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Forefoot varus wedging reduces hallux dorsiflexion?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Simon Spooner, Jan 25, 2011.


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    Maybe it's time to discuss this again. There seems to be this notion within the profession of late that forefoot varus wedging reduces hallux dorsiflexion and "causes" hallux limitus. I'm not sure where this idea comes from?

    You see we have Kilmartin's bone pin study which showed a 2 degree difference in hallux dorsiflexion with Root orthotics. Like wow, 2 degrees, and the error in your measurement? ...About 2 degrees? But we don't know whether the forefoot was posted varus or valgus. And then studies like:
    http://mortonsfoot.com/articles/halluxlimitus.pdf which show that forefoot varus wedging doesn't necessarily reduce peak dorsiflexion at the hallux... in fact, in the majority of subjects, it increased it. Indeed, a higher medial longitudinal arch in the devices reduced hallux dorsiflexion in more subjects than the forefoot varus wedging did. See figure 5, both kinds of devices increased the mean peak hallux dorsiflexion.

    Is this some kind of urban myth that is being developed? Am I missing something?
     

  2. Varus forefoot extensions, if done in isolation without a foot orthosis, will tend to reduce hallux dorsiflexion, in my clinical experience. Varus forefoot extenions will cause ncreased 1st metatarsal head dorsiflexion moment during late midstance, will cause increased plantar fascial tensile force, increased internal hallux plantarflexion moment and increased tendency for reduced hallux dorsiflexion during propulsion in walking.

    I think the variability in response with varus forefoot extensions comes when an orthosis is used along the varus forefoot extension since the orthosis may or may not modify the response seen of the varus forefoot extension, due to the large design variablity seen with foot orthoses. Howevr, I can't think, off the top of my head, of any research to back this up but have seen clinical evidence of this observation many times over the past quarter century.
     
  3. And that is the key, Kevin: a varus forefoot extension in isolation. And forgive me, but while we can create theoretical models which might demonstrate the effects you list above, have any of these effects actually been measured and reported for in-vivo dynamic function? The interesting result from the study I cited is that actually the varus forefoot post within the orthotic increased dorsiflexion at the hallux in more people than it decreased it in, and lets face it, they are probably used in conjunction with an orthotic, more often than they are not.

    Now, we did do a study in which we used forefoot valgus and varus extensions in isolation (at the same time that we did the study on rearfoot posts in isolation that was published in JAPMA) I just can't remember what we found though.:bash:

    The bottom line is that I want to know: do foot orthoses with a forefoot varus wedge cause hallux limitus? Do foot orthoses with a forefoot varus wedge reduce peak first MTPJ dorsiflexion? Do foot orthoses with a forefoot varus wedge increase hallux dorsiflexion stiffness? What does the literature tell us?

    Is increased hallux dorsiflexion stiffness a negative thing? Is reduced hallux dorsiflexion stiffness a negative thing? Does the hallux have a zone of optimal dorsiflexion stiffness? We have theoretical discussions of how too much stiffness might be detrimental, do we have any that describe how too much compliance might be detrimental? Or do we presume that the more compliance, the better? Flail hallux?

    So, if I wanted to study this, I might start with a forefoot varus extension of varying degrees placed under the 1st MTPJ and extended distally and measure hallux dorsiflexion stiffness (as oppose to peak dorsiflexion) in static stance... right MW
     
  4. efuller

    efuller MVP

    I agree with Kevin's statement above and would like to add... In feet with more medially deviated STJ axes, the first met head will be lateral to the STJ axis. So a forefoot varus wedge will tend to shift the center of pressure more medially, but it will still be in a location lateral to the STJ axis. (No evidence, just personal observation) So, the varus wedge may not decrease pronation moment enough to get the STJ to supinate to redistribute the load after equilibrium is achieved. So, the wedge will increase force on the first met head, attempting to dorsiflex the first ray and as Kevin stated, this will increase tension in the plantar fascia.

    So, in a foot with a more laterally positioned STJ axis, I would expect less stiffening than in a foot with a more medially positioned STJ axis. So, if you do the study assess STJ axis position.

    Eric
     
  5. davidh

    davidh Podiatry Arena Veteran

    Yup - and perhaps we could also discuss it 2012 - and 2013 ...............
     
