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Does Arch Flattening Cause Functional Hallux Limitus or Vice Versa?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Kevin Kirby, Mar 6, 2007.

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    I have not heard much lately from the sagittal plane theorists that had previously promoted the idea that functional hallux limitus (FnHL) caused pronation of the foot. In fact, I haven't heard much on the subject ever since the research by Bart VanGheluwe and coauthors showed that there was just as much late stance pronation in patients without functional hallux limitus as there was in the subjects with functional hallux limitus (Van Gheluwe B, Dananberg HJ, Hagman F, Vanstaen K: Effects of hallux limitus on plantar foot pressure and foot kinematics during walking. JAPMA, 96:428-436, 2006).

    Are we all in agreement now that if a flat longitudinal arch is seen along with FnHL that this most likely indicates that the flat longitudinal arch height caused the FnHL to occur and not the other way around?
  2. Oh dear. I'm going to get roasted. This has the feeling of a "do you think that girl is pretty" type question the Mrs asks when she is looking for a fight :(

    Certainly I can accept that a flattened arch can causes FHL. However i am not fully able to let go the idea that HL can (emphasis on can rather than does) cause increased late stance pronation and, over time, flattening of the arch.

    This is not based on research (sorry simon) so much as seeing lots of antalgic gait patterns in which the patient abducts the foot in order to reduce pain from HL, decreasing the saggital lever arm and increasing the lateral to medial movement of force through the foot.

    It just seems to make sense to me.

    Without having access to the full text of the study i can't really consider it very fully, however the Abstract does not mention and differentiation between painful and aysymptomatic patients. If i am reading the abstract correctly (and i may well not be!) the point seems to be that
    approx 19% would seem to imply about 4 patients from each group exhibited the retrograde midtarsal pronation. This for me is not an impressive sample size!

    I've just seen a gang of researchers go past the window with a cauldron of tar and a sack of feathers so i'll stop there.

  3. David Smith

    David Smith Well-Known Member


    I've always understood that the hallux phalanx can only rotate/dorsiflex around the met head if the 1st ray can plantarflex. FuncHL happens because of the functionally elevated position of the 1st ray and the its inability to plantarflex. If the 1st ray is elevated the MLA must be relatively extended and lowered.

    Cheers Dave
  4. Dear all,

    Being the first author of the article, I may shed some light, or beter, add some reflections that may allow a less "black and white" interpretation of the research results.

    First of all, the results and the statistics in our study are what they are and "stricto sensu" only valid for the population tested. Extrapolation to all functional hallux limitus people, therefore, should be done cautiously. In this way it may be useful to know that most of the subjects with hallux limitus in our study were young adults and did not suffer any pain. Therefore, it could well be that because they were at a rather early stage of FHl and, therefore without pain, they simply forced the 1st MTP joint into dorsiflexion. This seems to be confirmed by the fact that limited dorsiflexion angle of the 1st MTP joint during gait as measured by a Vicon motion analysis system was observed only with about 50 to 70% of the population affected with structural hallux limitus.

    The picture could have been different with a painful hallux limitus, especially at a later stage or with older people. Because of the presence of pain, missing dorsiflexion at the 1st MTPJ may over the years be compensated with forced midfoot dorsiflexion, in this way causing midfoot collapse, showing a heavily pronated foot even after heel lift. And that may represent the picture most clinicians are accustomed to. Because, in the absence of a pressure plate, most of times they will concentrate on FHl only when there are painful symptoms present at the 1st MTPJ, probably at a later stage likely to be accompanied with a collapsed midfoot showing retrograde pronation.

    To conclude. It is my personal opinion that functional hallux limitus is primarily caused by an unstable 1st ray (caused by midtarsal pronation), but that on the long run the continuous stress caused in the 1st MTPJ by FHl in its turn will aggravate midtarsal pronation resulting in a heavily pronated or even collapsed midfoot. It is a vicious circle starting with midtarsal pronation and ending with midfoot collapse, also presenting retrograde pronation.
    The latter still has to be experimentally confirmed. The results of our study reflects more the early stage of FHl.
    Last edited: Mar 6, 2007
  5. Bart:

    Thanks for taking the time to reply.

    From reading your paper, it seemed that your study did not show any more tendency for the FnHL feet to have late stance phase pronation than did the foot that did not have FnHL. In other words, FnHL was not signficantly more correlated with late stance phase pronation as non-FnHL. Is that correct?

