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Forefoot valgus wedge effect

Discussion in 'Biomechanics, Sports and Foot orthoses' started by admin, Aug 18, 2006.

  1. admin

    admin Administrator Staff Member

    Members do not see these Ads. Sign Up.
    I am grateful to Kevin Kirby and Precision Intricast for permission to reproduce this January 1998 Newsletter (you can buy the 2 books of newsletters off Precision Intricast):


    The effects of adding a forefoot valgus wedge underneath the foot is something I have experimented with and studied for the past thirteen years. The process involves adding a piece of flexible material, such as adhesive felt or korex, to either the insole of the shoe or to the foot orthosis directly plantar to the lateral metatarsal heads. Most of the time, the forefoot valgus wedge is placed plantar to the fourth and fifth metatarsal heads but it is sometimes extended so that it is plantar to the second through fifth metatarsal heads (Fig. 1). In addition, the forefoot valgus wedge is often modified so that it is longer proximally, extending to the plantar aspect of the styloid process of the fifth metatarsal, if it is used on the patient’s insole without a foot orthosis present.

    Figure 1. The diagram above shows the plantar surface of two orthoses. One has a forefoot valgus wedge under the fourth and fifth metatarsal heads (left) and one has a valgus wedge under the second through fifth metatarsal heads (right).

    I use forefoot valgus wedges mostly to improve the biomechanics of a patient’s walking activities. I have also experimented with using forefoot valgus wedges in running and side to side sports activities. However, since the effect of the forefoot valgus wedge on foot and lower extremity biomechanics is somewhat less clear to me for running and side to side sports activities, I will concentrate on the effects of forefoot valgus wedges on walking in this newsletter.

    The effect which these forefoot valgus wedges have on the function of the foot and lower extremity during walking is quite varied, depending on the individual. One might think that a forefoot valgus wedge would tend to cause increased midstance pronation of the subtalar joint (STJ) during walking, but this is simply not the case in most individuals. When a forefoot valgus wedge is added either to the shoe insole or to the orthosis, the result can actually be that the patient will have decreased midstance pronation of the STJ during walking. The addition of a forefoot valgus wedge to the orthosis or shoe can be the difference between the complete relief of symptoms and no relief of symptoms with orthoses.

    The extent to which the forefoot valgus wedge works at relieving the patient’s symptoms is very dependent on any other in-shoe supports or orthoses which are present under the patient’s foot. In other words, if a forefoot valgus wedge is added to the shoe without a foot orthosis or other insole modifications being present, then the effect of the forefoot valgus wedge is different than it would be if an orthosis or other insole modification was present. In general, I prefer to add the forefoot valgus wedge to the shoe in combination with some form of varus wedge for the rearfoot. The varus wedging in the rearfoot usually comes either from the heel cup and medial longitudinal arch of an orthosis or from layered 1/8” adhesive felt on the insole of the shoe (November 1993 Precision Intricast Newsletter).

    One of the areas of the foot which tends to respond favorably to the use of forefoot valgus wedging in combination with a foot orthosis is the medial band of the plantar fascia. There are times that my patients initially only receive partial relief from their plantar fasciitis with the orthoses which I have made for them. In other instances, there are patients who have irritation from the orthosis in the area of the medial band of the plantar fascia who never had plantar fascial symptoms initially.

    If symptoms in the medial band of the plantar fascia are occurring with foot orthoses, then I perform the following test: I add a piece of 1/8” adhesive felt plantar to either the second through fifth metatarsal heads or plantar to the fourth and fifth metatarsal heads either on the shoe insole or on the forefoot extension of the orthosis (Fig 1). This adhesive felt forefoot valgus wedge extends from the distal edge of the orthosis to the sulcus of the digits. If the patient has a plantarflexed first ray deformity then I will usually use a forefoot valgus wedge plantar to the second through fifth metatarsal heads. If the shoe insole has evidence of decreased ground reaction force (GRF) plantar to the fourth and fifth metatarsal heads then I will usually use a forefoot valgus wedge plantar to the fourth and fifth metatarsal heads. Many times, however, I will try both combinations of forefoot valgus wedging if my initial choice of wedging does not produce the improvements in gait or symptoms which I desired.

    I next have the patient walk while I examine their gait pattern with the forefoot valgus wedge in place inside their shoe. I especially pay close attention to the midstance and propulsive periods of gait. The desired effects of the forefoot valgus wedge are the following: 1) there should be no increase in STJ pronation in early midstance, 2) there should be either a decrease in late midstance pronation or an increase in late midstance supination of the STJ, and 3) there should be increased duration of the propulsive phase of gait. If all of these changes do occur then, invariably, the patient reports considerably less discomfort in the medial band of the plantar fascia during walking.

