Navicular drop + navicular drift = planal dominance?

Here is the second

http://www.youtube.com/watch?v=x830zLovvVU

Well I suppose so if you have a really sticky out navicular prominance. But how much surface area are you going to catch that way? The more surface area, the bigger the lump in the side of the arch and the more navicular drift, the more likely that is to cause irritation!

 

Your orthotic surface is too big, end of story. Take the card off of your pencil and use something about the diameter of your pencil. Then do it on a foot. In fact push with your finger with a 45 degree vector, the medial cuneiform still in the way? Of course not.
You're wrong on this Robert, and making video's doesn't make you right. We are talking here only about the orthotic surface which is in contact with the medial portion of the navicular, when you measure navicular drift and drop what's the surface area of the point you mark to measure this? Indeed what is the average area of the navicular on the medial aspect of the foot? 1.5 cm squared? Try with a smaller piece of card.

 

And in your second video once again the wedge is way too big and out of proportion. Funnily enough I did exactly the same thing today, drilling a cast and offering up a much smaller wedge, and guess what, there was no issue with it "occupying the space of the medial cuneiform". It's all a matter of scale Robert. Next....

Maybe I'll make some video's if I find time tomorrow and post them up here.

Yeah, that's why it's called the tuberosity of the navicular, because it's the sticky outy bulging bit

Your contention regarding orthotic irritation and "more surface area" is not well made and indeed by orientating the geometry of the orthotic shell perpendicular to the relatively small navicular area and perpendicular to it's plane of translation, shear forces should be reduced, reducing the friction and irritation, not increasing them as you maintain.

P.S. when you stuck your cocktail stick through your foam cast with the triplane 45 degree vector, you translated the position of the navicular anteriorly too, the stick should have exited from the same point as the first hole, only angled anteriorly.

"Lets see what response that gets". Yeah, lets.

Oh and I just spotted the dent in the heel section of the foam cast caused by your biplane wedge based on navicular drop and drift alone. Does this mean we should perform a heel amputation when you are prescribing devices based on navicular drop and drift, Robert? Maybe the next time we get together I can explain the concept of bias to you? Like I said, just because you made a video, it doesn't make you right. Although, as i'm sure you understand the power of marketing, TV ads cost more than paper ads for a reason.

 

Hello men.

Forgive me if I'm being a bit stupid here, but how do you hope to apply your equal and opposite force to the navicular to prevent the drift or drop using orthotics? I can't see a patient wearing an insole that does not generally conform to the shape of their medial longitudinal arch without complaining of severe discomfort. I'm guessing that this thread is more of a 'thinking exercise' about how your orthotic is effecting the particular point of interest rather than it being an immediately clinically useful discussion (please do not take that as being a criticism of the thread).

Lets say you can work out relative three dimensional rotation of all of the bones of the foot, or even 3d displacement, vectors, etc... - if you were to attempt to apply this to designing an orthotic that provides an equal and opposite force to each one of these bones at whatever point in their motion you like you would produce a very uncomfortable insole. We all know that there is more in a foot than just bones. I could be way off the mark here, but the idea reminds me of Rx lab's polysectional triaxial casting thing that Ray Anthony talked about some time ago. You probably recall that they would take the positive cast, cut it at key points where they sought to correct perceived problems, move the sections of the cast into the corrected position and plaster it back together. Then they would smooth it off and in-fill plaster here and there so if would not be too uncomfortable to wear. What they ended up with was an orthotic that was not significantly different to the standard thing you could have made via far simpler methods.

You may design an orthotic that perfectly resists your abnormal vectors, but then you're going to have to smooth it off so the patient can tolerate it. How much this will deviate your device from your ideal I do not know.

Edit - sorry Robert, just watched your second video and I agree with the last bit. You guys make more insoles than me and see more of these patients - how well tolerated are your devices and have you actually tried something along the lines of Simon's suggestion?

 

that probably tells you more about the lab than the prescription concept.

This is a theoretical discussion as you rightly point out. The point is we could theoretically manipulate the geometry and the stiffness of the shell, in discreet areas, so it doesn't necessarily = "smoothed out device", at least, the smoothed out device could have higher stiffness sections which will act in a similar way, while still providing a smoother interface surface.

Since I only actually thought of it last night.... and I don't think the navicular slide test is described in the literature, then I'm also fairly certain nobody has actually tried to create an orthotic surface normal to the navicular translation axis which interfaces with that area of the navicular.... I guess you could say its theoretical.... Like I said, reference this post in your paper.

 

That is all fair comment Simon. As far as material properties of your devices go I think it could be a great concept, but my materials science knowledge in and around orthotics is severely limited so I'll politely STFU regarding that . Do you think you still might have issues regarding comfort if you could provide such a device? I am thinking about the extremes of density in EVA orthotic materials placed next to each other. It must be tremendously difficult to provide a device that provides the right force in the right direction to a dynamic structure such as the foot whilst remaining comfortable. I wonder about the longevity of these devices?

