Forefoot Varus Predicts Subtalar Hyperpronation

Daniel-don't be dismayed by those that try to create their own "paradigm", as the medical community is full of these types. Doctors love to have their names attached to diseases, procedures, syndromes and anatomical structures. Podiatry is no different. As far as I'm concerned, these "new concepts" are just rehashing of old ones, with emphasis applied elsewhere as those that push it try to create the impression that a "new way of thinking" is evolving. Look at the way those that push this "new paradigm" treat others in the same field that don't hold their beliefs. Those that are completely comfortable with their approach don't demean, besmirch, smear, denigrate, belittle or personally attack others. It is not only wholly unprofessional, but it comes from a position of weakness and insecurity.

I view the lower extremity as a set of bones...the muscles are merely necessary to move or stabilize those bones and the ligaments, for the most part, hold those bones together at the joints. I am more concerned about range-of-motions of those joints and relationships of the bones not only to each other, but to the ground, then I am about whether the axis of motion is deviated laterally or medially, if the bisection of the calcaneus is precise or whether the forefoot deformity is called a supinatus or varus. When I decide how to order an orthotic for a patient, do I focus on how the anterior tibialis or peroneal longus muscle might react to the changes I prescribe, or am I more concerned about making the patient more neutral and therefore more comfortable? Am I making biomechanics too simplistic? Certainly, but your confusion lies with the fact that there are those that make a living out of over-complicating this science...for whatever reason. I started going back to the basics and working up from there...expanding my own frame of reference and creating my own "paradigm".

Arguing whether, or not, a calcaneal bisection is accurate, or even necessary, is an abject exercise in futility. If the bisection is off by even a few degrees...who cares? It's all relative...the line doesn't change while assessing maximum eversion to inversion, ROM or comparing NCSP to RCSP. Sometimes you need to trust your own intuition and go with what YOU know and have learned. I look back on orthotics that I had ordered for patients many, many years ago...and more often than not, I'm embarrassed. It's a learning process, for sure. But I learned a LOT more on my own, than I ever learned from many of my old teachers and those that consider themselves leaders in this science today.

Efforts are underway for you to receive a copy of Roots book, Vol. 2. It's wealth of information and a good starting point for you, as it has been for me. Hope it helps.

 

I agree, this is the ideal. Question is: How are we going to get there?

Daryl

 

What about a hand held dynamometer like this one: http://www.citec.nu/ and http://www.citec.nu/dwnl/MuscleNerve_Dynamometry_reliability_2008.pdf

Sincerely,
Daniel

 

Here's one solution: https://steinhardt.nyu.edu/scmsAdmin/uploads/006/435/41-04 Wilken 2.pdf

As Daniel said hand held dyno's may help. I know a UK colleague who was playing with gloves with built in load-cells.

 

I think the idea of golve with sensors is great ! How do you think it will function in the case of a supination test ? Associating the supination force with some displacement of navicular [through a position sensor on navicular] ? I think such kind of method will make possible the study of inter-rater reliability of this test !

Sincerely,
Daniel

 

I'm not sure a glove approach is the best way to measure load/ deformation curves at the navicular for supination resistance. Craig Payne, Ian Griffiths and myself have all designed jig's which already allow this.

Edit: Some refs.
http://www.podiatryinfocanada.ca/Public/Page/Files/542_CFPM4_The_Supination_Resistance_test.pdf
http://www.ncbi.nlm.nih.gov/pubmed/12756308
http://www.biomechanics-education.com/journals/Supination Resitance Test.pdf

 

How is said colleague, have not seen his name around here for a while, saw these gloves a couple if years ago

 

Don't know, he lost in space. http://www.jesusjonesarchive.info/demos/WhatsGoingOn-Vox.mp3 I have a pair which he got for me, but weren't callibrated in a useable manner. I'm sure with an arduino or raspberry pi, it'd be fairly simple.