    The biomechanical effect of the forefoot valgus wedge is to allow the lateral forefoot to become a more significant weightbearing structure in the latter half of stance of gait. By allowing the fourth and fifth metatarsal heads to bear more significant GRF, then the body’s proprioceptive mechanisms sense that it can begin to initiate propulsion more “actively” in the late midstance phase of gait without causing supination instability at the STJ. In other words, without the forefoot valgus wedging in the shoe, the body senses excessive GRF under the medial metatarsal heads in relation to the lateral metatarsal heads in the late midstance phase of gait. This will then translate to increased supination instability at the STJ due to the increased medially located GRF at the forefoot in late midstance and propulsion phase of gait.

    Therefore, the result of no forefoot valgus wedge may be increased late midstance pronation and increased weightbearing forces on the medial metatarsal heads, both of which will cause increased tension in the medial band of the plantar fascia during late midstance and propulsion. With the forefoot valgus wedge is place, the patient often has decreased late midstance pronation and a longer duration of propulsive phase which reduces the tension on the medial band of the plantar fascia and reduces the patient’s symptoms. The above outlined test is so easy and quick to perform that the podiatrist should, at the least, give it a trial on some of their patients with symptoms in the medial band of the plantar fascia.
    [Reprinted with permission from: Kirby KA.: Foot and Lower Extremity Biomechanics II: Precision Intricast Newsletters, 1997-2002. Precision Intricast, Inc., Payson, AZ, 2002, pp. 55-56.]
  2. Admin2

    Admin2 Administrator Staff Member

  3. conp

    conp Active Member

    Very interesting Kevin and thankyou.

    My question is:
    Although you have suggested 1/8" thickness of felt, would you start with this thickness and gradually increase the thickness if the changes in midstance and propulsion are not observed? And what would be approximately the maximum thickness before you start to cause more problems then good.
  4. I find the maximum eversion height test to be a useful indicator. Have pt. stand, then ask them to elevate the lateral borders of their feet, i.e. evert feet. Don't let them bring their knees together!!!! The amount of lateral elevation should give you a reasonable indicator as to how large a valgus post you can accomodate.
  5. I have noted that both the thickness and location of lesser metatarsal head padding makes a difference both in the patient's visual gait examination and in their subjective comfort. I nearly always start out with 1/8" padding since I keep rolls of 1/8" adhesive felt in the office just for this purpose. However, the lesser metatarsal head padding can certainly be modified to thicker or thinner padding, or to different locations on the lesser metatarsal heads if one desires.

    The best way to experience the mechanical effects of forefoot valgus wedging is to actually walk after placing different locations and thicknesses of forefoot valgus wedging on your own foot and then compare this experience to just walking barefoot over a non-carpeted floor. Then, I suggest also experimenting with placing varus wedging under the medial metatarsal heads (especially the first metatarsal head) and try again walking to note changes in your gait.

    In doing this same barefoot experiment on myself and hundreds of patients, podiatry students and podiatrists over the past 22 years, I have made a fairly consistent observation that even small amounts of valgus wedging will increase the duration of propulsion and increase the stride length of an individual whereas forefoot varus wedging, especially plantar to the first metatatarsal head, will decrease the duration of propulsion and decrease the stride length of an individual. Gait efficiency, gait stabiity, and subtalar joint (STJ) supination during late midstance and propulsion is increased even further in barefoot walking when the forefoot valgus wedge is also combined with a varus heel wedge and medial longitudinal arch (MLA) support of adhesive felt. These effects are not commonly noted with just addition of the varus wedging alone or valgus wedging alone, without the other pad to counterbalance the moments. Both pads seem to be needed to see or experience the full effect.

    The varus heel wedge and MLA support create a subtalar joint (STJ) supination moment and the forefoot valgus wedge creates a counterbalancing STJ pronation moment from ground reaction force. The combination of these two counteropposing STJ moments greatly increases gait stability, especially in those individuals (mostly female patients) with signs of foot instability during gait. The changes can be quite dramatic to observers and I use this type of demonstration during the many gait examination lectures that I have given during my national and international lectures on gait biomechanics.

    The question one must ask from analyzing these experimental findings is this:

    Why should a forefoot valgus wedge, that should increase the STJ pronation moment from ground reaction force due to it's lateral forefoot positioning, cause a paradoxical increase in STJ supination in late midstance and propulsion?

