PTTD, RF Varus

Dennis... seriously. Nothing good will come from this.

What's one of these look like?

Ok, so maybe I want to be clever. For PTTD, I want the orthotic to push in the same direction as the direction of pull of the posterior tibial tendon. In the saggital plane, it's fairly straightforward to see (see my picture). In the frontal plane, it's more difficult. I suppose it depends mostly on STJ axis position? And what the heck do you do about frontal plane forefoot position, if using this approach?

If we are thinking about orthotic design in this way, what are the best ways to modify the orthotic shape (surface geometry) so it pushes in the direction we want?

Do I cast/ scan it differently? Do I modify the negative/positive model? Do I post it differently, or add stuff to the covers/ forefoot? Or maybe a combination of all of these?

I guess i've got a few ideas of what I do, and what I think works. I'd like to see how others approach orthotic design and modifying the shape of the orthotic. It would be great for students to get an understanding of just how many ways there are to skin the proverbial cat, when it come to making foot orthotics.

 

I hope that the student question doesn't get lost in theory here.

I agree that PTTD isn't 'cured' by orthotic devices or braces and that ultimately decreasing the load to the tendon is a goal.

At Stage 1 we're really not into operative treatment considerations but I am all for aggressive bracing. I've long considered that pushing the foot upward (old fashioned 'insert therapy' used by many of my orthopedic colleagues) did little and hurt most of the patients we saw .

In our practice, having seen the debilitation of latter stage PTTD we aggressively treat. I like Ritchie type bracing since it reduces some of the leg forces. We use even more aggressive bracing for those we can't control simply - Arizona if necessary. I have on occasion casted OWB but there are risks there too and its debilitating.

I thoroughly agree that weight is a huge factor but also one of circularity (my foot hurts I can't exercise and ....) We do need to work with patients and the PCPs and nutritionists to treat the whole disease.

I think its a great topic . IMHO.

Irv

 

Like I said, we discussed those ideas previously: http://www.podiatry-arena.com/podiatry-forum/showthread.php?t=59869&page=3

 

P.s. the orthotic can only "push" in the opposite direction to the loading vector. So, unless the loading vector is exactly opposite the line of action of the posterior tibial tendon, the orthotic reaction force vector will not mimic that of the force vector supplied by the posterior tibial tendon. A better question might be: does it need to?

 

I agree with the above but would preface by stating:
The primary purpose of an orthotic is to develop a shell upon which to apply ORF's that is in as optimal a functional position as can be developed and most of us agree that that position is rarely, if ever STJ Neutral.

Dennis

 

In case Viv doesn't know what one of these is...



Focusing on the primary pathology seems a splendid notion to me. Busted PT tendon.

 

Given the limitations of using an in-shoe device that can only alter the reaction forces on the plantar foot, the custom foot orthosis can only act in certain ways to affect the mechanical changes that are necessary to relieve the stress on the injured structures, improve gait efficiency and not cause other problems. This being said, still the custom foot orthosis does not need to exert a compression force on the plantar foot in exactly the same direction as the direction of the pathological force causing the pain, it only needs to have one of its component vectors directed in the same direction of the pathological force in order to help relieve the pain from the injury.

 

Agreed. That's where I was trying to lead them to.

 

You have evidence for this?
or
Just opinion.

So you mean that if I have a sagittal plane deformity lets say, in the forefoot, then a frontal plane rearfoot correction will treat this condition as well as if you are treating on the sagittal plane.

IMHO, that goes against planal dominance, location for care and trying to limit unwanted biomechanical compensations in other areas of the posture which should be considered when formulating custom care.

Dennis

 

For those who are unfamiliar with the concept of component vectors, resultant vectors and vector addition, here is a nice little tutorial on the subject.

http://hyperphysics.phy-astr.gsu.edu/hbase/vect.html

 

Aw, c`mon Dennis. Basic physics? (coming from a blonde...)

Simplicity at its best.

 

Nice. It's important to understand that due to the superior surface geometry of the foot orthosis and due to the nature of the reaction forces that occur at the foot's interface (even upon a flat surface) during dynamic function, the reaction forces which occur at the foot-orthoses interface during dynamic function will almost always be comprised of 3 components: vertical; anterior-posterior shear; and medial-lateral shear. Kevin, Dave Smith and I, wrote about this here: http://www.ncbi.nlm.nih.gov/pubmed/21084541

 

Bel:

The problem for him is......it is basic physics.

