Forefoot Varus Predicts Subtalar Hyperpronation

Now is as good as time as any to re-examine my beliefs. I do cast the foot with a small dorsiflexion abduction force on the forefoot relative to the midfoot. Kevin, do you still load the midtarsal joint most of the time when you cast?

Kevin and I have discussed a mutual patient that we saw independently of each other. This patient had what some would call a flexible cavus where when the lateral forefoot was loaded the medial forefoot would plantarflex and create a very high arch and a large amount of forefoot valgus. We both casted this patient with a dorsiflexory load on the first met head. This patient was an exception to the rule on how I would cast a patient.

Anyway the reason that I started casting with a dorsiflexory load on the forefoot is what John Weed taught in class. That is, when the OMTJ is supinated this will create a higher lateral arch in the foot than there will be when the foot is loaded. John Weed described how this would tend to cause pain in the midfoot where the lateral arch was too high. I liked the reasoning and haven't changed this from what I was taught. I have added some additional reasoning. When you cast a foot with the lateral forefoot dorsiflexed, you will create a shape that will match the foot when the plantar ligaments are loaded. When the foot is on top of the orthotic the forefoot will be dorsiflexed to the position where the ligaments will be loaded. In this position there will be some upward force at the cuboid metatarsal and calcaneal cuboid joint that will decrease the dorsiflexion moment on the lateral column and the plantar ligaments will be preloaded.

Mert Root and others made the observation that an orthotic worked better when the midtarsal joint was dorsiflexed and abducted. I'm not sure how they explained it within their paradigm. However, I like the observation, but I like my explanation better. (pre load and no hump in the orthotic [well that was John Weed's explanation, but I'll think I'll keep it until someone gives me a better explanation]) However, I have not really tested this theory. Has anyone else tried plantarflexing the lateral column of the orthotic versus dorsiflexing the lateral forefoot while casting. (Ed Glasser casted my foot with both medial and lateral columns plantar flexed and the medial arch of that device hurt so much in the medal arch I didn't get a chance to evaluate the lateral arch.)

Comments?

Eric

 

Kevin,

Within the 2, 4, 6 and 8 second marks on your video (one one second intervals are too long for me to precisely give you the exact time) you will see a point at which the forefoot changes direction and no longer abducts but begins to plantarflex and adduct. You will also notice that the plane of the forefoot appears most everted at that same moment in time. If you run the video and stop it at these times, it is easier to see when this change in direction occurs. It would be much easier to identify with slow motion and fractional seconds. It is impossible to tell from the video if the mtj is maximally pronated since you are controlling the forces, but these points appear to be when the forefoot in its most pronated position. In the portion the video immediately following , you are abducting/adducting the forefoot and then plantarflexing/dorsiflexing the forefoot. Since this is not triplane motion, the foot can't be pronating or supinating at the mtj. Maximum pronation of the forefoot only occurs with pronantion and when we can observe the greatest range of simultaneous abdcution, dorsiflexion and eversion of the forefoot. As a result, I find it very easy to identify the point of maximum mtj pronation in your video.

Jeff

Jeff

 

Eric:

While I have your attention, could you please e-mail me a copy of your 2010 Podiatry Today article on "Reinventing Biomechanics"? Thanks in advance.

I always load the midtarsal joint with a forefoot dorsiflexion force under the 4th and 5th digit sulcus when I cast, just like I was taught by the professors at CCPM. However, I also load the medial metatarsal rays in either the dorsiflexion or plantarflexion direction, depending on the patient, in over half the patients during negative casting. This technique seems to work well for me and my patients. In fact, learning how to produce an effective negative cast is likely one of the most important things I learned in podiatry school, and for that I am grateful to Dr. Root and his coworkers for working this out for me and many other podiatrists who were similarly trained.

However, why this technique works so well is beyond me and I can only guess, as Eric also stated. I know that Mert Root had advocated plantarflexing the lateral column during negative casting to get foot orthoses to fit into dress shoes toward the end of his lecture career. I'm sure Jeff can give us a little more history on that.

 

Mert and John would teach practitioners that it was sometimes necessary to rub the plantar surface of the cast under the 1st met head in order to reduce the degree of 1st met (1st ray) plantarflexion in cases of ligamentous laxity when the 1st met tended to be plantarflexed from its neutral position due to gravity during the supine position casting process.

As far as plantarflexing the lateral column for dress shoes (typically in females with heels), it was done to increase the lateral longitudinal arch so that the orthosis would fit in the shoe. Some use in shoe casting for this same reason although we can also make modifications in the positive cast to improve fit in higher heeled shoes.

Jeff

 

Jeff:

The point I was making, and Simon also mentioned, was that in the ellipsoid shaped envelope of motion of the forefoot on the rearfoot, there is no one single point at which the forefoot can be "maximally pronated" on the rearfoot since it is dorsiflexed, everted and abducted at all of the points in one quadrant of the ellipse.

You may think you could find what you think is "the maximally pronated position of the MTJ" and you may think you could find what you think is "the calcaneal bisection" or "the forefoot to rearfoot relationship", and you may be good at repeating these "measurements" yourself, but 100 other podiatrists or researchers would not likely be able to duplicate your results since there is too much range for measurement error. You may believe they are there, and may, like your father, feel they are easy to find, but very few others can confirm what you believe to be true.

