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Positives of Negative Casting

Discussion in 'Biomechanics, Sports and Foot orthoses' started by MaddieM291, Nov 16, 2012.

  1. MaddieM291

    MaddieM291 Welcome New Poster

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    I am currently in my second year of studying Podiatry, and I am just wondering what the positives are of negative casting. I can think of a lot of negatives however not many positives.
  2. Craig Payne

    Craig Payne Moderator

    Depends on what you mean by 'negative casting'?
  3. Boots n all

    Boots n all Well-Known Member

    and then can you tell us what all the negatives are please?
  4. davidh

    davidh Podiatry Arena Veteran

    You're not confusing negative casting with neutral casting are you:confused:?
  5. Maddie.

    As my rt hon colleagues observe, you may need to clarify your question.

    Do you mean the positives of a system which creates a negative cast (vis, foam, plaster of paris or cast socks) as opposed to one which obtains the morphology without use of a negative cast (vis computer scanning or direct moulding)?

    Or do you mean positives of plaster of paris casting? Or as David suggests, neutral casting (which could be in any of the above).

    One of the key things in discussing biomechanics is that you need to use terminology which everybody understands. Negative casting is ambiguous.
  6. MaddieM291

    MaddieM291 Welcome New Poster


    Sorry for my vague comment, I am new to the forum. What I meant was:
    What are the positives of plaster of paris casting when the subtalar joint is in neutral? A way in which you can make a functional Orthotic.


    The above video outlines the negatives associated with negative casting, with regards to the small margin for error.

  7. efuller

    efuller MVP

    The video gives you some do's and don'ts of what they believe gives you a good cast that will hopefully give you an orthotic that solves the patients problem. It's not really disadvantages or advantages of the neutral suspension technique. I agree with some of the things in the video.

    But we should really step back and think about what you are trying to do. The finished product is an orthotic is an orthotic that has a certain shape that will apply forces to the foot in a manner that is different than if there was no orthotic. The change in location of these forces should change the load on various anatomical structures so that the patient problem improves. So, you have to know what shape you want the orthotic to be. There are many ways to get to that shape. You could take a block of plastic and a dremel drill and achieve that shape. It might be easier to get the shape you want from a lab that makes your orthotic if you do certain things when you cast the foot. The cast is a way to communicate to the lab some aspects of the shape you want the finished device to have. As you communicate with the lab, a consistent starting point (the cast) is important in your experimentation with orthotic shapes.

    As an aside, the foot will not magically sit in the same position that it was casted in when it sits on top of the orthotic casted in a certain position. In other words a foot will very, very, rarely sit in neutral STJ position when the foot was casted in STJ neutral position.

    A bigger question is what determines what shape do you want in your finished orthotic.

  8. Admin2

    Admin2 Administrator Staff Member

  9. As Eric says, Pop neutral is merely a way to get to a final shape for an orthotic. So you could argue that as with all systems, its good if you can use it to get that shape.

    But in terms of the sorts of things you're probably thinking of, what are the positives of neutral pop casting?

    There is more evidence for orthoses made this way than any other manufacturing technique.

    Its intuitive for patients which makes it a useful concordance tool.

    Its well recognised and thus legally safer than using a more esoteric technique.

    IMO, its harder to get wrong than many techniques.

    It captures a shape which will probably be somewhere "in the middle". Thus if you don't know what you're doing there's a reasonable chance you will exert at least some of the forces you desire (even if you don't know what they are).

    Thats all I can think of for now. All that said, I prefer foam ;).
  10. MaddieM291

    MaddieM291 Welcome New Poster

    Thank you for both of your answers, very helpful. I am currently a student studying in the UK however from Australia and I am just interested in extending my knowledge on certain aspects of practice beyond the UK.

    What would then be your take on off the shelf orthotics vs POP negative casting, or other forms of negative casting ?

    examples of off the shelf orthotics - Vector Orthotics
  11. it is about the correct fit for the response you want.

    The more options you have the more chance on finding the correct fit.

    ie and off the shelf device can do the exact same job as a custom device, but the key is your knowledge of what to use and when
  12. Common question, but its a catagory error.

    Like asking whats the difference between antibiotics and prescription medicine.

    It may be that the shape you want already exists, in which case a pre fab is a cheaper option.

    Or it may be that you need something with a shape which doesn't exist, in which case you need custom.

    As in, antibiotics are fine if you need antibiotics,

    But no use if you need something different.

