Forefoot Varus Predicts Subtalar Hyperpronation

Yeah and that doesn't just require a leap of faith but a rocket into a different dimension!! The easy answer is to qualify Mike's comments "all things being equal" - but I'll reply to that in a couple of days when I'm able. Good thread again.:drinks

 

It doesn't take a leap of faith, nor a rocket into alternative dimensions; I'll leave all that to you. It will take an understanding of physiology and biomechanics. I'll look forward to your response though, Mark. Tell me what isn't equal. I used to apply Janda, and say that the muscle length/ tension relationships were altered by the foot orthoses changing functional positions, yet modern research seems to suggest that kinematics are often unchanged in the presence of foot orthoses. Maybe the muscles firing patterns are significanlty altered, Mark? What does the literature tell us here? So, tell me what it is that prevents the foot orthoses weakening the tissues in their ability to withstand pronatory forces in a response to a foot orthosis designed to reduce pronatory forces acting on the body? Tell me that and we may need to re-write the laws of tissue remodelling.

While I've got time, lets take a quick look at Mike's caveats: 1) "the foot was not maximally pronated"= this doesn't make any difference to my suggestion. Let's assume the foot is maximally pronated and that sinus tarsi compression is preventing further pronation. We add a foot orthosis which do not change the foot's position, yet decreases compression forces at the sinus tarsi. What will be the response of the body to this decreased force at the floor of the sinus tarsi? Well it might decrease the thickness and density of the trabecular in this area. We remove the orthoses- will the remodelled bone with it's decreased strength at the floor of the sinus tarsi due to reduction in density and trabecular re-organisation be better able to withststand the forces now acting upon it. I'd say no, but clearly you know something I don't about biomechanics and physiology, Mark.

Mike's caveat 2) "the Ground was stopping any pronation": the ground has now become the foot orthosis, which is now "stopping" the pronation, we know that this may be in exactly the same position as the foot was in without the orthoses, or even in a more pronated position. so what's changed here?

Anyway, come back when you've got time Mark, in fact drop your mate a line and see if he'll respond as well this time.

 

That was a great answer until you pressed the self-destruct button on the last line. Little wonder why these debates go nowhere sometimes - and that's the real pity. I'll come back to you when I have the time and if I'm minded.

 

If only I could be as holy as though, Mark :drinks

 

God forbid..

 

"trabecular reorganization"? "Sinus tarsi compression"? "decreasing sinus tarsi compression without changing foot position"?

In my avatar above, I'm wearing chest high waders which seems to be a benefit when reading the contributions from our ignoble curmudgeon, because it's definitely getting deep in here. Maybe I'll add some more face paint too.

 

http://youtu.be/UL0UaP2ePVg

Just looked at the above video by drhunt1, whoever he is.

It's not the animation that is so bad, it's the dialogue that goes along with it....it sounds like Root biomechanics from 1979. Why haven't some podiatrists progressed in their biomechanics knowledge over the past 35 years? Don't they read outside the podiatry literature??

 

Before we can expect payment for a biomechanical examination we would need to show that there is value derived from the examination. If we are going to take a cast and just balance it to vertical or check use lab discretion on an order form, then there is no need to perform a biomechanical evaluation. In a fee for service world practitioners will perform a range of motion study just to get paid and not necessarily answer a clinical question. Which brings us back to the question of what do you do with the information from the classical biomechanical evaluation.

Eric

 

Eric,

A biomechanical range of motion examination can help identify hallux limitus, hallux rigidus, ankle equinus, a tarsal coalition, peroneal spasm, stj limitation of motion, and mtj laxity to name a few. Do you not consider these clinically significant findings? I have in front of me my son's dental bill. I was charged $52 dollars for a "periodic oral exam" which takes our dentist five minutes to perform. The findings were negative. Given the wealth of information that can be gained from a good biomechanical examination, it is definitely something that a competent podiatrist should be able to charge for.


As far as how this information can be used, it can be used to determine if the patient might benefit from an orthosis or not. It can be used to determine if the patient's cast should be corrected with the heel inverted, everted or vertical, if the patient might benefit from a more rigid material, if they might benefit from a deeper heel cup, if they might need a plantar fascia accommodation, if they might benefit from a Morton's extension or a reverse Morton's extension, a heel lift, etc. Don't you use any rom or non-weightbearing information in your orthotic prescription decision making process? If you perform a stj axis location examination, which takes almost as long as our dentist takes to examine my son's mouth, don't you think you should be able to charge for this? Don't you consider it to provide important information that helps you make treatment decisions? Why should the podiatrists services be free unlike the dentist?

Jeff

 

Kevin-that was my very first rendition, from my original animator and the voice over was my his, not mine. FWIW, Valmassy never saw this original video/audio segment. Remember also, who was my target audience...MD's = the gatekeepers. Do you really think they care about STJ ROM, MTJ axes, varus vs. supinatus, tissue stress model and last, but certainly not least, trabecular reorganization? No...they just want to take care of that patient and move on to the next. The balancing act between a presentation that becomes too tedious for MD's, and, at the same time, interesting enough for Podiatrists, is a precarious one. Consider that sequence a "teaser" for the nitpickers crowd at Podiatry Arena.

 

Simon,

Your graphic says that the data was taken at 15% and then at 50% of the contact period of gait. For clarification, do you mean 15% and then at 50% of the stance phase of gait or the data taken during the contact phase (period) only as in the contact, midstance and propulsive phases? Just curious because it seems potentially misleading to use the term contact period if it is actually meant to imply stance phase of gait.

