads to Sagittal plane compensations at the Ankle Joints, Knee Joint and Hip Joints.
    Participants walk with a rigid insole under the 1st ray to restrict 1st mpj dorsiflexion range of motion.
    Ankle joint dorsiflexion showed an increase during late midstance, and a reduction in ankle joint plantarflexion during the propulsion phase, which led to increased knee flexion and decreased hip extension.
    Sagittal Plane Compensations for Artificially Induced Limitation of the First Metatarsophalangeal Joint, A Preliminary Study, C Hall, CJNester, JAPMA, Vol 94; No 3; May/June 2004 – Level 2

    good discussion
    Bruce
     
  17. Thanks Bruce, I couldn't see the bit in this study where they measured the change in 1st MTPJ dorsiflexion with and without the insole though.
     
  18. Here you go, Bruce. See attached.

    Conclusions: Foot orthoses that incorporate a
    medial forefoot post do not have a consistent
    negative effect of reducing first MTP joint
    dorsiflexion during walking. J Orthop Sports
    Phys Ther 2004;34:317-327.
     

    Attached Files:

  19. Graham

    Graham RIP

    The discussion is interesting also!




     
  20. Bruce Williams

    Bruce Williams Well-Known Member

    Simon,
    Do you have this paper to share as well? Thanks.
    I'll look thru Nesters paper today again.
    Bruce
     
  21. Which one Bruce, the Nester paper or the Nawoczenski? I attached the pdf of the Nawoczenski in my earlier post. Hint: they didn't measure 1st MTPJ kinematics in the Nester study, BTW. :bang::bash::hammer:
     
  22. should we not be thinking in terms of dorsiflexion stiffness of the 1st MTP.

    ie by using the FF varus wedge we have increased the dorsiflexion stiffness of the 1st MTP and this will only become a problem if the forces required to overcome this increased dorsiflexion stiffness of the 1st MTP are too great for the muscles .

    as an example achilles tendon which has greater resistance to the plantarflexion moment ( due to the longer lever arm of the foot) it´s creating , which is required in propulsion.

    But if the gastroc/sol complex and tendon are strong enough to overcome this increased dorsiflexion stiffness of the 1st we may have no pathology.
     
  23. Bruce Williams

    Bruce Williams Well-Known Member

    Neither,
    Stefanshyn, Nigg I think you had a link to the abstract listed but did not have the paper linked, that one.
    Hint: I make my own assessments of a papers validity.:dizzy:
    have a swell day!
    Bruce
     
  24. Assess it all you like, they still didn't measure 1st MTPJ motion with or without the insole. So no-one knows whether the observed changes were related to a change in 1st MTPJ dorsiflexion. Kind of a fatal flaw in that paper, in my opinion. Particularly since the paper was called: Sagittal Plane Compensations for Artificially Induced Limitation of the First Metatarsophalangeal Joint. It would probably have been better to have been titled: Sagittal Plane Compensations for a 3mm Aluminium Mortons Extension on a Flat Insole. Yet since I don't generally use a 3mm aluminium Mortons extension in isolation when treating patients, I'm not sure how clinically applicable it was either regardless of it's misleading title.

    I don't think I have the full-text of the Nigg paper, we discussed a similar/ this study by these two workers previously, maybe it's in that thread.
     
  25. This maybe of interst.

    See full text below

    also full text of Hall and Nester paper for those who want a read.
     
  26. This is interesting from the paper Ian linked to above:
    "The MP joint was a large energy absorber with average
    absorption of 20.9 J during running and 47.8 J during
    sprinting. In both activities, the MP joint absorbed substantial
    amounts of energy yet did not produce or generate
    any energy at take-off. The MP joint dorsiflexed as
    the athletes rolled onto the balls of their feet and remained
    in this dosiflexed position during take-off. There
    was little or no plantarflexion of the MP joint during
    take-off which would be required for energy production.
    This corresponds to the finding of Mann and Hagy
    (1979), who viewed the MP joint with high-speed film
    during walking and found that the toes remained in
    a dorsiflexed position during take-off and were, therefore,
    unable to provide any sort of push-off.
    Thus, it appears that the MP joint is a dissipater of
    large amounts of energy. Athletes absorb energy at this
    joint as they roll onto their toes and fail to provide any
    plantarflexion or push-off at this joint as they roll off
    their toes during take-off. It is possible that incorporation
    of the toe spring (the raising of the forefoot of the
    shoe) [SPOONER- Or pre-loading the hallux with a Cluffy wedge or Kinetic wedge]
    in athletic shoes may be somewhat responsible for
    this energy dissipation since it forces the MP joint to
    remain in a dorsiflexed position during take-off. Although
    it is generally believed that toe spring leads to
    a more efficient stride due to a natural rocking onto the
    forefoot, Cavanagh (1980) stated that there was no conclusive
    evidence that this was true. In fact, the results of
    this study may indeed suggest the opposite. It may also
    be that athletic shoe mid-sole materials at the location of
    the MP joint are too compliant. Athletic shoes are generally
    manufactured with consistent mid-sole materials
    from rearfoot to forefoot. However, the compliance that
    is required for appropriate cushioning at the rearfoot
    may be totally inappropriate for the requirements of the
    forefoot."
     
  27. So... if the 1st MTPJ is an energy absorber, then in the presence of hallux limitus / rigidus it's ability to absorb energy is reduced? Where does that energy go? (I may have asked that before in a previous thread :eek:) but lets re-visit it.
     
