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3D technology in the science of orthotics

Discussion in 'Biomechanics, Sports and Foot orthoses' started by annakostrikki, Jun 13, 2016.

  1. I would like to make some points that, I believe, Dr. Spooner has already alluded to.

    In evaluating the procedures used to produce therapeutic, comfortable prescription foot orthoses for our patients, one must be careful to not lose sight of the step-wise process involved in evaluating and producing optimum prescription foot orthoses for our patients.

    Capturing an accurate three-dimensional (3D) scan of the plantar foot, whether by plaster, foam-box, or optical scanner, is only one of many links within the chain of events which must be performed accurately, and with good clinical skill, in order to produce optimum foot orthoses for our patients. Each link within the chain of events that goes into making custom foot orthoses must be done correctly or the whole chain will become weaker and the finished custom foot orthosis will not likely perform in an optimum fashion for the patient.

    What then are these links within the chain of events that go into making optimum foot orthoses for our patients?

    1. Proper evaluation of exact anatomic structure(s) of the body of patient which is injured.
    2. Proper evaluation of gait biomechanics of patient.
    3. Proper evaluation of anatomic structure, joint ranges of motion, muscle strength and neurological function of patient.
    4. Proper evaluation of shoe gear requirement/desires of patient.
    5. Obtaining an accurate 3D representation of the plantar foot in the proper loaded configuration of the foot which will produce the best custom foot orthosis for the patient.
    6. Prescribing the proper foot orthosis design variables which will best reduce abnormal internal forces acting on injured tissues of body of patient, will best optimize gait function, will prevent other pathologies from occurring and best functionally integrate with the shoe gear of the patient.
    7. Proper post-orthosis-dispensing evaluation of patient to ensure good orthosis fit, comfort and gait biomechanics over time.
    8. Proper education of patient on expectations and limitations of foot orthoses regarding their specific pathology, their shoe gear and their activities.

    As you can see, capturing an accurate 3D image of the plantar foot is only one small link within the chain of events that will produce the optimum foot orthosis for a patient. There are many other links within the chain of events that must be done correctly before the strength within this chain can be maximized to produce the best custom foot orthosis for the patient. However, without an accurate 3D representation of the plantar foot, this chain of events will be significantly weakened and will significantly decrease the prospect that the foot orthoses will work well for the patient.

    Good discussion.:drinks
     
  2. Dennis Kiper

    Dennis Kiper Well-Known Member

    annakostrikki


    Are 3D scanners accurate data collection apparatuses? It certainly looks like its the best way, but is it in real life?



    Fuller

    Again the hard part is knowing what the patient needs. There are many theories on what the patient needs.

    When you look at the sagittal view of the scan along the plantar surface of the lateral foot there is the shape of the lateral arch. If you add an intrinsic forefoot valgus post that shape is altered and the height of the orthotic's arch is higher than foot's lateral arch.



    Spooner

    If we can deliver the required changes in the external forces acting at the foot-orthosis interface which places the loading on the injured tissue back within it's ZOOS, the body will be happy. I was lecturing at a Biomechanics Summer School this last weekend and made the point: no-one knows what the optimal arch height is of a foot orthosis- basic knowledge that we just don't have.

    Back to the OP, we can have a system which is highly accurate at capturing an image of the foot- yet that is useless if we don't know what position we need to capture that image in, nor how to manufacture the best orthoses to that image.... And that, is the current state of play.



    Drakard


    Yes 3D scanners are accurate- but foot positioning can be an issue

    I will scan in various ways, or cast and scan that if it's easier to get the shape I want to start from. Why do I sometimes cast then scan it? Because I can't manipulate the foot the way I want and scan it at the same time. I also take quite a few measures of both foot and footwear to factor in as well. I can't remember when I last took a straight neutral suspension cast.


    bagnall

    a podiatrist should be able to achieve the same outcome with a scanner in the same way they would capture the foot morphology when performing a neutral suspension cast. The majority are either positioning the foot incorrectly or resorting to semi or full weight bearing

    So yeah there does seem to be quite a bit of fiddling. This seems to be very common these days particularly with digital labs.


    Conley
    was Root trained and couldn't fathom 'exact' measurements. I still eyeball, pt prone,

    After almost 70 years of podiatric theory and traditional orthotic technology, clinical tests, still haven't resulted in a significantly improved way to minimize overpronation without partial instability secondary to inherent flaws in the customization process compared to OTC orthotics.

    The problem is, casting or digital scans cannot accurately affect the internal structure of the foot.

    What makes it even worse, is that when you have a good functioning orthotic, you cannot accurately grow that orthotic with the pt's change in Rx. (how do you capture 1.3 or 1.5 degrees? Or how do affect all 3 pom when post are in only 1 or 2 planes?)