 

Looks like this thread has been wrung out, and left to dry by several of those that are frequent contributors. Let's see if I can help get this discussion back on track, even if it means "stirring the pot" some. Here's some pics of an orthotic I ordered for someone who had a very low ROM of the STJ and a severe, non-reducible forefoot varus deformity. Notice the significant correction taken all the way to the end of the orthotic. I have found this to be a very helpful addition in order to bring the great toe into contact with the supporting surface.

 

Matt,

Speaking of stimulating discussion Matt, here is an interview with Merton Root that appeared in the October 1989 issue of Podiatry Today. My thanks to Daniel Petcu for resizing the article so that I can now up load it to the PA.

Jeff

 

Thanks, Jeff, for that article from Dr. Root. While I was reading it, I could still hear Mert speak those same words that he so often said at many of the Root seminars I attended. I don't agree with everything he said but he certainly was a convincing speaker.

Like I said before, Jeff, you need to get your father's lectures on audio tape made into downloadable audio files so that people can hear him speak. I think that would make a great impact on peoples' impressions of Dr. Root, his personality and his contributions to podiatry.

 

Thanks for that pdf file, Jeff. Great stuff...a "blast from the past"...an oldie but a goodie!

Here's some glaring tidbits pulled from it:

1)Prior to 1954, no one had discussed STJ neutral in the orthopedic literature.[page 25, 2nd paragraph] (BTW-The concept of proprioception is one I discuss with all my post-surgical patients that have been immobilized).

2)His acknowledgement of soft tissue stress based on skeletal deformities, [page 27, 3rd paragraph]

3)His recognition that the foot pronates to vertical in the compensated rear foot varus deformity, (I am assuming at static stance). In his book, Vol. 2, he states the same on page 96...although he then states in that book that maximum pronation of the rear foot occurs at the end of contact phase...4-6 degrees everted, (page 137). I will continue to research this, as it ties into another project I'm currently considering to publish.

4)Top of page 76 is where Merton was asked a question about ankle sprains...and his answer mirrors what I discovered on my own about lateral instability, and something I have not heard lectured about extensively, even by Doug Richie. Shame. Your Dad was "all over" this problem over 25 years ago.

 

I would agree that this is the type of device I would prescribe for the patient you describe. I'm glad that you figured out something that works. I gave a presentation on this type of device at a seminar so long ago that I can't open up the powerpoint file with the most recent version of powerpoint.

The interesting thing about this type of device is the idea of the forefoot extension. I recall one of the regular contributors to podiatry arena saying that Root, Orien, or Weed, (I can't remember which) taught that a functional device had to end behind the metatarsal heads. I never understood how a device that ended behind the metatarsal heads could support a partially compensated varus deformity. There is an intersting gap in the though process in understanding the concept of a partially compensated varus and the "functional" orthosis that is needed to treat it.

Eric

 

Dear Dr. Fuller,
If you want to upload here the presentation, you can send it to me in order to see if I'll succeed to change it in a proper format. I think it will be useful for the general public.
Respectfully,
Daniel

 

Did you ever write about it...ever have anything published on it? When I did my research, the earliest article I read on forefoot extensions were an article by Subotnick and then Clement/Taunton in 1980, but it was for a soft device for runners.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2383477/pdf/canfamphys00265-0073.pdf

I haven't read anything since that time about forefoot varus extensions to the end of the toes in "hard" orthotics. By a process of trial and error, I came to order these by my own determinations. Considering that the orthotics lab has indicated that I'm currently the only Podiatrist ordering these devices with this prescription...it appears to be a not well known or utilized approach.

 

I first saw varus forefoot extension orthoses made for runners by Steven Subotnick, DPM, in about 1980. This was an unusual orthosis design by CCPM standards of the early 1980s and was criticized by Chris Smith, DPM, as this orthosis design was going to be a "bunion producer". As for my own practice, I've been routinely using varus forefoot extensions on orthoses for runners for about 25 years with great success when treating medial tibial stress syndrome and patellofemoral syndrome. However, I only use varus forefoot extensions about 3-4 times a year when treating walking patients with more severely pronated feet.