    I would think, if, indeed, FnHL causes late stance phase pronation, then it would show up even in these young individuals, just in lesser amounts.

    An alternative explanation for the association of FnHL with more severely pronated feet in older adults is that the same mechanical factors that caused just a little bit of arch flattening in a young adults may lead to more severe arch flattening and more severe FnHL in these same people as they age. In other words, it is my opinion that the presence of FnHL may have absolutely no bearing on producing arch flattening as an adult ages. FnHL is simply the mechanical result of the abnormal kinetics and kinematics of the 1st MPJ that results from longitudinal arch flattening.

    For example, when I perform a arthrodesis of the first MPJ, the result over time for these patients with no available hallux dorsiflexion, is not arch flattening over time but, rather, a stiffening of the first ray so that the first ray dorsiflexes less during gait. If, indeed, the pressure plantar to the hallux in late stance phase was the cause of arch flattening, then all those feet with first MPJ arthrodeses would also develop arch flattening over time. So far, I haven't seen one of these surgically induced hallux limitus patients develop arch flattening over time.

    This is a very interesting topic to me and requires further research obviously. Thanks to you and the other researchers for performing this research to give us some data to "hang our hat on" in regards to FnHL and arch flattening.

    Maybe when I'm in Belgium in a few weeks, we can talk about this further over a few Belgian beers. :)
  6. David Smith

    David Smith Well-Known Member


    I have often wondered about arthtodeses of the 1st mpj. I see many patients that have this and I often ask myself 2 things. Why does the surgeon fix the joint into a rigidus. And why does it not seem to negatively affect the patient in terms of pathological changes in gait, which in most it does not seem to. One would imagine that fixing the 1st MPJ would cause compensations that the patient would find inconvenient. This only seems to happen in a minority of cases.
    Kevin have you noticed any changes in saggital plane progression in these patients?

    All the best Dave
  7. 1st MPJ arthrodesis surgery is most commonly performed for end-stage DJD of the 1st MPJ but may also be performed to stabilize the 1st MPJ, such as in a flail hallux deformity. For example, I just performed a 1st MPJ arthrodesis a few weeks ago in a patient that had no extensor strength in her hallux and needed the hallux to not plantarflex in an uncontrolled fashion when walking.

    The improvement in gait function in these patients with successful 1st MPJ arthrodesis is almost universal in my experience. In general, their late midstance supination and propulsion efficiency is improved and they have less pronated feet in stance. Because of these clinical observations over the past 20+ years, I believe that podiatry tends to obsess over "normal function of the windlass" a little too much, tending to overlook the more important biomechanical factor that the increased first ray dorsiflexion stiffness gained by 1st MPJ arthrodesis not only helps prevent abnormal late midstance pronation but also allows the foot to propel with a more supinated fashion over the lateral rays so that more normal gait biomechanics may be reestablished.

    So to answer the question: yes, I have seen, on a routine basis, marked improvements in those patients that have 1st MPJ arthrodesis surgery in their sagittal plane progression. I believe that future research will demonstrate more positive, rather than only negative, biomechanical effects of properly performed 1st MPJ arthrodesis surgeries in those patients where this procedure is indicated.
    Last edited: Mar 8, 2007
  8. David Smith

    David Smith Well-Known Member


    This subject interests me very much.

    Yes I have generally noticed that subjects with hallux rigidus invariably have a limited 1st ray RoM and this applies also to those with a surgical arthrodesis.
    Why do you think this is? Does it develop pre or post fixing of the MPJ?

    Would you agree that these subjects can walk better with a rocker sole shoe or is this only the ones that experience problems such as IPJ d/flexion and subsequent nail impingement problems or pain in the IPJ or pain in the MPJ because it experiences increased forces due to increased moments from GRF.

    Cheers Dave
  9. Dave:

    This is an interesting subject. I believe the increased first ray dorsiflexion stiffness seen with 1st MPJ arthrodesis surgery comes from two factors:

    1. The hallux is surgically fixed in a position of slight dorsiflexion that slightly increases the plantarflexed position of the first ray and medial column during weightbearing activities.

    2. The lack of ability of the hallux to plantarflex relative to the first metatarsal in late midstance, as the first ray/hallux is loaded, causes the rapid increase in plantar fascial tensile force that normally occurs during late midstance to directly increase the first ray plantarflexion moment rather than this plantar fascia tensile force directly increasing hallux plantarflexion moment.