Thanks,
Jeff

 

Yeah, whatever. Do you know, I actually can't remember since I did that work 8 years ago. I'm not sure how it will mislead anyone though Jeff since it demonstrates what it was used to exemplify. That is, it demonstrates that the deformation of the foot orthosis is dependent upon the loading applied, which during gait is time dependent. For the record, if memory serves, I meant what I wrote- the period where the foot is in contact with the ground- perhaps we should look up the defnitions of "period" snd "contact", Jeff? But while you're in, I find the Root approach to podiatric biomechanics very misleading. Anyway, i was just quickly labelling a couple of diagrams for Daryl, as oppose to writing a couple of textbooks that would retard the development of my profession for twenty to thirty years, Jeff. Actually, that's not fair. It wasn't the textbooks that retarded the development, it was the blind acceptance by many of those that have followed and lack of scientific rigour applied, the lack of progression, the same old, same old being taught in the podiatry schools by lecturers who couldn't fight their way out of a brown paper bag when it comes to academic debate on the topic.... but you know more about the state of podiatric biomechanics in the US than I do, which has long since been viewed as the leading light in the field.

Jeff, I like you a lot as a person, but my honest opinion as an outsider looking in is that trying to hold on to the old order is destroying podiatric biomechanics in your country and as time ticks on, it's being viewed more and more as a joke by the other countries. All the time, it's being seen as less and less significant in your own country; it's dying because of the way it is being taught. The world has moved on, the skeptical student can see for themselves or read on the internet the problems in what they are being taught, this causes them to loose faith in their teachers... the rest as they say....

 

Simon,

I was just curious at what stage in the stance phase (weightbearing phase) of gait your graphics represented. I thought it was interesting, especially if one could measure deflection of the orthotic shell throughout the gait cycle. This is something (orthotic stiffness/deflection) that Daryl and I have had a lot of discussion about. Sorry if I somehow rubbed you the wrong way with my question. It wasn't my intention to upset you or criticize your work. I was just trying to interpret your terminology.

Jeff

 

Jeff, sorry for being prickly, I've a lot on my plate right now. Semantics aside, I did this ages ago, presented it (badly) at PFOLA in San Diego, it's interesting, but not without limitations. Someone with more funding than me can do something useful with it, I've no doubt. Yet I learnt a lot from this work. Lots about how foot orthoses work and don't work- took me back to first principles, which is what was missing. Daryl and I have been talking about this too. His physical testing is interesting, but sooner or later you've got to put the sensors in-situ, in-vivo, hopefully someone will do this. But, huge caveat, it won't help much on an individual patient basis at the moment unless practioners take on board what it implies and while we are still prescribing to "foot deformity", it has no role at all.

 

To continue Simon, your 50% slide looked more to me like a midstance representation of the orthotic during the gait cycle than it did something that might occur much earlier during the contact period of the stance phase of gait. In the event that Daryl and I talk about it, I wanted clarification of your terminology.

Jeff

 

Simon, no offense taken. I know tensions have been running a little high on the Arena lately so I can understand how you might have interpreted my question and comments as critical. Thanks for the additional information.

Jeff

 

Jeff, in basic terms the areas of the shell which demonstrate the highest load/ deformation characteristics are the areas where the highest reaction forces will be at any given instant during the contact period. This is determined by the shape of the shell; the thickness of the shell does not change the distribution pattern of reaction forces- only the relative magnitudes. So if redistribution and relative loading and centre of pressure position position etc are what are important then the shape is what is important not the material thickness/ choice. Since two identically shaped devices will give the same reaction force pattern regardless of whether one is 3mm or one 5mm polyporp, providing, we are loading the devices in their linear ranges and not bottoming out etc. If the absolute magnitudes are important, then that's a different matter.

Anyway, right now I'm looking at alternatives to podiatry- 26 years has been enough service, a paper round seems more appealing right now.

 

Simon,

But if the medial arch of the 3mm device deflects more under the same given load than does the 5mm device, then wouldn't that create a difference in shape of the shell and therefore a difference in distribution of force?

Jeff

 

"Jeff, I like you a lot as a person, but my honest opinion as an outsider looking in is that trying to hold on to the old order is destroying podiatric biomechanics in your country and as time ticks on, it's being viewed more and more as a joke by the other countries."

And we all can attest to the great contributions from the UK that has furthered our understanding, as the nitpicking, nattering nabobs of negativism take relatively straightforward concepts and make them so incredibly obtuse and unwieldy that no one wants to get involved or dares question the relevance. Jeff, instead of the academics trying to simplify biomechanics, (which would certainly make your job easier), and therefore more germane to our own practices, they have hijacked the sub-specialty and created a true elephant in the room. These academics I refer to are from various countries, not just the UK. (Please refer to post #9 on this thread for further explanation).

 

Simon, part of the problem is that podiatric education is dedicated to surgery leaving very little time to focus on biomechanics, especially the non-surgical application there of. Podiatry in the U.S. is going away from basic or routine foot care in addition to foot orthoses and related biomechanics. A few years ago the Pedorthic Footwear Association changed their name to the Pedorthic Footcare Association with no objection from any of the American podiatry associations. The pedorthists are now being taught foot orthotic theory and practice by podiatrists. I predict that the CPeds will greatly improve their educational requirements over the next few generations and will assume much of the role of basic foot care that was previously performed by podiatrists. Take a look at the Pedorthic Footcare's website (http://www.pedorthics.org/) and on it the following article about knee OA by Roy Lidtke, DPM who I assume you have met.
http://c.ymcdn.com/sites/www.pedort.../CP_Articles/PFA_Mag_Sept-Oct_2013_Motion.pdf

Also take a look the the associations page on terminology and tell me where they are headed: http://www.pedorthics.org/?page=Pedorthic_Terminolog

As further evidence, here is a comment on the yesterday's PM News:
"It is a sad state of affairs that we do not instill the importance of non-surgical care as well as surgery. Let's not give our profession away. It is the best profession around and no one does what we do better".
Ken Jacoby, DPM, Elgin, IL
http://www.podiatrym.com/pmnewsissues.cfm

Podiatry in the U.S. is in a much different environment than podiatry abroad and that is why it is headed in the direction it is. In spite of the effort of Kevin Kirby and others, you can lead a horse to water but you can not make him drink. It may be that the horse is not thirsty or he may not like the water you are offering him. In terms of foot orthotic therapy, we have a large market in the U.S. If someone has a better mouse trap (functional theory and clinical approach) then they should jump on the opportunity that apparently exists and make a go of it. If the options aren't practical and economically viable, then they will fail.

