Welcome to the Podiatry Arena forums

You are currently viewing our podiatry forum as a guest which gives you limited access to view all podiatry discussions and access our other features. By joining our free global community of Podiatrists and other interested foot health care professionals you will have access to post podiatry topics (answer and ask questions), communicate privately with other members, upload content, view attachments, receive a weekly email update of new discussions, access other special features. Registered users do not get displayed the advertisements in posted messages. Registration is fast, simple and absolutely free so please, join our global Podiatry community today!

  1. Everything that you are ever going to want to know about running shoes: Running Shoes Boot Camp Online, for taking it to the next level? See here for more.
    Dismiss Notice
  2. Have you considered the Critical Thinking and Skeptical Boot Camp, for taking it to the next level? See here for more.
    Dismiss Notice
  3. Have you considered the Clinical Biomechanics Boot Camp Online, for taking it to the next level? See here for more.
    Dismiss Notice
Dismiss Notice
Have you considered the Clinical Biomechanics Boot Camp Online, for taking it to the next level? See here for more.
Dismiss Notice
Have you liked us on Facebook to get our updates? Please do. Click here for our Facebook page.
Dismiss Notice
Do you get the weekly newsletter that Podiatry Arena sends out to update everybody? If not, click here to organise this.

The Method of Casting is Not Important?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by drsha, Sep 12, 2010.

  1. drsha

    drsha Banned


    Members do not see these Ads. Sign Up.
    Quote:
    Originally Posted by drsha
    You use a “STJ Neutral cast as described by Root et al” for your shells, yet you intimate that your work is an advance and replacement for Root and that STJ Neutral position is not measurable or optimal for many feet. You also blow off any other type of shell other than STJ Neutral out of The Arena waters? I would think you would be looking for an upgrade to Root’s Casting as exists in Ed’s or my work or the work of others?

    Eric Fuller's Response:

    I use neutral position casts because that is what I have learned how to modify. There is no reason that you cannot add a medial heel skive to semi-weight bearing cast. The method of casting is not important. How you modify the cast in the lab is important.

    So biomechanical science begins only after a shell exists and the method of casting is not important?

    Eric:
    A SALRE, TST expert can take any shell and by adding ORF eliminate foot pain?
    Quite a boast!

    I would have to assume that Dr. Fuller believes what he says and so as a leader and developer in The Tissue Stress Theory and a proponent of SALRE, as we work with SALRE and tissue stress, why don't we just use OTC Shells and save patient time and patient and government cost creating useless custom shells that serve no purpose and stop misleading the public into believing that a casting serves professional purpose and compensatable value?

    In Summary:
    Biomechanical science begins after a shell exists? Shell casting method has no importance.
    A SALRE, TST expert can take any shell and by adding buffering ORF to offset pathological moments can eliminate foot pain.

    Dr Sha
     
  2. Ultimately it is the orthotic that is important. End of story. Never had a patient yet whose symptoms resolved when I casted/ took an impression of their foot for a foot orthosis- not one. Biomechanical science begins when you take a history from a patient. The reason we don't use OTC's for everyone is because not everyone will fit into the pigeon holes created by the OTC"s. With modification we can broaden the holes, but ultimately some people are "square pegs" that don't fit into the OTC "round holes", hence custom devices are required. Similarly there are some people for whom foot orthoses just won't work. These usually get referred for surgical intervention. The reason I use a variety of casting techniques is to limit the amount of post casting work needed to provide an orthosis of the required geometry.

    Which brings us back (again) to how YOU vary the geometry of your devices to fit into YOUR pigeon holes, Dennis? I should have thought, given the pigeon hole approach of your foot typing idea, you would have a corresponding range of OTC devices to go with them.
     
  3. drsha

    drsha Banned

    Eric Fuller's Response:

    I use neutral position casts because that is what I have learned how to modify. There is no reason that you cannot add a medial heel skive to semi-weight bearing cast. The method of casting is not important. How you modify the cast in the lab is important.

    Sorry Robert:

    This one is hard to misunderstand, especially coming from someone as respected as Dr. Fuller.
    Dr Sha
     
  4. drsha

    drsha Banned

    You are so bad Simon. I hope the novices and students as well as those with an open mind participating on this forum can see what you are attempting to do to this thread.

    What does:
    it's very simples. Unless you are very incredibly... well...simples....MEAN?
    I tried the language translater but it didn't understand it either.

    and such a poor use of

    Jeff's rule #2. changing the subject.