    In other words, 1st MPJ arthrodesis allows the plantar fascia to directly produce first ray plantarflexion moment, since the hallux is now, post-arthrodesis, one continuous bone with the first metatarsal. This is opposed to the situation where, pre-arthrodesis, the plantar fascia is primarily plantarflexing the hallux, losing some mechanical efficiency for causing first ray plantarflexion moment by this hallux plantarflexion, and therefore is only secondarily creating a first ray plantarflexion moment by causing increased compression force at the anterior joint surface of the first metatarsal head.

    In answer to your second question, I have not had to use rocker-soled shoes in these patients. In fact, I performed a 1st MPJ arthrodesis in a 60 year old Iron Man male triathlete (one of the best in Northern California in his age group) a year ago and he is now running and walking with no pain and no decrease running/walking ability since the surgery, wearing only normal running shoes with no modifications.

    However, I do recommend rocker-soled shoes in patients with ankle fusions and sometimes in patients with painful hallux limitus/rigidus deformity.
  10. David Smith

    David Smith Well-Known Member


    Had to read that a few times :p
    Yes I see what your saying, however wouldn't this mean that the 1st ray is more dorsiflexed with GRF having a longer moment arm about the talar - nav joint and therefore more tension in the PF? Or would the increased tension in PF tend to dorsiflex the rearfoot at heel lift much the same as the windlass action would do in the normal foot, and so PF tension would remain about normal?

    Givin it some thought, Dave
  11. Dave:

    Let me try to explain it another way since if you can't readily understand this then probably 95% of the other readers can't understand it either.

    In the foot with a functional hallux limitus here is what happens:

    1. As the center of mass (CoM) moves anteriorly in late midstance, the Achilles tendon tension increases to slow acceleration of the CoM anteriorly, with an anterior migration of the center of pressure (CoP) being the direct result.

    2. As the CoP moves more anteriorly, the resultant increased medial column dorsiflexion moment causes a dorsiflexion of the medial column relative to the rearfoot, a flattening and an elongation of the longitudinal arch and an increase in the tensile force within the medial band of the plantar fascia.

    3. If the longitudinal arch is low enough and the subtalar joint (STJ) axis is medial enough, then the increase in plantar fascial tension does not produce sufficient first ray plantarflexion moment to cause first ray plantarflexion or STJ supination, so first ray plantarflexion doesn't occur.

    4. Because the first ray can't plantarflex, the hallux will continue to plantarflex on the first metatarsal during late midstance and very early propulsion due to the increased plantar fascial tensile force.

    5. The observable result on plantar pressure analysis is a decrease in ground reaction force (GRF) plantar to the first metatarsal and an increase in GRF plantar to the hallux in late midstance and early propulsion.

    However, if we now took that same foot and performed an arthrodesis of the first metatarsal phalangeal joint here is what would instead happen:

    1. As the center of mass (CoM) moves anteriorly in late midstance, the Achilles tendon tension increases to slow acceleration of the CoM anteriorly, with an anterior migration of the center of pressure (CoP) being the direct result.

    2. As the CoP moves more anteriorly, the resultant increased medial column dorsiflexion moment increases the tensile force within medial band of the plantar fascia and tends to cause a dorsiflexion of the medial column relative to the rearfoot.

    3. The resultant increase in plantar fascial tension directly produces first ray plantarflexion moment (rather than hallux plantarflexion moment in the functional hallux limitus foot) since the hallux is now arthrodesed to the first metatarsal. This new osseous arrangement of the first ray/hallux directly increases the dorsiflexion stiffness of the first ray and medial column.

    4. Since the arch doesn't flatten due to the increased first ray/medial column dorsiflexion stiffness, then the plantar fascial tensile force will have a longer moment arm to produce a first ray and medial column plantarflexion moment in the higher arched foot than in the lower arched foot. In addition, the increase in first ray dorsiflexion stiffness allows the first ray to more effectively resist dorsiflexion motion as the foot enters late midstance. The increase in GRF plantar to the first metatarsal head that results from the increase in first ray dorsiflexion stiffness will increase the STJ supination moment and the foot will supinate earlier in late stance phase as a result.

    5. The observable result on plantar pressure analysis is an increase in GRF plantar to the first metatarsal and a decreased GRF plantar to the hallux in late midstance when compared to the foot with a functional hallux limitus.

    Does this make better sense now? Maybe when I get back from Belgium and drinking beers with Craig, Bart and the rest of my Belgian colleagues..... maybe this could become a good start on a paper?? ;)
    Last edited: Mar 10, 2007
  12. David Smith

    David Smith Well-Known Member


    Yes that is more clear thank you.