    I believe that the correct amount and location of forefoot valgus wedging creates a proprioceptive effect of "potential propulsive stability" back to the individual's central nervous system (CNS) during late midstance that then allows the individual to fire their gastroc-soleus complex with more force and greater duration without causing potential injury-producing supination instability of the STJ during propulsion.

    One must remember that the gastroc-soleus complex produces not only a ankle joint plantarflexion moment but also a STJ supination moment with its contractile activity. Therefore, if we assume that the CNS has prior "awareness" of the mechanical effects of gastroc-soleus contraction, then the CNS may "choose" not to activate the gastroc-soleus fully during propulsion unless there is a more lateral positioning of the center of pressure (CoP) on the plantar foot (with forefoot valgus wedging) during late midstance that will, in turn, aid in resisting the expected increase in STJ supination moment that would occur with forceful and prolonged firing of the gastroc-soleus complex. I believe that this is either a learned or "hard-wired" CNS mechanism that is designed to protect the individual from inversion ankle sprains, and therefore, potential traumatic and disabling injury, during walking.

    I have yet to write up these ideas fully in a theoretical paper for publication, but thought that I would first offer my colleagues that read the postings to Podiatry Arena have a first go at it. I know that Simon Spooner and Tony Achilles have experienced the stride shortening effects of 1/4" felt padding attached plantar to their first metatarsal heads while on a lecture break at Ray Anthony's Biomechanics Summer School a few years ago.
    Last edited: Aug 19, 2006
  6. conp

    conp Active Member

    Kevin and Simon,
    Thanks for some insight into these interesting observations. This sort of information derived from forum poster's experiences is priceless. This is the sort of 'stuff' that fascinates me. To me it is important not to concentrate on just positioning of the foot but the added dimension of "time". i.e. where the foot is at what what time of the gait cycle. If the foot is in a position at a certain time that gives particular muscles about to fire a mechanical disadvantage or if the muscles (that are about to fire or involved in the next moment) are weak, then the foot will not be in the correct position at the next checkpoint (position and time) as the muscles have been ineffective to bring the foot in the right position IN time.
    Gee I think I have made it really confusing. And YES there are other factors to consider but I just wanted to illustrate the Position and Time.

    In relation to your write-up, your (Kevin's) clinical experience is suggesting that we are able to change the timing of propulsion or prolonging propulsion. This is an example of ways we can change the "Time" factor.

    Others will say that we are not only changing positioning with orthoses but also timing would be correct, but individual attention to each patient and the purposeful changes is what makes the podiatrist unique.

    I hope I haven't confused everyone.
  7. Peter

    Peter Well-Known Member

    I always considered that, with forefoot valgus posting/wedging, we sometimes create midfoot stability for efficient propulsion by pronating and "locking" the MTJs.
  8. Peter:

    Please define "locking of the midtarsal joint".
  9. Peter

    Peter Well-Known Member

    Hi Kevin,

    I should say pronating the calc cuboid joint to close pack it, and provide maximum stability.


  10. Interesting notion. However, assuming a rigid body approximation between the navicular and cuboid and the axial positions described by: Nester, C.J., Findlow, A., Bowker, P.: Scientific Approach to the Axis of Rotation at the Midtarsal Joint. J Am Podiatr Med Assoc 91(2): 68-73, 2001 then during the periods of gait when the forefoot post can be active, pronation (simultaneous dorsiflexion, eversion and abduction) is not possible about the MTJ axis identified. Unless it can be shown that the post modifies the axial position to an orientation which allows simultaneous dorsiflexion, eversion and abduction, we cannot use the terms "pronation" nor "supination" as labels for motion about this axis during this period of gait. Don't have Van Langelaan's data to hand, which may reveal something different...
    Last edited: Aug 21, 2006
  11. This is not a pick at Peter, I'm just using his post as a springboard for a question.

    Question: if a joint is moving (and accelerating?) is it stable?
  12. David Smith

    David Smith Well-Known Member


    How about this as a biomechanical explanation as to why a valgus post can result in greater supination of the STJ.
    (still can't work out how to put a picture in this text?)

    Attached Files:

  13. Nor me. The assumption that Achilles produces pronation moment is plausable, however, in our study of this effect none of the subjects were so pronated as for this to be true, yet the effect (increased step length with valgus post, decreased with varus) was still observed. You probably right in that first ray plantarflexion / windlassing is influential though. If I ever get around to agreeing to and making the changes required by JAPMA they may publish it- trouble is the reviewer insists the effect is due to MTJ "locking"!!! hmmm;) Sometimes when you don't agree with the reviewer sooo much, its easier just to leave it. Sad but true.
  14. Craig Payne

    Craig Payne Moderator

    nah ....forefoot valgus wedge --> plantarflexes first ray --> facilitates windlass --> stabilises the tarsus.
  15. Peter:

    As Simon said, there is probably not a motion of "pronation" at the calcaneal-cuboid joint (CCJ). The axis of motion is at the CCJ is probably determined by the direction and magnitude of external and internal forces acting on the foot at any instant in time.

