Forefoot Varus Predicts Subtalar Hyperpronation

Simon,

I have seen polypropylene orthoses with bonded poly posts fracture in the same manner.

Jeff

 

Eric,

If the mtj is fully pronated, then it can only pronate farther if the stj pronates because stj pronation will then increase the range of pronation at the mtj. So what I'm saying is that if the entire shape of the orthotic shell conforms most closely to the foot in one position, and that position occurs when the stj is in the neutral position and when the mtj is fully pronated, then the shell will create some degree of resistance to change in the position of the foot.

Jeff

 

In this case it was a glued on EVA post.

 

Eric,

Stable can be looked at in different ways. A skyscraper appears stable because you can't see it move. But in fact, it sways in response to the horizontal forces of wind. Skyscrapers are designed to sway because without this motion, they would be more brittle and could fail more easily than when they are designed to sway. So motion (instability) of a skyscraper actually improves total structural integrity and as a result, make the structure inherently more stable in response to horizontal forces.

Jeff

 

Jeff, the original question was at what point during the stance phase of gait are CCJ or TNJ "stable:? Answer: they are never "stable", unless you start trying to change the accepted biomechanical defintions of "stable". I think we've established that. Now you are suggesting that these joints could still be maximally pronated because the STJ is moving. However, the MTJ cannot be "maximally pronated" at any point during the contact phase of gait when the bones of the joints are continuously changing their position in three-dimensional space and the axis of rotation is not oriented such to allow pronation / supination motion to occur. The data reported by Nester and colleagues here: Nester C.J., Findlow A., Bowker P.: Scientific Approach to the Axis of Rotation at the Midtarsal Joint. J Am Podiatr Med Assoc 91(2): 68-73, 2001, shows axial positions that the net MTJ axis adopts during the stance phase of gait: a) heel strike to forefoot loading; b) forefoot loading to heel off; c) heel off to toe offf. None of the axial positions reported by Nester here should allow pronation nor supination motion to occur at the midtarsal complex. I'll repeat that: none of the axial positions reported by Nester here should allow pronation nor supination motion to occur at the midtarsal complex. What is it about this point that you don't want to concede? Perhaps you have data you can point me to which shows that the midtarsal joint complex does move in a pronatory- supinatory manner during the stance phase of gait?

Given that the Blackwod study http://www.amputation.research.va.gov/limb_loss_prevention/Midtarsal_Joint_Locking.asp questions your contention regarding the relationship between subtalar joint position and the available range of motion at the TNJ and CCJ, I should suggest that the position you are adopting here is undefensible based upon the published data that we have to date.

 

No worries. I'm now reading you loud and clear, Matt.

 

If Rohadur was going to fail, it was almost always anterior to the rearfoot post, where your FEA analysis shows the highest stresses.

 

A foot orthosis, will create resistance to the foots position whenever and wherever the foot interfaces with the orthosis, regardless of what position the cast for the orthosis was taken in. There is nothing magical about your so called "stj neutral position and mtj fully pronated position"; they assist in providing a shape to a cast of a certain foot, that is all. End of Story.

 

Take a pair of "stj neutral position and mtj fully pronated" orthoses and wear the right orthosis in your left shoe and the left orthosis in you right shoe. There is nothing magical about this either, it just happens to be extremely uncomfortable. Shape matters and casting position influence orthotic shape.

 

Yeah, you were one of the "older podiatrists" I'd already asked about this :drinks

 

Eric, Jeff, Simon and Daryl:

Your recent discussion on the terms "stability" and "stable" is the whole reason of why I replied to Daryl on his "Root Postulate" thread, that I said:

We have been having this discussion as to what "stability" and "stable" mean now on the Podiatry Mailbase and Podiatry Arena for at least 15 years and we have not made any progress in coming to an agreement of how it can exactly be defined. "Stability"and "stable", unfortunately, are terms we should probably not use in biomechanics for now unless we precisely define what these terms mean because, for now, these terms are too ambiguous and ill-defined to allow them to be used to help explain the complex mechanics of the human neuromuscular system.

