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Who should cast?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Bennepod, Nov 27, 2018.

  1. Bennepod

    Bennepod Active Member


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    Greetings.

    A podiatrist has carried out a biomechanical examination, gait analysis, imaging analysis etc, and has determined that a specific set of external forces would provide remedy for the presenting problem. The question is (keeping with best practice principles), who is the best person to cast the foot for the production of custom orthoses? Can this duty be delegated and still and still produce the specific forces desired? And if so to whom?

    Brendan
     
  2. efuller

    efuller MVP

    There's a lot that goes into answering the question of can casting be delegated. How important is it to get a "good" cast to apply a specific set of external forces? Do some of those specific forces require a "better" cast than others? What criteria are used to determine that a cast is good? Are some casting methods better than others?

    I used to teach casting to podiatry students. I'm quite sure that I could give the criteria I used to evaluate a cast to non podiatrists and teach a good percentage of them to take a cast that met my criteria.

    There is nothing magical about the cast. There is a questionable belief that casting the foot in a certain position will make the foot attain that position when standing on an orthotic made from the cast. The real magic happens in the orthotic lab where the finished shape of the orthosis is determined. You can add a medial heel skive to any cast, even foam block casts. The cast that the lab receives is just the starting point. What is important is the instructions that you give the lab on how to modify the cast and whether or not they carry those instructions out.

    Eric
     
  3. What Eric said.
     
  4. Petcu Daniel

    Petcu Daniel Active Member

    The one from the 'good percentage' will take a cast that met your criteria and I'm supposing another one from the 'not so good percentage' [or whatever you want to name those who aren't from the good percentage] will take a cast that doesn't meet your criteria. Practically, this means we'll have two different shapes which means 2 starting points and not only one. As the 'instructions' are the same, how modifying 2 different shapes with the same quantity will lead to the same result, at least in the terms of foot orthosis final shape?? Of course, both final shapes could provide the same kinematic/kinetic effect on patient but this is not for sure valid in all cases.
    My point is that in order to minimize errors the specialist who make the evaluation and prescription is better to take the cast. If he will not take the cast then he have to provide the evaluation criteria for the cast taken by other person and check if those criteria are fulfilled.
     
  5. efuller

    efuller MVP

    One of my criteria for casting is that the contour of the lateral border of the foot, when it is loaded should match the contour of the cast. This criteria is a hand me down from what I was taught as student. I was taught that an orthotic that was made from a cast where the forefoot was plantar flexed on the rearfoot would hurt. I've never experimented to see if this was true.

    However, I have seen labs fill in the lateral arch (in a foot with a high lateral arch) to create an orthotic that has not lateral arch. I imagine that they did this becaue they are worried about making an orthotic that hurts. So, even if you have two different starting points, you might get something that is very close in the finished product. (An cast that was plantar flexed and then the arch filled will look very close to a cast where the forefoot was maximally dorsiflexed.) I really want a high lateral arch in that cavus foot, with a high lateral arch, with metatarsalgia to increase the area of contact. If a lab fills in that lateral arch, that orthotic will not reduce pressures on the forefoot as well. So the practitioner has to also make sure the finished product was what they wanted.

    Eric
     
  6. Bennepod

    Bennepod Active Member

    Thank you all for your comments. Allow me to refine the question. I am approaching this topic from a policy (not pragmatic) perspective, to establish best practice and standards. How do we define the process to Insurance companies and governmental stakeholders (DVA etc). I think Pectu is on the same wavelength as me in terms of reducing error to ensure a device that is as close as possible to the desired product.

    Brendan
     
  7. Petcu Daniel

    Petcu Daniel Active Member

    In this case maybe you'll find some resources in ISO 13485 - 'Medical devices -- Quality management systems -- Requirements for regulatory purposes' [ https://www.iso.org/standard/59752.html ] even from my point of view this standard avoid to treat the specific problems of custom-made medical devices.
     
  8. efuller

    efuller MVP

    The doctor is ultimately responsible for the finished product. The doctor has to be sufficiently trained to take the right cast and know that it is the right cast. If the doctor can impart that knowledge to an assistant and the doctor trusts that assistant then the doctor is still responsible for the finished product. Does the doctor have to take a patient's blood pressure for the value to be correct? Someone had to be trained to take the measurement. (A cast is sort of a measurement). A person having a degree, or certification, does not necessarily make them better at taking a measurement.

    We should not really overthink this. There is not really any research on what method of casting, let alone evaluating that cast, produces the best outcomes. If we don't really know what the best cast is, we can't really say who the best caster is.

    That said, I have tweeked enough orthotics that were not working to make them work to know that a few milimeters here or there will make a big differnece. Where we earn our money is in the finished product, not in the casting.