    Secondly, the term "close pack" is also a little easier to define than "locking" but is not probably reality in the foot where, during running for example, the ground reaction force on the plantar foot are known to be close to 3X body weight. In other words, it is likely that the CCJ does not suddenly hit the "close-packed position" and stop its motion in running or walking. It deforms more in response to larger loading forces and deforms less in response to smaller loading forces. This is quite obvious even in walking when a lateral fluoroscopic image of a walking foot is viewed (I have this video from Don Green's fluoroscopic foot video study).

    Motion at the CCJ is better modelled to be spring-like in nature (i.e. something like a leaf spring in a car) which has a variable dorsiflexion stiffness (i.e. like the experimentally determined dorsiflexion stiffness in the first ray) with the magnitude of stiffness dependent on the amount of deformation of the joints involved (Fauth AR, Hamel AJ, Sharkey NA: In vitro measurements of first and second tarsometatarsal joint stiffness. J. Applied Biomechanics, 20 (1): 14-24, 2004).

    Now, we must next define stability of a joint to make your definition work for "midtarsal joint locking". What does that "joint stability" exactly mean? :confused:
  16. Simon:

    Good to see you back contributing again, Simon. By the way, it wasn't a pig after all......

    To answer the question I just posed to Peter, here is what I would say is a good definition of joint stability:

    Joint stability: That condition of a joint where externally applied forces to one or both of the segments of the joint produces a minimum of joint motion.

    Therefore, joint stability may be experimentally measured by plotting a load vs deformation curve of the joint in response to variable loading forces. Joint stability could also be considered to be synonymous with joint stiffness. In other words, joints that are stiff could also be said to be more stable and joints that are more compliant could also be said to me more unstable.

    I don't think, therefore, it is the acceleration of the joint that determines stability. Rather, it is the deformation of the joint relative to the load applied that determines its stablity. If 1,200 N over a 0.5 sec interval is applied to the forefoot and the calcaneo-cuboid joint (CCJ) rotates only 2 degrees in response to that load within 0.5 seconds, then the angular velocity is 4 degrees/sec but the stiffness is 600 N/degree. In this case, the CCJ should be considered to be stable since it has little deformation in response to the load being applied. However, the joint rotational velocity should not necessarily determine the stability of the joint, unless the loading force is also considered. Joint acceleration may be a better measure of stiffness since it takes into account the change in velocity but still needs to be referenced relative to magnitude of loading force applied in order to be meaningful relative to "joint stability".
  17. Dave,

    Below is your pdf file converted via CorelDraw into a jpg file so it may be readily viewed. The Achilles tendon is rarely ever located lateral to the STJ axis. Therefore, I can't agree with your analysis.

    Attached Files:

  18. Craig:

    Why would a forefoot valgus wedge necessarily plantarflex the first ray?? Why wouldn't a forefoot valgus wedge cause a subtalar joint (STJ) pronation moment and cause increased STJ pronation motion which would, in turn, cause increased first ray dorsiflexion and "destabilization of the tarsus"???
  19. David Smith

    David Smith Well-Known Member

    Kevin and Simon

    The model is simplified so that the principle can be seen more easily. In reality it is the relative position and not the absolute position that is important. So therefore if the relative position of the the AT to the STJ axis is more medial then it will produce more supination. Since the AT tension is about 2 - 2.5 times the GRF the change in position may be more significant than the change in position of the GRF on the f/foot.
    What do you think

    Cheers Dave
  20. Peter

    Peter Well-Known Member

    Hi Kevin, Simon, Craig et al,

    It was my understanding that a forefoot valgus post, close-packed the Calc-cuboid joint.
    I also understood that this position/attitude of the CC joint enabled a mechanical advantage to Per. Longus to permit weight transfer from lateral to medial ( and compress the tarsal bones). This was my rationale for my original post, however I am willing to be enlightened.

    BTW, I don't take any questions personally, it merely adds to the debate.

    Kind Regards,

  21. Phil Wells

    Phil Wells Active Member

    Just to add my two penneth to the discussion, I have treated a few juvenile runners (with lateral forefoot posting) who have seen a reduction in lap times when running 200-400m. However, the majority of them experienced gastroc discomfort for a period of weeks until they had 'acclimatised' to the new running pattern.