Where then does that leave us? It leaves us with your word against the word of others with not a shred of scientific research to back up your claims. This also leaves you in a very weak position to be able to defend your beliefs under the assault of scientific scrutiny. I would think that it would be unwise to continue to defend your claims unless you, or someone else, can gather some data to back them up.

That being said, this is a great discussion and I appreciate everyone, Simon, Eric, Jeff and Daryl for taking part. I've learned a lot.:drinks

 

Kevin,

I have been working on pictures for Daryl's lecture at the PAC/PFOLA conference next April. I am documenting the construction of a TMA device that I originally developed for a patient of John Iredale's many years ago, and which we have refined with Daryl's assistance. We use heel bisection and ff to rf in the construction, noting that there is much less ff to deal with.

I am also documenting the construction of a hybrid device that Daryl developed with my staff that has both functional and accommodative characteristics. Both of these devices utilize heel bisection as a means of orienting the cast and resulting device in the frontal plane during construction. Unfortunately I think I have a presentation at the same time as Daryl's. I hope you will be able to attend Daryl's lecture.

I realize that for a number of reasons these debates can become (too?) personal in nature, but as they say, no pain, no gain. Without some of the friction we would not have some of the meaningful and productive discussions and debates. It is important to keep things in perspective and recognize that we all do really want what is in the best interest of the patient in spite of any :boxing:, :craig: or :bang: that we might do!

Jeff

 

I still need to make my plane reservations and don't know quite yet if I'm staying for the whole seminar. I'll be sure to see you both there and hopefully can attend as many lectures as possible.:drinks

 

Jeff-look at the video provided by Kirby. Notice the "hypermobile" MTJ? I've seen this before...plenty of times...so much so that I'll make some predictions just based on the limited sequence of video I saw. If I had to guess, that patient has a collagen deficiency disorder like EDS mitis type. She probably has a calcaneal inclination angle of greater than 35 degrees and a lateral, WB plain film radiographic view might demonstrate the "see through sign" I've discussed before. Notice the slight abducted hallux, and the mild hammertoe deformities in NWB fashion? This patient, because of the mild type EDS, (and the hypermobile MTJ) is able to contract the soft tissue in the intrinsic muscles of her foot in order to bring the hallux down to the supporting surface, but not entirely...thus the flexor substitution in the FDL tendons. Not glaring, but there. Probably began as a more involved forefoot varus deformity...now, not quite as obvious. How do I come to these conclusions with just a brief sagittal plane view? Patterns...I continue to see patterns. Look at the pic I attached to this post...this was a pic of a 14 y.o. male kid that has similar problems.

The problem as I see it, is that Kevin and Simon want to argue delicate points with you about patient treatments and clinical data. And while you're a very solid orthotist with a LOT of clinical background, them arguing with you is analogous to them arguing with a musculo-skeletal radiologist about MRI results. Like yourself, a radiologist doesn't have the clinical presentation to supplement their readings. They have ZERO clinical exposure with the patient...only an idea of what the injury "may" be, and what the pending diagnosis is...according to the ordering physician. In other words...it's a gutless argument they make. But we already know about Simon and Kevin, which I so adequately exposed on this thread alone. I just tied the rope into a noose and handed it to them. They were the ones that put it around their own necks and stepped off the platform...no one pushed them. Simple.

Cheers!

 

I'm sorry that you want to bow out of discussing what I feel is the most pressing current need in biomechanics. It's interesting that only when I'm discussing on these blogs that I find myself using the name of Root so much. If you read my writings (except for those in which I'm asked to specifically comment, such as in Alberts book.) I rarely mention his name and use very few of his references. However, as the years pile up, I find the Root Postulate point to be ever more essential in my daily practice. Some of my reasons are:

1. The casting position -- I find that if the MTJ is not maximally dorsiflexed, abducted and everted (sorry that you don't like to use the term pronated any more to describe these three motions) that the orthotic is usually very uncomfortable to wear. Now sometimes the patient can get use to this and sometimes they cannot. However if I make sure that I use the "Root" casting technique of gently dorsiflexing, abducting and everting (which I will now abbreviate DAE) the forefoot against the rearfoot then most of the time the patient can comfortably wear the orthotic, no matter what the material it is made of, comfortably. Why do you believe that this is the case? Now in response to this I can express the following experiences.
a. About 10 years ago, Ed Glaser tried to hire me. I was very willing to listen, and I twice visited his factory. I gave him every chance to prove that his non-Root casting technique on both myself and my wife, and we both followed religiously his instructions for break-in. After 3 months we gave up as the orthotics were just miserable to wear. As I told Ed, if he could successfully make me a pair of orthotics that I liked, I was more than happy to come to work for him, but I had to end up turning his offer down. This experience also really started me thinking about the Root Postulate and since then I have become more of a convert than before.
b. In fairness to Ed, while the numbers are few, I have met two people wearing his orthotics who are happy as clams. I examined both of these people and found that their MTJs had very small sagittal plane ROM but did have significant transverse plane ROM. This has caused me great reflection, and points to a need to know who those people are that the Glaser orthotic works for. Unfortunately (and this is true of almost everyone's clinical practice) it is almost impossible to get data on the success or failure of anyone's theory of practice. Root, Schuster, Glaser, Kirby, Spooner, Fuller and Phillips, as well as countless others have failed to publish data on the success of their particular clinical practice theories. I do try to make every effort (I know that you do too) to make sure that each person is happy, and yes I have had my failures. (I explain to my patients right up front that the making of orthotics is not an exact science yet and sometimes it takes me a while to find the right prescription combinations that work)
c. In fairness to the anti-Root-postulate casters, we do see successes, but we don't have any data on the difference in feet that are successful and those that are not. While living in Iowa, I got to know Paul Coffin, Dick Schuster's nephew, well; and we discussed the various casting methods often. There is no question that many of the Schuster disciples successfully treat patients with that technique. I will never criticize clinically success, no matter whose theory it is. In my ponderings, I note that none of the semi-weightbearing casters advocate using thermoplastics (except Ed Glaser who uses HDPE), so the shape of the orthotic can be changed much more by the patient standing on it. We have no idea how a Schuster orthotic changes its shape between NWB and WB.