    Eric
     
  9. mr t

    mr t Active Member

    Hi Eric/all,

    Thank you for your comments thus far.

    If you don't mind I would like it if you would clarify a few points. As I agree with the majority of your sentiments, but I believe it can be slightly dangerous to undervalue the importance of consistency in foot capture. If this is not what you are doing then my apologies.

    Do you believe that the morphology of the foot as captured in the scan/cast is fundamental to providing the baseline shape from which negative/positive change are implemented at the foot orthosis interface?

    It seems logical that consistency in the methodology of foot capture would help in establishing a solid paradigm for how we should all be applying changes across different regions of the foot orthosis interface. I think we need to continue to advocate for a repeatable foot capture methodology, otherwise I fear that moving toward a scientific consensus remains more challenging.

    "There is not really any research on what method of casting, let alone evaluating that cast, produces the best outcomes. If we don't really know what the best cast is, we can't really say who the best caster is."

    Agreed. We really need research in this space. It might not even be about what is 'best', it might be about how a practitioners prescription need to adapt depending on how the foot has been captured. I would assume that in today's climate that if a practitioner captured the foot in a WB position and then captured the same foot in a NWB position that the prescription boxes would look pretty similar.

    Do you think that if you were to apply a 4mm heel skive from a WB vs. NWB position that there would be an identical outcome?

    To take this to the extreme, we could follow this line of thinking until you compared the scan of the foot with a spiky rock. There potentially would be some practitioners out there that could manipulate that spiky rock with a file and a chisel to achieve an appropriate clinical outcome, because they have an exceptional understanding of the required forces that should be applied and where they should be applied, but is that really an accurate and repeatable basis for our orthosis manufacturing processes?

    If a scan/cast shape is not fundamental baseline for achieving a more ideal clinical outcome, then why not just dispense prefabricated orthoses in all cases?

    I would assume that if a clinician is going to cast the foot it is because there are certain design features that can be more easily implemented due to the shape of the cast providing an initial conformity to the foot. I would argue that implementing these design changes would become more difficult when using an over the counter device, thus I would argue that whenever a cast/scan is taken it should assist in allowing for a less subjective pathway to the end product.

    I think that foot capture is a critical component of the overall orthotic manufacturing process and should not be undervalued. Practitioners with the most accurate 3d scanners that follow a strict methodology of measurement and positioning seem to achieve greater success while appearing to better understand orthosis prescription (yes, this is anecdotal).
     
  10. Mr t do you use the same capture (cast,scan) technique in all your patient cases?

    I do think capture techniques are important but not for the same reasons. I believe that capture of all the " lumps and bumps" is important to increase comfort.

    And yep you could if talented enough just prescribe prefab devices with modifications no problems at all but it would take more time
     
  11. Boots n all

    Boots n all Well-Known Member

    It doesnt matter who takes the cast, what is important is the outcome. Are you getting the desired outcome? Are you measuring the outcome? How are you measuring the outcome?
     
  12. Petcu Daniel

    Petcu Daniel Active Member

    When do you think the probability to achieve the desired outcomes for custom foot orthoses manufactured by an orthotic lab is greater: when the prescriber or when other people takes the cast?
    In a similar way, when the probability for a last to achieve the desired outcomes is greater: when the lastmaker or when other people takes the foot measurements?
    This is why is important to have very clear instructions for taking the cast or foot measurements! Because, this eliminates or reduce the unproductive discussions between who prescribe and who takes the cast in situations where the desired outcomes aren't achieved!
     
  13. mr t

    mr t Active Member

    Hi David,

    Just for clarity, would you agree with the following statement?

    It doesn't matter who takes the cast, what is important is the outcome of the casting process, as a consistent and accurate casting process can help to ensure less subjectivity in prescription and all subsequent manufacturing stages.

    Hi Mike,

    Thank you for the question. I actually do not cast as I am a laboratory owner and not a practitioner. I do work with many practitioners and try to keep up to date and we discuss these questions together at great length.

    I would say that anecdotally, a NWB 3D scanning process seems to provide my clients with more consistently positive clinical outcomes. However, it is not my place to tell a practitioner how to capture the foot. It is my place, however, to ensure that I accept all forms of foot capture and allow my business and software to adapt to any methodology as guided by current evidence. I believe proprietary hardware that is only capable of one capture method is an issue for the profession that inhibits this endeavour.

    I believe that there is more to it than simply comfort, as 1:1 conformity to the surface would appear to provide a more sensible baseline for +/- changes to be applied in a consistent fashion (especially when manufacturing orthoses for patient's with DFUs).
     
  14. Sure and I agree there is more too it than comfort. Especially considering the definition of how devices work but then it gets back to Eric's intial point
     
  15. efuller

    efuller MVP

    There are two different issues here. There is who should cast and should the cast be consistent. Anthony, as a lab owner, I'm sure you have some clients who are inconsistent. I'm a firm believer in consistency. A single practitioner has to be consistent in order to be able to learn from their mistakes and scientifically approach orthotic manufacture.