    I have always attributed this to the effect of loading the lateral border of the foot, via valgus forefoot posting, resulting in a change to the amount of dorsal excursion of the lateral arch.
    The un-corrected foot would be less propulsive in gait due to this dorsal excursion with the slack being taken up by the gastrocs - a bit like walking on sand.
    The pre-loading would lead to both an increased stiffness in the CCJ and increased tension in the neural structures - proprioceptive changes? Also a reduction in forefoot abduction would alter the COP.
    Does this make sense?

  22. Craig Payne

    Craig Payne Moderator

    Lateral forefoot wedge --> lowers force to establish windlass (we documented that) --> weight moves forward off heel easier/sooner (we documented that) --> maybe run faster (we not doucmented that, but have documented that they can jump higher).
  23. Dave:

    I still can't agree with this analysis due to the same reasons I posted to Craig. Could you please explain how increasing the GRF on the lateral metatarsals would not cause an increase in magnitude of STJ pronation moment, cause STJ pronation motion, cause increased loading of medial column, cause increased dorsiflexion moment on first ray, and tend to prevent normal windlass function?

    Dave, I think that you and Craig are simplifying this effect too much by only considering the windlass. Your explanation does not make mechanical sense the way you have described it since the increase in GRF laterally should cause a STJ pronation moment and cause STJ pronation motion, not STJ supination. This is why in my initial posting I said this is a "paradoxical" effect.

    While I agree that windlass function is very dependent on STJ axis spatial location, I don't believe that one can totally understand the forefoot valgus wedge effect unless one also considers the neurological control mechanisms that the bipedal human uses to position of its center of mass in a stable fashion relative to the center of pressure acting on the plantar foot during walking.
  24. Craig:

    The forefoot valgus wedge effect I am talking about is dynamic and I have not seen it present in the static foot, so establishing the windlass in the static foot probably doesn't apply to the dynamic function of the foot during gait.

    Weight moving forward off heel easier/sooner can easily be explained by CNS control of gastroc/soleus function in that the CNS allows more efficient use of gastroc/soleus during gait when it senses lateral CoP positioning on the plantar foot.

    Finally, I don't use these wedges often in runners since valgus wedges increase the risk of pronation related symptoms in long distance runners. Maybe they might work in a few sprinters, but I tend to doubt it will work for even half of the sprinters.

    Good discussion....more research obviously needs to be done and this subject has many questions that still needs to be answered! :)
  25. In reviewing a few physics texts today the term "stability" appears to be a concept applied to systems in or operating closely around their equilibrium, i.e. stable versus unstable equilibrum. My point was that if a joint is accelerating by definition it is not in equilibrium, thus the application of the labels stable and unstable to a system not in equilibrium appears questionable.
  26. Stability has many definitions that is used quite differently in different scientific disciplines. Therefore, joint stability should probably be considered a special definition that may be more applicable to the clinical world rather than the physics world. Here is what my encarta dictionary says about stability:

  27. efuller

    efuller MVP

    Craig, Kevin and all,

    There are two major factors that are critical to allowing the hallux to dorsiflex in either stance or gait. (staticly and dynamically) The first is grf on the first metatarsal head. This will dorsiflex the met until someting stops it. A likely candidate is tension in the fascia/ windlass mechanism. So, statically a forefoot valgus wedge may shift GRF from the first met to more lateral metatarsals. Thus, the hallux would be easier to dorsiflex, because there would be less tension in the fascia. Craig has demonstrated this effect in his research so it does happen statically.

    The second factor is pronation moment at the STJ. Activation of the windlass, in most feet, will create a supination moment at the STJ. For supination to occur the supination moment from the windlass has to be greater than the pronation moment from other sources. A forefoot valgus wedge, if it shifted the COP more laterally, would increase the pronation moment from the ground reaction force, but this may not be larger than the supination moment from the windlass.

    I have felt for a long time that late midstance pronation is the result of muscular activity and not from "joint instability" as I was originally taught. Often, those individuals who have late midstance pronation, have laterally deivated STJ axes and in stance, when they do the maximum eversion height test they exhibit calcaneal eversion. To have late mid stance pronation you have to have range of motion available in the direction of pronation. A maximally pronated STJ (lateral process of the talus touches the floor of the sinus tarsi) is quite stable in that there is no more pronation range of motion available at the STJ. What you see in these feet is initial pronation and then a stopping of pronation and then a restarting of pronation. I have called these feet muscular pronators, because I beleive the peroneal muscles are the source of pronation moment that cause further pronation.