 

So that means no evidence that the non dominant plane of deformity works equally well when it comes to biomechanics as we all know that physics doesn't translate perfectly to living things.

I guess we can control the knee rotation to fix a forefoot deformity if we work on any of the planes of the deformity?

Sorry, IMHO you are voicing an opinion that supports your SALRE theory that is unproven clinically.

Dennis

 

:bang::bang::bang:

Dennis, show me a living thing that does not abide by physics. Please?

 

Nice which brings me back to my ? Why is the Uni teaching Varus and Valgus when the above information should be taught

 

He tried flying last time

Eric drove a bus through that idea

 

Is that one of those fish that you get in a Christmas Cracker that curls up when you are lying? You really have been attacking the Christmas Crackers early haven't you?

 

We can treat successfully on all three planes but clinically is one plane better to treat than another? That is a research question?

Is one location better to treat than another?
That is another research question.

In a varus RF that would have a normal-lateral STJ Axis, why would we use s medial skive or a varus wedge instead of vaulting the foot on the transverse and/or sagittal plane which improves position and muscular leverage and function in addition to pain relief? (physics works here too Blin).

Dennis

 

Viv,

I hope this is nice demonstration(if you are still following this thread) of why varus/valgus RF etc terminology is flawed.

I think you were talking in your original question about a RF varus(Root style) as opposed to a varus rear foot which is mentioned above.

As I said before, why they teach it at uni is a mystery to me as it complicates matters greatly

 

There is something to be learned there, not a lot, but something. A partially compensated varus is an important thing to understand clinically. However, Root et al muck it up by separating it into forefoot and rearfoot varus. As far as the STJ can tell they are the same thing. There is no more range of motion and there is a lot of force on the lateral column creating a pronation moment and the medial forfoot cannot reach the ground without moving the tibia in the frontal plane, because there is no more available range of motion of the STJ or MTJ.

Although I do have a problem with the instructors expecting students to explain PTTD with the use of foot position. Position and stress are different things. It would be nice if they were trying to show the students that you cannot explain PTTD with the use of varus and valgus position. Viv if they ever try and explain it to you can post the explanation here and we can have some fun with it.

Eric

 

There are three levels here. Opinion with no logic to back it up. A logical theoretical explanation and then experimental evidence. There is no logical reason why supination end of range of motion would have anything to do with foot pathology. Dennis, why did you choose to classify feet based on SERM? As others have stated, Kevin's assertion is basic physics.

When you apply a force to the foot that causes the STJ to supinate, then the tri plane motion of the STJ will show an effect of that motion in all three planes. The foot is a three dimensional object. When learning about the foot, it is sometimes easier to understand things in one plane, but to really understand it you have to look at all three planes simultaneously.

Planal dominence is a simplification of three dimensional biomechanics of the foot. You can create a biomechanical treatment plan without using planal dominance.

Eric

 

Wow...what did I start? Now the forefoot supinatus/varus, rearfoot varus debate has started within the group. We put forward various ideas to lecturers who all had their own opinions!

Biomechanics is a minefield that easily explains my love of diabetes/wounds! I am trying to love bio though!

 

Relevance to thread please.

 

Somebody sent them in

Today, I am reflecting on laughter, which I think is one of the best things god gave us.

Also tomintoul, which is also right up there. Really it is.

Does an orthotic modification which exists in one plane have an observable effect In all three? Is the sub talar joint obligate triplanar? Does a large grizzly omnivorous mammal defecate freely in wooded areas? Is forefoot varus a disease? Can one apply ORF UPON an orthotic shell? How many angels dance upon the head of a pin and would the number be higher if the friction co-efficient was different?

Is viv keeping up with all this? Sorry viv. We diverted your thread into impenetratable physics and and old, old argument. Podiatry arena is like unto a cake. It's rich and tasty. Sometimes, too rich, too much goodness to enjoy. And something to avoid if you have a nut allergy on account of it contains lots.

Night all.






Yes.