    What does my knowledge of how a foot orthotic work have on Eric's stand that he:

    uses neutral position casts because that is what I have learned how to modify. There is no reason that you cannot add a medial heel skive to semi-weight bearing cast. The method of casting is not important. How you modify the cast in the lab is important. Casts are not important,

    Dr Sha
     
  5. Craig Payne

    Craig Payne Moderator

    Articles:
    6
    My answer to the question of this thread is that it is not important. What is important is that with whatever method you are using, can you manipulate the segments of the foot into the position that you want them to so that you can deliever the prescription variables that are needed for that patient.
     
  6. "I need a car to drive to doset. What make is best?"

    "it doesn't matter what brand car you buy! The bit that matters is taking the right roads."

    "so you're saying they are all the same?! you can drive a ford fiesta around brand hatch as fast as a ford gt, quite a boast"

    No. The point is that (generally) the METHOD doesn't matter. The cast does.

    As others have said on this thread, it's the cast that's important, not the method. Occasionnally I meet a foot where I can't get the shape I want in foam, so I get the pop out. By and large however, one can get the shape one wants from any of the 3 methods. And if not on the casting, a good technician can rectify almost anything.
     
  7. And that the method is repeatable by you - whatever method you use.
     
  8. Bruce Williams

    Bruce Williams Well-Known Member

    Ultimately orthotic casting is an area of podiatric biomechanics that has not been studied adequately.

    I agree with most of you that you can modify most any device either at the casting stage or to the finished device to improve outcomes if you follow Craig's line of reasoning on knowing what it is you want to achieve.

    I do think that there are ways to cast that can and will achieve a better outcome than what is regularly considered the correct approach, i.e. the root method.

    Unfortunately this is a discussion with no end to it other than to hear people strongly defend or not defend their positions, scientifically or anectdotally supported.

    There is most likely a best casting scenario for many different foot problems and not necessarily one for them all. I would imagine most of us will supinate the STJ more on some feet when casting and possibly the opposite on others. Most on this site will utilize plantarflexion of the 1st ray to some degree or another whereas many of our colleagues will not since it was not reinforced in Root's explanation of casting.

    Ultimately there is more than one way to skin a cat. Until someone or someones actually does some degree of testing of teh casting techinques we will not come to a true understanding of whether it really does make a difference or not statistically .

    I look forward to seeing those of you attending I-Fab in Seattle this week!
    Cheers
    Bruce
     
  9. drsha

    drsha Banned

    Dr. Payne:
    I realize that you are very busy and do appreciate you taking time to express your opinion to the question raised by this thread.

    Your response seems a bit vague and unscientific to me. It contains many assumptions, few definitions and seems to be justified by your expert opinion more than on evidence, even low level.

    I realize that there is little evidence that any of us can produce at a high level with regards to the nature of our clinical outcomes but possibly you could explain or expand on some terms and personal opinions you present in your response that will give them more clarity and credibility.

    1. What are the acceptable methods for negative casting?

    2. Which is the negative casting method (s) that you use most or recommend as a default for your patients and students?

    3. Would different acceptable casting methods require different prescription variables?

    4. Would different casting methods require different amounts of the prescription variables?

    5. Can you list or define the "prescription variables?

    6. How does one decide which and how much of the prescription variables are needed for each patient?

    7. How do you decide "what is needed by the patient" i.e. what is your goal set?
    By that I mean:
    elimination of pain
    healing of injury
    performance enhancement
    prevention
    quality of life issues
    postural alignment and improvement
    etc.

