POP casting vs Impression box casting

Foam boxes are by far the most inaccurate way of taking a patients cast I shall explain,

The contour of the heel is never I mean never accurate, the plantar surface can be bizarrely shaped, one side of the calcaneus can be lower than the other. The foam causes many discrepancies, it can push the arch higher, if the correct technique (if there really is one) isn’t used it can leave the borders of the positive device flared outwards or inwards. But I’m sure you will know this all.

A foam box is never a good cast!

It may be ok for an EVA full contact device but for a standard functional device they are near to impossible to work with.
Fabricating a functional device through a foam box by hand just isn’t worthwhile nor possible, there are way too many problems to begin trying to achieve the right outcome for the patient, it just wont work!
Well this is my opinion, however now cad cam is widely used and foam boxes are scanned to make the custom device, how custom really is this though another topic for sure

 

This is absolute drivel.

 

The contour of the heel is never I mean never accurate, the plantar surface can be bizarrely shaped, one side of the calcaneus can be lower than the other. The foam causes many discrepancies, it can push the arch higher, if the correct technique (if there really is one) isn’t used it can leave the borders of the positive device flared outwards or inwards. But I’m sure you will know this all.


I Would agree with the above statement. It is also true of every other casting system currently available. IF THE CORRECT TECHNIQUE ISN'T USED the cast will be rubbish. That's hardly rocket science but it doesn't make impression boxes bad as you can replicate this argument for POP or any other system you care to mention.

 

I'll second that

This is also absolute drivel

 

If you look on the patient self casting thread, there are some compelling arguements for the fact that there is no correct technique.

I bought some £2 insoles from Aldi 2 weeks ago after seeing something on another thread. They provide enough force to stop my plantar fascia getting "a bit achy". Structurally rubbish with very little shaping.

If I had had a cast made to provide the same force, I'm pretty sure that the majority of us would say that the correct technique hadn't been used as the only way to acheive such little shaping would be for me to stand up in a foam box and not try to correct my foot.

If it is enough to resolve my symptoms, does that make it wrong?

Have you ever had a patient come in raving about how great your orthotics have worked, only to find out that they have them in the wrong shoes? If it were the case that correct technique for capturing plantar topography were essential, how could you justify that these devices in the wrong shoes had worked?

The only answer is that it doesn't matter what the capture/casting/ correct technique or method is. The orthoses need to deliver a prescription variable or combination of variables in order to acheive the goal. How this is acheived is immaterial.

 

Good statement Robin, at the end of the day its all about the symptoms being relieved. Just like patients flocking into your practice asking to be sprayed with saline on their feet because it takes away their burning feet sensation. So, the working technique is the one that brings out good results for the patient, not a practitioner

 

You're talking a dangerous amount of sense mokgatle. :drinks. Might we know your name?

Duly carried.

Also seconded.

With respect Kursh, you are fundamentally mistaken on almost all the points in that post. I suspect you have not had a vast experience of Foam casting.

You appropriately suffixed your post with "in my opinion" which is fair enough. However you also prefix it with a statement which suggests a know fact. My advice is to think about that.

 

Foam casting is ideal when you need an arch support with a medial heel wedge. In this circumstance they can out perform plaster casts as they do this perfectly adequately without the mess. Also traditional Root balancing on a POP cast works progressively less well when you have a very pronated foot type and higher degrees of inverted forefoot "deformities". Foam casts are also better for softer devices for pressure relief.

The arena that POP casting works much better than foam casting is when you have an individual with a flexible everted forefoot "deformity". Non weightbearing casting captures this well and traditional Root balancing is perfect at creating the orthotic shape you need in these cases. These feet often have neuromas, other forefoot problems, fasciitis etc and the curved forefoot section in the orthotic created by Root balancing the forefoot is great. Not to say it couldn't be done in other ways but IMO it's what the POP cast with Root balance excels at

 

Evidence?

Not sure what you mean by curved forefoot section.

