"Original Root Postulate" on the Midtarsal Joint

How will this alter the shape of the finished orthosis?

 

Jeff:

That is not correct. Please read my earlier posting. Loading of the Achilles tendon with the negative casting position creates an internal STJ supination moment that counterbalances the external STJ pronation moment from you pushing, with any magnitude of force, on the plantar 4th and 5th metatarsal heads. However, with more medially deviated STJ axes, stabilization of the tibia from rotating may be need during casting to prevent STJ pronation.

I don't know how else to better describe it.

 

Yep, that's children for you- they are "warp beasts"- R.I.P. Ian Banks. My theory is that they have infinite mass and are therefore able to warp the fabric of space and time. This is why people (especially females) gravitate toward them.

 

You apply the force toward the STJ axis. If the force is applied toward the axis there will be no moment at that axis. I think this also how people are able to "find" neutral position with their eyes closed. It is a position that when a dorsally directed force, applied at the 5th met head will be pointed toward the axis. (The force may be a little off of strictly dorsal.) I can't think of any other anatomical basis for there being a neutral position.

Eric

 

:good: Yep, that'll do it. But surely a force applied directly to the STJ axis in any rotational position of the subtalar joint will result in no rotation, so theoretically we could have the foot in max STJ supination and apply as much force as we wanted (without causing tissue damage) at the fifth metatarsal head and so long as the vector is directed at the STJ axis it will still not pronate the subtalar joint from this position. Why don't we do this when we cast the foot then? Sorry to sound like a stuck vinyl record, but what difference does it make to the shape of the cast? Why don't we just cast the foot weightbearing (when the forefoot will be loaded with similar to weightearing forces as that observed in static stance) in a "corrected position" as advocated by Rose (1958): see attachment? It'll be more repeatable, that's pretty much for sure- as every study that has looked at weightbearing versus non-weigthbearing casting has shown improved reliability with floor-referenced, weightbearing casting. Given the motion available at the midfoot joints, in this day and age and with modern orthotic production techniques and materials how important is it to capture the "neutral position forefoot to rearfoot alignment"? With the Rose technique one can manipulate the medial longitudinal arch height and still be sure that the lateral 4th and 5th rays are loaded with weightbearing, static stance forces. What's the relationship between hallux dorsiflexion and 4th and 5th ray loading when performing the Jack's test? (Where was Jack from, BTW?).

So, Rose offered a casting technique which is likely more repeatable than a non-weightbearing approach, more consistent loading on the foot- approx. half body weight and the ability to manipulate the degree of "correction" in the cast via the windlass effect described by Hicks (but then Root clearly was unaware of Hick's work, since as I recall, his work was not acknowledged in Root's books... J.H. Hicks, Birmingham; was that Birmingham, West Midlands UK, or Birmingham, Alabama USA? I'd always presumed it was Birmingham UK).

I guess that what we see depends upon the lens we are looking through, Daryl. I see a potentially useful, under exploited casting technique. What do you see? I should be interested to hear the views of those with a leaning toward sagittal plane facilitation theory as to how applying this casting system with varying degrees of hallux dorsiflexion might impact upon sagittal plane facilitation during gait... All yours Bruce Williams, Howard Dananberg et al.

 

I think that what theory should be esposed regarding the MTJ is that the two joints CC and TN have a combined envelope of motion. That is with the talus and calcaneus held immobile there is a volume of space that can be occupied by the navicular and cuboid and that volume will be constrained by the ligaments that cross the CC and TN joints. The volume of space that can be occupied will vary depending on the force applied in a particular direction and this will be dependent on the stiffness of the ligaments that limit motion in that direction. When the joint is moved through its envelope of motion there will be zones of markedly different values of stiffness. As the joint is moved in one extreme of direction toward the opposite extreme there will initially be a zone of very low stiffness. After a point there be a zone of increasing stiffness as the ligaments that resist motion, in that direction develop tension. (This two zones of stiffness concept is one reason I'm not happy with changing dorsiflexed first ray to first ray dorsiflexion stiffness. Where the ligaments become tight matters.)