    I look forward to your reply.
    Dr Sha
     
  10. Craig Payne

    Craig Payne Moderator

    Articles:
    6
    The nonpartisan approach I take is to try and get some sort of systematic approach that can categorize each one and then can be broken down and looked at closer
    I do not think we have an answer - we all know about foam, plaster of paris, optical scanning, etc - they can all create a negative model of the foot that can be manipulated. The data shows that a weightbearing or semi-weightbearing foam is much more repeatable than the non-weightbearing plaster - that does not mean that it is better.
    We teach them all along with the pro's and con's of each and let them make their own minds up which is the better approach for them. My role is not to brain wash students,, but to give them the tools to evaluate for themselves. Personally I use both a MASS like foam impression sometimes and a neutral STJ plaster cast techniques sometimes - I even sometimes try and do a MASS position with the plaster non-weightbearing --- depends on what I am trying to achieve.
    Yes.
    yes
    This may just be a pedantic terminology thing here, but I consider a prescription variable to be something like, for eg:
    - the need to plantarflex the first ray
    - the need to provide more inversion force at the rearfoot
    - the need for more contact in the arch
    - the need for a heel raise
    - etc etc
    The terminology I then prefer is the word ‘design feature’ which would be things like (following the above example):
    -first ray cut out
    -medial heel skive
    -minimal arch fill
    -heel raise
    - etc etc
    The systematic, hopefully nonpartisan, approach we take is as part of the clinical assessment, you come up with a list of prescription variables that are needed for that patient. Then you decide, which is the best way to deliver that list of variables. Sometime a simple prefab can deliver them all; sometimes a weightbearing foam may be the best way; sometimes a Root device may be the best way to deliver them; sometimes a MASS device etc etc.

    For eg, if we take the prescription variable of "the need to plantarflex the first ray", this can be delivered in several ways:
    - plantarflex the first ray during negative model production
    - modify the positive model with more material under the first ray
    - use a forefoot valgus post
    - invert the rearfoot more
    - use a first ray cut out
    - etc etc

    I have no idea how to really decide between which is the best way to deliver them ... it may depend on what other prescription variables are also needed (eg maybe another clinical test suggests the need to a forefoot valgus post for another reason, so you go with that).
    All of the above!

    At the end of the day, the goal we are working towards is this:

    Clinical test --> list of prescription variables needed --> how best to deliver that list.
    We start we NO preconceived ideas as to which method of negative modelling to use or which method of positive modelling to use or which type of device to use. Its all about delivering the prescription variables that are needed. (Also thrown into the mix is negotiation with the patient as to goals, based on your list in question 7 above)

    Using this approach has shown a deficiency in our knowledge and evidence for a number of the prescription variables etc.

    For, eg, while I not a total convert to MASS, I do use it, but would prefer a better clinical test(s) to tell me when to use it compared to a STJ neutral. One thing that using MASS has taught me is that we can position the rearfoot in a number of different positions during negative modelling - it could be pronated (as in a tarsal coalition); it could be slightly pronated (as in an equinus); it could be STJ neutral (as in ...???); it could be more inverted than neutral (as in ...???); or it could be a full MASS position (as in...???).

    The ultimate aim would be to come up with a clinical test(s) that will tell me what position to negative model in ... working on it!
     
  11. What difference does the rearfoot position of the cast have on the geometry of the finished device? Ultimately there are only two things that are important and two things that you can change in a foot orthosis: it's geometry and it's load/deformation characteristics. So, tell me how any one "casting" process creates a situation whereby the geometry of the positive model produced via some other "casting" technique cannot be altered to create the exact same geometry and load/ deformation characteristics in the finished orthosis...

    You could take a weightbearing foam box cast, a neutral suspension cast, a mass position cast, etc. Go pour the positives and with enough care and attention you could end up with the exact same surface geometry in all devices. You press identical shells on them so you get the same load/deformation characteristics, would they function differently mechanically. No. Viz., the casting technique is insignificant. The geometry and load/deformation characteristics of the devices are significant. The point is, which technique gives the easiest starting point and minimises the work? For anyone who doesn't "get" that: I could take two negative impressions of a foot but take them different ways with the foot in different positions, I then pour them as positive models and then cover them both in plaster so that they are both the shape of house bricks, I could then put them onto a CAD/ CAM controlled milling machine and carve them back to result in two identical positive models- simples. Right, Dennis? Which is one of the reasons why CAD/CAM is the way forward.

    Here's an interesting question: when was the last time any of you did a positive "cast" (plaster or CAD) preparation?

    BTW, foot orthoses, in their passive form, work by altering the geometry and / or the load deformation characteristics of the foot's interface with the shoe, end of story. That's all they can ever do, given present technology. To save time, I've answered the question I posed to Dennis for him. The only other way they can work is psychologically.

    So, if we ignore the psycholoical components, you need to prove that "your" casting technique alters the geometry and /or the load/deformation characteristics in such a way that the same cannot be achieved by any other means... I'm not holding my breath.

    But, but, but.. Dr Spooner, what about... hold your breath. You are wrong.

    Obviously a much better question is: what is the optimal geometry and load/ deformation characteristics of an orthosis for foot a, exhibiting pathology b, ..etc. the answer to that really is the grail.
     