    Casting is a baseline, but it is not fundamental. You can get a similar outcome with different casting techniques. Again there are different issues here depending on your perspective. As someone who has made orthotics from the casts that I've taken, I believe I can work a lot of different casts to get what I want. The perspective of a lab owner is going to be a lot different. A lot of information can be lost in the communication between the prescriber and the fabricator of the orthotic. As a fabricator you will have a lot times when you don't know what the prescriber wants. (There are probably a lot of times when the prescriber doesn't know exactly what they want.) So, the fabricator has to do their work consistently so the prescriber can learn what the fabricator does.


    Here is where the language used by prescriber and fabricator needs to be more precise. Say I want 3mm of intrinsic forefoot valgus post, but I took a non weight bearing cast with a heel bisection line that shows the cast has 2 degrees of forefoot varus. I could also say that I want my cast to look like it has a 2mm medial heel skive. The fabricator could add that intrinsic forefoot valgus post, everting the heel more and then the fabricator would have to add a lot more skive (or other tricks) to make the heel cup be inverted. The prescription boxes should not necessarily be the same with different casting methods, because there will be differences between the cast and what the fabricator is expected to do with the cast.

    See above. It will takes some work to make them identical. However, if you have decided that a patient needs a medial heel skive, you can achieve that with both weight bearing and non weight bearing cast.

    If you can find a prefabricated device with design features that you want (e.g. intrinsic forefoot valgus post and medial heel skive) then why would you use a custom device. If you can't find what you want off the shelf, you should go custom.

    The question here is what factors from the cast are important in creating the finished device. Can those factors be measured some other way?
     
  16. efuller

    efuller MVP

    For those that come to us in pain, I don't think there is more to "it" than the comfort of relief of that pain. There is that thought out there that there is some ideal "normal" to be achieved. This idea comes from the magical thinking that capturing the foot in a certain position when you cast it, the foot will attain that position when standing on an orthotic made from that cast. When I have heard the argument that there is more to it than comfort, a lot of people making that statement believe in the ideal foot position.

    The shape of the cast will change with different casting positions. Therefore, the idea of 1:1 conformity of shape becomes problematic. The finished orthotic applies forces to the foot because of its shape. A foot casted in neutral position will tend to have a higher arch than a foot casted in a more pronated position. Labs learned long ago that to make the orthotic made from a neutral cast tolerable, they had to add medial expansion plaster to lower the arch height. A 1:1 conformity of cast to foot may not necessarily be comfortable.

    Diabetic foot ulcers are an entirely different thing than comfort. There, the goal is to reduce force/ damage at the location of the ulcer. \
    Eric
     
  17. Boots n all

    Boots n all Well-Known Member

    In this day and age of 3D LASER scanners, the clinician error or variation has been removed.
    A good example is the 3D LASER sales person who may have no clinical training probably does it best, the clinician that sees 1 client a week does it worst.

    So for me, its like anything in life, if your mentor doesnt instruct you correctly you will produce a bucket of...unusable casts.
    The same could be said for the prescription writing and the making of the device.

    Measured outcomes could be as simple as client feed back, client returning for mods or for the more complex CMT and Diabetic related clients in-shoe pressure mapping. As l said its all about the outcome, not who or how the product was created.
     
  18. Daniel Bagnall

    Daniel Bagnall Active Member

    Hi Eric,

    It is possible for orthoses to feel comfortable to wear but do not improve the patients symptoms. The opposite can also happen where a reduction in pain has occurred at the anatomical site you are trying to reduce force at, however, a secondary problem has developed elsewhere in the foot and/or lower extremity that requires an adjustment.

    1:1 conformity based on the captured shape to foot morphology is not necessarily the end goal but it could be depending on the shape you want to achieve. A 1:1 model of the foot relative to the shape that has been captured would typically be your baseline before any intrinsic changes are made otherwise taking a cast would be redundant. From this starting point changes are applied to different surface regions +/- of the foot model depending on what type of design features you want.

    Tolerance also has a lot to do with materials. For a patient that has plantar fasciopathy I might make an orthotic from a suspended cast where I invert the rearfoot and plantarflex the first ray without the need for any further intrinsic modifications and then machine this shape 1:1 using a high density foam such as 350 EVA. However, if I manufactured the same device using 4 mm polypropylene this would probably be quite uncomfortable for the patient to wear. I would probably have to alter the shape quite significantly by either adjusting or remaking the device. As a result, choice of material will also play an important part in the clinical decision making process when determining the shape of the orthotic.

    Daniel
     
    Last edited: Dec 4, 2018
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