The envelope of motion provides an explanation of why there can be an oblique axis a longitudenal axis, the axis found by Chris Nestor and any other axis that you want to look for. It is my experience clinically that the oblique axis happens to coincide with the direction of the largest range of motion.

The evelope of motion will be changed by a change in position of the STJ. Further research is needed in what I'm about to say. It is my opinion that the maximum amount of adduction of the forefoot on the rearfoot is not really affected by the position of the STJ. On the other hand the amount of abduction of the forefoot on the rearfoot is dramatically affected by the position of the STJ. As the STJ pronates the relative distance, in the transvere plane, between the talar head and the anterior aspect of the calcaneus increases. The anterior process of the calcaneus can act as a moveable "doorstop" for abduction of the forefoot on the rearfoot. The further lateral the door stop is moved, the further abduction of the forefoot is allowed. In some feet, with the STJ pronated, the cuboid can slide laterally to the door stop and there is a loss of some bony compression at the joint. An Evan's calcaneal osteotomy can move the doorstop anteriorly and restore some of the lost bony compression.

In terms of casting position for orthotics. A theory: When casted with the forefoot dorsiflexed on the rearfoot this will be a position where the plantar ligaments are tight and it will be in the zone of the range of motion where there is increased stiffness in the dorsiflexion direction. When standing on an ortohtic, with the lateral aspect of the orthotic having adequate height (maximum eversion height) the lateral aspect of the foot will be loaded. This will be important for reducing the load on the medial forefoot. (I've looked at many a positive cast and the one thing that seems most consistent across labs is that the countour of the lateral arch is the one thing that remains untouched. The medial arch will have more or less fill, but the lateral arch is what consistantly remains from the original positive cast.) Some feet will have very low stiffness (or a lot of dorsiflexion range of motion) in the lateral column. In these feet it is quite easy to get the cast to have a rocker at the base of the 5th met. (The forefoot is dorsiflexed on the rearfoot to the point where the styloid is inferior to the met head.) This is not aesthetically satisfying to me. I've had some orthotic failures with feet casted this way, but not enough that I'm sure that it's correct to cast with the forefoot parallel to the rearfoot in the sagittal view.

Comments, additions, subtractions?

Eric

 

Eric and Simon:

I contend that in most feet, that the force vector from the examiner's hand must be directed slightly lateral to the subtalar joint (STJ) axis, and not through the STJ axis, in order to produce no net moment (i.e. rotational equilibrium) about the STJ axis, when applying a dorsal loading force to the lateral column that also dorsiflexes the ankle.

The internal STJ supination moment, from Achilles tendon tension force, then counterbalances the external STJ pronation moment from the manual loading force on the lateral column during the negative casting procedure. If the force vector directed by the examiner's hand was located directly through the STJ axis, then a net STJ supination moment would occur during negative casting and the STJ would tend to supinate, instead of remaining in rotational equilibrium, due to this STJ supination moment from passive tension force within the Achilles tendon.

This really would be a great little paper.....I'll add it to the list.....

 

When most patients sit in a podiatry exam chair, they sit with both legs externally rotated at the hip and the foot in an abducted position relative to their body. When the leg is externally rotated and the foot is abducted as a result, as opposed to the foot being vertical, then lifting the foot vertically will cause a stj supination moment and an adduction (supination) moment at the mtj. This is a common problem I see occurring during casting. One of the keys to taking a good cast is to place the foot vertical (if the patient is supine) and then position the patient so that their tibia is not externally rotated. You have to accomplish this by re-positioning the patient’s hip. The patella will be close to but not necessarily in the frontal plane. So what I do is internally rotate the tibia in order to position the foot vertical and then rotate the tibia into a position where a dorsiflexion force applied to the lateral forefoot will produce little to no rotational moment at the stj. Once you cast the foot, you have to reposition the patient to cast the opposite foot. Those who don’t do this have a tendency to supinate the stj, mtj or both.