2. That the Postulate fits very well into the twisted plate concept of the FF-RF function. As time goes along, I am finding myself more and more of a believer in twisted-plate theory. (Interesting that you have never commented on my ideas about application of twisted plate theory in Albert's book) I utilize this concept quite a bit in my clinical practice to solve orthotic problems. I have told you that my father used to carve away the muscle belly of the abductor digiti minimi in the orthotic cast before making the orthotic. I didn't really understand this for years, but now I believe my father was right. Why? Because the lateral side of the orthotic is more flexible than the medial side, and by carving away the lateral aspect, he was in essence adding a forefoot eversion onlay (which onlay I am the first to say was originated by John Weed and should bear his name. I believe that we should call it the Weed-onlay) Today, about 50% of my patients I add extra material under the lateral column of the orthotic to solve a variety of problems. I explain to my patients that I am trying to make the lateral arch of the orthotic the same stiffness as the medial arch. Now if you want to stop sparring with me and give me a call on the phone, I'd like to discuss with you some real research ideas on discovering how orthotics work. I have enlisted the interest of a materials engineer here at UCF, and we have some graduate students, we just need a small amount of money. We've already designed the tools. Right now I am doing my current self-funded research (which I hope you read a little bit of on the Desert Foot site) in order to get some initial publications that will give my research grant applications more strength (hope to have money to attend ASB next year to present more data on the current research). I'm having a difficult time in finding someone pre-Sarrafian that used the term twisted plate, so if you want to help me out it would be welcome.

3. As I have pointed out, with twisted plate theory, the question is, what constitutes the EROM of the MTJ? This question started when I was in school, and I found out that the full-time CCPM faculty were using a lot more force in finding the DAE EROM than Mert did. I'm looking for easy to use instrumentation to try to document this. Wille killed the Elftman concept of EROM, but we don't have and further data. Howard Hillstrom started a research project on this, but didn't finish. I have a picture of his testing rig, and would like to get one made for myself. (need $3000 for you philanthropists out there) As I have made it clear, what we really need for any one patient is a force vs. FF-RF relationship curve (i.e. eversion force force on the X axis and FF-RF relationship on the Y axis).
a. In an upcoming paper, I will show that there was no difference statistically between the distribution curves of the traditional FF-RF relationship in two different random samples, separated by 23 years, and using two very different measuring tools. I didn't even look at this until 1 year after the 2nd research was done. Interesting, that this 2nd research paper reinforced my Root Postulate ideas.

While I was a great pursuer of STJ axis theory in my earlier years, and while I still preach its importance and use it in my practice, I believe that the real future is in understanding the MTJ and the lesser tarsal joint functions. Twisted plate theory is an essential part of this (but not all of it). I enjoyed reading Nester's multisegment paper that Simon referenced, and it will become one of those that I will use many times in the future. Interesting that I didn't find much to contradict "he-whose-name-we-do-not-say", but I would have been accepting if it had. Yesterday I had a discussion with our new acting chief of radiology, expressing my opinion that we needed to invest in Curve-Beam technology so that we can start doing better evaluations of the foot and also use it for research work. I see numerous ways of this technology opening up a whole new world of biomechanical research.

While I respect your desire to bow out of the Root Postulate discussion, I believe that anyone interested in the future of midfoot function has to have as part of the foundation a full knowledge of this Postulate and the evidence that supports and the evidence that invalidates it. Right now if I was to pass from this life, I think I would like to have as the Phillips Postulate say, "The normal foot during the stance period of gait shows the midtarsal joint moving from it's fully inverted to its fully everted state. In static stance the MTJ is at its eversion EROM or at its inversion EROM." Imagine that, I haven't used "neutral position" once in the above discussion (until now).

With best wishes,
Daryl

 

We discussed the "lamina pedis" model here: http://www.podiatry-arena.com/podiatry-forum/showthread.php?t=82910 and also another thread which is linked within one of the posts in the above link.

Macconail and basmajian described this model prior to sarrafian and if memory serves their original artwork is included in one of the above threads.