Jeff

 

Dr. Hunt1, prior to discovering Podiatry Arena, my knowledge base comprised mostly of Subtalar Joint Neutral Theory. I never felt I had a grasp on Biomechanics until I read a multitude of published articles and books recommended on Podiatry Arena.

The essence of Biomechanics taught here is based on the application of the laws of Newton to the viscoelastic structures of the corporeal body. When we use these laws, we can come to a better understanding and appreciation of the effects of the ground pushing on the foot statically as well as dynamically.

For me, and I believe for thousands more across the globe, Tissue Stress Theory together with Subtalar Joint Axis Location Rotational Equilibrium (SALRE) offers sound reasoning based on Newtonian physics. The theory explains why force (translational, rotational or both) is behind the motion of the joints and is based on many variables including external and internal forces, the perpendicular distance of the moment arm from the point of application of the force on the plantar surface of the foot to the subtalarjoint axis, orientation of the STJ axis relative to the plantar foot and the load-deformation (stiffness) response of the tissues. Static tests such as the Supination Resistance test, Jack's test, Maximum eversion height test and others provide valuable information regarding the orthotic prescription.

The biomechanical exam is also important as equinus, tibia varum, external/internal malleolar position, genu varum/valgum, internal/external femoral torsion, weak gluts, leg length discrepance et, can all influence the direction and magnitude of the GRF causing a rotational force and angular acceleration across the joint axis causing motion of the subtalar joint in the direction of either supination or pronation. We also have the input of the CNS which is why gait analysis is very important.

The terminology and the physics behind why this or that happens is important to me and has helped bring greater clarity to biomechanics and allows me to read other journals that use the SAME terminology. I also do not think Kevin, Simon, Eric, Craig and others make biomechanics more complex but rather more simple once you understand the underlying concepts as you can think it through why this or that tissue is being injured.

To be fair Dr. Hunt1, I think that you have a good understanding of clinical biomechanics and you are right in your treatment of flexible and rigid first metatarsus elevatus. I understand you are not applying a forefoot varus wedge to a flexible elevated first ray as you want to strive to reduce it to avoid functional hallux limitus and increased tensile stress within the plantar fascia.

I also really liked your first attempt at your animation video. I would learn best through a 4D animation video as would others and hope this can be expanded much further to include many biomechanical topics.

Lastly, I always respect the top posters here as they have contributed a wealth of knowledge to folks like me who do not do research or publish. Compared to them, my knowledge of Biomechanics is very small and I am here to learn. Kevin, Simon, Eric, Craig and others have selflessly given of themselves for the sole purpose of propeling Podiatric Biomechanics forward through research and teaching so patients may be served best.

In that vein, I would suggest that you respect others here and take the high road if you feel like you are insulted. Stay cool and calm and in time you may be embraced. You have been practicing a long time and I am sure you have had great success. In the end, the only person you have to prove anything to, is yourself. And so it is.

Steven

 

Steven-thanks. The point I'm trying to make is that there are those among us that are making this subject WAY too complicated. So complicated that it approaches unusable obscurity...minutiae. Instead of hair-splitting discussions of trabecular reorganization and whether rigid deformities actually exist, the academics should be trying to simplify their approach. Instead of denigrating those that are attempting to achieve that with animation techniques not before seen in Podiatry circles, they should applaud those that are. The real animation I produced has yet to be seen but by a few in our profession, and was met with nothing but positive feedback...a far cry from the garbage I read here. I treat others as they treat me, and while I have tried to be respectful, a line was crossed. Instead of concern about someone's name, mutual engagement of ideas is much more helpful to all...as long as it's not so damned obtuse that most readers throw up their hands and walk away. The "teaser" I gave to this audience is just the beginning...and a LOT more can, and should be done with it. The fact that it was part of a pilot study that, IMHO, resolves GP's in children and makes a link to RLS in adults makes it that much more intriguing. Much more to come...stay tuned.

 

Yes, the deformations will be higher in the 3mm shell but the relative deformations across the two shells stays the same. In other words, the point of the highest deformation of the shell will be in exactly the same place in both shells; the point of lowest deformation of the shell will be at the same point in both of the shells; the same is true for all points of loading and deformations across the shells provided they have the same initial shape, loading is applied in the same manner and linear deformation occurs. Viz the exact magnitudes of deformations will differ, yet their relative distributions remain the same across the structures of the two shells; across the foot-orthosis interface. So the distribution of reaction forces across the shell is determined mostly by shape and less by shell thickness in a single material, single thickness shell, whereas the magnitudes of the reaction forces are determined by the material thickness and durometer.

Here are two identical shells: one is made of low density polyethylene, the other from high density polyethylene. Loading is applied identically to both shells. Spot the difference in distribution patterns of the deformations, then look at the scale on the right, you should be able to tell me which model was which material. You see exactly the same in terms of deformation pattern with a 3mm versus 5mm shell analysis.

Want to know what happens when we add a rearfoot post and compare different posting angles?