 

Eric,

A Root type functional foot orthosis must end proximal to the metatarsophalangeal joints because the shell is made of a semi-rigid material would restrict necessary MTPJ motion. The device ends at the metatarsal neck because Dr. Root found that it was uncomfortable if the device extended underneath the met heads. The original top covers on Root type functional orthoses were shell length only (no distal extension) and were done by the first commercial labs that stated using polypropylene. They were for esthetic purposes only. Later on they were extended and Poron was added as a soft tissue supplement. Langer, PAL and Burns Labs popularized top covers. I was eventually able to convince Dr. Root that we should use top covers for functional purposes and that when made properly with high quality material, polypropylene orthoses could hold their shape in most cases.

Varus and valgus forefoot correction extended to the met necks does support the plane of the forefoot in an inverted or everted manner. On occasion patients will complain about the lack of toe purchases and in such cases it helps to use a varus or valgus forefoot extension. In order to support a ff varus, the device should have a tight radius at the distal medial edge and on the lateral edge for a forefoot valgus. The greater the inverted or everted position of the forefoot, the higher the correction and more pronounced radius at the distal edge will be.

Well, off to a Super Bowl party now!

Jeff

 

Kevin-do you still adhere to what Chris Smith told you? Why would this orthotic produce bunions? Enclosed is a pic of a 15 y.o. patient I saw. Notice the hallux hammertoe deformity already forming, along with HAV. Notice the hammertoe deformities of digits 2-5, as the FDL is being substituted for propulsion. This patient already has a bunion "in the making", and presented with a forefoot varus deformity, with decreased hallux purchase. By definition, he already has a metatarsus primus elevatus. Slowing the progress of these deformities was my concern. And fwiw, I prescribe a LOT more of these extensions than just 3-4 times/year.

 

Matt:

I never "adhered" to what Chris Smith told me over three decades ago, either on this specific subject and on many other subjects. However, the general theory, I believe, from what I remember, was that by using a varus forefoot extension on an orthosis in walking, a functional hallux limitus is created which can cause increased risk of bunion deformity. I believe we don't have enough data yet to know if this is true or not. I haven't seen it happen.

As for my patients' walking orthoses, I use more reverse Morton's extensions and forefoot accommodations plantar to the 2nd metatarsal head only, or plantar to the 2nd and 3rd metatarsal heads only as forefoot extensions. I use forefoot extensions on about 1/3rd of the orthoses I dispense.

 

Jeff, I'm not clear about how Dr. Root felt about off weight extensions. For example, the patient with a long 2nd met. How would have Dr. Root felt about adding 1/8" cork under metatarsals 1,3-5? Or adding a varus extension like the one in the picture in Matt's post?

The intrinsic forefoot valgus post, even relatively large ones don't usually cause problems. On the other hand the intrinsic forefoot varus post, just doesn't make sense. If it is working as intended the first met head is not bearing weight when the heel is on the orthotic. This will tend to put too much pressure in the medial arch and tend to be uncomfortable. In gait, after heel off, the first met head is up in the air and ... what's supposed to happen next? Jeff, what do think happens in gait, after heel off, with a large amount of forefoot varus intrinsic post?

Eric

 

I guess no one ever bothered to point out to Chris Smith the fact that in a structural FF varus that is non-reducible, there already exists a metatarsus primus elevatus which, in turn, creates a hallux limitus. We've all see these feet in our offices...the hallux that "looks like a thumb", because of the demands on the IPJ to dorsiflex secondary to the lack of motion at the MPJ. Intrinsic corrections for this deformity have not been satisfactory, therefore, I went with an extrinsic FF extension that 'brings the ground up to the great toe'. These patients are satisfied with the result. Attempts at sagittal plane corrections have not worked out real well for me...and a hallux limitus is a sagittal plane problem, at least, in my mind. The way I've worked around this is to recommend rocker soled shoes in combination with these types of orthotic devices. The results have been positive.