 

Great point Jeff. I cast most patients prone and have them (those who can) flex their opposite leg, abduct it and place their foot in the crook of the posterior knee of the leg being casted to avoid hip rotation.

 

I have included some illustrations that show the mechanics of negative casting the foot with a normal subtalar joint (STJ) axis and the foot with a medially deviated STJ axis.

In the foot with a normal STJ axis (top), the manual pushing force plantar to the 5th metatarsal head from the examiner will cause an external STJ pronation moment since the force from the examiner's hand is lateral to the STJ axis. However, the manual pushing force on the lateral forefoot by the examiner will also cause an external ankle joint dorsiflexion moment which will cause increased tension force on the Achilles tendon.

The pushing force by the examiner will be proportional to the Achilles tendon tension force so that the manual force on the forefoot will be approximately 1/2 the Achilles tendon force (depending on the ratio of ankle joint moment arms from the manual pushing force vector compared to the Achilles tendon force vector). Since any increase in the manual pushing force on the lateral forefoot will also cause a simultaneous increase in Achilles tendon tension force, and since the Achilles tendon tension force causes an internal STJ supination moment, then to maintain the STJ in a position of static equilibrium (i.e. rotational equilibrium), by definition, the STJ pronation moments must be exactly equal to the STJ supination moments.

Therefore, when casting the foot with a normal STJ axis location, the manual pushing force vector from the examiner's hand must be directed lateral to the STJ axis in order for static equilibrium of the STJ to occur in order to counterbalance the internal STJ supination moment being simultaneously generated by passive Achilles tendon tension force, which, in turn, is also due to the manual pushing force from the examiner's hand. Contrary to Jeff's assumption, this does not depend on the magnitude of pushing force from the examiner since both the manual pushing force from the examiner and Achilles tendon tension force restricting ankle joint dorsiflexion from the examiner's pushing force occur simultaneously and are always proportional to each other.

However, when casting the foot with a medially deviated STJ axis (bottom), since the examiner's pushing force now has a much greater STJ pronation moment arm, then a much greater external STJ pronation moment is generated by the examiner's manual pushing force on the lateral forefoot. Also as a result of the medially deviated STJ axis, the supination moment arm of the Achilles tendon will likely also be decreased which will, in turn, decrease the internal STJ supination moment from Achilles tendon tension force.

As a result of this greater external STJ pronation moment and smaller internal STJ supination moment, the STJ will tend to accelerate into pronation when the negative casting procedure is attempted in the foot with a significantly medially deviated STJ axis. One way to avoid this excessive pronation moment and pronation motion during negative casting a foot with a medially deviated STJ axis foot is to have the examiner use a more medially-directed pushing force on the lateral forefoot while negative casting so that the manual pushing force vector is moved closer toward the spatial location of the STJ axis.

Hope this helps explain things better.:drinks

 

While I always enjoy reading the whys of a technique working, I find it interesting that when I learned to cast for orthotics, I knew nothing about how to find the STJ axis. However the technique I was taught was to internally (or externally rotate) the entire leg until a force under the 4th and 5th metatarsal heads, that was perpendicular to the ground and provided a mild dorsiflexion moment around the ankle joint, also brought the STJ to its neutral position.

While I'm a great believer in STJ axis theory, the above technique still works.

Best wishes,
Daryl

 

As I've said for many years, I believe that what we find as the subtalar joint (STJ) neutral position is actually the point of maximal congruence of the posterior articulating facets of the STJ.

In addition, I believe that this posterior STJ facet congruency is "formed" (i.e. osseous adaptation) during our early years of weightbearing when the compression forces across the posterior facet are of the largest magnitude, during late midstance and early propulsion, when the Achilles tendon tension forces are at their greatest magnitudes.

Therefore, there is not only an anatomical basis for the STJ neutral position but also a functional reason for it's existence, in my opinion.