 

I assume you agree with my first assertion on foam casts, hence you did not ask for evidence on that ;-)
 
Regarding the curved forefoot section: For those Pods that are not well-versed in lab manufacture, intrinsicly posting a cast increases the curvature on the distal edge of the orthotic shell. Varus forefoot posts increase the medial anterior curve and valgus increases the lateral anterior curve in the orthotic.
 
Its complicated to explain but when you capture a non-weightbearing shape that has a forefoot valgus it will tend to have a high medial arch. If you then add a forefoot valgus intrinsic post it increases the lateral arch height and increases the curvature of the shell at the anterior-lateral aspect. This creates an orthotic shape that greatly increases the loading to the metatarsal shafts and midfoot regions. IMO this lowers force on the forefoot and 1st ray = good in some people.
 
I think that it is hard to not dorsiflex the 1st ray whilst taking a foam cast. Doing so negates what you are (or what I am) trying to achieve in certain feet. Not to say its not possible to adjust the shape of the resultant cast to counter-act this problem but thats making work that is solved by the POP technique.
 
As I said before foam casts remain perfectly good for many feet especially where medial heel posting is used ie the majority!

 

Do you now igs:

Understand what you mean by curve now.

Thats arguable. Obviously it will depend on how the foot reacts to the device, Does increasing the lateral bulk elevate the lateral side of the foot and reduce the load on the first met or does it wedge the foot over pushing the COP medially towards the 1st met. I suspect it depends.

I'd disagree there. Hard to dorsiflex the 1st ray, in foam. Quite easy to plantarflex it.

 

If you increase the lateral arch profile of a device the CoP should be more lateral.

ie a device CoP at point X then bend the device to increase the lateral arch contour the CoP should be more lateral.

I don´t get how you can push the Center of Pressure medially by increasing the lateral arch ? Does not make sense

Sorry for interrupting

 

The answer is always,

It depends.

Yule Et al, A STUDY OF DYNAMIC PEAK FORCE AND CENTRE OF PRESSURE (COP)
DISPLACEMENT, IN SUBJECTS WITH FIRST METATARSAL PAIN

 

Where did they increase the lateral arch profile ?

Eric will probably tell me I´m wrong, but as I write this I 99 % I´m correct in my thinking.

A medial skive works by moving the CoP more medially which increases the STJ supination moment.

So increasing the lateral arch contour will move the CoP laterally - what Im saying is you can´t push the CoP medially by increasing the lateral arch contour of a device.

What it will do if the CoP is lateral to the STJ axis by moving the CoP laterally will increase the external Pronation moment which may mean a Kinematic change and pronation.

So as CoP moves anteriorially we will get changes in the Position but increasing the push on the lateral aspect of the device will not push the CoP medially it will move laterally .

 

I understand! Its a bummer.

And Yet

Did the Van gheluwe / Danenburg paper on this give subject specific data? My japma subscription is on the fritz.

Perhaps the key is in the timing. If the lateral wedge creates a kinematic change as you suggest, that would cause a medial deviation in the STAL right?

Or perhaps the distinction lies in the constraint mechanisms of the mid tarsal joint complex. If the available eversion is taken up by the wedge, then the pronation of the sub talar complex will create more load on the medial forefoot than otherwise?

Maybe even neuromotor stuff going on?

I don't know. How do you think that 30% managed it?

 

Nigg also found some strange going on with CoP readings and devices

Answer 1 neuro stuff

Answer 2 problems with scan technology

Answer 3 combo of 1 - 2

Answer 4 N.F.I

Answer 5 combo of 1-2-4

So probably from me personally answer 5

 

I like number 4. NFI / other. Not willing to writing it off as technological difficulties just cos I don't like the data (we didn't put the results we were expecting down to that after all. 1 is entirely possible.

I still like the idea that the kinematic change is accomodated differently in the later bit of mid stance. If the available eversion in the MTJ is taken up by the wedge, perhaps when the TS tensions and creates more pronation moment the first met is held against the ground rather than inverting out the way... or something.

One might even say

 

N.F.I. - Negative Force Inversion?

 

NFI- Nicely Formed Insole?

 

no f**king idea

 

I prefer the others

Nebulous force Ideas?