 

The question was about an orthotic with a forefoot varus extension.

Matt, why do you think bunions form? In my windlass paper I put forth my theory on why bunions form. I think they are caused by the "reverse buckling" created by compression forces at the first MPJ. Increased load on the first met head will tend to cause dorsiflexion of the first ray, which will increase tension in the plantar fascia, which will increase compression forces and the tendency to buckle the first MPJ in the transverse plane. Yes, it is all theory, but it is quite plausible.

Additionally, STJ axis theory is important here. with a more medially deviated STJ axis, upward force on the first met head, still causes a STJ pronation moment. You can observe this for your self with a patient seated in the chair and you push upward on the first met head. Some feet will supinate, some will pronate, some won't move at the STJ axis. The problem here is that the feet that you want to supinate will still be pushed toward pronation with increased load on the first met head. So, if your goal is to reduce stress on the 1st MPJ by attempting to supinate the STJ, a forefoot varus wedge may actually increase stress on the first MPJ.

The test that I feel is best for deciding if a forefoot varus extension is warranted is the test described by John Weed in his lecture syllabus. In static stance you try and slide your fingers under both the medial and lateral sides of the foot. If you can slide your fingers under the first met head the patient should get a forefoot varus extension. The exception is for those patients who are actively contracting their posterior tibial muscle. That test is not the only test I would use in deciding.

Eric

 

Eric,

Dr. Root continued to talk to customers and to do some consultations for Root Lab up until shortly before his death. Like all of us, he learned how and what modifications seemed most logical for the pathology being treated. So he was advising podiatrists to use 2nd met head cutouts, Morton's and reverse Morton's extensions, varus and valgus forefoot wedges and other top cover modifications depending on the symptoms and the structure and function of the foot being treated.

As far as intrinsic and extrinsic forefoot varus posts causing pathology, I don't think there is any real evidence to support this. Interestingly enough, Dr. Root was a huge advocate of the need for 1st ray plantar flexion after heel lift. That is why he designed the anterior width of the Root type functional orthotic to end lateral to the 1st met head on the non-weightbearing cast of the foot. He also periodically made the anterior width even narrower and in some cases, recommended a 1st ray cut out in the orthotic shell.

If a foot with forefoot varus is pronating excessively, and if the forefoot varus is contributing to that excessive pronation, and if using intrinsic or extrinsic forefoot varus support (correction) help reduce the degree of pronation or helps promote resupination of the foot, then it makes sense to me to use it. Why? Because if the foot is excessively pronated after heel lift, then the 1st ray is probably not plantar flexing anyway, so you already have an environment that can cause functional hallux limitus. So I guess we could ask this question: Is the patient better off with a malfunctioning 1st ray in a more pronated foot or a less pronated foot? I believe that the more pronated foot is more likely to cause HAV than the less pronated foot. And it is also possible that by reducing stj pronation with a varus post, we are improving 1st ray plantar flexion and the range of hallux dorsiflexion. That's certainly what Dr. Root believed.

Jeff

 

Eric-books have been written on the subject of the first question you asked, and you want a condensed version here? LOL! First, there are two different types of bunions...dorsal and medial. Which one would you like to discuss?

 

Perhaps not, but it is theoretically plausable and biologically coherent. It's interesting to note some of the studies of one of my PhD supervisors here:
This was a bone pin study:
http://www.ncbi.nlm.nih.gov/pubmed/1920102 What it shows is that the orthoses reduced the extension of the hallux on it's metatarsal, they didn't increase the extension.

And this was the PhD, in which similar devices were employed and showed a non-significiant increase in HA angle among the orthoses group compared to the control:
http://eprints.nottingham.ac.uk/11917/1/261039.pdf

Conclusion- these types of orthoses certainly didn't help in slowing the progression of juvenile hallux valgus and MAY have made it worse than doing nothing at all. Did the orthoses cause the pathology? No. Did they help? No.