 

Thanks for your reply, Eric

At least you show that you're thinking about some of my thoughts. I wish you and I could sit down with a couple of mechanical engineers to really discuss the idea of bisections. I think that you will agree on a basic concept that if we want to measure any type of motion, we have to have reference points that we can all agree on. (I love the discussion of Rupert Sheldrake about the new tautology of setting the speed of light as a constant that can't vary -- don't know if he's right or wrong, but it reminded me of the tautology of the STJ neutral position). If we're going to measure angular motion, we have to have lines of reference. The simplest is to have only two lines, especially if we're going to measure in only one plane.

Using the center of mass as one criteria would greatly advance us forward. I'm surprised that you question the need to know where the center of mass is. Any type of kinetic analysis requires that one know where the center of mass is located. You can talk all you want about moments around the STJ axis, but in doing the kinetic analysis to calculate the moments round the STJA you have to know what the moment of inertia is around the axis (which is computed by the sum of the I(CoM) plus the mass times the distance of the CoM from the axis squared.) David Winter's Primer on biomechanical analysis lays it out very simply, in easy to follow steps. You'll never get beyond a qualitative discussion of simple foot mechanics without knowing the center of mass of each of the structures. Erin Ward started a project to determine the center of mass and the moment of inertia around the CoM of each of the bones almost 20 years ago.

Your comment about the forefoot contributing to the moment around the STJ in WB is true only if there is some type of stabilizing force across the MTJ and lesser tarsal joints. If those joints are "free to roam", then force against the forefoot will only produce midfoot motions, and no STJ motions.

As to why should inversion and eversion moments be equal? Sir Arthur Keith was an excellent analyzer, and was a great proponent of the need for muscle strength to maintain the arch. He and (un-knighted) Dudley Morton had many heated words for each other, not un-similar to the words written in this forum. Arthur Keith wrote about the need for stay-wires to hold any structure upright, and likened it to the foot and the body balanced over it. His arguments were good, however if one has a series of structures, each aligned with their center of masses truly vertical to each other, you theoretically don't need any of the stay-wires to keep it vertical. And the more closely you can have that condition, the less the stay-wires that are there will be stressed. So I cannot imagine that anyone purporting to be a tissue-stress person wouldn't want perfect alignment of the center of mass of the os calcis under the center of mass of the talus, under the center of mass of the lower leg.

Use of the medial skive still needs to be better investigated. I have used it, but find a great many people find it mildly to moderately uncomfortable. No one has yet addressed whether there are any long term problems that can develop in the soft tissues of the calcaneal fat pad when subjected to higher pressures on one side. I certainly would be very cautious of using it in a diabetic (which constitutes a large proportion of my practice) I find that increasing the lever arm is much more comfortable and effective in increasing the moments around the SJTA on one side of the other.

Finally, your comments about hallux valgus and the windlass mechanism. They were indeed vague, so I really can't comment. Believe it or not, I am a great believer in the importance of the windlass mechanism. When there is increased tension on the medial slip of the plantar fascia, the first does dorsiflex, due to the hallux being pulled down. From your statements I'm not really sure if we agree or don't agree. If you're proposing that it's only the windlass, then I disagree, but if you're saying it's part of the process, then I'll agree.

Happy New Year,
Daryl

 

Steven:

I have seen this same response when lecturing at a large podiatric surgical meeting in San Diego a few years back. I was lecturing on subtalar joint and first metatarsophalangeal joint biomechanics and, of course, used the term "moments" to describe the rotational forces acting across both of these joints. At the question and answer panel discussion after my lecture, one of the other speakers (very well known podiatric surgeon that lectures extensively on podiatric surgery around the USA) asked me why I thought it was so important to use such an unusual term as "moments" to describe such simple concepts that could be explained much easier using more simple terms.

I can't remember a time in the last three decades of teaching that I was at more of a loss for words. I was dumbfounded. Here was an otherwise very intelligent podiatrist complaining I wasn't making things simple enough for him. In other words, I was simplifying the mechanical analysis of joint kinetics down to the basic terminology used within the international biomechanics community to try to educate a couple hundred podiatrists and then being criticized for doing so.

This is the same thing that Drhunt1 is saying: He doesn't understand basic biomechanics and engineering terminology and doesn't think other podiatrists need to know this material in order to more deeply comprehend the kinetics and kinematics of foot and lower extremity biomechanics and complains when we use terms he thinks are too difficult for him to understand because he would have to learn something new.

Rather, his approach is to barge on to this international podiatric academic website, not give us his real name, criticize those who have a far greater knowledge than he does in foot and lower extremity biomechanics when they speak above his own level of knowledge and, then, expect us to be thankful that he made some videos that he can't show us and expects us to be impressed with a paper he hasn't yet published.

Simon was right. Drhunt1 is putting on a very good display of the type of arrogant and ignorant behavior which will be the downfall of podiatric biomechanics within the USA podiatric medical community within the next few decades. Everyone following along, please watch the response of Drhunt1 and you will see the future of why podiatric biomechanics will continue to go downhill within the coming years here in the USA.

 

Simon,

I suppose it depends on where one is in the gait cycle. However, I suspect when you add a rearfoot post there will be increased pressure in the heel area and that the area of deformation in the medial arch might occur farther anteriorly and to a lesser extent. If you invert the rearfoot post alone and don't add an angular grind for motion, and if you don't add and extrinsic forefoot post to support the anterior edge to the same degree of inversion as the rearfoot post, I suspect it will create torque in the shell material especially since polyethylene is a relatively flexible material as compared to polypropylene. What did you find?

Jeff

 

Kevin-are you now "putting words in my mouth"? First, I have already stated that I am not a "biomechanics guru, nor have I ever professed to being one". Second, when have I ever mentioned your discussion of 'moments' while stating that the academics are making biomechanics too difficult? Never. (And fwiw, I didn't just "barge in here", I've been lurking for awhile).