 

I didn't say shape didn't matter, I merely said that there is nothing magical about your "STJ neutral and MTJ pronated" shape- it's just one of an infinite number of shapes. Which, after all, we alter in the positive model anyway. And, every study that has ever been performed shows that weightbearing casts are more repeatable. Not saying they are repeatably more valid, just more repeatable. It's just a starting point, a shape- I could carve from a solid block and still get the same shape. But this notion that there is one, ideal position to cast the foot in, is patently none-science. Along with the idea that the foot is somehow locked and fixed on top of the orthosis- madness. Interesting that in central Europe very few cast in neutral, yet would claim their outcomes are on a level with anywhere else in the world.

But while you're in, anyone who's been in the game long enough will have had a patient come back for review wearing their orthoses under the wrong feet, left device under right foot and vice versa- some of them think this is great!

 

Stability is well defined and understood in both mathematics and engineering- no reason to start adopting different definitions here.

 

Yes, it does get pretty complicated when there are multiple definitions of stable. Perhaps Simon is correct in that we shouldn't make up new definitions for the term. One variation of the definition of stable was one of low tissue stress. Perhaps we should just teach tissue stress as it is much simpler and easier for a student to understand. It is also easier to apply to foot and ankle surgery.

Eric

 

What you are actually saying here Jeff is that: a) instability can be good, b) there is no cause for alarm when a structure is unstable. c) we shouldn't necessarilly try to make an unstable structure more stable. Agreed :drinks

Of course, at some stage we have to acknowledge the elephant in the room- there appears to be a presumption here that foot orthoses somehow infer "stability" across the midtarsal joint, when obviously there is no good quality evidence to suggest this is the case; then we have to battle with the inference that only foot orthoses made from the foot which has been cast in a certain way can achieve such stability; which is again, is an apparent presumption here.

 

Not necessarily. We should teach whatever the best available knowledge tells us, not that which is simplest and easiest to understand- I've seen the damage that teaching what appears to be "simple" can have in my country (sorry for my nationalistic posting, Daryl) when podiatric biomechanics teaching changed in the 1980's here. It's plain to see in the UK literature where we went from physics/ anatomical/ physiological based approach to a "biomagic" based approach and the retardation period that ensued due to this.

 

The problem is, now you've quoted it, I see it too. Kevin, this dude can predict pathology based only upon a video of a Root assessment of forefoot to rearfoot alignment, which is more than any prospective study has ever done... he must be a sub-genius.

 

Then take the challenge, Kevin. There's actually much to see in those videos even without the aid of WB X-Rays and examination sequence of the STJ ROM. Perhaps this is where we will delineate between those academics from the clinicians. This might indeed get to the "root" of the differences.

I have no doubt Mike Weber won't touch this.

 

I think we can agree that instability (motion) is essential to locomotion, and that instability can sometime be pathological in nature. Orthoses should be designed to enable and promote essential and healthy motion and when possible, resist pathological motion (pathological instability). The challenge comes in identifying pathological instability.

I also think that the terms stability and instability have a different connotation to engineers that they do to most podiatrists. Most podiatrists think of instability as a negative thing, as in lateral postural instability, ankle instability and midtarsal joint instability. Interesting that equinus is dorsiflexion stability and is often viewed as a negative thing! This is really a semantics issue.

Jeff

 

The problem here, Simon, is that to orthopedic surgeons and podiatrists or any other clinician, the term "stability" may mean a very different thing than that from an engineer. The terms "stability" and "stable" are used quite freely and frequently in clinical science while, as is the case in other clinical terminology, the same terms used by engineers may be quite more restrictive and more well-defined, but has different definitions depending on which branch of engineering the term "stability" is being used.

For example, on Wikipedia, under stability in engineering, there are ten different types of subgroups of definitions listed for "stability":

http://en.wikipedia.org/wiki/Stability

There are also 19 other definitions of "stability" listed in the fields of mathematics, natural sciences, exercise and sports medicine and social sciences. So, these terms can be defined, but which of these 29 definitions do we use every time we use the term "stability" to discuss the kinetics and kinematics of the human foot and lower extremity?