 

Simon,
I certainly agree that it is important for 1st ray plantar flexion to occur in conjunction with hallux dorsiflexion after heel lift and that we do not want to create functional hallux limitus with orthoses.

Jeff

 

And therein lies one of the potential problems of forefoot varus posts, agreed? It's likely less of an issue with orthoses designed for runners, but is a potential issue for "walking" patients. Personally, in hallux valgus (or bunions if you will) I try to lower the dorsiflexion force acting on the first met head, not increase it for the reasons that Eric described and I think Snijders (?) did too.

 

I believe that I have posted these before on the PA, but here are two articles Dr. Root wrote for Podiatry Arts Lab's (PAL's) newsletter back in 1981 and 1982. He addresses many of the same issues we have been discussing in this thread including the history of the development of the Root type Functional Orthosis as well as 1st ray and hallux function. In the 1981 article he writes: "The Root Functional Orthotic has not yet been fully developed. It is still developing as more specific variations of the human foot are identified. As I recently said, he knew it was a work in progress.

Jeff

 

Question was what causes bunions.

The nice thing about the windlass mechanism explanation is that it explains both. The difference between dorsal and medial is the ability of the met cuneiform joint to resist frontal plane movement of the metatarsal. I've seen a chapter or two in a book, but no books on the subject.

Why do you think dorsal and medial bunions have a different cause? If you think they are different, pick one and discuss, if you think it is different than the reverse buckling mechanism.

Eric

 

Which is why many practitioners now plantarflex the 1st met (or 1st ray) in their casting. It sounds good in theory but ideally we need evidence to support this practice.

Jeff

 

Personally, I'd go back a step and work out the mechanics of the forefoot varus post, intrinsic, extrinsic and extension. Then I'd hypothesise on the biomechanical effects of these. Eric has gone some way toward this. Then you can define the above for a casting postion in which the first ray is plantarflexed, but being mindful that casting position is only that- I can still make a forefoot varus post for an orthosis in which the first ray was plantarflexed during casting.

 

Here is another article written by Dr. Root in 1982 that demonstrates his thinking. In this one he says:

"Those podiatrists who have little or no knowledge of biomechanics but attempt to convince the public and the profession that they do, are distorting biomechanics, and will eventually destroy it as a valid scientific basis for understanding the foot. The science of biomechanics will continue to grow and flourish in other medical specialties but will die in confusion within the profession of podiatry.

And:
"A functional orthosis only resists abnormal forces and promotes improved foot function. Functional orthoses were conceived on the basis of the following premise. Biomechanics indicates that a foot only moves abnormally when that foot is subjected to abnormal forces. Those forces that cause foot malfunction can be either compression or tension. There are no other forces acting upon a foot. Compression or tension forces can become abnormal when they vary from normal in either their direction or their strength within the foot".

As you can see, he had a legitimate concern for the future of podiatry, especially here in the U.S. And you can also see how forces were a central part of his thought process.

Jeff

 

Not true.

 

Matt,

Those are some nice orthotic pictures. As you know, in the diabetic arena, 90% of our orthotics extend (and are even molded) to the ends of the toes. Extrinsic forefoot posting all the way to the ends of the toes is utilized a great deal of the time, however we have to be very careful in not creating interference between the toes and the toe box of the shoe. So that is the tricky part.

I believe that the forefoot posting to the end of the toes, that matches the forefoot posting under the metatarsal head should be reserved for those people that you don't expect the inverted forefoot deformity to reduce (i.e. those who were classically said to have true forefoot varus rather than forefoot supinatus.) If the lift under the hallux is greater than that under the first metatarsal, it can be acting like a cluffy wedge to try to create first metatarsal head plantarflexion. The important thing is that the orthotic not prevent the first ray from plantarflexing. I do notice that in your frontal plane picture that there is a very straight line from the medial edge of the arch to the lateral edge, with very little convexity under the lateral column. This could be due to 1) that is indeed the actual shape of the foot when the forefoot is everted to the rearfoot 2) an optical illusion in the way that the picture was taken, or 3) high degree of supination of the LAMTJ. I also note in the sagittal plane view that the height of the orthotic under the 1st MCJ is the same as the height under the navicular, which seems a little strange. (Again, I haven't seen the foot so I don't know).