If you really want to point out to others arrogant behavior, just have them read Simon's responses to me and your increasingly intolerant and disrespectful attitude to the points I'm raising. I have no problem discussing 'moments' or tissue stress models as long as the author also describes what it means to us everyday Podiatrists in casting techniques, orthotic Rx's, orthotic additions, etc...you know...the things that REALLY matter. I have not, nor will not, dismiss your entire body of work, some of it peer reviewed, some not. It is important for the profession to have nitpickers, hair-splitters and pedantic critics. But there are many, besides myself, that view dogmatism as prohibitive to positive patient outcomes as overall lack of biomechanical acumen. It works both ways. For instance, after viewing my initial animation, how did you respond? Precisely. Instead of constructive criticism or acknowledging the potential for such media, you only slammed the narration and took another swing at Dr. Root. You did that again above. How does that further our profession...here or abroad? Spend your own money, hire your own animator and produce your own voice over videos that show how your approach is worthy of our time and consideration.

Let's assume that you are correct in that I'm an ignorant Podiatric cretin that has no place walking, much less talking, with the Gods of Podiatric Biomechanics. Then how does it make you feel that I have potentially resolved the mystery of GP's in children and made the connection to RLS in adults? Is it a case of "even a blind squirrel finds an occasional nut", or does it have something to do with my approach?

Perhaps a truce is in order here between you and I. Lab Guy wants me to take the upper road and that's fine with me. Your call.

 

That the change between 4 and 8 degree rearfoot post doesn't make a whole lot of difference to the deformation distribution patterns and only a very small amount to the magnitudes. Here's a couple of polyprop copolymer models. It's the addtion of a post to the shell and specifically the shape of the post: internal oblique v external oblique v standard type post which makes a much bigger difference than the posting angle per se.

 

I only asked you if your first name is Michael. I'm still not sure if it is or not. "You don't have a name, so I'll give you the name of Michael": Michael- A House. Call me blue https://www.youtube.com/watch?v=4gu-N93sBV4

 

Fine. Provide me your name and we can have a discussion like professionals. My time is too valuable to have lengthy academic discussions with individuals who don't have the common professional courtesy to tell me their real name.

 

Do you have any other examples of what you think is way too complicated beyond the trabeculations of the calcaneus? Don't you think it is appropriate to think deeply on an academic web site. The trabeculation example was higher level thinking on some biomechanics facts that are useful in clinical practice. Everyday practitioners need to understand the cause of sinus tarsi pain. That pain occurs at the end of range of motion of the STJ in the direction of pronation when the lateral process of the talus slides all the way down the posterior facet of the talo calcaneal joint and hits the floor of the sinus tarsi. It is quite simple to extend that thought process to stress on the calcaneus to change in trabeculation patterns of the calcaneus.

drhunt1 your earlier comment about how we should think more like architects and not like engineers was troubling. I recently had an architect make plans for the remodeling of my house. I also had pay for an engineer to create the specifications for building the foundation and the additional structure so that it would not fall down. It was money well spent.

drhunt1 do you understand the difference between kinematics and kinetics? A video is kinematics. It is nice that you can show the motions of the bones of the foot with a video. Have you ever seen Don Green's flouroscopy video of steps of a couple of different feet. I first saw it in 1987. It was a video of the motions of the bones of the foot. We also don't have to worry about artist's misconceptions for accuracy in that video. But getting beyond kinematics, kinetics explains the motions that occur. Things don't break because they move. Things break because of the forces applied to them. If we see arthritis of the first MPJ we can model the forces on the MPJ to give us the clinical solutions to reducing pain in that joint. We can explain why things like dancer pads should work. So, understanding the physics helps us explain why treatments work. Just looking at motion only makes us think we know what's going on.

Eric

 

Eric-thanks. No, I never saw Dr. Green's fluoroscopy videos...great idea but unfortunately imparts a LOT of radiation onto the patient/subject, especially with continuous exposure periods which gait analysis requires. "First, do no harm" comes to mind. Animation doesn't have that problem.

You wrote: "The trabeculation example was higher level thinking on some biomechanics facts that are useful in clinical practice." What are those facts? Let's cut through the detritus and get to the real material value of that discussion. While we all know trabecular patterns are indicative of forces delivered to that bone, I don't know ANYONE that shoots plain film radiographs for inspection of the trabecular patterns and/or changes seen over time. Heck, Podiatry has yet to publish a book showing serial X-Rays on any one individual patient(s) to account for the growth patterns we see in our patients. That would be really useful information...agreed?

When discussing biomechanics, it seems to me that a more rudimentary level of understanding needs to be agreed upon, or at least arrived at by a majority of those that study it. This is not the case. We're still arguing about the existence of fixed, (structural) deformities vs. soft tissue adaptations!

Your anecdotal example of an engineer vs. architect is interesting, but misses the point I've been trying to make all along. We need to SIMPLIFY the teachings to our cohorts and Podiatric students, and discussing the forces delivered to and through the foot as an engineer would, doesn't make the information any more palatable. However, an architect isn't as concerned with vector analyses as he is with foundational support. If you believe that viewing foot function through the eyes of an engineer helps you out in private practice...fine. But when Podiatrists are seeing 30-40 patients/day or more, we need to make their job of biomechanical evaluation streamlined. We are no longer reimbursed for biomechanical evals here in the US, so we need to be able to determine the patients' needs and fill out the orthotic Rx quickly and efficiently...and accurately.