  12. drsha

    drsha Banned

    :good:
    amazing stuff, no moments, supinatory torques, stiffness.
    just pure good stuff.

    thank you even more for taking the time to answer my questions.
    They reflect an open mind and serve as an excellent foundation to prepare any potential student or practiitoner for entering the world of biomechanics.

    For me, I have spent 30 years in the other direction, looking for answers without engineering or evidence as a clinician and again, for me, functional foot typing serves as your unknown to provide the clinical tests that tell me how to cast, post, etc. (bias, commercial, blah blah)
    I told you that four years ago in NYC and it has only grown since then.

    It took me two years to get to this moment, Craig, where do we go from here?

    Dr Sha
     
  13. drsha

    drsha Banned

    As do other labs, at FootHelpers, we are capable of altering the geometry of any cast to fit the prescription needs. However, we prefer a plaster cast, doctor taken as this will give additional perspective and information to the practitioner as to the custom needs of the patient.

    I'm sorry to make mention of how I work but the greater the PERM-SERM Interval when functional foot typing a patient, the more sagital and frontal plane expansion and vault collapse you will have in foam or semi or weightbearing. The greater this expansion, the harder it would be to correct at the lab site.

    This would affect shoe fit, mechanical advantage of the ligaments and muscle engines and in effect may result in transfer pain and overuse syndromes and performance and quality of life tradeoffs that I believe a professional should avoid.

    The big unproven absolutely no evidence driven piece of your statement is that "with enough care and attention you could end up with the exact same surface geometry in all devices".
    What a load of self indulgent, expert opinion, "Simon Says" bunch of crap.
    Please rant off all your personal experimentation and documentation for this statement, if not.................

    My purpose is not which is the easiest starting point and what minimizes my work. It is what is the best method for my patient that enables me to inject my education and practice in EBP into a clinical plan of action, in spite of opposition.

    I am dedicated to working my butt off for my patients while you are working easy and minimally.

    I alluded to the psychological aspect of EBP with my verrucous reference.

    I have stated that CAD?CAM is the future unless practitioners fight to leverage our opinion to patients that the doc should stay in the box.

    We live in different universes with different grails.
    The only difference is that I can live along side yours and you want to eliminate mine.

    Dr Sha
     
  14. [​IMG]

    Unusually slow of you not to have picked up on that already Simon. :deadhorse:
     
  15. drsha

    drsha Banned

    Originally Posted by drsha View Post
    As do other labs, at FootHelpers, we are capable of altering the geometry of any cast to fit the prescription needs. However, we prefer a plaster cast, doctor taken as this will give additional perspective and information to the practitioner as to the custom needs of the patient.

    I'm sorry to make mention of how I work but the greater the PERM-SERM Interval when functional foot typing a patient, the more sagital and frontal plane expansion and vault collapse you will have in foam or semi or weightbearing. The greater this expansion, the harder it would be to correct at the lab site.

    This would affect shoe fit, mechanical advantage of the ligaments and muscle engines and in effect may result in transfer pain and overuse syndromes and performance and quality of life tradeoffs that I believe a professional should avoid.

    The big unproven absolutely no evidence driven piece of your statement is that "with enough care and attention you could end up with the exact same surface geometry in all devices".
    What a load of self indulgent, expert opinion, "Simon Says" bunch of crap.
    Please rant off all your personal experimentation and documentation for this statement, if not.................

    My purpose is not which is the easiest starting point and what minimizes my work. It is what is the best method for my patient that enables me to inject my education and practice in EBP into a clinical plan of action, in spite of opposition.

    I am dedicated to working my butt off for my patients while you are working easy and minimally.

    I alluded to the psychological aspect of EBP with my verrucous reference.

    I have stated that CAD?CAM is the future unless practitioners fight to leverage our opinion to patients that the doc should stay in the box.

    We live in different universes with different grails.
    The only difference is that I can live along side yours and you want to eliminate mine.

    Dr Sha
    I hope The Arena readers can absorb that I answered (as I have before) Simon's questions asked and that the reaction from Simon is not to respond in kind or use the same standards as he judges me with upon himself.
    He gave no reaction other then another thug comment.

    The main topic he avoided is:
    The big unproven absolutely no evidence driven piece of your statement is that "with enough care and attention you could end up with the exact same surface geometry in all devices".

    I bet Robert 50 cents that Simon will say that he will respond to this query if I respond to his questions of me. That is his usual #2 reaction.