Thanks for your good contribution.
Daryl

 

Simon,

Technically not true, but you need to consider it in the context of the article:

"An orthosis that is prescribed to resist specific abnormal forces identified by examination and is designed to promote improved function of the foot is called a functional orthosis. A functional orthosis does not support the arch of the foot.
A functional orthosis does not "balance" a foot. A functional orthosis does not hold a foot in any position. A functional orthosis does not accommodate lesions or painful areas of the foot. A functional orthosis only resists abnormal forces and promotes improved foot function. Functional orthoses were conceived on the basis of the following premise. Biomechanics indicates that a foot only moves abnormally when that foot is subjected to abnormal forces. Those forces that cause foot
malfunction can be either compression or tension. There are no other forces acting upon a foot. Compression or tension forces can become abnormal when they vary from normal in either their direction or their strength within the foot."

You need to understand that this was an editorial letter, not a scientific paper. It was written in response to an article that appeared in Consumer Reports criticizing "orthoses". Functional orthoses do support the arch but that is not necessarily their primary goal. He was trying to differentiate functional orthoses from arch supports.

Jeff

 

Eric-The following is a fairly simplistic explanation, and one I have developed to instruct my patients. Typically, dorsal bunions are caused by a hallux limitus condition, secondary to a metatarsus primus elevatus. The joint doesn't bend (dorsiflex) under load. A lot of the times, these patients will have "the big toe looks like a thumb" scenario, as the IPJ has to dorsiflex due to lack of motion at the 1st MPJ. Further, these patients will swing their foot out and around, in "egg-beater" fashion, as their great toe can't clear the supporting surfaces, (or so they think)...you will see an abductory gait in swing phase. Plantar callouses under the head of the proximal phalanx are not an uncommon finding with this patient group. When one performs surgery on these patients, you will witness a lot of cartilaginous proliferation with degeneration on the upper 1/3 of the met head...above and beyond the boney exostosis witnessed on lateral plain film radiographs. One can palpate this mass of cartilage as well.

Medial bunions are formed over time when the medial column is not stable at the time the FDL muscle fires, thus pulling the tendon in the propulsive phase of gait, (launching the patient forward against GRF). If the 1st met is unstable at the time that the FDL muscle fires, a slight adductory, retrograde force is applied to the head of the 1st met. The idea behind performing bunion surgery is simply to re-align the bones of the first ray over the top of the FDL tendon. One of the reasons why bunionectomies fail, when the deformity returns, is the lack of adequate support of the patients' foot post-operatively...thus the same mechanical reasons why the bunion formed in the first place is not addressed.

"When all one has is a hammer, the world looks like a nail".

 

Daryl-thanks so much. In all honesty, I'm still "experimenting" with this design and approach. The example I showed is a really drastic correction...~10 degrees of forefoot varus correction. I don't order too many this "acute" at all. But I got really frustrated having to re-order orthotics when I used intrinsic corrections that did not support the hallux distally. Further, I began to realize the importance of hallux purchase in propulsive phase of gait above and beyond what we were taught. With intrinsic corrections, and no distal support, the patient would then need to "roll inwards" in order to gain hallux purchase for balance and propulsion. This applied more pressure under the first met base, medial cuneiform resulting in increased patient complaints while trying to wear the orthotics. I basically "threw in the towel", started over, and ordered different types of orthotics for those I couldn't "cast out" of the supinatus, ie., a structural, non-reducible varus.

Yes...all the diabetic plasitzote insoles I order are full length. I have the orthotist correct for some of the more glaring biomechanical problems they have.

