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Digital Imaging of the CAST, not foot

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Ann PT, Sep 28, 2010.

  1. Ann PT

    Ann PT Active Member

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    Hi everyone,

    I recently learned the lab I have used for many years switched to a digital imaging system (they called it "Systems Manager" and said the specific programming is determined by each lab individually) a year ago which scans my casts to "produce a 3D image of the cast" but does not evaluate the forefoot. I learned that the system does not evaluate the forefoot when I called after seeing their new prescription form and the option of "forefoot posting according to cast" was no longer available.

    I spoke with the lab today and did not get satisfactory answers on how this system works and the differences between balancing a cast to neutral by hand vs. using a digital image of the cast. I was told that unless I told them a specific amount of degrees to post the forefoot, they would just post it at zero. If I told them to balance the cast 2 degrees inverted, they would post the forefoot at 2 degrees. To balance a cast to vertical I believe that involves a forefoot correction (assuming the heel bisection isn't vertical to begin with). If they are no longer using any forefoot correction when balancing to neutral then what are they doing? Is the end result just a shell that models the patient's foot with the emphasis on arch contour? Then they add whatever extrinsic hindfoot post and accessories I ask for?

    I have read various threads on Podiatry Arena under the digital imaging tag and negative cast production tag but most of the imaging and scanners that are referenced are imaging and scans of the foot, not the cast.

    Can anyone help me understand this system and what is happening in the forefoot? Did I overlook threads that speak about digital imaging of casts as opposed to feet? I hope to speak to someone else at the lab tomorrow to get more information but I thought I'd put the question out there on the forum now to help me prepare for that conversation.

    Thank you for any insight and help you can give!

  2. Jeff Root

    Jeff Root Well-Known Member


    I can't comment on this system, but a number of CAD/CAM systems do allow the lab to scan the negative cast and then position the balance platform in order to intrinsically correct any forefoot varus or valgus (ff inversion or eversion) just as one can do with plaster of Paris. The cast can be corrected with the heel inverted, vertical or everted. This should not be a problem for any good manufacturing system since most are designed to replicate conventional orthotic manufacturing techniques.

  3. Phil Wells

    Phil Wells Active Member


    The issue may be one of the CAD technician relying too much on the digital scan i.e. not assessing the cast for forefoot to rearfoot alignment etc. If they use a laser based scanner it will not be able to transfer the heel bisection lines to the digital image. this means that it can be difficult to find a rearfoot reference from which to assess from.
    You could always ask them to assess the cast manually and then this would be the forefoot Rx that they are asking for.

  4. Ann PT

    Ann PT Active Member

    Thanks Jeff and Phil for your input. I spoke with the VP of the lab today and apparently a new system designed in-house was put into use a year ago by a different VP. With this system, they measure the arch height, length, and width of the cast and then come up with a positive mold from that information. Apparently they looked at their "library" of positive molds and prescription information over the years and came up with the top 10% of combinations and used this information to come up with thousands of prefabricated positive molds. They try to match the scan of my cast to one of these prefabs. However, they do not look at the forefoot at all. The digital scan doesn't look at it and the technicians don't look at it on the cast. Essentially they do not balance the cast to neutral and instead just look at arch height. They will balance a cast inverted a designated number of degrees if asked. Is this making any sense? It sounds more like a contoured arch support with extrinsic hindfoot posting added versus a balanced device. I need to think about this (just got off the phone with them). Any thoughts?
  5. David Smith

    David Smith Well-Known Member

    :morning: "Any thoughts?"

    Yes, send your casts to Phil and get a proper job done

  6. Jeff Root

    Jeff Root Well-Known Member

    Ann, any lab that is using a library system has a moral and potentially a legal obligation to let the practitioner know in advance that they are using a library system. Here in the U.S., insurance coding is dependent on knowing how the device was manufactured. A true, custom manufactured functional orthosis made from a patient's own foot model is coded differently for billing purposes than a device made from a library of positive models, digital mold files, pre-made orthotic shells, or digital shell files.

    If audited, the insurance company could retroactively deny claims for improper billing and if the practitioner knows it was a library device, they could be guilty of insurance fraud. I am a strong believer in truth in advertising. Some labs are very clear and ethical about their use of library systems while others are not. This is a huge Pandora's Box issue!

    From a technical and clinical perspective, if you're asking for intrinsic forefoot correction and you're not getting what you ordered, I would have an issue with that if I were you.