    Minimizing overpronation with a generic orthotic is just as effective as a custom device about 50% of the time.
    I've seen statements by others wishing to advance the ability of a biomechanical Rx compared to visual acuity. As long as there is no science basis for why and how the technology affects motion, biomechanics will continue this discussion and guesswork.

    Spooner

    no-one knows what the optimal arch height is of a foot orthosis- basic knowledge that we just don't have.

    There are 2 reasons optimal arch height is unimportant:
    1- arch height is only functional at midstance (the leg is moving as well as momentum and transference of motion within the foot structure)
    2-it's no longer adequately functional when the leg moves just past vertical, vector force is released with heel off and you have unlocked the kinetic chain?result is instability with propulsion and unlocking the kinetic chain up to L5-S1. This repetitive instability will potentially open the door to biomechanical dysfunction, even if it helps the initial problem (if it helps) the orthotic were prescribed for.
     
  3. Daniel Bagnall

    Daniel Bagnall Active Member

    Hi Eric,

    I was reading through this again and I'm not sure I understand you. Let's agree that you could scan the foot NWB in any position you like. I don't think Mr T is talking about forefoot to rearfoot alignment strictly in a Root sense but more from a reference perspective so the cast or foot can be aligned in CAD to the position it was captured in. The forefoot to rearfoot alignment could be any angle depending on the position you captured the foot in NWB; not necessarily based on perceived STJ neutral position. You would use this frontal plane measurement in CAD in the same way you would when aligning the cast to vertical which would then be your starting point. Your prescription variables would then take effect from that starting point. For example, if I ask a lab to balance a cast 4-degrees inverted I would assume the lab balances the cast or foot to vertical and then inverts an additional 4-degrees. Correct me if I'm wrong but I assume labs are still balancing casts or feet to vertical initially unless the podiatrist specifies otherwise? To the best of my knowledge this has always been standard methodology in a traditional sense so in principle it shouldn't be any different in a CAD environment. Has the methodology changed or what is your view on this?

    Simon is correct in terms of using the 1st and 5th MTPJ as a reference in CAD to measure a forefoot angle. Technically it should be the lowest points which aren't necessarily the 1st and 5th MTPJ bisections. You can measure any angle you like from this reference but this isn't what I'm getting at. If you are going to use the forefoot as a reference plane in CAD then you would still need to know what the relative forefoot angle is depending on the NWB position you scanned the foot in. This can be any position you like. If you don't know what this measurement is then you will be balancing the foot/cast arbitrarily. Therefore, if the goal was to scan the foot in such a position to minimise plaster work or get the shape of the orthotic as close as possible to the end shape then the position becomes redundant if you can't align the foot/cast to this position in CAD. I would agree that forefoot to rearfoot measurement is not needed under the assumption that the heel bisection is perpendicular to the camera (not the glass plate) at the time you capture a NWB scan which is extremely difficult if not impossible.

    I understand capturing a foot is a link in the chain but I think it is a fairly important part of the process, especially if we have gone to the trouble of working what the most effective prescription variables might be to reduce pathological loading forces. My view is that if there is no consensus between the clinician and lab in regards to foot position when scanning NWB this can adversely effect our prescription variables. This is particularly relevant if the clinician has manipulated the foot segments in a certain way to achieve a particular shape in a NWB fashion.

    Thanks.
     
  4. efuller

    efuller MVP

    I would work from front to back, rather than back to front. Say you have a cast with a 2 degree forefoot varus and you have decided that you want 4 degree intrinsic forefoot valgus post. You add the forefoot post and if you do nothing else, the heel cup should look 6 degrees everted. However, you can alter the shape of the heel cup (medial heel skive) to make the cast look like it was balanced vertical. Yes, a lot of labs will have a problem understanding what you want, but you should be able to find one that does.




    Actually, one of the easier ways to get the lab to understand what you want is to manipulate the foot when casting. Take my example above. If I do nothing, I have a cast with a 2 degree forefoot varus. If I plantar flex the first ray (remove the supinatus), when I am casting, to the point where the cast has a 4 degree forefoot valgus relationship, I can just tell the lab to give me a 4 degree forefoot valgus post and don't worry about the rearfoot.

    Eric
     
  5. Eric:

    Good luck in your debate tomorrow with Drs. Phillips and Glaser. I'm sure you will do very well. Should be interesting.;):cool::eek:
     
  6. efuller

    efuller MVP

    Just finished. They tell me that it will be available on the web soon. I'm assuming from the ACFAOM website.
     