    Dr Sha
     
  16. Alex Adam

    Alex Adam Active Member

    Correct casting technique is essential as we need to have a reference point in the initial cast to allow the laboratory to continue the reference point throughout the pours, posting and correction techniques prior to pressing of the device.
    Adding all the 'lumps and bumps' after the plates are pressed are counter productive as we can't determine the correct physics behind the process.
    The cast must reflect the needs of the skeletal system and not just the foot.
    This is determined by the Podiatrist in their examination and history.
    Non weight bearing supine for standard soft tissue restraining and prone for cases of ligamentous laxiety. In both cases the pelvis and lower limb is in the position determined by the Podiatrist.
    It is about the physics behind the gait pattern and realising we only have milli seconds to allow 'normal' propulsion. Understanding the proprioceptive response to everything we do, and ensuring the body is not just compensating somewhere else in the body, no point in fixing one problem and producing another.

    {ADMIN NOTE: The inner ear stuff is followed up here}
     
    Last edited by a moderator: Sep 18, 2010
  17. admin

    admin Administrator Staff Member

    I will be going through this thread soon and deleting everything that does not add value. I also won't be reading any emails about the deletes.
     
  18. Craig Payne

    Craig Payne Moderator

    Articles:
    6
    Sorry, I been on the road; a huge amount going on behind the scenes here and just keeping on top of reporting on iFAB .. I have drafted a reply in my head ... just not had time to write and post...
     
  19. admin

    admin Administrator Staff Member

    OK. Put my other hat on. I removed a lot from this thread. All posts that added no value to the topic are gone. Please don't email me or private message me about it as I will just delete the message without reading it. I get damned if I do and damned if I don't.

    A lot of Podiatry Arena members here at iFab are commenting on the nonsense and how it is putting off new members from contributing to the community

    From now on the meaning of the word "REPLY" (ie the button you push when replying to a thread), will now mean "add value to the discussion". Any posts that do not add value will be deleted (not only this thread but in others). I struggling to stay on top of it all at time, so please use the the I with the red triangle at the top right of each post to alert the moderators to a post that you think does not meet the criteria of "add value to the discussion"
     
  20. Alex Adam

    Alex Adam Active Member

    [I choose not to change an existing geometric alignment rather that stop the motion at a point when the anterior muscle groups are firing and just prior to the posterior group is about ot fire. I can only do this with a non weightbearing cast. Any weightbearing or semi weightbearing technique includes the geometric deformation/compensation].
    [No not wrong because at least we are thinking about it]
     
  21. drsha

    drsha Banned

    This is a great day for The Arena.

    As with all others who hold our science and the needs of humanity for closed chain medicine and care as a high priority, I pledge to do my best to comply.

    I will only disturb the administrator if a posting has major offensive negative value or serves as a real distraction to the flow of the thread and I will try to keep my need to alert the moderators about posts to a minimum as I realize they are volunteers and have busy lives to attend.

    Here's to the future.
    :drinks
    Dr Sha
     
  22. While I'm sitting here at Sea-Tac waiting for my plane to take me back to Sacramento after the i-FAB meeting, I thought I would add a few thoughts on this important subject.

    Therefore, each method of casting-scanning for the production of custom foot orthoses will have pros and cons that will determine how well they fit within the above ideal characteristics.

    I hope this list provides a renewed starting point for the academic discussion of this important subject for the podiatric physician.
     
  23. efuller

    efuller MVP

    That is a fairly good summary. You don't even have to be a tissue stress expert to modify a cast or orthotic to relieve pain. You have to know how cast modifications change the shape of the finished orthotic. That is what make the device custom. Is there really any point to making a custom device that looks exactly like an over the counter device? An intrinsic forefoot valgus post will lift the area plantar to the shaft of the fifth metatarsal higher off of the ground. A medial heel skive will lift the medial part of the heel cup higher off of the ground than the lateral part of the heel cup. The clinician's decision to add these variables is what makes the device custom.

    I haven't seen anybody take the counter argument to the statement that the method of casting does not matter. Is there anyone would like to explain why method of casting does matter?

    Eric
     
  24. Alex Adam

    Alex Adam Active Member

    One of the problems with the arguments is we are assuming the laboratories know what to do. Having been in the manufacturing field for twenty years I have noted that the techs have no standardized training and one labs method is totally different to anothers. So is the Podiatrist truly recieving what they ordered??
    By having a standardized casting technique that your laboratory is familiar with allows a more acurate device, providing the control the practioner wants for the patients treatment regime.
     
