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What the different methods to rectify casts?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Kursh Mohammed, Jan 18, 2011.

  1. Kursh Mohammed

    Kursh Mohammed Active Member

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    I am trying to find as much literature on the different methods of rectifying casts (moulds) for functional foot orthotics.
    Are there any books which outline the correct protocols and techniques?

    Certain clinicians prefer functional foot orthoses with little or no rectification to their casts and some prefer otherwise.

    Are there any journals or books that contains this vital information?
  2. Not sure if this what your after. I found this a couple of years ago. Maybe Shane can post if he has time.

    Info on positive cast preparation Intrinsic - extrinsic posting etc Ive found hard to find.


    Any specific positive cast work that your looking at ?
  3. Kursh Mohammed

    Kursh Mohammed Active Member

    Thanks for the reply. I am finding it extremely difficult to find literature on cast correction methods / techniques.

    The PDF you have attached is helpful. It shows the method which I have used.
    But is there a set method that we should follow.

    When a POP cast is corrected how are you able to differentiate how much plaster you should add to the medial and the lateral side. Are there certain specific parameters we should follow?

    For example – I have just taken a POP cast of a patient and they have a pes cavus foot type with clawed toe deformity – now how do you distinguish how much plaster fill do you add to the arch and lateral side (after correcting the forefoot to rearfoot).

    We have some clinicians in the UK who prefer cast correction by reducing the forefoot (reducing plaster) not placing a nail to the 1st and 5th met and adding plaster and moulding the material around the cast.

    Whereas some use the method of adding plaster – This is where I am finding it extremely difficult to find the literature!

  4. Kenva

    Kenva Active Member

    The amount of plaster addittion on the medial/lateral side is dependant on what you want to realise with you device and what materials you're using.
    The more contact you want between the the foot/device, only little plaster addition will be necessary. Resultant will be a better distribution over the plantar surface of the foot, hence lowering the pressure on contact area (force per cm²). The harder your orthotic material the more addition you have to ad around the heel/lateral side (in case you took the negative cast NWB) this is for fatpad expansion. Medial additions are again defined in relation to the correction.

    I suppose this is in case of a forefoot supinatus.
    I've never seen anybody mould thermoplastics on negative casts. I can't imagine they would keep the "correct" footshape...
    Nothing wrong with reducing the forefoot/rearfoot relationship when you have a supinatus deformity (or "pronatus ;-) )

    The result of what you describe would be a very thight fitting device, again, i could think of a certain foot where you want to achieve such a result...
  5. footdoctor

    footdoctor Active Member

    Quote:For example – I have just taken a POP cast of a patient and they have a pes cavus foot type with clawed toe deformity – now how do you distinguish how much plaster fill do you add to the arch and lateral side (after correcting the forefoot to rearfoot).

    Yeah, all comes down to what you want the device to do.

    For example if this foot has a laterally deviated stj axis (which it probably has) and the symptoms are that of peroneal tendinosis I would suggest that a lot ( reduce the arch profile of the positive by 75%) of plaster is applied to the positive cast in the medial longitudinal arch area. In this case doing so will result in less external supinatory force being placed on to plantar medial arch area of the foot. If in this example you were to leave the arch "as is" the chances are you would worsen the symptoms by furthur supinating the foot.

    It may however be that you have a mobile pes cavus foot which exhibits low dorsiflexion stiffness of the 1st ray and lowering of the MLA on w/b. This (apart from affecting 1st mpj function) with increase the tensile load on the plantar aponeurosis, which may it turn produce tissue damage. Here you may wish to keep the true contour on the MLA and include a deep fascial groove to prevent P/F band irritation.

    As for lateral arch plaster addition, it largely depends on fatty pad expansion (given that your cast was taken NWB) Personally I measure my patients' standing calc width with digital calipers. Alternatively draw round the foot and measure the distance from med calc border to lat calc border.Then make the appropriate lat plaster expansion.
    Remember though, the inclusion of med/lat skiving will alter this value. Also remember that the device has to go into a shoe!! Studying and noting the internal values of the patients shoe gear can save you a lot of hastles.

    Good luck to you.

  6. Kursh

    Free your mind my friend.