 

To answer the question is the first ray better off in a more pronated foot or a less pronated foot: It depends on which direction the STJ will tend to move. Speaking about the foot in gait around the time of heel lift. If the more pronated foot has a net supination moment and the more supinated foot has a net pronation moment, as the heel lifts the more pronated foot will be moving toward supination and the more supinated foot will be moving toward pronation. So, we can't decide if the first ray will be better off based on position of the STJ.

Now we look at the foot that is supported proximal to the metatarsal heads by a forefoot varus posted orthotic as the heel lifts. The medial forefoot will lose its support and the STJ will have to pronate to load the first met. There will still be force on the lateral forefoot that will be generating a pronation moment at the STJ. An alternative explanation is that the first ray plantarflexs to touch the ground. When the ray is plantar flexed there are no ligamentous forces resisiting dorsiflexion. The only thing that can hold the first ray down against ground reaction force is the peroneus longus muscle. When I was doing my cadaver work on the peroneus longus muscle, I noticed something interesting. When the first ray was unloaded, tension in the muscle would plantar flex the first ray. When the first ray became loaded, tension in the peroneus longus tendon would cause STJ pronation as long as there was STJ range of motion in the direction of pronation. This is why a forefoot varus posted orthotic, ending behind the metatarsal heads does not make sense to me.

Eric

 

What is lacking in that explanation is the assumption that met primus elevatus limits first MPJ range of motion. The first met going up is not what is limiting the motion. What can limit motion is tension in all the structures that attach through the sesamoids into the base of the proximal phalanx. Tension in those structures will cause increased compression of the joint surface. Increased compression of the joint surface will cause the joint surface changes that you have observed.

When you start with a plantar flexed first ray and then load it so that it moves to its maximum dorsiflexed position, the plantar fascia will become tight and create the compression forces in the joint. So, you can get functional hallux limitus without met primus elevatus. In functional hallux limitus the forces are present to create the dorsal osteophytes and surface erosions associated with hallux limitus.

Occam's razor

Agreed that when the forces that cause flexion of the MPJ are not alligned there will be a tendency toward medial or lateral deviation of the phalanx relative to the metatarsal. However, you also need to include the flexion forces from all sources. Hicks noted that the force from the windlass was several times that of the muscle. A good way to look at it center of pull and center of push acting on the proximal phalanx. The center of pull is average location of pull in the sesamoids (and FHL) versus the average push is the center of pressure of the MPJ joint surface. These two forces, when not alligned will create a force couple that will tend to cause rotation of the joint.

So, both dorsal and medial bunions can be explained by the same mechanism.

Eric

 

Eric,

We would need to know the net force acting at the 1st mpj after heel lift to know if it is pathological at the 1st mpj. If there is a net abduction and eversion force after heel lift, this will contribute to HAV. If there already exists an angle of hallux abduction due to the presence of HAV, then there could possibly still be a net abduction and eversion moment at the 1st mpj in a severely pronated foot due to the angle of the hallux, even if the stj starts moving in the direction of supination. However, the stj supination might act to reduce the net moment some.

The varus contour of the orthotic shell still provides varus support between the medial forefoot and the interior surface of the shoe after heel lift. How can the medial metatarsals (forefoot) evert when there is an orthotic shell creating varus support along the entire shaft of the metatarsals? To demonstrate this concept, think about the apex of the medial arch when wearing an orthosis. After the heel lifts, there is still an influence from the orthotic that acts to support the medial arch because of the reaction force between the orthotic shell and the shoe. With an intrinsically or extrinsically posted orthosis, the distal edge of the device acts as an axis of rotation in the frontal and transverse planes during heel lift. In fact, we can see in some cases where the distal edge of the orthosis actually cuts into the shoe or the sock liner because of the force exerted on the distal, medial aspect of the shell after heel lift. The same thing can occur laterally in a valgus posted device.

Some people argue that the orthosis doesn't have an influence once the heel comes off the ground. I disagree with that.

Jeff