 

I know we've discussed this paper before but didn't these guys find maximal congruency at the posterior facet at a position of 10 degrees everted?

 

I asked:

Jeff replied:

Ignoring the fact that these changes in forefoot to rearfoot alignment with modification of STJ position perhaps do not occur at the MTJ and are more likely occurring at the cuneiform articulations and tarso-metatarsal articulations (see the Blackwood study), see the attached. They were trying to maintain the plane of the forefoot at the metatarsal heads perpendicular to the heel bisection and noted that differing amounts of force at the forefoot were required to achieve this with differing STJ positions. So, presumably if a clinician (or two) put the subtalar joint into the exact same position, but one applied 2 lb of force to the forefoot while the other applied 10 lb of force, the resultant casts should have very different forefoot to rearfoot alignments (assuming the vector direction of the applied force is similar)? Yet, these two clinicians would probably both claim to have excellent results with their foot orthoses? Interesting that the differing STJ positions didn't seem to make a lot of difference to the overall shape of the cast so long as the forefoot to rearfoot alignment was maintained, but the 2 degree STJ everted from neutral did throw up some spurious results- what would be the 95% confidence intervals for the average clinician trying to put the subtalar joint into "neutral"? +/- x degrees?

I look forward to your comments...

 

Simon, as you indicated, in the study you referenced (see excerpts above) they intentionally maintained a perpendicular ff to rf relationship in the casts that were taken in different stj positions. In reality, when practitioners cast for functional orthoses via the Root method or modified Root method of casting, they do not and should not maintain the ff to rf in a perpendicular relationship. They are instructed to pronate the mtj to its end rom using a controlled amount (ounces, according to Root) of force. So as you apply a constant mtj pronation force and then move the stj into an increasingly pronated position, the forefoot everts exponentially (Daryl Phillips proved this). So the forefoot to rearfoot angle can change dramatically and this can result in significant changes in the plantar contour of the foot. Conversely, as you supinate the stj with the mtj fully pronated, the opposite occurs. So when practitioners maximally pronate the mtj but select (intentionally or unintentionally) different stj casting positions, the plantar contour of the cast and the ff to rf angle is influenced significantly, especially in some feet. The reason that some feet are affected more than others, probably has more to do with the axis of the mtj (and the other joints anterior to the stj) than the stj itself. As you supinate and pronate the foot, there are also appreciable changes in arch height. I have always maintained that practitioners have more problems related to mtj positioning (and the anterior joints) than they do with stj positioning during casting.

 

Kevin,

In my experience, if you push firmly against the plantar, lateral aspect of the forefoot while the stj is in the neural position, the tibia will internally rotate indicating that there is pronation occurring at the stj. I don’t necessarily agree that equilibrium is easily achieved because the manually applied force is lateral to the stj axis and this seems to have a tendency to pronate the stj. I’m willing to bet that in order to counter this, you are applying a simultaneous adduction force to prevent stj pronation. If you apply a purely vertical force, I think the stj will pronate way from neutral in most people.

Since Root taught practitioners to place the palmar surface of their thumb in the sulcus and then evert the forefoot at the mtj to resistance, this is not simply a vertical force. When too much force is applied in this direction, the stj pronates. Perhaps we can spend some time looking at this at the Western Foot and Ankle Conference next week. Looking forward to hearing you speak!

 

Jeff:

We will try to get together if we have the time this next week at the Western. At least we can have a photo taken of the two of us together for Podiatry Arena to show how much more hair you have than I do.

I would tend to agree with you that I am automatically placing a slight adduction direction to my forefoot loading force during negative casting in most feet. And, honestly, I don't know exactly how much force I use to cast since I've never measured it, but I would guess I use between 5-10 lbs of force.