  25. Apples and oranges. If the problem is that techs have no standardized trainging then sure the solution is to simply find a tech / lab which does what you want OR to create said standardized training.

    If the problem is one labs method is different to another then a standardized casting method won't make any difference because your standard cast will get a different result depending on where you send it.

    So, out of interest, when you send off a cast you took prone weight bearing, of a size 7 foot, how much plaster expansion, in MM, will the lab add to

    A: the lateral heel
    B: the medial heel
    C: the posterior heel
    D the medial arch

    Cheers
    Robert
     
  26. Jeff Root

    Jeff Root Well-Known Member

    Robert,

    Another potential variable is how and therefore, where, do they orient the cast in the frontal plane. If the cast is corrected or "balanced", the plantar surface of the balance platform will be perpendicular to the heel if the heel is positioned vertical or it will be at a prescribed angle to it when the heel of the cast is positioned inverted or everted to the floor. So in addition to the modifications listed above, the relative position of the cast can have a profound influence on the shape of the resulting orthosis and the corresponding orthotic reaction forces.

    I believe that there is too much variability in heel bisections and I also believe that standardization of this technique can lead to decreased variability. If practitioners and labs were using more consistent heel bisections, then we would be better able to evaluate the significance of variability in casting and cast modifications.

    Jeff
     
  27. Jeff Root

    Jeff Root Well-Known Member

    For those who don't think that the "method" of casting is important, I have uploaded an article that I wrote with Doug Richie, DPM that appeared in the September 2007 issue of Podiatry Management. An orthotic device changes forces via the interface between the supporting surface and the foot. Casting influences the shape of the orthotic device. So how can the method of casting not be important?

    Jeff
     

    Attached Files:

  28. Jeff:

    I believe that the method of casting-scanning is not near as important as whether that method of casting-scanning allows the clinician to achieve an accurate and reproducible cast-scan that represents the three-dimensional shape of the plantar foot. I prefer the neutral suspension casting technique with plaster splints and modify it widely in my clinical practice to achieve the foot shape I want in the resultant custom foot orthosis. However, other methods of casting-scanning can also be used by other clinicians to produce similar results.

    Do you disagree with my six ideal characteristics of a cast-scan?

     
  29. joejared

    joejared Active Member

    For a heel Skive, Eric is correct. A heel skive applied to semi-weight bearing or non weight bearing has approximately the same angle as the rule, not the exception, at least from my understanding of what a medial skive is supposed to be.

    In the context of his statements, I actually don't see the point of arguing in this thread.
     
  30. Yes you are wrong.

    Next, I responded already to Dennis telling me that what I had written was a bunch of "Simon says Crap". Craig saw fit to remove it since he didn't believe it added to this thread, yet Dennis telling me that what I had written was a bunch of crap obviously does. Never the less, I maintain my contention that you can take negative casts different ways and by manipulating the positives end up with the same surface geometry. I'll upload the image again tomorrow.
     
  31. Jeff Root

    Jeff Root Well-Known Member

    Kevin, no I don’t disagree. However, just because the clinician thinks that they have placed the foot in a position that "will best achieve the goals of foot orthosis therapy" doesn't necessarily mean that they actually have placed the foot in the best position to achieve those goals. This is the crux of the debate about the SoleSupports theory of casting. Different casting methods and techniques do result in intentional or unintentional differences in the shape of the resulting devices. Therefore, if the shape of the devices can influence clinical outcomes, then I would have to say that the casting technique and position does matter.

    In theory, I could hand carve a positive cast out of a tree branch and end up with the same shape wood mold as I get from a laser scan of a foot using a CAD/CAM system . However, it is highly unlikely that I would actually end up with the same shape wood molds and it would be impractical to carve them by hand. The issue really boils down to which system is best because the individual components of different systems might be similar but how they fit into a treatment system determines their actual benefit.
     
  32. The reality of it all with this day and age it could be argued that you don´t even need and cast or scan to create the perfect device.

    If you have enough reference measurement from the cardinal body planes and the skill in Computer design you could in theory create the perfect foot orthotic.

    Jeff wrote the above quote which was also going to be another point - If you had the skill you could also hand beat the perfect designed device from a flat piece of metal.

    Having a modified cast or modified scan will allow us to make repeatable objects.