 

Yet according to this paper:
http://www.sciencedirect.com/science/article/pii/S1877056813001254

The concept of the "twisted plate" was already known in 1917, they reference:
H. Strasser Lehrbuch der Muskel und Gelenksmechanik
4J. Springer, Berlin (1917), p. 71

 

Daryl:

It's more of a time constraint than anything that I don't want to spend time trying to see if Mert Root was right or not in another thread. I don't have time to discuss every topic here on Podiatry Arena with seeing 30 patients today, then driving into downtown Sacramento after work today to do my 1.5 hour monthly free screening clinic at the largest running shoe store here, and also working currently on three separate writing projects....my plate is very full.

From looking at your comments above and in other threads, I can see we are miles away in our opinions about how the midtarsal joint work. You and Jeff Root seem to be on the same page regarding midtarsal joint function, whereas Simon Spooner and Eric Fuller and I are very close to how we view how the midtarsal joint functions. I simply don't have time in the day to continue beating my head against the wall debating "Root facts". I'm much more interested in debating the current research from those scientists who are living and actually have done research on midtarsal joint function within the last four decades.

In other words, I don't view the midtarsal joint through the Root-lens and, rather, prefer to view the midtarsal joint through the lens of the latest research, my own clinical research and clinical observations. Good luck with your endeavor to see if Mert Root was the first to think that the maximally pronated position of the midtarsal joint (which it can't possibly possess) is the position of greatest foot stability (whatever "foot stability" means).

 

Technical question: How do you upload a video or Youtube video to the Podiatry Arena so that it appears as a clickable video and can be run directly within the Podiatry Arena like the one on mtj motion that Kevin posted?
Thank you in advance,
Jeff

 

[yo utube] [/yo utube]
jeff copy that remove the space between tge ][ and the 2nd youtube on the YouTube video you will notice v= and a group of random letter and figures they go between the ][

Make sense?

or quote this cut and paste and change the video code

 

Mike,
Not sure exactly what you mean.
Jeff

 

Jeff: It looks like this:

 

Sorry Jeff pressed post a bit to fast see my post again

 

Kevin, Simon, Daryl and all,

I grabbed one of my employees and shot three quick videos to try to better illustrate my point about pronation and motion at the midtarsal joint. In the video I explain the observable motion and forces when I demonstrate the techniques.

This first video demonstrates how to fully pronate the mtj:




This second video shows how to examine the "oblique" axis of the mtj. Yes I know that there is no "oblique axis" but it does show how to evaluate the rom of the mtj in relationship to the sagittal and transverse planes.




This third video demonstrates how to examine the frontal plane motion ("long axis") of the mtj:



I hope these videos will give you a better idea of what I was talking about earlier in this thread.

Mike, thanks for your technical help!

Jeff

 

Contrary to popular belief, I have the same time constraints as you have and have limited time to even read all the posts that are put up, let alone reply to very many. You made a recommendation that I start a thread, and I have done so, but then you back out of participating. I will maintain that every time you cast the patient for orthotics with the MTJ maximally pronated you are reverting to the Root Postulate, whether you want to admit it or not. When you tell me that you are doing a majority of your orthotics from foam-box impressions, then I'll believe that you have "moved beyond" the Root Postulate. You accuse me of looking at the MTJ through the Root lens, I maintain that you yourself do so, though I really don't know how you define what that lens really is. You may think that you are so enlightened than me in the current literature, but I don't see it in your blog posts. No, I don't read anything in the barefoot running literature because it is not applicable to my needs. I have read your chapter in Albert's book and found no disagreements and most of it I was already doing, so in that regard how do you consider that I am so Neanderthal in my thinking. My main clinical focus has to be the diabetic literature. The diabetic biomechanics literature is essential in my current daily work as I struggle to save limbs from amputation. Of particular interest to me currently is the literature on soft tissue biomechanics. I have never seen any discussion from you nor have I seen anything in the literature on how the force from any shoe insert gets from the skin to the bone structure and what happens to each layer of tissue. I have already expressed my concern, and Eric has acknowledged such, about doing calcaneal skives in diabetics -- i.e. we need more information on the soft tissue effects.

Maybe you could point me to the one recent literature article that you feel has totally buried the Root Postulate, I will be happy to review it here and if I agree with you will gladly admit it. I am not afraid to admit my misconceptions. I have already pointed out (as I did in Albert's book) that Nester's work has never negated the Root Postulate. I have also pointed out that I have questioned for the last 30 years the Hicks MTJ axes model being totally correct (it is not the Root model, it is the Hicks model). I have shown that mathematically Nester's functional single MTJ axis is still consistent with a multi-axis MTJ model -- all multiaxis joints have at any point in time only a single functional axis. I have called for improvements in the MTJ measuring process, both the NWB ROM quantitative and directional measurements and also for EROM measurements. I believe that we can argue about the EROM of the MTJ the same as we can argue about the EROM of the MTPJs, the knee joint, the hip joint, and most other joints that are dependent on ligamentous restraints for their EROM. If you say that goniometry has no place in trying to determine where the EROM is of the MTJ, then you have to throw away goniometry for determining the EROM of all joints of the body, because I can make the same arguments that the EROM is determined only by how much force you are putting on the ligaments that constrain the joint.