When negative casting I believe that I am automatically adjusting the angle of my pushing force according to spatial location of the STJ axis relative to both the forefoot and rearfoot to produce rotational equilibrium at the STJ at the STJ neutral position during casting so that regardless of the magnitude of manual force used, the STJ will not rotate from the neutral position. However, if the STJ is highly medially deviated, I will stabilize the tibia with my other hand to prevent STJ pronation and tibial internal rotation.

Hope this makes sense.

See you next week.:drinks

 

I would be more excited about their results if they had actually loaded the Achilles tendon to make it a more physiological loading situation across the talo-calcaneal joint. There is virtually no time during walking or during standing when the Achilles tendon is not loaded with tension forces.

 

Agreed http://www.asbweb.org/conferences/2011/pdf/76.pdf . It is interesting to note that when the muscles and tendons were kept intact and loaded in the Choisne et al. study, the force transmission to the posterior facet was pretty much the same as had been identified in the Wang study http://www.sciencedirect.com/science/article/pii/002192909400076G which had not applied tendon loading, but the contact area was higher with tendon loading.

Do you think that the contact pattern distribution reported by Chen would change completely with Achilles loading, or just that the contact areas would all increase relative to one another at each joint position?



See also:

http://www.sciencedirect.com/science/article/pii/S026800339786723X

 

Yes, it did seem an odd approach, and does seem to suggest that the Root method of casting is not being widely applied in Australasia, although the same is probably true in the UK and central Europe, where Root's technique of casting is certainly not widely employed. However, if we take this quote from the book- Root et al. Neutral position casting techniques (1971): “Neutral position casting duplicates the joint positions assumed by a normal foot on weightbearing." And then take the biophysical criteria for normalcy advocated by Root in which the plane of the metatarsal heads is perpendicular to the bisection of the heel with the subtalar joint in neutral etc. it is easy to see why this approach of aligning the plane of the forefoot such that it is perpendicular to the heel bisection might have been propagated in Australasia. Interesting. Has there been a similar study to the one above in which the forefoot was loaded using "Roots" method? What this study also infers though is that as the STJ position is modified, the forefoot to rearfoot stiffness is altered too.

As we established near the start of the thread, the MTJ doesn't lock; the deformation produced at a joint will be partly dependent upon the load applied and variation in forefoot to rearfoot stiffness is likely to exist between individuals. So, if we take two experienced clinicians and have them put the STJ into the exact same STJ neutral position (although in reality it would be unlikely that two clinicians would agree on the exact same neutral position- lets assume it for now), when practitioners used the Root method to "maximally pronate the MTJ", unless they provide exactly the same loading force, the two casts they produce for the same patient will have different forefoot to rearfoot alignments- right? Now, given that two practitioners can seldom agree upon the STJ neutral position, the shape of the cast produced should show even more variation between them. This contention being supported by the literature on cast reliability.

Given the individual variation in forefoot to rearfoot stiffness, if a practitioner applies the same loading force to all patients during casting, the percentage of the total available deformation he produces at the forefoot on the rearfoot with his hands will be different in each subject, so there is no continuity between patients by applying a standardised loading either, unless the forefoot to rearfoot stiffness is taken into consideration and loading modified to accommodate this.

Given that forefoot varus and valgus are fixed osseous deformities at the midtarsal joints (CCJ, TNJ) then assuming we had a way of validly measuring this, which we don't, then there should be a finite degree of deformity- agreed? Isn't the casting process supposedly "capturing" the degree of the deformities? If so how can this be achieved with any certainty given that a) we have no way of measuring it, b) the forefoot loading and deformation produced during the casting process is not specifically loading nor capturing the position of the MTJ?

With regard to Daryl's paper, I think it is an interesting study, but since he did not quantify the loading applied at each trial, it is difficult to be certain that the loading was consistent throughout. Indeed, if the forefoot to rearfoot stiffness changes with STJ position, then a non-constant loading force should be required as implied above- this suggests no end of difficulties when trying to perform this experiment. It would be good to see this experiment repeated with modern imaging techniques though or with bone pins inserted.