  28. My theory = achilles tendon
     
  29. Why??
     
  30. pod29

    pod29 Active Member

    Hi Craig

    I'm not sure of you are comparing apples with apples here.

    From my understanding (I may be wrong), a forefoot varus extension will fill the space (angle created) on the anterior edge of the orthosis when the rearfoot of the orthosis is placed in a position that is deemed to be "neutral". This rearfoot position may be inverted, perpendicular or even everted with respect to the supporting surface. If this prescriptive variable was applied to both the rigid and flexible device, you would theoretically have the same angle/contour in the rearfoot. Therefore the amount of force applied to the subtalar joint would be similar ( depending on the compressive characteristcs of the flexible material). My point is that if the contour at the rearfoot is similar between devices, the level of force applied to rearfoot will also be similar.

    On the other hand, if we add a varus extension to an orthosis (rigid or flexible) after the device is made....The flexible device will indeed cause a dorsiflexion moment to be applied to the first metatarsal and may cause all the problems you have discussed. BUT, if you do the same thing to the rigid device, the heel post/counter will not be balanced and this will also have a significant effect on the ability of the device to apply a supination moment to the STJ. Additionally, it may also cause other patholgy due to instability of the orthosis inside the shoe. In order to balance the orthosis in this instance, you would need to add the same level of wedging to the rearfoot. The end result would be a device that you have discussed with Phil and Kevin used for MTSS and runners varus.

    Your thoughts?

    Cheers
     
  31. Heres my thinking

    1st MTP sagittal plane motion reduced = energy absorption reduced

    there would also be increased tension on the planat fascia so sagittal plane motion at the MTJ and STJ would be harder to achieve and the lever arm of the foot will be longer .

    So then the achielles tendon must absorb and overcome this energy to plantarflex the ankle.

    My theory is that this absorption and then need to overcome this energy can lead to achilles tendon overuse.

    does that make sense.
     
  32. CraigT

    CraigT Well-Known Member

    Is this a real question, or we about to have a Spooner thinking lesson?

    Transferred to the ground as propulsion... is this what a sprinter is utilising?
    You are increasing the the forefoot lever arm, and assuming the T-MTjoints would be in a maximally dorsiflexed position- the flexors of the foot would have to absorb this force (or would be under strain). This would include FHL, instrinsics, medial slip of the plantar fascia etc etc...
     
  33. They're all real questions, Craig.;)
    According to the paper, in order for power to be transferred to the ground there needs to be plantarflexion of the toes, this apparently is not observed. So if one of the MTPJ's roles is to absorb energy via dorsiflexion, if the MTPJ doesn't dorsiflex as much, it must go somewhere else. I'm not sure where, but my initial thoughts were along the same lines as yours.
     
  34. David Smith

    David Smith Well-Known Member

    All

    Craig wrote

    Having read thru all the posts quickly, I may be wrong but I think you may talking at cross purposes.

    I think Craig means that with a rigid device with a varus post (intrinsic or extrinsic) the leverage available from the front medial leading edge of the orthosis acts as a lever against the rearfoot. However the flexible device cannot achieve this since it is compliant in all directions except compression.

    Therefore regardless of whether or not the medial forefoot rests on it there is still a supination moment acting from it (the leading edge) about the stj. Therefore the medial column does not require to be fully dorsiflexed and the mid foot fully pronated for there to be extra moments about the STJ via the varus posted orthosis.

    I may be wrong and I might have missed that someone already made this point, apologies if so.

    regards Dave
     
    Last edited: Dec 1, 2010
  35. Saab

    Saab Member

     
  36. Saab

    Saab Member

    oooops thi is a continuation of the above quote...
    Weber,
    when you say that it will be too great for the muscles to overcome do you mean the muscles of the plantar foot that collectively insert to the plantar aspect of the proximal phalangeal joint ( Abductor Hallucis, Adductor Hallucis and Flexor Hallucis Brevis)?
    If these are unable to create enough plantarflexion moments of the 1st Ray and plantarflexion moments of the 1st MTPJ forces to overcome the dorsiflexion stiffness, can these lead to these muscles straining and be a reason for Trigger point formation?

    Just trying to get some better understanding about the stiffness :)
    Steve
     
  37.  
  38. efuller

    efuller MVP

    Stiffness is the amount of movement (or deformation) that occurs relative to an applied force. As pointed out, you can have different stifness values in different directions. When muscles create the stiffness, then the stiffness will vary with the force of contraction of the muscle. In the case of the 1st MPJ, tension in the plantar fascia and tension in the muscles that you mentioned will all create a plantar flexion moment on the first proximal phalanx at the mpj. At heel lift in gait, the ground will create a dorsiflexion moment on the proximal phalanx at the mpj. How much the toe dorsiflexes will depend on the the stiffness of the joint, which depends on tension in the above structures.

    There was discussion in another thread about how the toe does not plantarflex prior to toe off and thus does not add energy to walking.

    I'm not sure how, or if, this applies to trigger points.

    Eric
     
  39. Saab

    Saab Member

    Thanks Weber for the detailed reply .
    :drinks

    the muscles that you talk about that need to overcome the increased dorsiflexion stiffness caused by the ff varus wedge or else a problem would occur, would be the same ones I mentioned along with Peroneus Longus and the PF? because these all create a plantarflexion moment right,

    and what sort of problems are u referring too?

    would I be right to say that increased dorsiflexion stiffness Is a functional hallux limitus?

    Steve
     

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