If I wasn't up on the literature, Kevin, you would not find me writing NSF grant applications and trying to do and present a little research myself as well as get others outside our profession helping me. I would not be attending ASB meetings. So to paint me as some type of nonprogressive non-thinking Root-idolizing robot who just isn't in the current stream of the cool thinkers is very unfair. You may have not used these words exactly, but it is exactly the meaning you impart. Since you don't have the time to reply here any more about the Root Postulate, I would ask that you go to the Desert Foot web site and read my poster presentation and make your comments. This is only an initial report, and we hope to present more as ASB this year (if I can get there).

With that said, got to get to work this morning. With best wishes,
Daryl

 

Relax, Daryl. You are going a little overboard here. I don't think you are "some type of nonprogressive non-thinking Root-idolizing robot". You have a great mind but we are worlds apart on some topics, including midtarsal joint function, it appears.

As far as your Root Postulate goes, as I said in my first post on that thread, I think it is dead in the water from the get go, as I already explained. Go ahead and post up your poster presentation from the Desert Foot website here and I would be happy to read it and comment on it, as will others hopefully.

This is your Postulate so let's see some objective evidence of a "pronation-supination only axis of the midtarsal joint" that would allow the midtarsal joint to ever be "maximally pronated" within its envelope of motion and that greater magnitudes of forefoot input force will not move this "pronation-supination only axis of the midtarsal joint" past the range of "maximum pronation" and into an "even more maximum pronation" range.

 

Nobody every criticized me for being nonpassionate. So thanks not responding with what I thought could be inflammatory passion.

Currently my postulate is just that - a postulate. It has only come about because of many years clinically plotting the ROM of the STJ and MTJ against stance measurements in a clinical situation. I have noted clinically that with the graphs I draw that I can make the argument as being possible. I gave an argument for such possibility in the Albert book. If you haven't actually tried to measure both ends of the ROM of the MTJ, then of course I don't expect that you'd jump at accepting what I'm saying. It is still not a testable hypothesis yet. It will become a testable hypothesis when we have the instrumentation to take reliable ROM measurements of the MTJ. I have already ordered the runScribe, that Simon was good enough to point me to, as I want to see if that can be utilized to do MTJ ROM measurements. If it can, then I'll start working on providing data to prove the postulate.

You may access my poster at:
https://podiatry.com/images/desertf...f Orthotics Made From Different Materials.pdf

Take care,
Daryl

 

I have found success with casting the foot while applying forces to the distal forefoot that will abduct and dorsiflex the forefoot on the rearfoot. My explanation for that success is that I am pre loading the lateral plantar ligaments when the foot is on the orthotic. I am not doing it because I want pronate the MTJ. If I do the same thing Root taught, but for a different reason have I abandoned the Root postulate. This is a semantic question.

This brings up the definition of postulate. One definition is: something taken as self-evident or assumed without proof as a basis for reasoning.

We should explore the reasons why the Root postulate might be true. I have the hardest time remembering what exactly you believe the Root postulate is. When I have a little more time, I'll go over to the other thread and ask that question.

I have the same concern about neutral position casts. Casts of the foot taken in neutral position will tend to have a higher medial arch than semi weight bearing or fully weight bearing casts. An orthotic with a higher arch will tend to put more pressure in the medial arch than one with a lower arch. I believe one of the mechanisms of how a neutral position cast works is that the high arch can become uncomfortable and in response the person will increase activation of their posterior tibial muscle. This mechanism would not happen in the insensate foot.

Daryl, you are correct we have been treating a difference of opinion on the MTJ as a modern versus anchient paradigm arguments. As Dennis Shavelson has shown us, new is not necessarily better. I think the argument should be is there an anatomical basis for the OMTJ/ LMTJ model of the MTJ. I can make the case for a hinge like model of the STJ, but I cannot for the MTJ. I don't think it is a matematical thing, I think it is an anatomical thing.

Eric

 

Daryl:

OK, Daryl. I have a little more time now before I see patients this afternoon, so I will try here to better explain my problems with your "Root Postulate".

From August 2001 to December 2001, I wrote a series of five Precision Intricast newsletters on the midtarsal joint (MTJ) which included five illustrations I made for these newsletters which were all subsequently published in my second book (Kirby KA: Foot and Lower Extremity Biomechanics II: Precision Intricast Newsletters, 1997-2002. Precision Intricast, Inc., Payson, AZ, 2002, pp. 67-78.)

At that time, now over 13 years ago, I reviewed all the available midtarsal joint research that I knew of and also, since I had been in personal communication with Chris Nester on his research about that time, had formulated some opinions on how the midtarsal joint actually functioned. Key in this observation was my prior reading of VanLangelaan's 30+ year old thesis on subtalar joint (STJ), MTJ and ankle joint function where he critiqued all the previous studies done on STJ and MTJ function (Van Langelaan EJ: A kinematical analysis of the tarsal joints: An x-ray photogrammetric study. Acta Orthop. Scand., 54:Suppl. 204, 135-229, 1983).

It became clear after reviewing VanLangelaan's study and Nester's more recent MTJ data, along with reviewing all the previous research from Root's books where the MTJ "axes" were not determined accurately, that the concept of a pronation-supination axis to the MTJ was no longer supportable or was, therefore, untenable. Currently, I accept the research findings of Nester and coworkers where they clearly show that the midtarsal joint will move in multiple directions along multiple joint axes at different times during gait which is likely due to how the external input forces act on the forefoot and rearfoot from ground reaction force (GRF) are resisted by the internal restraining forces of interosseous compression forces and ligament, tendon, and muscle tension forces acting across the MTJ during weightbearing activities.