 

I'd like to my opinion proved wrong, I see over 20 or more foam impressions a day and comparing that to a POP cast - there are way to many discrepancies.
If it's not an accurate way to cast then it's not right.

 

Righto.

L. C. Trotter and M. R. Pierrynowski Ability of Foot Care Professionals to Cast Feet Using the Nonweightbearing Plaster and the Gait-Referenced Foam Casting Techniques J Am Podiatr Med Assoc, January 1, 2008; 98(1): 14 – 18

Compared POP to foam and found foam to be significantly more repeatable. That's not to say its a BETTER position, but it is more consistant than POP. The POP had more variation meaning it was inaccurate at least some, or more, of the time.

Vivienne Chuter, Craig Payne, and Kathryn Miller Variability of Neutral-Position Casting of the Foot J Am Podiatr Med Assoc 2003 93: 1-5.

Compared a number of POP casts of the same foot and found a 16.5 degree (!!) range in the forefoot / rearfoot alignment. Thats not very good really.

That can be true. I've had my share of crap foam casts to work from. But IMO thats a weakness of training rather than an inherent flaw in the method. People assume (correctly) they need training in POP and its always covered in undergraduate education. When I trained (10 years ago) Foam was still all funky and new, so there was no training in it. As such, several generations of Podiatrists just "had a go" at using foam without any kind of training. Result, bad casts.

The students I have on placement have generally not done very many foam casts under supervision. Its an expensive medium to let students practice with. But practice one must or poor the casts will be.

A foam cast, done well, can be as hard or harder than a pop cast. But any eejit can just plop a foot in a box and send it off to the lab for the poor plaster tech to try to rescue. This, however, is a fault of the podiatrist, not the medium.

PS, Sorry Ian. That one was addressed to you, but I took liberties. Beat me later.

 

Would you be kind to explain how a standard functional device is manufactured through a fox box impression? And if the treatment outcome is as good as a POP cast?

How about taking a foam box impression and a POP cast of the same feet and fabricating a standard functional device using both types of casts (by hand) and let me know if the orthosis were any good, more importantly work for the patient as you imagined? I will answer this for you, you will not receive the same treatment outcomes as you would consistently with POP casts.
The clinician has no way of knowing the rearfoot to forefoot relationship (using my words very carefully) when the feet are inaccurately pushed into the foam box. Is the foot really stable during this method, do you take an accurate cast of the plantar surface of the foot which obviously would help, is the arch contour accurate, if I push down to much at the forefoot what will this cause when a forefoot balance platform is created?

I am not talking about cad-cam, handmade manufacturing techniques using a foam box.

 

Oh dear.

Answer the man Robin. I don't know where to begin.

 

For someone that works in a lab Kursh, you don't seem to have a great grasp of the negative model production 'debate'...

 

I simply say foam boxes are inaccurate - and cannot produce a correct standard functional biomechancial device as accurately in comparison to a POP cast?

Whats there not to get.

 

I see my fair share of shoddy casts, likewise with POP casts.
You’re going to need to some serious bionic eyes to see if the forefoot to rearfoot relationship is (I continue to say ‘accurate’) accurate when using a foam box regardless of having experience using this method.

 

Sheesh.

Kursh, believe it or not, I'm trying to be helpful here. But there is so much wrong with what you're saying I don't know where to start.

Are you familier with the references I gave you? That's as good a place as any to begin.

 

Metatarsal parabola

 

Robert, I’m not trying to be patronising but and after all this is just my opinion, yes I am familiar with the references you have quoted, it doesn’t mean I agree with what they have written and researched when I see all types of negative impressions, just my opinion as a technician and as a clinician.

 

Super. We're neither of us trying to be patronising then.

The thing with research is that its... well, research. You can dislike, or dispute it, but you can't ignore it.

All of the research in hand shows that casting methods which use a base plane (foam or laser) are more repeatable than those which don't (suspension casting). Thus to say, as a blanket term, that foam is less accurate than POP, is not a supportable position.

By the same token, the data on suspension casting (like the chuter study) shows massive variability. That means that in the literature, POP cannot be said to be very repeatable. If its not repeatable it cannot be consistent. If its not consistent it can't always be accurate. There may be exceptions, there may be people who can be consistent, but they've never participated in the studies.