    If you don´t think this is true then look to the car and motorbike industry - just turn on a few of the custom car or motorbike programs and see how the design 3d shaped objects to fit in certain places with specific measurements.

    But the realitly of this it´s just not practical - thats why casting and scanning is.

    As soon as any modification is made by manipulation of the cast or added plaster, the amount that the cast matters less and less.


    A cast is just a 3d reference point to begin from - can a device be made without a cast or scan yes is it practicial no.
     
  33. What a great debate this has turned into!

    I think a big chunk of it is based on what one considers the desired shape of the device. Depending on how close one wants the geometry of the device to match the geometry of the foot has a big impact on the importance of the casting method...

    I think Jeff made a really excellant point here.
    Its easy to overlook this. Heel bisections are very inaccurate by and large and that makes a profound difference to the surface geometry. That's the primary reason I favour foam. Whatever else you might think of it, it DOES give an absolute reference plane. One does not have to work out the position of the ground from a measurement of the calc, one can work out the position of the ground... by the position of the ground.

    Ref Kevin's points:-

    How repeatable is POP for doing this? Chuter (2003) found a range of 16.5 degrees in the forefoot to rearfoot relationship from the same foot using POP!

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

    And

    Why?

    The final positive, if it receives the normal expansions and additions, especially if it gets "arch fill" will not be the same shape as the foot when the material is moulded to it anyway! What are the variables for "shape"? Your three dimensions. The cast corrected cast will be different in at least two of these (width and height). The only variable which is truly preserved is length, The heel to forefoot dimension is not adapted.

    As Alex said, different labs have different protocols for "cast correction" (homogenisation would be a cynical name for it).

    So to sum up.

    The bisection of the heel, and thus the angulation of the surface anatomy is not repeatable.

    The forefoot / rearfoot relationship has, at best, question marks over its repeatability of it.

    The lab will add an amount of plaster known only to them to the device to "correct it".

    So the actual end point, the surface geometry of the device, is defined by these three "random" factors. If these were controllable I would agree that the method used at the outset to get the raw negative is of vital importance. But they are not, so I would dispute the importance of the method used.

    And as a final point, even if we agreed that the method WAS important, it would then lead to the question of which method is best (again). Been a while since we've been around that stump ;).
     
  34. Not really a debate so far as Eric points out.... Everybody seems to be saying the same thing in different ways.

    There must be someone who thinks that cast a very important ...

    The floor is all yours ..............
     
  35. Jeff kinda did...

    I can argue that position if no one else will ;)
     
  36. Alex Adam

    Alex Adam Active Member

    Simon tend to agree with you however not many Podiatrists have the luxuary of having their own Lab and so we need to be able to transfer data in a way that the Labs can pickup and follow through with. So some form of standardization between the Podiatrist and Lab is needed.
     
  37. Oh hey alex.

    Any news on the cast modification question I asked? How much expansion, in mm or as a %, do you advocate as standard, and on what basis?

    And how does this fit with you assertion that an insole can hold the foot in the position in which it is cast
     
  38. The negative"cast" is ultimately not important, the positive and/ or the resultant surface geometry of the foot orthosis are.

    This advert gives a good analogy to my point:
    http://www.youtube.com/watch?v=RGQf9dn0pDk
     
  39. Alex Adam

    Alex Adam Active Member

    OK the principle of an orthotic by it's own definition is to alter the geometry of the human body, the important thing is the device should not produce a negitive effect so balance is desirable.
    How much expansion should be used? Purely dependant on the type of cast taken. Suspension cast produces forces down the lateral column so the lab has to accomadate the fat pad expansion.
    Foam ipressions capture the fat pad expansion so less accomadation is needed.
    Medial column expansion is purely dependant on the desired control point, CCP or medial cunioform/navicular area. If there is an apparent forefoot/rearfoot dysfunction the medial expansion will allow for this and this information is within most perscription forms.
    In most cases the foot will determine the amount of plaster used.
    The general information laid down by Whitman in 1906-07
    The CCPis what our lab uses exclusively and is based on Lewis' 1980,C. Oxnard, M Benjamin 1990's, Bleck 1980's Bannister etal 1995 Perry 1983 and Jones 1944.
    The simple principle is to stabalize the GRF while controlling gravitational forces the are being transfered through the lower limb.
    If a practioner has a system that is effective for their work then that is the main point of the discussion, who is right and who is wrong, not the point. If your cast technique allows for the corrective treatment for their patients symptoms that is all that matters. Biomechanics dynamically in a living patient can't be a pure science due to all the variabilities within the individual.
     