In addition, I have been heavily influenced over the past three decades by Don Green's fluoroscopic video he did while at the Pennsylvania College of Podiatric Medicine (D.R. Green, T.E. Sgarlato and M. Wittenberg, Clinical biomechanical evaluation of the foot: a preliminary radiocinematographic study. J. Am. Podiatry Assoc. 65 (1975), pp. 732–755). This fluoroscopic video clearly shows the MTJ functions more as a spring, which deforms more under increasing load, than as a "locking mechanism", that somehow "locks" then moves no further during gait. This also makes sense considering the results from other studies which clearly show that that longitudinal arch of the foot is a spring-like mechanism that can both store potential energy and release kinetic energy that has the potential to significantly affect running performance (Ker RF, Bennett MB, Bibby SR, Kester RC, Alexander RMcN: The spring in the arch of the human foot. Nature, 325: 147-149, 1987). Because of these research findings I now believe that to say the MTJ "locks", is not only inaccurate but also contrary to available research.

Therefore, with all this in mind, if you wanted to change the wording of your "Postulate" from "The foot is most stable when the midtarsal joint is fully pronated" to a new postulate that says "The forefoot will become stable against the rearfoot at the MTJ upon dorsiflexion loading of the lateral column when the plantar ligaments of the lateral longitudinal arch develop enough passive tension force within them to resist further forefoot dorsiflexion motion on the rearfoot", then I have no problem with the postulate. Unfortunately, Mert Root was not the first to describe this mechanism since DJ Morton talked about this mechanism of plantar ligamentous restraint over three decades before Root arrived on the scene (Morton DJ: The Human Foot: Its Evolution, Physiology and Functional Disorders. Columbia University Press. Morningside Heights, New York, 1935).

Hope this explains my reasons for resisting debating you further on what are original Mert Root ideas or not in regards to MTJ function.

 

Kevin and Daryl,

One definition of stable is: Resistant to change of position or condition; not easily moved or disturbed (http://www.thefreedictionary.com/stable)

One definition of unstable is: Tending strongly to change; Not constant; fluctuating (http://www.thefreedictionary.com/unstable)

At times the midtarsal joint should be stable (not moving) and at other times it should be unstable (moving, changing, fluctuating). So I think we need to discuss what contributes to mtj stability when the joint should not be moving in order to resist motion and pathological forces; and what contributes to healthy instability (motion) when the joint should be moving in a manner that does not contribute to pathology.

For example, if after heel lift the forefoot should be plantarflexing and adducting relative to the rearfoot at the mtj (what has been called oblique mtj axis supination), then the mtj is unstable (moving) but we see that motion as healthy and desirable. And when active supination of the mtj during propulsion is occurring, we tend to describe this as a stable mtj or foot. If however the mtj allows pronation at this time, we might describe this and an unstable foot.

I think what Daryl and I have been suggesting is that the mtj, when fully (sufficiently?) pronated, has a level of pronation resistance that requires less of a demand on active tissue (muscles) and more on passive tissues (ligaments and bone). When the foot is cast with the mtj fully pronated, the orthotic shell that conforms to shape of the foot acts to resist further pronation. If we supinated the mtj during casting, the shape of the orthotic shell might provide even greater resistance to mtj pronation, but has typically proven to be less comfortable unless you use a more flexible shell material that enables more mtj pronation. So it seem that nature has determined that during relaxed stance, the mtj should function at or virtually at its most pronated position. Why? Probably because it would require muscle activity to maintain the mtj supinated during resting/relaxed stance and this would not be efficient and would cause muscle fatigue during relaxed stance.

Jeff

 

The best available data we have shows the TNJ and CCJ constantly changing positions during the stance phase of gait. Viz. they are never "stable" by your definitions. I'll ask again why should "stability" be desirable in a dynamic moving foot?

 

Actually, Kevin, we're really not as far apart as you may have said we are. Eric may have expressed it best when he said that we may be arguing more about semantics. You're talking about the sagittal plane, only of the lateral column of the forefoot and I'm thinking in terms of the entire forefoot on the frontal plane, but I'm thinking that the results may be very similar. I will consider your proposal for modifying my postulate. What is interesting so far is that in our current research project, we have been able to fracture two acrylic orthotics (hope to fracture more). I can give you the details of the torque needed to fracture, which I don't believe anyone has recorded before. Examining fracture patterns of orthotics can give us great ideas about forces that the foot is producing on the orthotic. Most of the fractures that we see are torsional fractures around the long axis of the orthotic. As I invited you before, give me a call to discuss some real research using some technology that the engineering department has designed on paper. The hypothesis on my upcoming paper is that the forefoot to rearfoot relationship is determined by the plantarflexion angles of the forefoot. The results of this paper indicate that yes, part of the forefoot to rearfoot relationship is determined by sagittal plane relationships, but there is still more than that.