In other words, which one of these definitions of "stability" are we to use when we talk about "joint stability", "stability of the foot during walking", "stability of the midtarsal joint", "stability of bipedal stance", "stability of the subtalar joint", etc. Like in engineering, stability is used so frequently and so liberally, we would need to specifically define it and agree on the term together before we could use the term to move forward in an academic discussion. That is why I told Daryl I wasn't going to discuss his "Root Postulate" further until he provided me a definition of what he meant by "foot stability".

Here is what wikipedia lists for the definition of "joint stability" and "joint instability":

http://en.wikipedia.org/wiki/Joint_stability

I don't think I can agree totally with this definition and, therein, lies the problem. "Stability" is a vague term that is over-utilized that has multiple meanings depending on who is using it and depending on what that word is being used to describe.

 

Matt:

My midtarsal joint range of motion video is of one of my family members and I am not going to discuss any health information about this family member on this public website.

Here is what you said about the video, Matt:

Suffice it to say, this individual does not have a "collagen deficiency disorder", does not have a "calcaneal inclination angle greater than 35 degrees" and does not have a "forefoot varus deformity", as you said she had. She competed in high school, running and swimming sports, also competed in intercollegiate sports at a major California university, competed in triathlons, and currently runs and plays soccer pain-free with no foot pathologies.

Other than that, I will not be discussing any more information about this family member. I am simply grateful that she allowed me to use her foot as a model for my video since it does demonstrate, quite nicely, the wide envelope of motion that some very functional and asymptomatic feet have within their midtarsal joint range of motion. So much for the midtarsal joint having one "maximally pronated position".

 

"How do I come to these conclusions with just a brief sagittal plane view?"

Who knows because the video you posted was a frontal plane view, Kevin.

"Patterns...I continue to see patterns." It's called apophenia.

 

I think this is the issue, terms

many maybe on a similar page with thinking, when you read the posts a terms of Root used, you can´t help but think the thinking is the same as 1977 or earlier

edit see that discussion has occured

 

not going to predict anything from a video

don´t work that way

fix the damaged tissue Matt and do no harm.

making assumptions from a video or an assessment re position and motion without considering the diagosis 1st will lead to problems Matt

There is no normal and abnormal foot Matt, or Motions just abnormal forces

the pic was to suggest the pie throwing won´t help get you any respect or help you with orthotic presriptions

 

Be careful how you use the A word! Are you saying a rocker bottom foot is normal but the forces that create it aren't? Really?

Jeff

 

Kevin-you were the one that posted a video of a family member...I just commented on it. Conjecture? Most certainly....based on VERY limited information, I might add. First, I asked you, (Mike Weber) about the 3 videos that Jeff put up on one of his employees for discussion, not the video YOU posted. Second, don't use videos of family members to show whatever point you were trying to make, if you're not willing to discuss it further. Third, I'll take your word that she doesn't have a 35 degree calcaneal inclination angle, but that is fairly common in the female patients I see with a HYPERMOBILE foot. How do you know she doesn't have a collagen deficiency disorder...and what does competing in sports have ANYTHING to do with that? Remember Olga Korbut? Remember the iconic pic of her on the balance beam with her toes out in front of her? Let me refresh your memory...

https://s-media-cache-ak0.pinimg.com/236x/49/aa/75/49aa75f1c2dd4fcd111b614c3cc82585.jpg

Is that normal flexibility?

How about Nadia Comaneci...remember her?

https://pleasurephoto.files.wordpre...perfect-e2809c10e280b3montreal-1976.jpg?w=450

The truth is ALL female Olympic gymnasts have a form of EDS, (IMHO), otherwise they couldn't perform the necessary maneuvers that the judges like...in other words, they couldn't compete. Therefore, your statement that because she competed in college in sports is an indication that she doesn't have a collagen deficiency disorder doesn't fit the facts or the evidence.

I'll take your word that your family member can't pull her thumb back to the radius pain free, just like I'll take your word that she doesn't have a calcaneal inclination angle of or greater than 35 degrees. But she IS hypermobile.