I know that in another thread Kevin was questioning the "exponential" fit of the data that Daryl reported, when only three data points were represented but since Daryl is now writing on here, I'm sure he will comment on this.

 

That's hard to know. Certain the contact areas would all increase, but they would probably redistribute also due to the transfer off GRF toward the forefoot that the Achilles tendon load produces. With just tibial loading, as in this experiment, the GRF will shift heavily toward the rearfoot which, I imagine, would change contact patterns at the talo-calcaneal joint quite significantly versus the late midstance phase of gait. This is another reason why I never liked Kogler's research on the plantar fascia...he never loaded the Achilles tendon in his cadavers.

http://jbjs.org/data/Journals/JBJS/787/JBJA0811014030.pdf

 

Very good, Dr. Spooner. You remembered.

Three data points in no way cause an "exponential" fit of data in a scientific experiment. No exponential relationship of the midtarsal joint was "proved" by Daryl's experiment. However, an exponential relationship is one of the many possibilities of mathematical relationships that could go be offered as a fit for just three data points.

 

Simon,

Root would measure the ff to rf relationship in the patient’s foot and then measure it in the resulting positive cast before the cast was modified for fabrication of the orthosis. This was a very good way to help check accuracy of the cast. Although this is just a frontal plane comparison, if the cast and foot do not measure within a reasonable tolerance, the practitioner can recast. My lab still has practitioners who ask us to measure ff to rf and report it back to them or who ask us to call if their measurement isn’t within a certain number of degrees of their cast. The practitioners who do this tend to have very consistent results because they have gone through the learning curve of measuring the foot and then casting the foot in a manner the makes the contours (according to ff to rf measurement) extremely close.

Loading the lateral column to resistance, whether or not the mtj is maximally pronated at that point, places the mtj in a position where any additional pronation would be met with increasing resistance due to increasing tensile forces in the ligaments. Therefore the shell of the functional orthotic helps stabilize the lateral column of the foot. According to Root, this would occur when the ff to rf was perpendicular in the “normal’ foot. But in the case of ff varus, you can’t pronate the mtj enough for the plane of the forefoot to become perpendicular to the rearfoot. So how can it be cast with a perpendicular ff to rf? It can’t. And in the case of ff valgus or any other everted ff to rf condition (i.e. pf 1st ray), the forefoot should be cast everted relative to the rearfoot so that the orthotic shell will help support the ff valgus.

It is interesting that many practitioner are now accentuating this effect by plantarflexing the 1st ray or the medial column while casting. In other words, they are increasing the mtj pronation moment as compared to how Root cast the foot. If they inverted or supinated the ff during casting, it would be opposite of the direction of force that Root advocated at the mtj during casting.

 

Jeff:

One of the problems with comparing the prone measurement of forefoot to rearfoot relationship and the supine negative casting technique as advocated by Root et al is that the mass of the medial forefoot will be more plantarflexed by gravitational acceleration in the supine position versus the prone position of the patient. Therefore, in general, a couple of degrees of more forefoot valgus (or a couple of degrees of less forefoot varus) will be present when supine negative casting a patient than when measuring their forefoot to rearfoot while prone.

As for me, and the podiatric surgical residents I teach on a weekly basis, I advocate either dorsiflexion, plantarflexion or no repositioning of the medial column of the foot during negative casting, depending on the patient and the clinical situation. Therefore, modifying and moving away from the strict negative casting position advocated by Root et al seems to have given me much better clinical results over the past quarter century of making foot orthoses for patients.

 

Kevin, I'm not suggesting that one shouldn't alter their technique from the standard Root method when they feel it is justified. Root took some pronated and some supinated casts. All I'm trying to do is explain the technique and explain why some people may have difficulty when attempting to replicate the technique or the results. There have no doubt been many important changes since the 1970's and early 80's.

 

Jeff:

I was just trying to clarify that, like you said, there are many modifications of negative casting technique as advocated by Root et al, some of which may lead to better treatment results.