    Make sense?
  13. drsha

    drsha Banned

    Maddie, I am not trying to dissuade you from following the advice of The Arena faithful. I am simply trying to give you another take that may impact a student with an open mind to biomechanics.

    1. biomechanics applies forces to an orthotic shell in order to reduce or remove tissue stress that is causing clinical complaints that bring patients to caretakers. These forces are applied to a dynamic, multifaceted (think weight, activity, shoe gear, lifestyle, quality of life) biological structure that is different for all of us (even our own two feet (think limb length). To summize and accept that there is one universal position that all these feet should be cast in seems very illogical especially in light of Dr Fullers comment that the shell does not place feet in neutral position when a person stands on them.
    IMHO, it only becomes logical if you believe that you can apply the perfect set of forces that is required for eliminating the complaint without producing compensatory tissue stress that leads to functional or symptomatic pathological unwanted gifts which is the sole of Arena Biomechanics. These men and women will try to convince you that they have evidence to prove their case But;
    This is very important:
    There is and probably will never be any high level evidence that this can be accomplished! Read my annual threads here on The Arena calling for the members to list the evidence they have produced that have clinical relevance. This will be the third year that they have no high level evidence to document, only excuses.

    I ask you if we should be revisiting STJ Neutral and logically shoot for some optimal functional position that each foot should be custom cast in that pays proper custom respect for the structural snowflakes that we apply our ORF's to. That would necessitate a professional biomechanist and a custom orthotic instead of the prefabs that this group accepts and wants you to use to apply physical laws to.

    Subtalar joint neutral is a thirty + year old, multigenerationally accepted diagnostic and casting position that leads to a single, totally unproven position for our orthotic shells that you are being sheepishly promoted to follow.
    I ask you, in feet that over pronate in the rearfoot or over supinate in the forefoot (they collapse when they go from open to closed chain), is it logical to cast these feet COLLAPSED in STJ Neutral Position? Is there a more optimal functional position, that would reduce the forces we need to apply to reduce tissue stress? Wouldn't that OFP reduce the pathological compensations to the posture that STJ Neutral casing has gifted our patients with for 30 years?

    I can quote many of the brilliant biomechanists who have posted responses to your thread but I believe Robert Isaacs to be a real straight shooter and genuinely interested in promoting great biomechanics so I will quote him:

    My responses for you to ponder:
    1. Roberts statement about evidence is true but falls short IMHO.
    All the existing evidence on this subject is weak and of little clinical import. It is relatively worthless. That's why we are always calling for more that never seems to appear.
    There is no evidence of any import that shows that subtalar joint neutral casting is better, more predictable or more reproducible than others. NONE!

    2 Is Robert trying to say that we can use the subtalar joint neutral pitch to get patients to accept orthotics? Is he saying it is more acceptable and harmonious and leads to more orthotic sales?
    I see no science in this train of thought at all.

    3. Well recognized does not make it right. It was well recognized that the world was flat until.....
    Legally safer! There is absolutely no science in that! Scientists don't think safe, we think scientifically.

    4. So I guess we should not, as professional practitioners of biomechanics be teaching students like you a more difficult but better way to cast because you might make mistakes or it is too difficult to teach, or...?

    5. Should "somewhere in the middle" be our goal in order to place apt respect for the biological structure upon which we are applying our forces?
    and "If you don't know what your doing" Robert suggests STJ Neutral instead of teaching you what to do.
    Dr Isaacs then actually degenerates here and rambles about forces you will exert even if you don't know what they are? to apply forces knowing some will work?
    Any logic here? any organized thought flow here?

    6. He then finishes by stating that he (seemingly proudly) uses foam, recognized as the weakest method of STJ Neutral Casting!

    Summarily, if, like Robert suggests,
    You don't know what you are doing,
    If you don't know what forces to apply to a shell then;
    You are bound to do something right even if by chance and
    if you take a foam subtalar joint neutral cast then you will graduate a biomechanist.

    I await your reaction.

  14. Don't never change buddy ;).

    I might get back to this drivel point by point if I can be bothered. I don't like being misquoted but then on the other hand, Cluck cluck (splat) cluck. Clatter clatter. Cluck. Craig, can we get an emoticon of a chicken? Anyone else want an emoticon of chicken? I want an emoticon of a chicken.

    I would merely point out that what maddie asked for was the advantages of POP neutral casting, not a critique of it. I could do that as well if you like, but thats not what she asked for.

    Maddie probably long gone now so Perhaps I won't bother.

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