Now Nester's recent segmental kinematic paper is very interesting in that it shows very little frontal plane motion occurring in the MTJ functionally. I'm still considering all that is in the paper, how it fits with current thoughts and what thoughts needs to change. I have to admit I haven't paid much attention to the Green paper, but will go back and review it more. It's too bad that they didn't graph their findings instead of verbally describing them. As I noted before, I am very interested in getting a force vs. frontal plane relationship of the FF to RF curve. I'm also pushing our VA to look at Curve-Beam technology with one purpose to be able to do more kinematic research on the foot.

Again, I appreciate you taking the time to express your thoughts that looks more at how close we could be instead of how far apart we may be.

Have a good day,
Daryl

 

I agree that in the moving the foot the MTJ is constantly moving. I think that in the static standing foot, the word stability is synonymous with no motion. In the moving foot I believe that we should look at the frontal plane leverage of transferring weight to the medial side of the foot. I believe the original intent in using the word 'stable' was to convey the idea that the foot was not having to work excessively to counter a tendency to fall laterally. Maybe a different word could have been used. That is my current interpretation of the original use of the word. Wish we could get Bill Orien to participate in these discussions to better find original intent.

I thank those who pour water on flames of rhetoric, in order to find common ground from where to move forward,

Daryl

 

Slightly different FEA plot for you this time Daryl, this time a stress plot. What the FEA shows is that the addition of the rearfoot post acts as a stress riser across the distal edge of the post, the other is a picture of an orthosis that fractured during use that a patient presented with (he'd carried on wearing them) I did not make them, but I'd guess they were polyethylene- see images attached. BTW the loading in this FEA was vertically downward force.

 

Rather rare to see polyethylene crack. I've never seen black polyethylene. Is it forefoot inversion crack or a forefoot eversion crack line, or is a straight dorsiflexion crack.

I'm well aware of the stress riser at the distal end of the heel post. Our current low-budget-low-tech project requires that all our orthotics have a heel post. We've got to start somewhere. I've seen some interesting things that happens in our project when we introduce heel post motion. While heel posting works, and I use it extensively, yet I don't believe it works for the reason that Mert and John said it does. So our initial project requires only heel posting with no motion. This is a variable we're trying to keep from becoming a confounding variable. We are seeing some trends right now in the torsional modulus when graphed against the polar moment of inertia with various materials. It's too soon to make any final declarations.

Take care,
Daryl

 

It was blue, not black. Who knows what the movement that caused the crack was- it was cracked straight across the distal edge of the rearfoot post. Never seen a polyethylene nor polyprop-cracked before either, which is why I photographed it. What does need to be considered is cyclical loading and unloading over millions of steps and the fatigue this induces in the material, not going to be the same magnitude to failure in a used device as it is in a shiny new one.

One other thought- operational temperature of the device.

 

Jeff:

I am very familiar with what you and Daryl are suggesting since this is the same thing I was taught by your father, John Weed and the rest of the biomechanics department of CCPM over three decades ago while I was a podiatry student and Biomechanics Fellow. All that in consideration, I believe it is best we move forward, using more standard biomechanics terminology and with our knowledge of foot anatomy and function, to come up with newer and better ways of describing the biomechanics of midtarsal joint motion. Therefore, the terms "pronation of the MTJ", "supination of the MTJ", "oblique MTJ axis", "longitudinal MTJ axis", "midtarsal joint locking", and "maximally pronated MTJ" are basically obsolete terms that should not be used any more.

 

Let me get this right, "stable" shouldn't mean "stable" and we should re-interpet the meaning of words to make them "fit" what we should have hoped the people who used those words might have been trying to say. OKKKKKKAY. Alternatively, we could just say that at no point during the stance phase of gait are the CCJ nor TNJ stable and admit that those that said that these joint were stable at this time were wrong.

 

Simon,

In the dynamic moving foot, some joints will be moving and some will be stable at any given moment in time. In order for a joint to reverse its direction of motion, it must first be stable (stop moving in one direction in order to begin moving in the opposite direction). Therefore joint stability in the dynamic foot is just as important as motion in the dynamic foot. Joints should function in a direction and of range of motion that is not pathological. PTTD that progresses to adult acquired flatfoot is an excellent example of how joint stability, when compromised over time can lead to pain and deformity of the foot.

When we cast the foot, all the joint are stable (not moving)! And when we cast the foot we should intentionally position the various joints of the foot in a position that is deemed consistent with the mechanical goals of the orthosis being prescribed.

An orthosis has several functions (def: orthosis /or·tho·sis/ (or-tho?sis) pl. ortho?ses [Gr.] an orthopedic appliance or apparatus used to support, align, prevent, or correct deformities or to improve function of movable parts of the body). An orthosis should be designed to resist pathological forces. Therefore the design, including but not limited to the shape (joint position during casting and cast modifications) and stiffness of the device, should meet the needs of the individual patient. That means enabling certain motion (forces) and reducing or resisting other motion (forces).

Some patients with severe adult acquired flatfoot demonstrate significant abduction of the forefoot on the rearfoot when you fully pronate the mtj. It may be desirable not to fully pronate the mtj during casting in some of these individuals order to reduce some of the angle of forefoot abduction that exists in the foot. The reason is that the adaptive changes that have occurred at the mtj exceed the normal range and direction of motion of the joint. Since we want to resist these excessive pronation forces with our orthosis, and since we do not want to encourage the deformity, we might reduce the angle of forefoot abduction during casting to help reduce the excessive and undesirable abduction (pronation) moments at the mtj.