 

Not all orthoses are made of EVA, Bob. And there is more than one way to skin a cat

 

I know Simon, I was just giving it as a simple example given the varying material properties idea.

 

Modulation of thickness = modulation of stiffness

 

Are there any materials available that will not fail at varying rates given varying thickness or stiffness?

 

Not sure I understand your question. Are you asking if material "strength" is related to material thickness? Or something else?

 

Really? I thought that was because it was something to do with root vegetables!

Meh. I'm not sure. If what I'm thinking your thinking is what your thinking then what I'm thinking is that there has to be a protruberance in the medial flange of the orthotic. Or "bloody great lump" as patients like to call them.

Duly noted.

Could try it I suppose. Hard to get volunteers for a study I guess. Ethics would be a B**** as well.

The big surface was as you say, big. A smaller one (your 10p size) brings its own problems. That has to be a lump to get in front of the navicular tuber.

Yours or mine? Or both? I'm pretty sure I read a book about it once.

It surely doesn't. And saying I'm wrong on this doesn't make you right either . Quid pro quo clarice. Since, as you say, the idea of making a surface perpendicular to the triplanar vactor, using navicular slide as an indicator, is a shiny new idea and has never to our knowledge been used on an insole, we neither of us really know do we?

Yes indeed. Although advertising implies I have something to sell, and I don't. I just happen to disagree with you. Assuming, as I say, that I've understood you right. I just don't see how an orthotic shell can be modified to place a surface normal to the vector of the navicular, or even the navicular tuberosity, without creating intolerable pressure on the medial side of the medial cuniform. But I am open to be proved wrong, and I would love to see a picture (no need to do a video) of such a surface. Whittle yourself a foot, or an insole shape, and show me the sort of angled surface you have in mind!

Nope. This concept is new to me today. And I don't make a precise (hahaha) angled measurement in my orthoses. I use it as a gross indicator. If its loads of drift, I'm thinking high flanges in strong footwear. Loads of drop I'm thinking shank dependant in a softer material and not getting stressed over footwear. Points in between make points in between.

By the by, this is not a private barny. Everyone else is invited . This must be the longest run that Michael has not posted in for months!

 

Robert, you're beginning to irritate me, and I don't want to be irritated by you. So I'll leave this for now.

Like Kevin, I feel it may be time for a break, I'm sure now that the Arena has a new breed of biomechanics experts, life will go on.

 

I'm wondering if there is a material out there that can fulfil your needs to create a shell that provides your equal and opposite force whilst still remaining comfortable, but does not fail (or wear out) at different rates so that it has a reasonable shelf life? Your earlier post that mentions "..higher stiffness sections.." got me thinking that the lower stiffness sections may wear out sooner and cause some discomfort?

 

Oh don't be like that! You know that its not my intention to irritate and certainly not to piss you off. You've had people disagree with you before. I just want to understand why I'm wrong, not least because I have a sneaking suspicion I have the wrong end of the stick entirely!

We both know I can't do what you do. I'm not ripe yet so don't you dare bugger off.

I just don't geddit is all! Someone, Kevin, Craig, Eric, Ian, Mike, someone pitch in here on this.

 

I need a break Robert, nothing personal. I've presented some new ideas, make of them what you will. I'm tired and I can't be arsed to fight.

 

Fair enough. Take your break my friend. They ARE good ideas.

 

I know. Good night, God bless and thanks for having me.

That's all for now folks (until someone writes something stupid).

 

4,3,2,1 and GO ED.

Night my friend.

 

AND this is the last one for now: "here is your stage Robert. Stand upon it. And if anyone should ask or question, be sure to tell them that I sent you..."

Now, I am ****ing off for a bit, so stop ****ing replying - give me a ****ing break,...K? K.

 

Simon, Robert and Bob:

Sorry I have been out of commission for awhile now, unable to take the time to follow threads. Getting my lectures ready for Spain, writing an article for Podiatry Today on Biomechanics of Subtalar Arthroereisis, reviewing a paper for JAPMA, setting up all new computers in my office, and seeing my patients.....not enough time to allow for Pod Arena lately.:wacko:

I haven't had time to thoroughly read over all the postings here, however, I thought I would start with Simon's original question. I have never been too big a fan of the concept of planal dominance, but I think Don Green still teaches it. It basically is used mostly as a radiographic evaluation technique for planning reconstructive surgery of the rearfoot/midtarsal /midfoot joints by evaluating static angles of the rearfoot/midstarsal/midfoot joints clinically and on radiographs. Planal dominance probably has nothing to do with axes of motion of the STJ or MTJ.