    When you prescribe an orthoses you should have an image in your mind of what shape you desire the insole to be. See the finished product. The cast you take is merely a tool you use to get to this finished product. Take the cast in the position which most closely matches the insole shape. Modify the positive to bring it to the shape. This may involve adding plaster or indeed taking it away! There are no rules, no ratios, no maths. Not as clumsy or random as a protocol, an elegant method of a more civilised age.

    See the finished insole. Make the cast into its shape. You must rule the shape, not the shape rule you. The cast should be as the water, the insole shape concept, the glass. Be the glass my friend, see the glass, and let that guide the shape of the water.

    This is the zen of insole production.
  7. “Hokey religions and ancient scouring pads are no match for a good grinder at your side, kid.”
  8. You don't believe in the zen, do you.

    I find your lack of faith, disturbing.
  9. "Kid, I've flown from one side of this world to the other. I've seen a lot of strange stuff, but I've never seen anything to make me believe there's one all-powerful orthotic controlling everything. There's no mystical proprioceptive insole that controls my destiny. It's all a lot of placebo and nonsense."

    "Your over-pronation is your weakness"
    "And your faith in your devices is yours"
  10. Should I let go my concious self and act on instinct?

    Bet you £5 I can make a pair of insoles from rough casts to moulded (not ground) with the blast sheild down.

    You'd call it luck!
  11. In my experience, there's no such thing as luck... Too easy. Take the poly out of the oven, mold and grind... all without gloves. If you can do that with the blast shield down, "you've earned your crate of beer for that one".

    p.S. for anyone following, it's a Star Wars theme, although I have just gone into Apocalypse Now.
  12. Um.


    Ok, I fold.

    I think doing the cast prep, material in the oven, out of the oven, to the vacuum former and oven correctly, blindfold, would be my limit.

    Much to learn, I still have.
  13. What, you've never done poly out of the oven without gloves? It's all mind over losing your fingerprints.
  14. Oh done that loads of times. Just never blindfold.
  15. Chicken. When it comes to grinding: feel the force of the grinder, let go your feelings... and flesh.
  16. We've hijacked this poor mans thread. I feel shame.
  17. Ian Drakard

    Ian Drakard Active Member

    Yeah but it just cheered up my lunchtime reading:D
  18. Now shame tinged with a hint of cheerfulness.

    I tried dressing a cast blindfold today. Easy. Might get my students doing that.
  19. Kursh Mohammed

    Kursh Mohammed Active Member

    Well some clincians do not specify how the cast should be rectified. Do you have any books or papers which define the standardised techniques you are using?
    I have seen your video of youtube, which is great but it is not easy at all to relate what you have said to our technicians, though I totally understand what you have stated.

    Well our clinicians take a NWB cast using a foam box and the orthotic material is then thermoformed around the negative cast. Not many people use the technique and it is a debate on it's own.
  20. Kursh Mohammed

    Kursh Mohammed Active Member

    Hi Mate,

    We can create an image of what type of orthotic we want for our patient's but, surely there is a standard approach to be able to rectify casts. As far as I am aware, if I were to send my impression away to any lab, they all have different methods - and each company will produce something totally different.
    I am only really talking about functional devices.

    I can be adding plaster, taking away plaster from different locations of the cast and not get anywhere if I don't know what I am following to.

    I understand there is a book which is called, Neutral position casting techniques written by Merton Root, does anyone know if this will help?

    From experience some clinicians in the UK, they won't really know if the cast has been corrected when they recieve a posh lookng device, if it fits the foot! It can be merly a off the shelf device to fit to that size/shape feet!

    It's easy if you know what you are adding or taking away, but where is the hard evidence to say this is how a cast should be corrected.

    Is it all guess work?
  21. Ian Drakard

    Ian Drakard Active Member

    I've attached the old RX lab prescription guide as another reference. Having a quick read through just now, there's a lot which I find quite painful to read but hopefully some useful stuff too.

    There is no evidence to say a particular method of casting is 'correct', so evidence for a 'standard' cast correction from there is also going to be limted.

