Does Gravity Cause Pronation?

Some more questions:
1. Is any measure consistent enough across patients to establish a 'normal' foot type?
2. Is Calcaneal Stance Position in isolation a valid measure for pathology?
3. Is there such a thing as 'neutral'?
4. Can we even measure the rearfoot to a reliable and relevant margin of error?

 

Steve:

Both Drs. Mert Root and John Weed were very clear that the clinician should not try to determine subtalar joint (STJ) neutral position by palpating for talo-navicular joint (TNJ) congruency, as is widely taught in many podiatric medical institutions. They both strongly felt that this technique of palpation for TNJ congruency would not lead to accurate results since transverse plane angular deformities, such as metatarsus adductus and metatarsus rectus, would affect the transverse plane positioning of the navicular to the talar head. I have been told that this technique of palpating for TNJ congruency for determining STJ neutral position was something that Sheldon Langer started teaching on the East Coast of the US and then continued to be taught as standard technique by Langer Labs in their education of podiatrists as to what their interpretation of ideas and techniques of Root and coworkers were. I know for a fact that this TNJ palpation technique of determining STJ neutral positon was being taught by Langer Labs in their neutral position casting technique lessons during my student days at CCPM from 1979-1983 since I had a poster of theirs that described this exact same technique for negative casting.

Root and Weed taught that you should try to palpate the talo-calcaneal joint, instead of the TNJ, for congruency to determine STJ neutral position. However, I never found anyone at CCPM or at the Root seminars who actually used this technique due to its technical difficulty.

I never saw the 2:1 ratio that Simon mentioned being used to detemine STJ neutral position by either Root or Weed in any of the numerous demonstrations I attended of theirs or in the week I spent at John Weed's office as a fourth year podiatr student. This 2:1 ratio technique was however written up in their first book and I believe they felt it was more of a guide for students and clinicians to help them understand the concept of STJ neutral position.

The STJ neutral determination technique that I saw both Drs. Root and Weed use the most, and the one that I still use in my own examination of feet, is where they loaded the plantar lateral forefoot (4th and 5th metatarsal heads) and "felt" the range of motion of the STJ by moving the STJ in pronation and supination until a "flat area" occurred within the STJ range of motion. This was always their preferred technique and didn't see them ever palpate the TNJ to determine STJ neutral position. They also mentioned using the curves inferior and superior to the lateral malleolus to make them more alike in shape to find neutral position.

Dr. Chris Smith, who was one of John Weed's classmates and was one of my (and Eric Fuller's) biomechanics professors at CCPM advocated looking for relaxed skin lines on the sinus tarsi area while the patient was in the supine position to aid in determining STJ neutral position. However, this technique can't be effectively used while the patient is in the prone position.

Neither Root, Weed, Smith, Ron Valmassy, Bill Sanner, Rich Blake or any of my other professors in biomechanics spent much time discussing talar head position relative to the plantar foot and the only discussion about STJ axis location was in discussing its sagittal plane inclination, not its medial or lateral deviation, during my podiatry student and Biomechanics Fellowship days. Eric Fuller should be able to also provide you with his recollections of this interesting period of biomechanics and technique development at CCPM since Eric was four years behind me at as a podiatry student and Biomechanics Fellow.

Hope this helps.

 

It depends on the usage of the normal foot.

[/QUOTE]
2. Is Calcaneal Stance Position in isolation a valid measure for pathology??[/QUOTE]

No. I would bet that there will be a correlation between the position of the STJ axis in static stance with posterior tibial tendon dysfunction and peroneal tendonitis.

[/QUOTE]
3. Is there such a thing as 'neutral'??[/QUOTE]

We can make up a definition, but that does not mean that the definition has any useful meaning.

[/QUOTE]
4. Can we even measure the rearfoot to a reliable and relevant margin of error?[/QUOTE]

Once, at CCPM we had everyone in the biomechanics department try and bisect the same calcaneus. There was a 5 degree range in the position of the bisection across the "experts". Heel bisection is clearly not an accurate way to measure the rearfoot.

Cheers,

Eric

 

Why is there a flat spot in the arc? If the STJ had a fixed axis there should be no "flat spot", so what is occurring to the spatial location of the STJ axis as the joint passes through this area during dynamic function?

 

This is my recolection as well. I don't really see what they think they were palpating on the lateral side of the joint.

John Weed did have the 2:1 ratio in his sylabus. Countless hours were spent calculating theoretical problems with calcaneal inversion/eversion to leg measurements. The important lesson from those calculations was assessment of maximally everted position relative to the leg and ground. Specifically, it is possible to run out of range of motion of eversion before the medial forefoot becomes fully loaded.

John Weed's lecture sylabus referred to this as the "dell" in the arc of motion of the STJ. Kevin, you and I have discussed what causes this feel before. One possibility of the cause of the "dell" is that there is a decrease in the range of motion of the MTJ at a certain point in the STJ range of motion. The reason that I think that the MTJ is part of the cause of this phenomenon is that you cannot feel the "dell" when moving the the STJ from the distal aspect of the calcaneus. Another explanation of the dell is that the force applied to the fifth met head is very close to the STJ axis when the STJ is in neutral position. So, if you move the foot in one direction, it will tend to keep going in that direction. If you move the foot in the other direction it will tend to keep going in that direction. Chris Smith described it exactly like this. This movement will put your point of application of force further from the axis and it will increase the lever arm with which will increase the moment you are applying to the joint, so it will keep moving in the direction that you have pushed it.