  40. efuller

    efuller MVP

    From the article I took these points as those that would support the argument that casting method matters. Let me know if I missed any.

    First quotes from article. (In column like, red text.) Then I will summarize the points, if they need it. and then state my argument against the point.

    had the
    following benefits:
    1) It was logical to manufacture
    an orthosis from a neutral position
    cast in order to encourage
    the subtalar joint to pronate at
    heel strike and then re-supinate
    during midstance and propulsion.


    I really don't understand how a neutral position cast promotes pronation at heel strike more than going barefoot. I can see how a higher arched device will tend to promote resupination. Force applied to the medial arch is generally medial to the STJ axis. If you took a fully weight bearing cast you could decide that you want an arch height of x mm. If the arch height of the weight bearing cast was x- 4 mm you could carve some of the positive cast plaster away to create an arch height of x mm. Often a medial expansion plaster is added to neutral suspension casts that effectively lowers the medial arch height. The rationale for adding the medial expansion plaster is to prevent pain from the arch being too high.




    2) It was important to capture
    the plantar, non-weight-bearing
    contour of the heel, so that the orthosis
    would conform to the
    anatomical shape of the heel and
    capture it in all three planes (triplane
    heel cup).


    2 points here.
    It is really difficult to get "control" from a heel cup. A 14mm heel cup just does not have the leverage to prevent eversion of the heel on top of it. Additionally, the foot is more likely to evert the orthotic than the orthotic is going to prevent the heel from everting when it is on top of the orthotic. This is just speaking of the heel cup part of the orthotic.

    Lateral expansion plaster is usually added to the heel cup region to make it wider than the heel cup of the non weight bearing cast. A heel cup with insufficient expansion is really uncomfortable. The amount the fat pad expands is quite variable and the outliers on the side of more fat pad spread need more expansion plaster to make the orthotic wearable.

    3) Fully pronating the forefoot
    on the rearfoot would capture the
    midtarsal joint in a position of osseous
    stability so the orthosis will
    support this relationship and resist
    compensatory motion (forces) at the
    midtarsal and/or subtalar joint.


    2 points here
    This is the support the deformity idea in explaining how neutral suspension orthoses are supposed to work. One flaw in this is that the foot does not stand in neutral position. As the foot pronates from neutral position, the range of motion of the midtarsal joint increases. So, the forefoot to rearfoot relationship that you are allegedly supporting is incorrect.

    It is possible to add an intrinsic valgus post to a forefoot varus cast. Yes, this will evert the heel cup. However, if you have a round heel this will not dramatically change the shape of the heel cup as Kevin described in his medial heel skive article. If the bottom of the heel is flatter you can add a medial heel skive or plantar lateral expansion to change the shape of the "everted" heel cup to an "inverted" (varus wedge effect) heel cup.

    4) Casting the foot with the midtarsal
    joint pronated and the subtalar
    joint in neutral was clinically reproducible
    among similarly trained practitioners utilizing the same technique.


    The key thing is being able to communicate with lab about what you want the finished orthotic to look like. When I make my own orthotics in my lab I can easily do the skive/ plantar lateral expansion to make an everted heel into an inverted heel. I'd have to develop a pretty good relationship with a lab to get them to do what I want. In a different clinical setting, I sent a cast to a lab with a very good reputation in Root type biomechanics (It wasn't Jeff's). I asked for an intrinsic forefoot valgus post. When I sent the orthotic back because I did not get the intrinsic post, the lab tech did not know what I was talking about. The lab owner had to explain it to him. So similar training is important, but it may not be consistent across all labs or practitioners.

    As others have said, given any cast of the foot, you can create the shape of the orthotic that you want. (Given a block of polypropylene and a dremel you could create the shape of orthotic you want. It will be a little easier starting with a foot shape. However, neutral position casts require medial and lateral expansions to make them effective. So, even with neutral position casts you have to do some work with the cast to get the finished product. With different types of casting methods you will have to do different work to get what you want.) I will concede that it may be very difficult getting that shape if you are not the one making the device. I have sometimes found it difficult to get the shape I want even using standard neutral casts and what I thought was standard terminology.

    Cheers,

    Eric
     
    Last edited: Sep 21, 2010
Loading...

Share This Page