As for me, I think the subtalar joint neutral position is a great place to cast most feet in since it has worked so well for me and my patients over the years. In addition, as Daryl commented earlier, loading the lateral column of the forefoot to produce a loaded equilibrium position of the lateral column (Root's "locking of the midtarsal joint) to enable the joints of the lateral column to become more congruent with each other (i.e. increase their uniformity of contact pressures) also I think is a great idea for negative casting.

However, leaving the medial column dangling in space while negative casting, with the talo-navicular, navicular-cuneiform and cuneiform metatarsal joints and medial band of the plantar fascia all unloaded really makes not sense if one is trying to capture the three dimensional shape of the loaded position of the midtarsal or midfoot joints or plantar fascia. This is where I find the most fault with the Root et al casting technique and is the primary reason why I modify the position of the medial column, either dorsiflexing with simultaneous dorsiflexion of the hallux to preload the plantar fascia or plantarflexing it, during my own negative casting procedure.

 

Kevin, Mert’s thinking was that the pronation force applied during casting would fully pronate the mtj and that the 1st ray would be in a neutral position. He did make an exception for ligamentous laxity and in that case he would dorsiflex and support the 1st ray in the neutral position during casting. He also recognized that some feet didn’t fully pronate about the “oblique” axis of the mtj, so he would hold the heel and abduct the forefoot to get to the end range of abduction. He described this as having excessive verticality of the oblique mtj axis. So in practice and when lecturing, he did things that weren’t indicated in the “Neutral Position” casting manual because they were more advanced techniques and he was just attempting to present the basics in the manual.

 

After a quick read of the paper, I'm not sure that we can conclude STJ position from the description of what they did. They loaded a cadaver foot when the foot was on an inclined plane. The study notes maximum congruency when the foot is on top of a 10 degree abducted. I didn't catch it on the first read through, but it appears that abducted would be on top of a 10 everted and a 10 degree dorsiflexed plane.

A foot can stand in it's maximally pronated position of its STJ with no plane at all. Then adding a wedge underneath that could certainly change the contact pressures, but may not change the position of the joint. However, we don't know if the STJ position changed during the study. That said, the paper does seem to be supportive of my contention that there is maximum congruency closer to maximum pronation.

When you look at motion of the posterior facet, with any supination, there will be part of the calcaneal sied of the posterior facet closest to the floor of the sinus tarsi that will not have contact with talus. This also happens at the posterior part of the talocalcaneal joint. With supination the posterior aspect of the talar surface of the joint will hang over the posterior margin of the calcaneal side of the joint. Kevin, I believe that your figure from your rotational equilibrium paper demonstrating interosseous compressive forces between the talus and calcaneous shows this effect.

So, Kevin, I don't see how the maximum congruency point is not maximally pronated.

Eric

 

Or remeasure. How would you know if it was the measurement or the cast that was incorrect?

I may disagree with what Daryl called the Root postulate. (I keep forgetting what exactly that was.) However, I like how Jeff has described it here. Dorsiflexing the lateral column to resistance and then casting the foot in the shape, and then making the orthotic have the same plantar lateral contour, will encourage "pre stressing" the lateral plantar ligaments so that the lateral column can increase its load bearing easily. Especially, if a forefoot valgus intrinsic post is added that will also increase this lateral load. (This is a good thing for symptoms resulting from medial column overlad, but bad for symptoms that are a result of lateral column overload.)

This loading of the lateral column may have the same effect as "pronating the LMTJ while casting," but I believe that it is a slightly different concept. If you look at the joint surfaces of the TN and CC joints and then start thinking about LMTJ motion things get interesting. So, with LMTJ pronation does cuboid move dorsally at the same time the navicular moves plantarly? If you look at where Manter (?) put the location of the STJ axis, it would have to. How can this occur when weight bearing? How is one of these two bones move plantarly in the presence of upward ground reaction force being applied distally?