 

The pt's STJ range of motion is not affected. The lecturers are leaving us to decide how to present this, as long as we can justify/evidence our results and are we aware of other theories. They have agreed on trauma/repeated micro-trauma, which works with forces leading to progressive tissue stress. A forefoot supinatus as a result of PTTD has been suggested but I would expect this to then be unilateral (as is the PTTD). In simple terms, I'm inclined to go with a varus foot/excessive lateral force/pronation to bring medial forefoot to the ground ready for propulsion. So, we need to control the rearfoot motion without preventing the forefoot motion.

 

Micro trauma is the actual damage or breaking of the tissue. You have to apply force to the tissue to break it. Therefore I'd say the stress (force / unit area) is what leads to the microtrauma and not vice versa.

I'd agree that you would tend to see a supinatus with PTTD. Again, what comes first. If the PT tendon doesn't slow STJ pronation (less muscular force because pain inhibts use of the tendon) then when the foot hits the ground the medial forefoot will be what stops STJ pronation. This will tend to dorsiflex the medial forefoot which creates the appearent inverted forefoot (supinatus). This assumes that there is enough STJ ROM available to get the medial forefoot to the ground. If there is not enough range of motion then the lateral process of the talus hitting the floor of the sinus tarsi of the calcaneus stops further STJ pronation. You will also often see sinus tarsi pain with PTTD.

On controlling rearfoot motion. I've yet to see an orthosis heel cup that can prevent the medial forefoot from reaching the ground if he STJ has range of motion available. The way biomechanics was taught many students wood assume that if you balanced a cast 5 degrees inverted that the heel would sit 5 degrees inverted when standing on top of the orthotic. That doesn't happen. A varus wedge type of heel cup (either medial heel skive or inverted cast technique [Blake]) will attempt to invert the heel, but you will rarely see an actual change in heel bisection position. The position may not change, but the force on the anatomical structures will change.

Eric

 

Biomechanics also explains diabetic neuropathic ulcers, Viv. Biomechanics is not difficult, unless you are being attempted to be taught the subject by individuals that don't understand it well.

 

or those who only allow their school of thought to be taught!

I added the word "MY" to Kevin;s quote so that you can get its full meaning and power.

Do you believe that I don't understand Biomechanics?

Dennis

 

Yes , your posts show you do not understand the mechanics section of the word.

 

Dennis, you HAVE had the opportunity many, many times to `teach` us the clinical rationale behind your foot typing theory. Only yesterday Eric explicitly asked this of you;

Personally, I believe you do understand biomechanics, but you are so focused on pigeonholing everything that you often miss the point of what others are discussing.

Cheers,
Bel

BTW, good to see you posting frequently again, Mike :drinks We need some decent music around here.

 

I think biomechanics (the study of human locomomotion) is pretty complex. MSK podiatry on the other hand, can be very simple.

Where it all goes runny is when people get the two muddled up.

 

Ditto.

Dennis

 

Huh?



..

 

Ditto

 

Actually, don`t bother listening to this....go straight to the 3rd link down

 

Viv:

It was very good of you to bring such an important question here to Podiatry Arena. I now have a little time in my schedule to try to explain things further to see if I can help your level of understanding on this very important subject.

There are many ways that one can use to try and explain what causes the pathological tension stresses within the posterior tibial (PT) tendon in posterior tibial tendon dysfunction (PTTD). However, in my opinion, understanding how the spatial location of the subtalar joint (STJ) axis affects the mechanical requirements of the PT tendon is far superior to any other method of explanation. Here is some reading that will help better explain these concepts.

In a foot with a medially deviated STJ axis, the ground reaction force (GRF) acting on the plantar foot, often represented as the center of pressure (CoP), will cause an increase in external STJ pronation moment during weightbearing activities since the CoP will have a longer pronation moment arm to the STJ axis in the foot with a medially deviated STJ axis. In addition, to complicate matters, the foot with a medially deviated STJ axis will also have a shorter supination moment arm for the PT tendon to cause an internal STJ supination moment (see illustration). Therefore, the PT tendon will be at a mechanical disadvantage to produce STJ supination moment in a foot with a medially deviated STJ axis since, simply, it has a shorter supination moment arm than normal.