Jeff Root will probably agree with the fact that orthotic construction/manufacturing techniques aren't as accurate and "fine-tuned" as the biomechanical discussions on this blog suggest. STJ axes are useful information in an instructive application, but is it more helpful to the practitioner than determination of full STJ ROM when ordering the orthotics? MTJ axes discussions are also helpful and useful but is the forefoot to rear foot measurements more important than determining the forefoot to ground measurements? If we don't evaluate the latter, is that why our static measurements typically underestimate foot position to GRF in gait analyses? It's perfectly acceptable to me to discuss "moment of inertia" issues when discussing foot function, but we need to bring that discussion back to the Podiatric practitioner that is taking the cast/impressions and filling out the orthotic prescription. At this stage, I'm less concerned about rotational forces acting around the 1st MPJ than I am about GRF operating at the level of the STJ, for example. Who's right, and who's wrong? Perhaps both schools of thought. In the end...it doesn't matter, because it's the patients that will ultimately improve...or not. We can assist those practitioners for better patient outcomes by instructing them to be able to better assess the patients' needs, not by making biomechanics more complicated, but by simplifying it. Hope this helps...and Happy New Year!

 

A good place to start is the van Langaalan paper. When he measured the movements of the bones, he looked at both the relative motion between the bones and the motion between the bones and "the room." All you need to define a reference for a bone is three non co-linear points. So, a bisection of a bone is not really a good reference as you need a line and a point not on that line to create a three dimensional reference. We have to remember that when we measure motion of the foot in one plane it is a simplification of three dimensional motion. So again, a bisection is just some random line we use to represent the position of the bone. A line we choose to represent the bone in one plane will probably not have significance in another plane. So, there is no need to be concerned whether that line splits the bone in half (bisection) in a particular plane.

The moment of inertia is one of the variables in a equation for motion of an object. I'm not saying that you never need to no the location of the center of mass. What I am asking is whether the relative contribution of the moment of inertia of the calcaneus is large enough to be relevant in relation to the other variables in the equation. If the contribution of the moment of inertia is a hundredth of the contribution of moments from other sources it is ok to ignore the contribution from the moment of inertia.

So, my statement would be true the vast majority of the time as ground reaction force on the forefoot and body weight applied to the top of the talus will constrain the motion of the forefoot relative to the rearfoot. Here is where we run into problems with how we model the midtarsal joint. If we model the midtarsal joint like a universal joint with two independent axes of motion your statement above makes a little more sense. However, if we model the midtarsal joint as two planar joints that are side by side whose motions are constrained by ligaments between all four bones of the joint then forces applied to the forefoot will create moments about the STJ most of the time. Which of those two midtarsal joint models is closer to reality.

I believe this part of our discussion was about how the bisection should be in a place where there no moments about the STJ. So, I don't see how you can eliminate moments from the forefoot because the forefoot will be weight bearing a lot of the time.

Daryl, it's not about what I want, It is about what is. When the foot is weight bearing, there will be moments from the forefoot adding to the net moment about the STJ. I don't see how you can isolate the calcaneus so that there are no inversion or eversion moments.

I've told this story about the medial heel skive before. Someone told me about it and before I red the paper I ran down to the lab to make the modification on my own personal casts. I pressed the devices. Initially I liked how they felt, but after a little while longer it did hurt where the approximately 4 mm long skive was. After reading the paper, I realized that the skive should be over a centimeter. I have not had any complaints of heel discomfort when I make the skives long enough. However, I would agree that one should be very careful in the insensate population.

Daryl, I'm not quite sure what you mean by increasing the lever arm.

Always good talking with you Daryl,

Have a happy New Year.
Eric

 

Eric,

The calcaneal bisection technique developed by Merton Root was not a random line. Root described simultaneously palpating the medial and lateral margins of the posterior surface of the calcaneus and constructing the bisection at the mid-point between the tips of the examiners fingers. If you look at the posterior surface of the calcaneus, it is often (but not always) parabolic in shape. So the bisection, by definition divides the posterior surface of the superior 2/3 of the posterior calcaneus into equal halves. Here are some pictures I took for an article I wrote years ago for Podiatry Management Magazine. Interpractitioner variability occurs or is increased by inconsistent bisection technique between practitioners. Heel bisection is one aspect of clinical biomechanics that has become unnecessarily complicated by many practitioners, researches and biomechanics "experts".

Jeff

 

Thanks, Jeff. Even if the line is slightly off, it makes for a good reference point for the practitioner to compare NCSP to RCSP. It saves time.

 

I'm still not quite sure why you have your feet so planted that you're not willing to give an inch to any argument that would give reason for doing things that you're not doing. Yes, just like Van-Langaalan, anyone can set up a system of 3 markers on any bone and measure relative motion of two solid objects against each other. But that is relative motion. While you can compute the moments around the joints this way, is there any podiatrist, or even any other clinician, that is going to implement this into a clinical practice. Wouldn't it be great if there were skin markers that everyone could agree on, that would make it easy for clinicians to take some measurements to determine if the patient has used up their reserve of pronation when standing? How do you feel about concept of a person having a reserve of pronation? How does that fit into your tissue stress model? The big question I have is this: What goniometric measurements do you take in a clinical practice? Which ones do you wish you could take? I am the first one to admit all the current weaknesses of current goniometric techniques, but I also want to raise the cry that the problems are solvable.

As you know, I have advocated taking many measurements in clinical practice that Root never talked about. Does that make me a Rootian or a non-Rootian? If you read my 1985 and 1992 papers, you will see that I identified both a posterior calcaneal bisection line and a plantar calcaneal bisection line, and I used both of these to take ROM measurements. Now there is a small technical error in my description of measuring the transverse plane angular motions of the subtalar joint, but they are not significant in the final calculations. I also take linear translation measurements when the STJ moves. When it comes to measuring FF to RF, I take not only the traditional Root measurements, but also the FF to RF relationship when the MTJ is fully pronated and the STJ fully pronated, when the MTJ is fully inverted and the STJ is neutral, and when the MTJ is fully inverted and the STJ is fully pronated. What I really want to measure is not just the frontal plane mobility of the MTJ (and other lesser tarsal joints), but the mobility in all three body planes, and I want to know what that mobility is for all STJ positions. And then, beyond that, I want to know the EROM in both directions vs. a force curve. If we can get to that clinical point, then we'll be able to really discuss tissue stress.