    On the function of the peroneals:
    Yes, it was taught that the peroneals shift the weight toward the opposite limb. This is not true. If you are in single limb stance and the peronal muscles contract, distally the STJ will pronate shifting the center of pressure more medially. Proximally, the attachment of the peroneals is pulled downward. Neither of these actions will cause weight to be shifted toward the opposite limb. You fall toward the oppisite limb when your center of mass is medial to your center of pressure. The farther the center of pressure is from the center of mass the faster you will accelerate. A medial shift of the center of pressure, from the contraction of the peroneals, will decrease the distance between the center of mass and the center of pressure. Therefore peroneal activity at the level of the STJ slows the progression toward the opposite foot. Proximally a downward pull from the muscle and the upward force from the ground would create a force couple that would cause the top of the tibal to shift away from the opposite limb. Therefore part of the analysis also does not shift weight toward the opposite limb. Question what you were taught.

    Back to static versus dynamic effects of the forefoot valgus wedge:
    Conceptually, the forefoot valgus wedge is very close to the reverse Morton's extension. I believe they both shift weight away from the first ray. (I choose the wedge over reverse Morton's when there is a long 2nd/ short 1st met.) The wedge will create less tension in the fascia, if it creates less load on the first metatarsal. Less tension in the fascia means the hallux will dorsiflex easier. This effect will be true statically as well as dynamically. So, gait can have a longer stride with the wedge because the hallux will dorsiflex easier. There will be less pain avoidance because there will be less stress on the structures of the windlass with the wedge.

    Now, if the wedge moves the center of pressure more laterally, there will be an increase in pronation moment from the ground. This will make the foot more "stable" because it is less likely to have an unexpected supination moment from the ground. When the center of pressure is very close to the plantar projection of the STJ axis there will be very little moment from ground reaction force. So, when the Achilles tendon add its simultaneous ankle plantar flexion and STJ supination moment there will be a net STJ supination moment. There is nothing to oppose this moment except for peroneal muscular activity. That is why I call these feet muscular pronators. They have more laterally positioned STJ axes and exhibit STJ pronation in the late stance phase of gait. The valgus forefoot wedge decreases the need for this peronal acitivity. There was a very interesting paper that came out of Japan in the mid 80's that looked at balance and muscle activity. It showed that when there is a tendency toward supination there was an increase in peronal activity and when there was a tendency toward pronation there was an increase in posterior tibial activity. So, the muscles don't always fire like they do in the published charts and this should make perfect sense, because not all people, nor are all situations, the same.

    Additionally, in gait the parabola of the metatarsals comes into play. The first and second mets are longer. So, when there is plantar flexion of the ankle, without STJ supination, a lot of STJ supination, the foot will pivot around the longer mets and there will be little or no weight born by the shorter mets. (This pain can be avoided by walking apropulsively) Or this high stress on the first and second mets be avoided by placing a wedge under the lateral metatarsal heads. This will spread propulsive stress over the entire forefoot. Watching barefoot walking you can often see the fifth met and toe off of the ground while the first met is still on the ground.

    So, there is both a static and dynamic component to how the wedge works.


    Eric Fuller
  28. Good posting Eric. One point I wanted to make, however, is that in late midstance, the windlass is not active since the hallux is not dorsiflexing. A lateral COP in late midstance should cause an increase in STJ pronation moment in late midstance due to the effects of GRF across the STJ axis. However, if some other source, such as muscular contraction, causes an increased STJ supination moment, then a paradoxical STJ supination motion may occur in late midstance with a forefoot valgus wedge. This will not occur generally unless there is some increased varus wedging in the heel and medial arch to resist STJ pronation along with the forefoot valgus wedge. The varus wedging in the heel and medial arch, by itself without the valgus wedge, will not produce this same late midstance supination.

    Interesting phenomenom I think which is best explained by a proprioceptive mechanism, rather than just by "establishing the windlass".
  29. efuller

    efuller MVP

    Hi Kevin,

    Some agreement and some disagreement. The toe does not have to dorsiflex for the windlass to be "active". In my foot, and some others, the fascia is palpably tight in static stance. I would say that in my foot the windlass is creating a supination moment and supporting the arch without dorsiflexion of the hallux. I agree that there is more to foot function than establishing the windlass. The windlass is one contributor to moments that act on the foot during stance and gait.

    I also agree that a rearfoot varus wedge is not enough to cause late stance phases resupination in some feet. I also agree that resupination is probably the result of muscular activity.