  6. efuller

    efuller MVP

    A good question is what causes hallux limitus. I believe that it is a continuum of functional hallux limitus. In my own feet, I know that I used to have the range of motion and it has decreased over time. (From looking at shoes that I had when I was young with a wear pattern sub met and hallux and then in later years a wear pattern sub just hallux.

    It seems like a large portion of the population develops hallux limitus. It would be interesting to look at what foot characteristics are present in feet that don't develop hallux limitus.

    In testing my own medially deviated STJ axis foot, yes a forefoot varus wedge does increase stiffness. And an orthotic with a reverse Morton's extension decreases stiffness.


    If the cause of increased stiffness is increased tension in the plantar fascia, then I would maintain that stiffness beyond a certain point is a bad thing. (My personal observation is that a lot of people who have hallux limitus will have increased tension in their fascia when standing and dorsiflexion of their hallux is attempted.) The reason that it is bad that increased tension in the fascia will increase compressive forces at the 1st MPJ. I remember a study looking at the developement of osteoarthritis and it noted that motion with low loads and compression of the joint with high loads without motion both did not cause OA. On the other hand compression with motion did cause OA. So, when you walk, heel lift attempts to dorsiflex the toe at the same time there is high compression of the joint.

    Too much compliance: I feel that the purpose of toes is to increase area of contact to reduce pressure. The energy studies show that there is energy absorption, rather than production from the MPJ's at toe off. So, they don't add energy to gait. So, a floppy toe will have little force applied by the ground and body weight will have to be supported by the met heads after heel lift. So, it is certainly possible for pathology to develop in the presence of an overly compliant toe.


    Eric
     
  7. RobinP

    RobinP Well-Known Member

    Instinctively, I read this study and found it contrary to what I see clinically. That is to say that, in cases where I think that increased dorsiflexion stiffness of the first metatarso-phalangeal is the cause of the pathology, "improving" or reducing the dorsiflexion stiffness via a reverse mortons extension or similar seems to have a beneficial effect on the pathology.

    So, it was with a degree of skepticism that I read the results acheived in this study. Difficult to pick many gaping holes in the study, I thought.

    There were a couple of things I thought were worth pointing out

    1. The FF POST devices had a forefoot posts that terminated proximal to the 1st met head, not FF varus extensions

    2. All subjects had 10 degrees of FF varus. That's FF varus, not supinatus. In such participants, will the lack of 1st ray plantarflexion not significantly affect the results, or are they talking about FF supinatus?
     
  8. You are right, Robin. The "forefoot varus post" in the orthosis ended distally at the distal trim line of the orthoses at the metatarsal neck area. This will have a very different effect from a varus forefoot extension plantar to the metatarsal heads.

    Like Simon, I also think we must be careful assuming that varus forefoot extensions or varus extrinsic or intrinsic posts on orthoses will always limit hallux dorsiflexion of all feet. We simply don't have the research to back up this idea. However, from what I have seen clinically, a varus forefoot extension has much more "power" in producing reduction in hallux dorsiflexion than does a varus forefoot post, ending at the metatarsal neck.
     
  9. Doesn't the cited paper also question the perceived notion of the need to use first ray cut-outs on the shell to prevent "jamming" of the 1st MTPJ?
     
  10. That was one of Mert Root's ideas that he lectured on. This idea has been continued for years by others. I've been making orthosis plates to the full width of the shoe for over 25 years and haven't seen an functional hallux limitus develop as a result. The only thing first ray cut-outs do are weaken the ability of the orthosis to resist eversion forces from the foot inside the shoe.
     
  11. Indeed. Not only by reducing the medial-to-the-axis surface area of the orthotic, but also by weakening the shell and allowing the whole unit to evert inside the shoe. One of my peeves.

    I think there are a few things to consider here. Firstly, I agree with simon that we must get away from sweeping kinematic statements like "reduce hallux dorsiflexion" when what we mean is "increase hallux stiffness". Sometimes I want to increase hallux stiffness and in those cases a FF varus extension is a good thing.

    However I also agree with Kevin and Eric that, in general, forefoot varus wedging increases hallux stiffness. Something I've not seen anyone yet state (sorry if I've missed it) is that increasing the dorsiflexion moments and the plantarflexion moments by the same amount won't affect the movement of the hallux but it WILL increase the interarticular compression within the 1st MPJ. And that, in my experience, is rarely a good thing.