Now...back on track...I wanted to discuss Jeff Root's employee's foot, and I'm sure Jeff will not mind, nor his employee...correct me if I'm wrong.

 

I asked him if I could video his foot for this purpose and he didn't mind. This was the first time I ever looked at his foot other than to notice on the lab floor that he had very low arches one day when he was wearing a shoe with a very soft (canvas) upper. I did not look at his stj rom or anything else or do anything other than what was depicted in the video. I also did not know any of his history until I asked him a few questions after I posted the video.

Jeff

 

Mike-is that why you think I'm here...to gain YOUR respect? I'd take the gratification of dozens of satisfied patients because I solved their problems over your respect any day/week/month of the year....because that's why we do what we do...to successfully treat patients. N'est pas?

OK...so you won't bite on commenting on the videos. Let me give you my take...and it's NOT to gain your respect that I do so, it is simply to make a point about patterns I see and certain predictabilities. Notice that when Jeff loads the lateral column with what he stated was ~50lbs of pressure, only the lateral column dorsiflexes. Mets 1-3 really don't move. Notice the varus orientation of the forefoot to what would be the plane of the supporting surface using your imagination. This is a structural forefoot varus deformity. GRF will force the foot into further pronation at whatever joint it can, (STJ), in order to bring the hallux into contact with the supporting surface, just like I stated in the second video I offered. I predicted that Adam had growing pains as a child based just on the video I saw shot in the sagittal plane showing his frontal plane motion/arrangement. I called Jeff on the phone and asked him if he would kindly ask his employee if that were the case. Adam couldn't remember. I then asked Jeff via text messaging to have Adam ask his mother, as my experience is with some of these patients, they may not be able to recall this experience, but mothers rarely forget. Sure enough, Adam's mother confirmed that Adam did indeed have GP as a child and that she used to rub his legs at night. All of this can be confirmed by Jeff.

Without knowing STJ ROM, I can't state how I would prescribe the orthotics, but gave Jeff some ideas on how I would approach it. Is my way THE only way? Nope. But it's a start...here and in our offices. And THAT'S why I'm here, Mike. If I never get asked to speak at any conferences, that's OK with me...that's not why I'm in practice. Padding my CV does not help my patients or yours. Distributing the information I have discovered certainly does. And fwiw...the article probably won't be published until April, sadly. I was hoping sooner.

 

True should have been better with Excessive force

:drinks hope your having a nice weekend Jeff

 

According to Bill Olson, polypro and polyeth at room temperature are above their glass temperature, which means they shouldn't fracture. The temperature had to drop below the glass temperature in order to have fracture. Anything special about this particular poly? Know what the outside temp was (i.e. oil platform in the north sea).

No question that the stress-strain curve shifts with time, and possibly the fatigue and fracture points. Right now I'm measuring the stress-strain only of never-before-worn orthotics, and it is only slightly nonlinear. However testing a couple of well-worn orthotics indicates that the curve becomes ever more non-linear.

Take care,
Daryl

 

Bill Olson was wrong (God rest his soul too), this fractured in the running shoe of a marathoner who had been running the streets of Plymouth in the relatively mild South West of England. As far as I can tell, there was nothing remarkable about the patient, foot orthoses design, nor material- the orthoses had simply broken in half.

 

All I can say is, "Wow". Bill Olson was no slouch, either. Can you get any more information about the particulars of this particular olefin from the orthotic mfg. co.? Do we know what its melting and glass temperatures are? When you evaluated the fracture line, was there a torsional component, or was it a straight bending failure?

Daryl

 

That photo was taken about 7 years ago so details are sketchy. I might still have the device hanging around in my lab somewhere, I'll see if I can find it. As I recall, it was a Langer made device. I really didn't evaluate the fracture line under an SEM, Daryl; it was cracked, broken, kaputt. I took a snap because I'd not seen a fractured poly before, other than that I didn't examine it too closely. When I took it out of the shoe (he was still wearing it), it was being held together by the top-cover.

 

Don't expect you to do a SEM on it, but you can usually tell by putting the pieces together, which direction the break took place. Similar to analyzing the direction a bone breaks by the configuration of the fracture line.