Again, your argument that the moment of inertia isn't important around its CoM is no argument at all, because you have no calculations to demonstrate that it is or isn't. I would ask you to get some support from a member of the ASB or ISB who does these calculations every day to agree with you. Put some numbers up, and then we'll see whether your argument is valid.

One of the things that Root started (but didn't finish) was to get people to start breaking down the foot into various segments, identifying pathologies at each segment, and then identifying compensation at the joints distal and proximal. While most of the individual components had been previously discussed in the literature, Root seemed to have a unique way of putting the parts together that I don't find in any authors prior to him. You can argue that even using plaster strips to take molds had already been introduced, but his idea of the casting foot position was unique. He seemed to be able to create a real bridge between literature about joint movements and the end clinical practice. I bring this up, not to defend Root (so I don't want to hear whether you love or hate the guy) but with the argument that I like the idea of knowing the individual component properties, then summing up all the components to get a final picture. That's why I really would be interested in knowing the CoM and moment of inertia of each segment of the foot. Only in the past few years are we starting to see some papers being published breaking the foot down into a multisegment model. As I referred to previously, new CT technology opens up some possibilities of new advances in understanding the kinematics between the heel and the toes.

Yes! I agree that in the weightbearing foot, that forefoot forces play a very important part of creating the total WB moments around the STJA. In fact the moments are significant in all three planes; I find it interesting that we never see anyone discuss the creation of moments around the STJA by the frictional forces on the forefoot. I've done some calculations that show that these may be highly significant moments. But we have to ask ourselves how is it that the forefoot can create these moments? What exactly is happening in the midfoot that allows this to happen. I'm not satisfied in waving my hands saying that it's some type of magic. You asked whether the MTJ was two universal joints or two planar joints? I would say neither. It is one ball-in-socket joint and one saddle joint. One side of the joint shows two bones, heavily constrained by ligaments, so that there is very little motion between the two, and the other side has two bones that do freely move against each other. You do stir some of my thought processes on how we can develop a better model of the MTJ than either of the two proposals you give.

BTW, I am not making any medial heel skives myself. I have had it made by several different orthotic labs. Maybe we can have a training session at PFOLA on the techniques of making medial skives as there may be quite a few different ideas of doing this. Maybe the inventor of the skive is having today the same consternation that Root had when he saw all the various labs putting out different versions of the Root orthotic. As I've contemplated it, I hope that the skive doesn't end up being the "Optigrab" of the 21st century. In diabetic feet, it's not just the insensitivity factor, it's also the diseased collagen (i.e. shift of the length-tension curve) and also the PVD factor. It's quite easy to flare a heel post medially 1/4" inside a shoe and get some very different results, especially in the subjective analysis by the patient. I don't have any objective data to present, as of yet. I also flare the heel area of the shoe medially sometimes. I find shoe flares to be very effective in treating MDSTJA. They can be much more helpful than Richie braces as the Richie brace does not take advantage of the fact that vertical forces are much higher than horizontal forces, so you don't need lever arms as long. Of course we have people that won't wear such flares, so we have to work with what they will wear. I'm not treating runners, that is a completely different population about which I refuse to make any comments.

May your 2015 be prosperous and wonderful!
Daryl

 

The problem is that even experienced podiatrists teaching biomechanical examination techniques to students on a daily basis bisect the calcaneus differently from one another.

When I was in my Biomechanics Fellowship at CCPM in 1984-1985, the podiatry students I taught and I all knew this so that we would, sometimes, have one clinician come in and bisect a calcaneus on a patient and then, when that one clinician left, we would have another clinician come into the room and tell them we needed his bisection to see how far off we were. Sometimes these two (very well-known) professors would be as much as 5 degrees off from each other with their "calcaneal bisections".

I once asked Dr. Root from the audience at one of his seminars how he could be so sure of whether he could be so accurate in his "calcaneal bisections" and make such minute adjustments to orthoses on the bases of these "calcaneal bisections" when I had personally seen my own biomechanics professors from CCPM be off from each other by as much as 5 degrees in their own version of a "calcaneal bisection".

You know what Dr. Root said, in a very loud voice with his face getting redder by the second? It was something like: "Even a monkey could be trained to accurately bisect a calcaneus. I don't know what those professors at CCPM are now teaching these students and they can't teach students any better at doing such a simple thing as make a calcaneal bisection. Ever since I left CCPM they don't seem to be able to teach these simple principles right so I don't know what they are doing!" This may not have been Dr. Root's exact words, but this was definitely his meaning....all the while as a 28 year old Biomechanics Fellow, I was sinking lower and lower in my seat while he was raising his voice in anger toward me during his tirade for asking such a ignorant and offensive question.

Now, we must ask ourselves this question: if the professors teaching biomechanics, who were students of and trained under Dr. Root and who taught hundreds if not thousands of podiatry students and podiatrists over the years this technique, can't agree on what a "calcaneal bisection" should be, then what how accurate and "easy to perform" can this calcaneal bisection procedure be to perform? Furthermore, how close do you think one average podiatrist will be to another average podiatrist in making a "calcaneal bisection"?

Eric Fuller did a survey at one of our meetings of "experienced podiatrists who regularly preformed calcaneal bisections" where he had about 20 podiatrists (Eric may need to come on here to tell the story more accurately) performing calcaneal bisections on the same foot and found they were +/- 5 degrees apart from each other. In other words, one podiatrist may have thought this patient had a 5 degree forefoot varus, another podiatrist may have thought this patient had a 5 degree forefoot valgus, and another podiatrist may have thought this patient had a perpendicular forefoot to rearfoot, all measuring the same foot!