    I suspect so! I don't know where they would find that many people with forefoot varus!
     
  12. Forefoot varus is very common in feet being examined by podiatrists, or other clinicians, that draw their heel bisections everted and hold the subtalar joint supinated from neutral when assessing forefoot to rearfoot relationship.

    Even early on in the history of Root et al biomechanics, forefoot varus was much more common than forefoot valgus at the California College of Podiatric Medicine. Jack Morris, DPM, when he came back to CCPM to teach biomechanics after having been in private practice for about 15 years, said that when he left CCPM as a student all the feet had forefoot varus and when he got back to CCPM in 1984 to teach all the feet now had forefoot valgus. We both laughed about that one.

    In addition, if you ever get a chance to inspect one of the original measuring devices advocated by Root and Weed to measure the forefoot to rearfoot relationship, what do you think you see printed on the device? Not "forefoot to rearfoot measuring device", not "forefoot varus/valgus measuring device" but this.....FOREFOOT VARUS MEASURING DEVICE.

    Makes you wonder, doesn't it?!
     
  13. True thing.

    The more we learn the less we know.

    Seriously though, short of X rays, how easy is it to tell if an inverted forefoot relative to rearfoot is caused by a talar head which is rotated or if it is caused by a forefoot inverted at the talus / nav joint, the nav / cuniform joint or the cuniform / met joint?
     
  14. Honestly, I don't know of anyone who can differentiate a "forefoot varus" from a "forefoot supinatus". Why? Because both "forefoot varus" and "forefoot supinatus" are "made-up terms" that rely on the erroneous assumption that an inverted forefoot to rearfoot relationship is either only congenital or only acquired, when, in fact, the adaptive response of the joint positions of the foot probaby are changing throughout our lifetimes in response to internal and external joint moments and are never just based solely on only "congenital structure" or based solely on only "acquired position".
     
  15. RobinP

    RobinP Well-Known Member

    One of the great things about direct milled devices is the ease with which a first ray cut out effect can be replicated but leave the device full width for stability inside the shoe and increasing the second moment of area of the material by effectively adding a corrugation.

    Phil Wells would be better explaining it than me. he calls it the "new first ray cut out" that Salts can do. Not sure if it is new, but I have utilised it quite a bit with some success. It's not impossible in the traditional fabrication method but requires a lot of plaster modification.
     
  16. Nothing new, ostensibly you make the shell relatively more compliant along the 1st ray area of the shell. A better question might be, why would you want to do this? It'll probably shift the CoP relatively more lateral, compared to a similar device without this modification. I guess this could be useful in some circumstances.
     
  17. OK, back to the plot... are there any published studies which demonstrate a reduction in first metatarsophalangeal joint dorsiflexion in association with foot orthotics, other than the Kilmartin study I mentioned above, which showed a 2 degree reduction (and I can't remember if they took into account the heel lift effects of the devices in this study, which was a key weakness in ours :eek:)?

    For example, do we have any studies looking at the kinematics of the 1st MTPJ in association with Morton's extensions?
     
  18. Not that I know of.

    But my new toy arrived yesterday so if you want to do a kinetic (kinematics, pfft) study in static WB along the lines we discussed, using a mortons extension and testing 1st met stiffness with and without, it could be done without too much difficulty. I have some calibration to do but that should not be too hard...
     
  19. Thanks for the offer, Rob. I already have the tools to do this. I just need to be able to get all the right people together at the same time and venue......
     
  20. efuller

    efuller MVP

    I think it was Jack who pointed out that podiatrists on the East coast of the US saw a lot more varus than those on the West coast of the US. That was in the era before wide use of the internet. At the time I didn't even consider what kind of measurements were being made across oceans.

    It does make you wonder.

    Eric
     
  21. Could it be linked with palpation of the talar head (Langer) versus calculation using a 2:1 ratio (Root) to identify STJ neutral? Yet, I think it was somewhere in Valmassy that it was stated that the commonest alignments were rearfoot varus with forefoot valgus. Given the West coast theme of that book, that's a swing away from the "forefoot varus measuring device". BTW I'd love to see a picture of that.

    BTW I have an antique measuring device that my old boss gave to me, I'll take a photo and post it up.
     
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