The navicular is not a good marker to use for determining STJ axis of motion since the naviicular and talus go opposite directions during closed kinetic chain pronation motion (i.e. navicular abducts relative to talus, talus adducts relative to calcaneus). Also, one must discriminate between a changing STJ axis spatial location and simply rotational motion about a joint axis, since these are very different kinetic and kinematic ideas.

Hope this helps with this discussion some.:drinks

 

I´m around, maybe we should take a step back and slowly work through it all again maybe I can help or maybe we can get lost together.

But in reality Ive been up since 2.30 with a 4.5 month old who thinks he is still in Australia and can´t see why sleep is a good idea, so may be a little slow on the up take and I should really getting some thoughts down on paper for something else, but finish one thing 1st.

as an aside

Robert have you read do you want a copy ?

Van Langelaan EJ: A kinematical analysis of the tarsal joints:
An x-ray photogrammetric study.

Acta Orthop. Scand.,54:Suppl. 204, 135-229,

 

Question: can you introduce an orthotic shell section angled at 45 degrees to all three cardinal planes at the level of the navicular without amputating the forefoot at the level of the medial cuneiform?

First take a foot, mark the navicular then take a semi-weightbearing plaster of Paris cast of said foot, I inverted mine slightly from relaxed stance position. I didn't take a photo of myself casting the foot, but I'm sure you get the idea...

Pour the positive ensuring the navicular marking is re-marked so as to facilitate transposition to the positive cast.

On the positive cast drive in a nail at the inferior / distal aspect of the navicular marking at a 45 degree angle to the cardinal body planes.

Then using an electric file remove plaster from the cast in the area of the navicular, medial cuneiform and proximal portion of the medial aspect of the first metatarsal around the nail.

Remove nail carefully. Take a circular disk of polypropylene attach it to the nail so that it is perpendicular to the the spike of the nail and parallel to it's head and drive it through the same hole left in the cast by removing the first nail. Recheck angulation then back fill plaster as necessary to ensure the disk is secured to the cast. Recheck angulation.

 

Continued from above:
Press 3mm polypropylene to cast, grind to shape and topcover, in this case I used a 1mm split of eva. They're a bit rough and ready but this was a design exercise

Place orthotic on cast to check fit.

Place foot in orthotic.

Ensure forefoot has not been amputated.

So to answer the original question: can you introduce an orthotic shell section angled at 45 degrees to all three cardinal planes at the level of the navicular without amputating the forefoot at the level of the medial cuneiform?

Yes.
QED.

 

I stand corrected. (bows head humbly).

Next question, will such a modification be tolerable to the patient?

I think I might try that on one of my feet. The principle is sound. Its the application I question. I suspect much would depend on just how prominant the navicular is, and the angle of the vector is in the other two planes. If the vector was in the sagittal plane (hypothetically) then the motion would be forward and down and I see no problems. The closer it is to the frontal plane the more medial component there will be and the harder the insole will have to work to control navicular drift. My concern is, would the shelf cause irritation?

So here is an interesting question. If the shelf is moulded to the morphology of the skeleton rather than the surface anatomy, will this mod actually decrease peak pressure medial to the navicular by spreading the load over the cuniform area as well? Or will it create a new peak pressure medial to the cuniform. Or will that depend on the depth and nature of the soft tissue over the cuniform?

Glad to see you back Simon!

 

Simon / Robert

Love the idea and can see the purpose.
A couple of none technical questions (technical way above my grey cells) relates to footwear fit. Does the presence of such a high medial flange mean an:
issue to footwear selection in terms od device to shoe and foot fit?
issue of increase skin surface pressure when the shoe is laced against the shell?

So would, provided the device to shoe fit is okay, you be including some pressure distribution material in the shell bit?

 

Those devices are pretty uncomfortable on me and I wouldn't want to wear them for very long. But then I don't have a navicular that translates along an axis angled 45 degrees to each plane! I doubt whether anyone actually does, do they?

Its a bit of an arse to do, if I was doing it again I'd probably section the cast at the naviculo-cuneiform joint in the frontal plane to grind off the navicular at the desired angle then reattach and grind back to blend the distal section along the medial cuneiform and 1st met. If you do one, it might be worth actually doing the assessment and making the device to your prescription, rather than a 45 degree for the sake of it. I only did a 45 degree to demonstrate a point (as you know) because you said it couldn't be done. Men and their ego's, right ladies?

It's the forward motion (slide) that's the problem.

I don't think the shell is moulded to to the morphology of the skeleton, its moulded to the positive cast AND I removed a whole load of plaster from the original positive model. But then what do you do when making a medial heel skive?

Seems to increase pressure at my navicular a lot!!!

No issues with fit in shoes, Ian. But I had a pair of trainers on.

JUST TO BE CLEAR, this was done to prove a point. I would not use this modification with a real patient until the technique has been further refined and tested.