    I also have never really liked the term proprioceptive for what we are describing. proprioception is the ability to sense position. What we are talking about is a motor phenomenon. I would agree that proprioception is part of the whole phenomenon, but once you know where your joint is, now what do you do to explain why the foot moves into the position that it does. I don't really have a good name for it, but I know I don't like proprioceptive effect/ mechanism. Perhaps balance maintinaining/pain avoidance mechanism. Any other ideas?

  30. Eric:

    I believe that when we are talking about the "windlass effect of Hicks" we are speaking in reference to the observations that John Hicks originally made on cadaver and live feet when he performed hallux dorsiflexion on these specimens/individuals (Hicks, J.H. The mechanics of the foot. II. The plantar aponeurosis and the arch. Journal of Anatomy. 88:24-31, 1954). Therefore, if someone was to say to me, "activation of windlass", I assume that they are referring to the time of gait when the hallux is dorsiflexed relative to the first ray, in other words, the propulsive phase of gait.

    Having a plantar fascia that is under tension is a normal occurence in weightbearing stance when the center of mass is in equilibrium anterior to the ankle joint axis in relaxed bipedal stance and throughout the whole stance phase of gait. Its tension peaks at late midstance and early propulsion with it's tension being proportional to Achilles tendon tension (Erdimir A, Hamel AJ, Fauth AR, Piazza SJ, Sharkey NA: Dynamic loading of the plantar aponeurosis in walking. JBJS, 86A:546-552, 2004; Carlson RE, Fleming LL, Hutton WC: The biomechanical relationship between the tendoachilles, plantar fascia and metatarsophalangeal joint dorsiflexion angle. Foot Ankle Intl., 21:18-25, 2000). If you wanted to use a name for the plantarflexion moment generated at the first MPJ by plantar fascial tensile force then generally the term "reverse windlass effect" is used. Hicks also described this effect in his 1954 paper. I agree that the plantar fascia adds STJ supination moment to the foot unless the STJ axis is severely medially deviated.

    Perhaps there is a better way of describing this phenomenom instead of saying it is a "proprioceptive" effect. However, I believe that the effect does originate from the body being able to sense either pressure or joint force or joint position that sends an afferent signal to the CNS that sends an efferent signal to the gastroc-soleus complex which determines its temporal pattern and magnitude of contractile activity. The main point is that the mechanical effect observed from forefoot valgus wedging is contrary to the direction that the foot should move in response to a direct force across the STJ axis caused by an increase in ground reaction force lateral to the STJ axis. Possibly we could say that when the forefoot valgus wedge causes STJ pronation motion then this is a direct mechanical effect of foot orthoses and when the forefoot valgus wedge causes STJ supination motion then this is an indirect mechanical effect of foot orthoses. However, I prefer the more descriptive and accurate terminology of saying that when the forefoot valgus wedge causes a STJ pronation motion then this is a direct mechanical effect of foot orthoses and when the forefoot valgus wedge causes STJ supination motion then this is an proprioceptive effect of foot orthoses.

    I believe this falls somewhat in line with Benno Niggs theory on "preferred movement pathway" (Nigg BM: The role of impact forces and foot pronation: a new paradigm. Clin J Sport Med, 11:2-9, 2001) with the orthosis acting as a "filtering agent" for ground reaction force for the CNS. Whatever we decide eventually to call these orthosis mechanisms, I believe this line of reasoning corresponds quite nicely to my experimental and clinical observations over the years and our current understanding of the physiology of the neuromuscular system of humans.

    Good discussion, Eric.
  31. conp

    conp Active Member

    Hi Eric,
    Can you elaborate on this a little?
  32. efuller

    efuller MVP

    This is the sagittal plane blockade associated with a functional hallux limitus described by Dannanberg. You need to pivot somewhere between the foot and the floor. The pivot point can be at the ankle, mpj, or tip of the toe. It can be any combination of those during a particular step. When the pivot point is the tip of the toe Dannanberg describes the longer lever of the foot creates a physical blockade that prevents forward progression of the body over the foot. And then you get a shorter stride. I agree with Dananberg that you get a shorter stride, but I disagree with him on the explanation. I beleive pivoting over the tip of the toe would hurt and so people "choose" to walk with a less propulsive gait, with a shorter stride, so there is less stress on the toe. Some people choose to walk the same way when their hallux does not dorsiflex and they get ski tip toe (hyperextension of the IPJ). I apologize for skipping the steps in the explanation. An extreme example of the behavioral adaptation to changes in foot leverage is trying to walk normally with swim fins on. You have to walk flat footed or you trip.