As a result of this three-dimensional (3D) shift in the STJ axis to a more medial and internally rotated position relative to its normal 3D location, the PT muscle-tendon complex must generate much larger tension forces during weightbearing activities in order to generate any given magnitude of internal STJ supination moment when compared to when the foot has a normal STJ axis location. The shorter STJ supination moment arm of the PT tendon in the medially deviated STJ axis simply makes the PT muscle have to pull harder to produce the same supination rotational effect on the STJ than in the foot with a normal STJ axis, where the PT tendon has a much longer moment arm to produce STJ supination moments.

The increased tension forces on the PT tendon in the foot with a medially deviated STJ axis, over time, will start to make the PT tendon fibers become subjected to much greater magnitudes of tension stress which will cause the PT tendon to start to be subjected to tension forces which are out of its desired elastic region of function and into a pathological plastic region of function in its stress-strain curve (see illustration).

As a result of the PT tendon being subjected, over time, to pathological magnitudes of tension stresses which cause it to start functioning in its plastic range, the PT tendon will either partially tear, completely tear or will pathologically lengthen (as a result of the tendon fibers sliding on each other). This creates either a structural or functional weakness in the PT muscle-tendon complex so that, as a result, the PT muscle-tendon can no longer generate the magnitudes of tension force that it had been able to before it became injured.

Over time, this decrease in the ability for the PT muscle-tendon to generate normal magnitudes of internal STJ supination moment due to tendon damage, along with the increase in external STJ pronation moments that results from GRF having an increasingly longer STJ pronation moment arm [which is due to the progressive medial deviation of the STJ axis as the talus adducts further relative to the forefoot which is common as PTTD progresses from stage I to stage IV] causes even larger mismatches of the internal STJ supination moment being generated by PT muscle-tendon tension force to the external STJ pronation moments being generated by GRF. The result is further progression in deformity of the foot due to stretching or tearing of the structural ligaments that normally resist STJ pronation moments during weightbearing activiities (i.e. spring ligament, deltoid ligament, medial fibers of central component of plantar aponeurosis, etc).

I believe that my accompanying illustrations should help to explain these concepts more clearly.

Also, Viv, never let those who seek to "sell" you their patented or trademarked ideas get in your way of seeking the truth as to how the foot and lower extremity functions, both normally and abnormally, during weightbearing activities. There will, unfortunately, always be those, who are loud and obnoxious, who will try to sell you their ideas, not for the good of our patients, but rather for their own personal gain. As one of these "salesmen" dies off or fades away, another one will show up. However, Viv, if you strive toward having a good understanding of basic physics and biomechanics principles in your possession at all times, this will allow you to always separate the wheat from the chaff in your coming years of education on foot and lower extremity biomechanics.:drinks

 

As usual, I almost totally agree with Dr. Kirby's explanation of the forces in play once you buy into the fact that the STJ Axis is the primary focus of the PTTD in question (in a medially deviated STJ Axis PTTD).
However, if I am understanding Viv correctly, the FHL and 1st ray supinatus as she is calling it may be the primary focus of this PTTD as it's STJ Axis is not medially deviated.
The forefoot collapse is having proximal impact on the STJ, "pronating" it on the transverse and sagittal planes causing stress to shift in a medial direction (Physics calls that a pronatory moment).

Where Kevin and I differ, I think, is in our casting and prescribing package when creating the orthotic and our use/nonuse of muscle engine training as a reactive force to be dealt with in the architecture and physics of this case.

So Kevin:
What is your casting position and what is your complete Rx for this case involving a normal-laterally displaced STJ Axis that is presenting with the symptoms of PTTD?

Viv: None of the scientific or biomechanical substance of this debate has anything to do with Patents or Trademarks. Truth lies in the content and not in my personal choices for delivering my work to the world.
In debating what Kevin is doing is deemed unfair and possibly even devious.
He is delivering what is known as a slippery slope argument that gets you to agree with a small first step (in this case that STJ Axis rotation is better than any other method) and then leads you to believe in the rest of the argument that follows.
I would hope in future posts he can reduce his personalizations and unproven opinions.

 

I'd agree with Kevin. Biomechanics is not that hard. You have to know the anatomy and some physical principles. It gets complex when people add in abstractions like locking joints, foot vaults, hypermobility, or neutral positions that are all concepts that are hard to define. The hard part for a student is separating the good information from the bad.

Eric