    A lot of the points you make above just reinforce the message that you need to have an idea what you want the orthotic to do, look and behave like. If what you've produced or what comes back from the lab matches up then fine. It's not guesswork- it's educated guesswork ;)

    As a pet peeve I hate this use of the word functional to describe a certain method of orthotic production- it implies that any other device is non-functional and therefore has no effect. Or is it just me?

    Attached Files:

  22. Not just you.

    Ah, a SWAG.
  23. Ian Drakard

    Ian Drakard Active Member


    Acronym Definition
    SWAG Scientific Wild Ass Guess
    SWAG Souvenirs, Wearables And Gifts
    SWAG Stuff We All Get
    SWAG Sourceware Archive Group (Pascal program sources)
    SWAG Semantic Web Agreement Group
    SWAG Silly Wild Ass(ed) Guess
    SWAG Special Warfare Group (Philippine Navy)
    SWAG Stolen Without A Gun
    SWAG Studies in Women and Gender
    SWAG Southern Women Aging Gracefully (book by Melinda Rainey Thompson book)
    SWAG Super Wild Ass Guess
    SWAG Stupid Wild-Ass Guess
    SWAG Sophisticated Wild Ass Guess
    SWAG Sealed with A Gift
    SWAG Stolen While At Gig
    SWAG International and National Snow, Weather and Avalanche Observation and Recording Guidelines
    SWAG Some Wild-Ass Guess
    SWAG Standard Written Agreement
    SWAG Sold Without A Guarantee
    SWAG Still Wondering and Guessing
    SWAG Shock Wave Generator
    SWAG Southern Whippets and Gazehounds
    SWAG Simulated Waste Access to Ground Water
    SWAG Swinging Wild Ass Guess
    SWAG Stuff We Acquired Gratis
    SWAG Sour Water And Gas
    SWAG Smart Wild Ass Guess
    SWAG Southwest Ag, Inc (Bayfield, CO)
    SWAG Semi Wild Ass Guess

    There's a few acronyms there that fit the bill ;)
  24. In the words of han solo, thats the real trick isn't it.

    Is it a scientific wild ass guess, a stupid wild ass guess or a smart wild ass guess.

    I have my views...
  25. Ian Drakard

    Ian Drakard Active Member

    That's determined before you even get near a cast IMHO

    (although I was hoping for Southern Whippets and Gazehounds)
  26. Whats easier, making a good insole from a bad cast, or making a bad insole from a good cast...

    I guess it depends.

    Are you repeatable Ian?
  27. Whats easier, making a good insole from a bad cast, or making a bad insole from a good cast...

    I guess it depends.

    Are you repeatable Ian? ;)
  28. Ian Drakard

    Ian Drakard Active Member

    not sure if it's you being obtuse or me being dense (sorry if it's the latter) but can you rephrase the question?
  29. Assuming the point of your earlier is that the position / way in which a foot is being cast is more important than the rectification thereafter, how repeatable (ie accurate) is your casting?
  30. Ian Drakard

    Ian Drakard Active Member

    Thanks. Not sure I was explicitly making that point- in fact I think I said there was no evidence to say one method of casting was better.

    More generally saying that from assessment you should have an idea of what you want the orthotic to do and therefore some idea of the geometry of the device. This may inform decisions about casting, but if the orthotic prescription is not appropriate it won't matter about the position/way the foot is cast, or any rectification that follows. If I know what I want the shape of an orthotic to be I could arrive at this with a bad cast (although it might take more work) or without taking a cast at all (although again casting is often easier) and still have the desired effect.

    Regarding your specific query I'm not sure how repeatable my casting is- haven't got around to doing a comparison yet but since inter clinician casting is variable (but orthotic benefit is still generally supported) it is interesting what key data does the cast itself consistently give me to arrive at orthotic geometry. It's not FF to RF relationship, it's not arch height, it's possibly not heel width (although weightbearing casts may give you this more). A lot of whats left I'm going to alter anyway.

    Kursh seemed to be after a method of cast correction with 'hard evidence' behind it- I guess I trying to say he's looking in the wrong place for evidence in that a cast is just one way to end up with a shaped piece of plastic or foam.
  31. There is not a single thing there I disagree with.

    Best line I've read this year.

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