 

I've probably dispensed over 10,000 pairs (20,000 total) of polypropylene orthoses over the past 30 years of practice. I have seen a total of 2 of these orthoses fracture spontaneously in my 30 years of dispensing these orthoses that I know of. Polypropylene orthoses can fracture but I suspect the ones that do fracture were due to some defect within the supplied polypropylene from the manufacturer. I routinely have patients bringing their 15-20 year old polypropylene orthoses back to me and ask me if they are still "good"...amazingly, most of them look very good.

On the other hand, when I was making Rohadur orthoses, I estimate the fracture rate within one year was about 2-5%, or I saw a fractured Rohadur orthosis nearly every month of practice. The same goes for the TL materials (Bill Olson's brainchild) and the other graphite laminates...I expect them to all develop fractures within five years and am surprised when they haven't fractured during this time.

 

Agreed, in 25 years I've only ever seen one fractured poly, the one I photographed- seen plenty of carbon's split.

 

Haven't seen a poly fracture yet, but in medicine anything can happen.

FYI, so far we have been able to torsionally fracture two of the acrylic orthotics we've tested. The first had a cross sectional area of 285.6 mm^2 and a polar moment of inertia of 12.17 cm^4, and it fractured on its 2nd eversion torsional test at 70 in-lbs. The second had a x-sectional area of 273.2 mm^2 and a polar moment of inertia of 10.66 cm^4. It fractured on its 7th inversion torsional test at 65 in-lbs. I'm not aware of any other published tests on the torsion needed to fracture acrylic orthotics. Most of the spontaneous fractures I've seen are torsional, not bending.

I've seen many fiber-orthotics fatigue and micro-fracture. I now call fiber-impregnated materials, fickle friends, as you really can't predict the results as well as you can with homogenous materials. My impressions with DBX6 so far is that it tends to lose its shape fairly quickly. I'm a little bit surprised to find a significant difference in the torsional stiffness between polyethylene and polypropylene. Again, what really counts isn't fracturing but changes in the stress-strain curves for the material. I realize that I'm treating only a tiny number of people who run, but the two materials I utilize the most these days is acrylic and cork/leather laminates. This is an ongoing initial research project; should have more to report in the future.

Daryl

 

No abnormal feet, Mike? Only abnormal forces? Perhaps that's why you're struggling with simple concepts...you haven't taken my advice and attempted to simply biomechanics, or conversely, taken Kevin's advice to 'think like an engineer'. There IS only one force...it's called gravity. Engineers, when designing a bridge, for instance, first take into consideration this force. Then when designing a bridge, they take into consideration the forces of sheer, stress, strain, wind, water, etc. In foot biomechanics, we're only concerned about the force of gravity, ie., GRF. It is NOT abnormal...it is predictable and defined. It's the foot type that may be unable to accept or accommodate these forces that is abnormal. Patients with 'normal' feet, ie., ones that accept and accommodate GRF adequately, are rarely seen in our offices because of biomechanical insults. An example of an exception might be a child that has Sever's Disease. But your statement that there are no normal or abnormal feet is, IMO, WAY off the mark.

 

Matt, you have simplified too much. Gravity pulls the body toward the center of the Earth. Ground reaction force is the force that is needed keep the body from accelerating toward the center of the earth. So, when looking at an isolated foot, there is downward force applied by the tibia to the top of the talus and there is upward ground reaction force applied to the plantar surface of the foot. Those are the external forces that create internal forces. There is more than one force acting on the foot.

Eric

 

Don't forget the additional forces

If you are moving forward, there is the horizontal GFR breaking and accelerating you. Also the movement forward shows the CoM moving side to side sinusoidally, so you have to have medial and lateral shear forces. And of course the GRF varies inversely to the vertical acceleration And finally if you live in Cheyenne, Wyoming you have one heck of wind resistance, no matter if you're moving or standing still. The one force that never changes, though is gravity (unless you're in an airplane or elevator, though I notice that here in Florida I seem to weigh more than when I lived at 5200 ft elevation).

Best wishes,
Daryl