Moving on.

So bearing in mind that the the forefoot / rearfoot relationship measurement hinges on a bisection of the rearfoot which is notoriously unreliable, and the Chuter study, on what basis would you say that forefoot / rearfoot relationship IS reliably (repeatable) reproducible with pOP?

 

Sorry Robert, I was doing the school run then dinner bath and bed

Kursh

You can have your opinion about which makes a better device, foam or POP, but when you make these statements

without seemingly having any cogniscence of the current thinking on kinetics vs kinematics/applicability of measurable variables/validity of forefoot to rearfoot measurements, you open yourself(and by proxy, your manufacturing lab) up to a whole load of criticism.

I don't have to explain this

You made the statement that foam boxes were never good - you prove it.

The reality is that it doesn't matter. I think Robert has been far too lenient with his criticism but that is his prerogative as an educator. I can't complain, he was similarly understanding when I used to make ridiculous sweeping generalisations.

But he is right, it is difficult to know where to start because you are making compounded assumptions and leaps of logic that mean nothing in todays biomechanics.

You ask me to explain how a standard functional device can be made....etc etc

This is preceisely what we are talking about. You are asking me to talk about terminology that doesn't exist in my(nor many others on here)clinical practice.

standard - why would I want to manufacture a standard device? Moreover, what is the point of taking a cast/impression if your lab is going to knock me up a standard device?

functional - I have no distinction between a funtional and non functional device. If it is not functional, then it is not performing its function. It doesn't matter to me whether it is made from polyprop, EVA or carpet tiles. If it alters the forces sufficiently, its functional.

forefoot to rearfoot relationship - What does this measure actually tell us clinically? What do you base the FF to RF relationship on? Sub talar neutral? If so, tell me the relevance of sub talar neutral, if such a position exists.

calcaneal bisector - what you really get from a POP is a calcaneal bisector which gives you a reference point. What is that reference point?. It is nothing more than a reference on which to fabricate a prescription that comes into a lab which, as it is being manufactured by a third party, requires some reference point.

Robert has posted three papers that say otherwise

Define correct. Like I said before, I have £2 insoles from Aldi that resolve my plantar fascia pain - are they not correct?

See above for why this is irrelevant

Accuracy does not make an orthosis that resolves pain. Reduceing the stress on an injured tissue reduces pain. I can do that with a trainer sock liner, SCF and a wedging strip from Algeos. That is about as innacurate as it gets.

.

Good job you are not being patronising, Ian is a pretty firey character, he could have easily been offended by this.

I used to think the same way. I got slapped down for being arrogant and cocky. I now know why.

Regards,

Robin

 

Damn good post!

I hope, kursh, that you appreciate it as such. We really are trying to help you, not rag on you. Think ont.

 

Without having any knowledge on current thinking about kinematics, that’s absolute nonsense. It’s surprising to see that you have plucked a prejudgment from a few posts about criticism on a foam box. Crazy.
My experience has shown that a foam box creates deformity that isn’t even there, so how can you justify that this is a suitable method.

See below.

I really think you need to compare the two types of casts using the same feet to be able to understand that both results will be different.

Terminology does exist, quite simple really.

Right, I don’t think you understand what a Standard biomechanical device is? Or compared to a root device? I think you have mistaken me mentioning the word ‘standard’.
The width of the device is different of course between the two in simple terms and the Standard type device cut lines are used 90% of the time for a functional rigid orthosis. So probably your devices are a standard in some way, or if they are a UCBL, MOSI etc then they wont be obviously.

Well you’re correct, hard to argue against that. Though in old texts a functional device is made from rigid materials and EVA is compressed and lose and is not classed as a functional orthotic material.

Not about measuring anything, not what you assume. My point was if the rearfoot isn’t pushed enough and the forefoot pushed (vice versa) further this will obviously lead to a huge discrepancy, likewise if the rearfoot was pushed medially more this can cause an inaccuracy of the heel and lead to a unintentional intrinsic post. So this is why we have no control over how the plantar surface looks when it is pushed into foam.