  7. Ann PT

    Ann PT Active Member

    Thanks Jeff. I do have a major issue with what has happened and that it happened without my knowledge. I told the VP at the Lab my thoughts today. As for insurance billing, the facility I work for does not bill insurance companies for orthotics. They are a private pay item. They do bill the insurance company for the evaluation. Thanks for the information. I will look into whether there are any issues around the evaluation charge.

    As for the forefoot problem, I was told they will look into how they can take this into account with their system and get back to me by the end of the week. I definitely am dissatisfied. This is the same lab that had the strike last year which I was not told about in a timely fashion either. At the time I switched labs but switched back because I wasn't thrilled with the lab I switched to. For over fifteen years I've sent 99% of my work to the same lab and been very happy, but the last year has been rough!

    Thanks everyone for your thoughts! I welcome any more!
  8. Vote with your feet: find a new lab if you are not happy. A custom device is just that, not a library edition.
  9. As far as I'm concerned, an orthosis lab that uses a "library system" for their customers' orthoses is simply giving their customers pre-made orthoses, but charging a custom foot orthosis price. Ethical? Only if the customer is informed before-hand of the limitations of their system.

    There are plenty of foot orthosis labs that will never do library orthoses......it's not always about doing the cheapest product....it's all about doing a quality product for your customers.
  10. Jeff Root

    Jeff Root Well-Known Member


    I'm not here to criticize other labs but I am interested in promoting orthotic education and sound orthotic manufacturing practices. We use a non-proprietary orthotic manufacturing system that enables our lab to control a variety of variables including but not limited to the heel cup depth, heel width, medial and lateral fat pad expansion, arch height and importantly, the amount of intrinsic cast correction (balancing) applied to the scan of the negative cast.

    I have posted a screen shot below that shows the balance platform (red line), the angle of forefoot to the rearfoot as measured by the system (3.7 degrees of ff varus in this case), and the medial and lateral expansions at two frontal plane sections. We can invert or evert the balance platform or correct it perpendicular to the heel as in this case. A system like this allows us to make computer based cast modifications in much the same way that we do when using plaster-of-Paris.

    I hope this gives you a better idea of how CAD/CAM can be used.


    Attached Files:

  12. Jeff Root

    Jeff Root Well-Known Member


    We bisect the heel of the negative cast as usual, being sure to extend it inferiorly as much as possible. We then cut the upper aspect of the negative cast at the outside tangent so the laser can "see" the inner, plantar surface of the cast. We use a protractor to position the heel inverted, vertical or everted as necessary during the scanning process. We can also alter the frontal plane position of the cast in the system, but we need to know how it was scanned in order to determine the effect of inverting or everting in the image.

    After we cut down the negative cast, we are dealing with a shorter heel bisection segment and it is drawn on the rounded, posterior heel surface. As a result, it is very important for the technicians to view it from the same angle in which it was applied, otherwise there is a greater chance of error due to optical illusion. If you adduct or abduct the negative cast, the residual heel bisection can look very different. We bisect the heel with the lateral border of the foot perpendicular the technician. In the case of an adducted forefoot, the posterior half of the lateral border of the cast is perpendicular to the technician. It is very important for us to have consistency in how the bisection is viewed. We train our technicians to keep both eyes open because if one tech uses both eyes and another closes one eye, the angle of view changes. I have found this can easily produce a one or two degree error.

  13. Craig Payne

    Craig Payne Moderator

    I have no problem with library systems provided that:
    1. The customer knows they are usuing it
    2. The library system is extensive enough
    3. They do charge less for the library device.

    I have spent time looking at several of these systems, have visited with several labs that do it and we do discuss them at the Boot Camp. If the library system is extensive enough and its used properly, then you will get exactly the same device if the plaster cast was filled, modfiied and plastic molded ... you just get it with those steps cut out and should be charged accordingly.
  14. gaittec

    gaittec Active Member

    As Jeff's post demonstrates, the bisection of the heel and balancing of the fore-foot is more dependent on the lab practice and the orthotic software available than whether it is from CAD/CAM or plaster.

    Also, it is important to differentiate between a library system and a template library. In the first, the shell is chosen; and, basically unaltered from an extensive selection. In the latter, a template is used to select the type of device to make;and, then that template is modified in the software, to meet the custom needs of a patient. The template has only served to save several design steps in acquiring the type of shell needed.

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