Yes, as the calcaneus everts the plane of the metatarsal heads that are on the ground will invert relative to the heel bisection. However, as has alaready been mentioned, this motion may not, and probably is not, occuring at the MTJ.

So, I think Root et al. were on to something in loading the lateral forefoot while casting. I just don't like their explanation of why what they were doing works.

Eric

 

Eric:

From observation of cadaver feet and bone skeletons since I was a podiatry student , I have noted that the posterior facet seems to be more congruent when the foot is close to "neutral position", rather than when the foot is maximally pronated. The attached photos are of the skeleton that is on my desk at home and shows the following:

1) with maximum supination, the posterior portion of the posterior talo-calcaneal (TC) joint opens up while the anterior portion of the TC joint is in contact,

2) with STJ neutral, the posterior TC joint is most congruent, and

3) in maximal STJ pronation, the anterior portion of the posterior TC joint opens up while the posterior portion of the TC joint is in contact.

This is consistent with many other skeletons and cadavers I have had the opportunity to examine over the past 30 years. Therefore, from these observations over the years, I believe that this congruence of the posterior articulating facets of the TC joint in the "neutral position" of the STJ is why one can feel, with careful STJ range of motion, a "flat area" within the range of motion of the STJ that corresponds to the STJ "neutral position".

Would be an interesting research study.

 

Good question Eric. Drs. Weed and Root would measure the ff to rf. The heel bisection line was drawn with pen or an indelible pencil on the foot and would transfer to the plaster-of-Paris negative cast so that the same reference line could be used to compare the ff to rf measurements on both the cast and the foot, thereby reducing heel bisection variability. If the measurements weren't within a certain range, then they had a decision to make. In some cases they would have the patient back in and re-measure and possibly recast them. In some cases, recasting resolved the discrepancy. In other cases, it still existed and then a decision had to be made. For example, they would sometimes reduce an everted ff by moving the 1st met into a less plantarflexed position during casting if they thought they had one of those patients whose 1st ray had a tendency to plantarflex during supine casting as compared to when the foot was measured with the patient in a prone position. Needless to say, Drs. Weed, Root and Francis were all extremely good at measuring and getting very consistent results in their casts.

 

Take a look at the anterior and middle facet(s) of the calcaneus. The middle facet has a plantarly oriented anterior slope to it. The anterior facet is everted. These two articular surfaces have very different orientations relative to the cardinal body planes. When you examine the foot in the open chain, the calcaneus rotates about a static talus. I believe what we "feel" in the neutral position occurs at the instant the head of the talus reaches the transitional point between these two facets. In other words, the facets create a valley with walls that contrast in their orientation. What we feel seems to me to be related to the directional change created by the facets as the talus transitions between these two facets. Even when the facts merge to form a singular facet, their contrasting orientation remains.

 

I've done some cadaver dissection looking at other things while moving the STJ. I think the anterior capsule of the posterior facet limits the additional motion that you are calling maximal pronation. I agree in bones without the capsule and ligaments that the picture you have of maximally pronated does have less joint contact. When you take actual bones and move them through STJ motion it feels smooth up until the point the anterior edge of the lateral process of the talus runs out of calcaneal posterior facet. Continued motion creates sort of a grinding "feel" that does not feel like natural motion. So, i'm 60 to 70% sure that the ligaments don't allow that additional motion.

Of course there is the question of whether maximal congruency means anything functionally.

Eric

 

I tend to doubt that the joint capsule and ligaments at the leading edge of the lateral process of the talus would be able to "limit" the motion of the talar lateral process abutting up against the floor of the sinus tarsi of the calcaneus, especially if the patient has a medially deviated STJ axis.

 

However, with the "bare bones" that soft tissue is not there. Sinus tarsi pain may come from compression of that soft tissue. The original Talliard article mentions synovial hypertrophy. That little bit of extra motion, that you see with just the bones, could come from the absence of that additional soft tissue.

An interesting research question.

Eric