 

You know when you mobilise a joint and you perform an accessory glide? That's what I think the navicular shelf modification is doing. It's basically attempting to provide a medio-lateral, inferior-superior and anterior-posterior "glide" simultaneously on the navicular. Which is probably why I was able to add that 45 wedged shelf and still wear the device, by gliding the navicular slightly laterally, posteriorly and superiorly relative to the medial cuneiform.

The reasons it was uncomfortable was probably as much to do with increased tension in the tissues that restrain these movements as it was to do with direct pressure on the bone itself.

What tissues restrain the navicular? Free-body analysis time, Michael.

 

Indeed, if you can stop the movement in one plane, you'll stop it in all three (the navicular is a rigid body). If you can stick something against the medial side of the navicular which eliminates motion in that plane, you've eliminated it in all three planes. So why bother...

 

I was looking for good anatomy picture with everything marked, may not be much point . I guess there will some "slop" but then bone compression should do the rest.

Tis a tangled web

 

The axis is not changed by navicular drift, but the location of the forefoot relative to the axis is changed by navicular drift. So, the moment from ground reaction force will be changed with drift.

Eric

 

In thinking about talonavicular motion there are three degrees of freedom. Dorsiflexion- plantar flexion, abduction-adduction, and inversion eversion. This is because the TN joint is a ball and socket. The motion of the TN is limited by capsule around the joint including the spring ligament plantarly. Additionally the navicular cuboid ligaments will also be critical because limitation of cuboid motion will also limit navicular motion. The calcaneo cuboid joint has a medial curved portion and a lateral flat portion (most of the time as the joint is quite variable.) The cuboid, in maximum abduction relative to the calcaneus will have the flat parts of the joint abut and this is in a fairly good position to limit further abduction of the cuboid relative to the calcaneus. When the cuboid is prevented from further abduction, the navicular will quickly bump into it and its abduction will be halted as well. (When we were discussing, in another thread, navicular cuboid motion I kept thinking that the motion between the cuboid and navicular was so small that it would probably not make much difference clinically.)

So, I think it is possible to move the navicular in other directions if the motion is stopped in one direction. On the other hand, in the presence of ground reaction force and body weight, those forces will tend to push the navicular into dorsiflexion and abduction relative to the talus.


The discussion of the navicular shelf/ medial flange is very interesting. I've thought about it in the past and as I see it there are two components you have to think about. The position of the flange and the stiffness of the flange. Additionally, if the flange pushes the foot from medial to lateral, you are probably going to want the orthotic to also provide a force from lateral to medial to keep the foot from sliding off of the orthotic (think lateral flange.) The distance between the medial and lateral flanges and the rigidity of those flanges will determine the force applied to foot and hence the comfort of the foot.

The forces applied by the flanges are going to be similar to those of a gauntlet or an AFO with a strap that goes from the underside of the device around the navicular and up to an attachment on the lateral leg. The strap seems much more easy to adjust to get the amount of force that does some good but does not hurt at the point of application of the force.

Eric

 

Yesterday, I was thinking about the concept of three point fixation with a lateral heel flange, a medial navicular flange and a forefoot lateral flange making up the triangle- easy when we only have a single joint to contend with, but in the foot...?

 

Or indeed the internal fixation strap which one can request on specialist Paediatric footwear. I use such modifications regularly to control movement in the transverse plane.

I've been mulling this. An orthoses with high medial and lateral flanges, like a UCBL or a smafo, does not work simply by modifying GRF. Indeed they work without GRF. A Smafo can be applied to, for example, a foot with spastic hypertonia in the peroneals by restricting the width of the foot. Works weight bearing and non weight bearing. Pronation makes the foot wider. As Simon alluded, the lateral heel and the lateral forefoot stay still and the medial midfoot moves medially. Containing this is the principle behind many AFO variants and elastic type devices as well as different types of footwear.

To incorperate the concept of anterior slide, we must also attempt to prevent the foot getting longer. This is fairly straightforward with strapping but a bit of a mare with an orthotic. I wonder if another way to think about this would be around manipulating frictions under the forefoot?

 

What if we prevent a reduction in calcaneal inclination angle by controlling the rearfoot?

 

That what what I was going to say believe it or not not the same way with 10 miss spellings but the same idea , patients got in the way.

Robert does love a friction vector though

 

In which plain?

If you say sagittal is Craig going to jump out and say "aha, lateral arch!!" at me?

One day I shall write the biomechanics version of the "my favourite things" song.

 

In reality it's all three planes, but since it's the posterior-anterior slide component we're discussing.......

 

Can only be sagittal plane for the inclination angle . confused how can it be anything else. ??

My understanding is inclination angle is the angle of calc in the sagittal plane - how can it be all 3 - would that be inverted-everted and or abducted-adducted . ??

is not the inclination angle of the calc- ? Dbl Confused

 

What planes does the calcaneus simultaneously move within during dynamic function?