Yes it is used to create a forefoot platform, and relevant for this. Important during lab prep.

A negative cast which is indentical to the plantar aspect of the feet.

I wouldn’t waste my time to patronise anybody, nor am I acting cocky, there is a difference of opinion for sure, I am open to criticism and always willing to learn, but if I have from firsthand extensively experienced the comparison between the two types of cast methods in a manufacturing setting then I feel I am right in my way to voice my opinion.


[/QUOTE]

Not many people clearly understand the manufacturing ways of creating foot orthotics, and what can be achieved during each method.
Robert I see it as a constructive criticism and I am not one to sit on a fence and agree, with what I have learnt myself - so of course I will have an opinion and some will agree and some will not.

 

This of course is correct. No matter how you push the feet into the impression box it's greatly difficult to capture the contour of the foot properly.

Imagine this guys guy's, your pushing down, and the foam will automatically play some resistance and can cause a inaccuracy.

Take it easy on the man, it's a valid point.

Peace out

Arthur

 

If "standard functional device" is defined as a Root device, then Kursh is correct. This cannot be produced from a foam box since the non-weightbearing forefoot to rearfoot alignment is lost in the foam box approach. I'll post up a couple of my slides from Biomechanics Summer School regarding Rootian casting protocols, if I find time later.

 

Sorry gents. Had a weekend off.

Hey Arthur.

Not sure I accept this. If the foam causes some resistance and causes the soft tissue to compress / deviate, is that an inaccuracy? Or does that make the cast more representative of the weight bearing foot?

What are we seeking to capture when we cast a foot. Is it the shape of the soft tissues or the bony structure beneath? And why?

Agreed.

Is the forefoot to rearfoot alignment reproducable with a useful degree of repeatability in POP?



And here is another question. Lets say I take a non WB POP cast and send it to Kursh. Lets suspend disbelief and say that I WAS able to capture ff - rf with a degree of accuracy,igs: that my calc bisection was correct igs:igs: and that the shape was in any way you take it "Perfect".igs:igs: and lors more pigs.

Is that the shape the insole will be? Nope. First the cast must be "corrected". Medial and lateral additions to the heel to simulate weight bearing. Medial expansion. Very possibly arch fill.

In which case the geometry of the cast I get back will bear little resembelance to the geometry of the cast I sent in. No matter how well one captures the "correct contour of the foot" (a concept I would dispute in and of itself), the first thing that happens in a lab is that that contour is changed to simulate their estimation of the weight bearing contour!

Nor am I in control of this alteration to the geometry. How much heel expansion will I get on a "standard" size 6 NWB cast in mm? How much, in mm is "moderate arch fill?

Whereas with as foam cast, the expansions for weight bearing will not need to be added (or not so much) as average 71% of the change in the width of the heel on wb is acheived in the first 25% of load. I can decide for myself how much "arch fill" to apply and how much change I want to make to the shape of the medial part of the device.

C'mon, really? No control?

Fair play, :drinks. But if you make a statement you must be prepared to justify it.

I've no particular beef with POP. I use it quite often. But I do hate this concept that its the ACCURATE way of casting the foot to give the RIGHT shape. Calcaneal bisection is the core of Rootian casting and that has been shown to be so inaccurate I would not be able to use it in the same paragraph as the word "accurate" without blushing!

A cast, of whatever type, is the means to the end of getting to the shape of insole we want. That shape very rarely matches the shape of the non weight bearing foot.

 

Thats right, I was referring to the standard functional device.

That would be fantastic if you could post a few of your slides, shame I couldn't be there. Hopefully next year if there is another one held!

Kursh

 

I quite agree. However, this is what Kursh wrote.

If it had said a Root style functional orthosis, I would have had less to say on the matter. I suppose this is where I feel Kursh's use of terminology is a little out of touch.

Kursh,

This is the crux of what I am trying to get across

I could take two completely different casts from the same foot and modify them in completely different ways. I could manufacture them from completely different materials with completely different spec with regard to postings/angulations. I could put them on a patient with a pathology and both devices could resolve the problem.

How is this possible if one method is so superior(and I don't care what the method is)

Robin