The reason that I'm talking about the reasons for this dell phenomenon is that these are not very good reasons for making neutral position a special posiition that is relevant for how the foot works.

I agree, that this was not addressed much. It was a real big aha experience when I heard James Ganley describe the two unit tarsus concept after I graduated from CCPM. (Two unit tarsus: the rest of the foot deforms around the talus. Well, that's the brief version) It's a short step from there to describing the importance using of the position talar head relative to the weight bearing surface of the foot to describing foot function. But, that was not taught at CCPM. I think I heard the two unit tarsus before I read Kevin's paper on the technique to find the location of the STJ axis. Ganley's two unit tarsus concept is an excellent precursor to Subtalar Joint Axis Location Rotational Equilibrium (SALRE) theory of foot function. The Ganley perspective was extended by Kevin, with the explicit addition of physics into the description of foot function.

Prior to Kevin's paper there was a lot of Bio, but not a lot of mechanics in biomechanics. When I was in podiatry school, students thought that biomechanics was orthotics. We kept wondering why there wasn't a journal of biomechanics. The few of us who actually found the Journal of Biomechanics wondered why they didn't talk about neutral position of the STJ. Little did we know we were missing out on a whole lot of helpful information. :wacko:

Cheers,

Eric Fuller

 

I must admit that I have never heard of the technique of finding the 'flat area' or 'dell' as Eric calls it. I will sometimes make note in my own exam when the STJ has no similar stable position in OKC but I have not tried measuring this position prone in the 'normal' foot.

I have a problem with relying on skin congruency to determine STJN. You would expect skin being a soft tissue to conform over time to a pathological position. In those patients relying on skin lines will give a false reading. There would also be issues regarding patients with a past history of sprains or any type of edema.

What we need is a reproducable position that we can use as a reference point. Calling it neutral is probably not accurate and may just be confusing. This reference point should then be valid for each patient in isolation rather than in comparison.

Kevin and Eric I find your recollections very interesting. Someone has to write a history of CCPM someday.

All of these recollections really make you understand how far we have come.

"We stand on the shoulders of giants." Bernard of Chartres

 

CP often talks of a position of the STJ that just feels different to any other position. That is probably the flat spot, or as CP says: its probably the bottom of the curve if the STJ has an arc of motion. In my experience, I would agree. It is also remarkable that how often when you have the STJ in that position that there is also talonavicular congruency.

 

While, in the midst of trying to make changes in the curriculum I read Thomas Kuhn's The nature of scientific revolutions. It was a fascinating book on the history of science and how paradigms shift. It was especially helpful when living the paradigm shift. CCPM itselft wasn't particulary interesting, but a paradigm shift certainly is.

regards,

Eric

 

I believe that "dell of the arc" or "flat spot" within the range of motion of the subtalar joint (STJ) that we were trained to feel for, and I still use clinically to this day, is best described as that position within the STJ range of motion, when the STJ is significantly loaded by compression forces, where medially and/or laterally directed forces on the forefoot will produce less tendency toward pronation and/or supination motions. In other words, I believe this "dell of the arc" or "flat spot" that I (and many others) call STJ neutral position, is actually a position of increased STJ rotational stiffness (when the STJ has significant compression forces acting on it that comes from loading the lateral forefoot with a dorsiflexion load that combines Achilles tendon tensile force and tibial-talar compression force). I believe, anatomically, that this situation where STJ neutral position is manually perceived by the examiner as having a "dell of the arc" or a "flat spot" arises when there is maximum congruency of the posterior articulating facets of the talus and calcaneus of the subtalar joint.

 

Simon:

We know that the STJ is not a fixed axis so the "flat spot" is possible. All I can think of intuitively is that this "flat spot" is somehow caused by increased congruity of the articular facets of the STJ. Will need to give it some more thought some day.

 

In order for there to be a flat spot in the arc of motion the axis must be translating at some stage. At the start and end of the flat region?

More here on STJ congruence:http://www.cmj.org/periodical/PaperList.asp?id=LW2008418576870605870

The found maximal congruence was in the foot position of 10° of abduction, 20° of dorsiflexion and 10° of eversion does this concur with where the "flat spot" usually is?

 

Hi all,

Can someone clarify one doubt I have?

The term "momentum" is not exactly the same as "torque". http://en.wikipedia.org/wiki/Torque


But in English language, and here in this great forum :drinks, do they have some relevant different meaning?

Best regards,

 

Momentum is equal to mass x velocity.

Torque = moment = Force x lever arm.

Momentum is different from moment. Perhaps that is the confusion. Is there a bug in the translation?

Regards.

Eric

 

efuller,

Thank you. I don't think there is a bug.
I just wanted to make sure. I've seen a few times some confusion in some texts, specially translated ones.

I prefer to look stupid once and not to be ignorant my whole life. :bang:

Regards,

Romeu

 

Romeu:

"Moment" is also known as "moment of force" and is the same as "torque" and is basically a rotational force, as Eric stated. However, the similar sounding term "momentum" refers to the mass x velocity relationship of an object and is quite a helpful concept when trying to understand how energy is transferred from one colliding body to another, such as in the law of "conservation of momentum". The colliding of billiard balls in the game of billiards is often used to describe the concepts of conservation of momentum.

Hope this helps. By the way, I never took an engineering class in my life, never took a biomechanics course until I reached podiatry school, and took one physics course in high school and one physics class in undergraduate college.

 

Thanks Kevin!

Now I am sure of it. I just doubted because I heard a few "reliable" persons (related with engineering) talking differently and did not agreed between them...

Regards,

Romeu