  33. efuller

    efuller MVP

    I will concede the definition of activating the windlass. My point was that activating the windlass and the reverse windalss are the same thing in terms of moments applied to the first ray and STJ. Some people might think that they are different things because we have different terms for them.

    good discussion

  34. Thanks for that Eric.

    Now what do you and the others, Simon, Craig, Dave, lurkers, think about the terms that I am proposing:

    Direct mechanical effect of foot orthoses: That mechanical effect of a foot orthosis where the alteration in distribution of ground reaction force from the foot orthosis creates a moment or motion of one or more segments of the foot that is in the same direction as the change in direction of ground reaction force that is caused by the orthosis.

    Proprioceptive effect of foot orthoses: That detectable change in position or motion of one or more segments of the foot that can not be readily explained by a direct mechanical effect of the foot orthosis acting on the plantar foot and is mediated by central nervous system control of the muscles involved in the given weightbearing activity.

    I believe that such a delineation of terms is critical to readily explain the known kinetic and kinematic effects of foot orthoses on the foot and lower extremity and to allow better understanding within the podiatric profession of the therapeutic potential of foot orthoses.
  35. efuller

    efuller MVP

    Kevin, thanks for putting forward a good definition. How about indirect effect or CNS mediated effect of foot orthoses. As I said before propioception is sensory and this effect is in part motor.

    Last edited by a moderator: Aug 25, 2006
  36. Phil Wells

    Phil Wells Active Member

    I am not trying to be difficult but why create these definitions?

    The reason for this question is that although I agree with them, their clinical application is difficult e.g. as a clinician I might have a pair of orthoses that are not having the mechanical effect I was expecting. To explain why, would I have to create a very accurate diagramtic representation of the individuals GRF etc (Possibly calling Dave Smith everytime I needed to do this) to ensure that the magnitudes of orthoses posting are correct before assuming that a CNS mediated mechanism is occuring, which may be an important clinical clue as to what is happening (eg neurological disorder)
    Can I realistically obtain enough data through my assessment to acheive the above?

    Just to re-iterate, I like the idea of being able to classify orthoses effects in this way and feel that this approach is a very significant thought pattern to follow.


  38. Eric, Simon and Colleagues:

    I agree with you both, Eric and Simon. I think that the term "proprioception" is probably too restrictive of a term. I think, however, that the term "indirect" is so vague, that it is probably not that helpful or beneficial. I like the term "CNS mediated effect" since it is more inclusive than "proprioception" and certainly is quite descriptive. I think that this term accurately conveys the physiological mechanism by which these effects occur.

    So here are my "corrected definitions" with some further clarifications to the definitions to make them more accurate:

    Direct mechanical effect of foot orthoses: That mechanical effect of a foot orthosis where the alteration in distribution of ground reaction force from the foot orthosis creates a moment, and possibly a motion, of one or more joints of the foot and/or lower extremity that is in the same direction as would be predicted by the change in location and direction of ground reaction force that is caused by the mechanical interaction of the foot orthosis with the plantar foot.

    Central nervous system mediated effect of foot orthoses: That detectable change in motion of one or more joints of the foot and/or lower extremity that can not be readily explained by a direct mechanical effect of the foot orthosis acting on the plantar foot and is, instead, mediated by central nervous system control of the muscles involved in the given weightbearing activity.

    Any further comments on these definitions would be appreciated.
  39. conp

    conp Active Member

    Hello admin,
    How do we vote to get this thread a 5 star rating?

    Well this has been very interesting. My gut feeling is that the "CNS mediated effect on foot orthoses contributes to static and dynamic changes more than we think."

    This is an area that is largely unexplored and I believe the reason why although we might predict certain patients will respond well with the predicted mechanical effects of orthotic therapy there are many times that suprises us (WELL MYSELF ANYWAY) that some people do not respond and vice versa. This may well be due to varying individual CNS mediated responses to orthotic intervention.

    Although this CNS mediated response consists of many complex variable systems and would be difficult to research analytically, we know it is certainly a factor. A very basic example would be varying degree of compliance with even the thinnest of felt paddings. I usually apply a felt padding to most of my patients to get a "feel" of how aggressive I can be with the orthotic prescription.

    HOWEVER it would be great to be able to identify some proven clinical and medical indicators that would act as predictors to the success of any plantar mechanical intervention.

    Oh by the way. I have enjoyed the discussion for the mechanical effect also of forefoot valgus wedge because it has given me some detailed understanding of the reasons why it may cause some changes in gait.

  40. admin

    admin Administrator Staff Member

    At the top of each thread, towards the right, there is a "Rate this Thread" option...
    This software is so cool ....:cool:

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