An orthosis can be used to improve function of the foot by improving joint stability, which in essence often means that we are reducing instability of a joint or joints within the foot, not stopping all motion at those joints.

Jeff

 

I agree. However, take another look at Nesters bone pin data and tell me at what points in time are both the TNJ and CCJ simultaneously stable in three-dimensional space? I've already looked at this some time ago, so I'll give out a clue here: never. In fact, take a look and tell me when either of these joints on it's own is three-dimensionally "stable"?

I thought we'd be over that by now, "fully pronate" is undefinable in a clinical situation and lacks validity when applied to the midtarsal joint complex. As Kevin stated, the sooner we move away from such undefinable terminology, the better. However, one can model the MTJ complex however one wishes, and if you wish to model the MTJ this way, then so be it Jeff. Do I think the model you are using is valid? No. But it's your prerogative to use such a model. Do I think your model will move the science forward? No. But each to their own. Your own, just isn't mine. "It's not my cup of tea" as we say in England.

 

I have seen this type of fracture before. It can occur when the lab technician uses a grinder to abrade the plantar surface of the orthotic in order to attach (glue) the rearfoot post. Our technicians only grind the post area parallel to the long axis of the shell. Some technicians will make a grind on the shell near the anterior edge of the rearfoot post perpendicular to the long axis of the shell (i.e. parallel to the anterior edge of the post) in order to create a clean anterior line and the they then grind (abrade) the rest of the surface parallel to the long axis of the shell and have these die into the transverse grind. This can lead to breakage, especially if they use the edge of the grinding drum (wheel) and create a deeper fault that parallels the anterior edge of the rearfoot post. Breakage of this type is much more common in acrylics than in the poly materials but it can still happen. This may be the case here.

Jeff

 

Here's a simple challenge to Mike Weber, since he took it upon himself to attempt to mock me in post #249. Mike...take a look at the three videos posted by Jeff Root of his employee in post #259 and tell us about that foot. Then, make some predictions about that patient...possible prior symptoms, complaints, foot issues, etc. Let's see what you've got Mike. Darned good thing that Simon and Kevin have me on ignore because I'd ask the same of them.

This is where the rubber meets the road, IMO. This is where we take our didactic education expanded by our clinical acumen learned by treating patients and put it to good use. Nitpicking about variances in calcaneal bisections, MTJ axes of motion, STJ positions comparing RCSP vs. NCSP are basically meaningless unless it actually translates to better patient outcomes.

Here's your chance, Mike...give it a shot.

 

Agreed, but this was not the case here as I took the device apart and there was no evidence of this. It was just a fatigue fracture in an area which FEA analysis predicts as a point of high stress. I've talked to several older practitioners who used acrylic and they have all said that the area across the distal edge of the rearfoot post was the most common area for fracture in Rohdur devices. I should be interested to hear the views of others with experience of this material.

 

Simon,

If the stj is pronating or supinating then there will probably always be motion simultaneously at the mtj during closed kinetic chain function. So if the mtj is maximally abducted and dorsiflexed (pronated about an oblique axus) and the stj is moving, then the point of maximum abduction/dorsiflexion (pronation) at the mtj is constantly changing in response to stj position. This explains why there can be motion at the CCJ and TNJ even though the mtj remains fully pronated.

The two axis model of the stj enables us to visualize mtj motion relative to the cardinal body planes. The oblique axis allows us to look at the adduction/plantarflexion and abduction/dorsiflexion components of motion while the longitudinal axis enables us to look at the inversion/eversion components of motion. If you resolve this about a single axis of motion, the motion at the mtj can still be compared to the cardinal planes of the body without using the two axis model.

One problem with terminology using the two axis model is that adduction/plantarflexion and abduction/dorsiflexion are biplane motion and therefore it is technically incorrect to call this motion supination and pronation. I agree that we need a more contemporary model for the mtj but we also need for clinicians to be able to relate that motion to the cardinal planes of the body. Nester's work is excellent but we need to be able to have clinicians communicate and discuss motion, position and pathology in a practical and meaningful manner.

I'm concerned that some podiatrists are turned off by the impression that foot biomechanics is becoming less practical and to esoteric. Many of the institutional podiatrists in the U.S. are spending their time on foot and ankle surgery. Those in private practice have to deal with increasing regulation and more complex billing processes and as a result, have many demands on them that make it difficult for them to find or justify the time spent learning about functional models that they don't perceive to be clinically practical.

Jeff

 

This got me to thinking. The above definition of stable is different than what Jeff described earlier. Earlier stable was where the bones lined up with the forces that are applied. That definition of stable goes on to point out that when the bones are not aligned with the forces rotations will be created that will create stress in anatomical forces when that motion is resisted. I think this is where the rationale for stable is good comes from. I agree with Simon's point that we need to define stability and question whether the definition we come up with is something that is beneficial or not and whether it exists or not. I don't think the lining up of the bones applies to much more than the position of the calcaneus and leg in the frontal plane.

Jeff I'm still trying to wrap my head around your comments in your second paragraph. Are you saying that a pronated MTJ prevents further STJ pronation or that the orthotic made from a cast prevents further STJ pronation or just that the orthotic resists pronation?