    So what you find is that compared to the FuncHL foot the arthrodesis foot has a shorter moment arm to GRF about the TNJ in late stance.

    The reason I relate to the TNJ is that in terms of modeling I make the assumptions that, the arch of the foot has a pin joint at the TNJ, which is approximately the apex of the arch. The osseous joint itself cannot transmit moments. The TCJ is a pin joint and the apex of the foot triangular truss and allows dorsiflexion of the foot as a whole unit or the rearfoot to rotate in the Z axis or saggital plane. The STJ is a joint that has only X axis or frontal plane rotation in terms of the calcaneous but in terms of the Talus has only Y axis or transverse plane rotation. These rotations are relative to each joint local axis set and may be oblique to the global axis set and each other.
    Therefore the arch of the foot flattens when the 1st ray dorsiflexes about the TNJ and /or the rearfoot plantarflexes on the TCJ. I have previously modeled the plantar fascia as the tie of the arch and the FHL tendon as the prime tensioner due to hallux dorsiflexion.
    By your findings do you think it would be more appropriate to model the plantar Fascia as primarily the plantarflexor of the hallux and secondarily the tie of the arch or in other words the plantarflexor of the 1st ray. Plantarflexion of the first ray is only possible when the hallux is resistant to GRF. Such as when the joint is surgically fixed or the hallux is free to dorsiflex. Therefore the lever arm of the hallux act as a cam tensioner for the PF which in turn plantarflexes the 1st ray and inverts the calcaneous/STJ to restore the height of the arch.

    I know the latter is what normal should happen physiologically speaking but I haven't considered modeling like that until now.

    Going back to the the fixed MPJ, what about at the late propulsive stage. Is GRF higher at this stage plantar to the hallux distal phallanx?

    Cheers Dave
    Last edited: Mar 10, 2007
  13. No. The plantar fascia causes a plantarflexion moment across the 1st MPJ axis (i.e. plantarflexion moment of the hallux). The plantar fascia secondarily causes a plantarflexion moment of the first ray via the posteriorly directed interosseous compression force from the base of the proximal phalanx of the hallux being pulled posteriorly by the plantar fascia tensile force onto the first metatarsal head. First ray plantarflexion moment will largely be determined by the magnitude of plantar fascia tensile force and the height of the longitudinal arch of the foot.

    I don't understand you here. If first ray dorsiflexion occurs then hallux plantarflexion will occur. Hallux plantarflexion is resisted by the hallux dorsiflexion moments created by GRF. Have you mistakenly switched first ray plantarflexion and dorsiflexion here, Dave??

    In my newsletters and lectures on functional hallux limitus (FnHL) and arch flattening over the past few years, I have used a model of the foot with the hallux attached to the plantar fascia to better describe these mechanisms.

    With the first MPJ arthrodesis, if the increased STJ supination moment that results from stiffening the medial longitudinal arch causes increased STJ supination and increased GRF plantar to the more lateral metatarsal heads during propulsion, then GRF plantar to the hallux distal phalanx may be less than in the FnHL foot. Therefore, this STJ supination effect of the 1st MPJ arthrodesis must be considered when trying to determine its effects during propulsion, especially when comparing it to the increased STJ pronation moments during late midstance and propulsion that are the cause of FnHL.
  14. David Smith

    David Smith Well-Known Member

    Sorry Kevin

    For some reason I was writing dorsiflex when I meant plantarflex ( must have been the beer last night) Doh! I changed it now so it should make sense.
  15. efuller

    efuller MVP

    The above is the observation. Yet we should talk about the explanation of why this occurs. In the cadaver lab I cut all of the attachments at the proximal plantar end of the proximal phanlanx and dorsiflexion of the metatarsal no longer had effect on the ability to dorsiflex on the head of the meatarsal. So, the structures attached to the sesamoids are responsible for the above phenomenon.

    This leads to a second thought about what Kevin said about 1st MPJ fusions. A fusion in which the proximal plantar part of the proximal phalnx was cut to allow the fusion would not have a direct attachment of the plnatar fascia to bone. There are other attachments, but not so direct. Kevin, do you leave the attachments of the sesamoids intact when you do a fusion?

  16. Yes. I use a rotary burr to denude the cartilage on the base of the proximal phalanx before fusion. This does not affect the sesamoidal ligament attachments to the base of the proximal phalanx of the hallux.

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