No wonder so many podiatrists simply "gave up" on biomechanics after school. It didn't make sense to them then while in podiatry school and it didn't make sense to them in practice, especially considering the lack of agreement on basic measurement techniques they experienced among their own professors. I saw we needed a change early on and I have been writing about that change for the past 30 years.

Hopefully, we will continue to progress together toward a better way to treat our patients in the coming years.

Everyone have a great New Year!:drinks

 

All of which of course is interesting, but well known to anyone who has ever dabbled in podiatric biomechanics. The real questions become: why do we need to bisect the skin overlying the calcaneus at all? Michael suggested that it allows us to measure NCSP and RCSP, yeah and so what? The presumption being that either of these positions have any bearing on anything... Do they? I doubt it.

FEA analysis suggests that the reaction forces exerted at the foot-orthoses interface may be pretty much the same whether the orthosis is posted at the rearfoot to 4 degrees or 8 degrees. If we follow Meat-Pie philosophy, everyone gets a four degree rearfoot post anyway- right? Given that the error is larger than the post, and that the environmental surface angulation variation is likely to be larger than either, that the orthoses will embed themselves into the sockliner of the shoes and find their own level within the shoe, that the heel of the shoe will wear down..... who cares about a few degrees either way?

I don't buy the "we need a reference point, so neutral fits the bill", there are many, many reference points that can be taken if we view the foot through a lens outside of that of Root's. Can anyone explain why they think we need a reference which isn't the ground? Assuming a reference is required at all.

Back to "structural" versus some other deformity: so, in a "structural" deformity the foot somehow escapes reality and Newtonian mechanics? I think not. If I apply an increased force beneath the head of the 1st metatarsal and the hallux it will apply a dorsiflexion moment to the medial column, whether the stiffness of the medial column is high or low, end of story. The difference is, when stiffness is low the deformation per unit load will be greater than when the stiffness is high. This does not preclude deformation, which may well be of the plastic variety if the load is great enough. This is very, very, very basic mechanics.

Simple and easilly understood does not necessarilly = valid. That's the key, we can make podiatric biomechanics easilly understood, but it has to be accurate and valid, not just easy. I can make a video of an animation of a foot and talk a load of old bollox while it runs, but if the bollox I'm talking is, well, frankly bollox then I'm detracting from our understanding rather than adding to it. If the valid solution is hard for some to understand, then so be it. If it's too hard for some, then podiatric biomechanics isn't for you. Yet given that biomechanics should be applied to every aspect of podiatry, if you don't get the application of Newtonian principles, you should probably think of a different career (like wearing face paint and waders, then proudly posting a picture of yourself dressed like that on the internet- each to their own).

Oh, Happy New Year.

 

Kevin, is it possible that he was not upset with you but rather frustrated and angered by his profession? I think so. He often and publically criticized his profession for being lazy for not wanting to think and learn, for wanting a cookbook approach to biomechanics rather than using reasoning to make treatment decisions, for being too surgically oriented, etc. Back at those Root Lab seminars in the 1980's he predicted that podiatry would lose biomechanics and non-surgical treatment of the foot to physical therapists and others who at the time in his opinion, were showing a greater interest in biomechanics than his profession.

The Root method of calcaneal bisection is a very simple technique. Why other apparently intelligent practitioners found it difficult or resorted to other variations of the technique is beyond me. However, I witnessed my father teach many practitioners in the treatment training room at Root Lab and he always taught it the exact same way I demonstrated in the pictures above. You palpate the crest of the posterior superior aspect of the calcaneus with the tips of both index fingers. You then make one or two short line segments and re-palpate the same location on the calcaneus to check for accuracy, making any adjustment if the segments are not equidistant from your fingertips. You then palpate slightly inferior to your last line segment(s) and repeat the process until the upper 1/2 to 2/3 of the parabolic portion of the calcaneus is bisected. You then draw an extension of the bisection down the remainder of the heel.

Why is it that I see so much questioning on the Podiatry Arena of the accuracy of heel bisection but not the same level of scrutiny for the STJ axis location technique? Has anyone done any studies on STJ axis location accuracy and repeatability like we have seen for heel bisection (comparing a group of experienced and a group inexperienced examiners)? Why does one technique get a free pass while the other does not? These are both very similar techniques that require proper instruction and practice in order to master the technique. And both are clinically useful.

You can't have standardization unless you describe and define the technique. Root did this for heel bisection. I have witnessed many practitioners doing heel bisection. Some adhere to the Root technique and some do not. Have you ever seen anybody do a poor job with STJ axis location technique? I have. So do we blame their instructors, the practitioner and or the technique itself?

Jeff

 

It doesn't. Both the validity, within tester and between tester variation of the palpation technique have been tested by our friends in Belgium and published in JAPMA.

Here's the problem as I see it, Jeff: the theories regarding tissue stress are theoretically coherent and biologically plausable with some aspects yet lacking in scientific scrutiny; whereas much of subtalar neutral theory are not theoretically coherent, have highly questionable biologic plausibility and have been demonstrated to be scientificaly invalid. That's not to say that the former theory will be proved to be any more valid, rather that the latter theory has been demonstrated time and again to be invalid... You talk as if bisecting the heel has some bearing on anything- it doesn't outside of your fathers theory. Once we disassociate ourselves from this theory we see there is no rationalisation for bisecting the heel using your father's method. I honestly doubt that any other medical theory has received so much attention in the literature and has been shown to be lacking so often and yet still manages to prevail in your country. Viz. it's time to let the old theory go. I know you will never be able to do this, nor will many others who supported your father, but such thought is holding back the developments in our field and positively destroying the topic in your country.