  7. Daniel Bagnall

    Daniel Bagnall Active Member

    Hi Eric,

    I need to pick your brains further on this discussion.


    You still wouldn't be working from the position you cast or scanned the foot in as a beginning point. In your example your starting point would be 2 degrees everted instead of balancing the forefoot 2 degrees inverted (as you captured the foot). Using a medial heel skive to make the cast look like it was balanced vertical is also discretionary. Wouldn't your forefoot valgus post cause the rear foot to evert 4 degrees? I don't doubt you could probably do this with a bit of tinkering but I would doubt labs would have the patience to do the same and is not really a repeatable methodology. It would also become extremely subjective. Also, a medial heel skive isn't always necessary nor should it be used to bring a cast back to vertical. If you clinically measured 2 degrees forefoot varus and captured a 2 degree forefoot varus whether that is a scan or a cast this position would still need to be your baseline reference. If you're not working from this beginning point (the position you captured the foot in) it makes capturing a position redundant. It does not make logical sense to me why a clinician would therefore manipulate the foot segments NWB to get as close as possible to the shape they want in an orthotic and not be able to ascertain what that position was in CAD.



    You can manipulate the foot anyway you like as long as there is a clinical measure. If you're not going to use the heel bisection you would still clinically need to know what the frontal plane alignment is of the forefoot depending on the position. In a sense you would need to figure out the position you would scan or capture the foot in beforehand and then figure out a way to measure the relevant forefoot to rearfoot alignment. It becomes quite tricky NWB as it would be very difficult in a lot of cases to measure as you are using two hands to influence the foot. The only method I can think of to align (or balance) a manipulated foot without measuring the forefoot angle is by reverting back to using the heel bisection as a reference i.e. you would align the heel to vertical thus giving you the relevant forefoot angle you captured as per your example. Heel bisections cannot be transferred across onto 3D (STL.) files in CAD resulting in guess work.

    Thanks.
     
  8. efuller

    efuller MVP

    Dan, are you familiar with Kevin Kirby's medial heel skive article. One of the reasons that he decided to invent it, was because he was seeing a lot of round heels and inverting or everting a circle, did not change the shape of the heel cup very much. If we decide that we want to supinate the foot more, we need to change the shape of the heel cup. There are some feet where the soft tissue inferior to the calcaneus has more of a flat appearance and if we end up everting that flat calcaneus, and we don't really want evert the STJ, then we need to modify that heel so that it does not attempt to evert the STJ. Yes, this subjective. However, if we decide that we want an intrinsic forefoot valgus post and the cast in front of us has a forefoot varus, we will have to evert the heel when we put that intrinsic forefoot valgus post in. But, what if we don't want the orthotic to have an everted heel. We can change the shape of the heel to the wedge, or lack of wedge that we want. We certainly shouldn't put the foot that we want to supinate in a valgus wedge heel cup. There is nothing magical about the shape that we captured the foot in.

    Yes, the lab work can be easier, if you manipulate the cast into the shape that you want. Some labs generically suggest to plantar flex the first ray while casting. (this creates more forefoot valgus). We can do the manipulation before or after the casting if we know what we want. However, the neutral position cast may not be the shape that we want. We can use the cast to communicate with the lab the length of the orthotic, and the lateral arch shape that we want and then we can change everything else in the lab, with proper communication.



    To do forefoot to rearfoot without a heel bisection you need to lines and to know what plane you are in. A plane is created by the most plantar part of the heel, the most plantar part of the first and fifth met heads. Now you've got 3 points. Your forefoot to rearfoot angle is in a plane that is perpendicular to the first plane and intersects the first plane at the first and fifth met heads. That's a forefoot to rearfoot angle without reference to the heel bisection. Now, you can make your heel cup shape relative to the first plane. If you want no inversion, or eversion, you pick the center point of the heel and as you go medially and laterally (in a plane that is perpendicular to the long axis of the foot) at each mm, medially and laterally, from the center point the heel cup the heel cup is the same height off of the first plane. If you want a varus wedge heel cup, the medial heights will be greater than the lateral heel heights.

    Hope this helps.
    Eric
     
  9. Daniel Bagnall

    Daniel Bagnall Active Member

    Hi Eric,

    Thank you for clearing this up. Essentially the method you are using to provide reference to your laboratory is similar to me. We are both clearly defining a reference measurement prior to manufacture of orthoses.

    If you don't mind I have two final questions:

    Firstly, you have made it clear that you provide a reference to your laboratory so that a 3D scan maybe aligned correctly prior to manufacture. Do you believe that sending a reference measurement is a pre-requisite for a podiatrist sending 3D scan information?

    Secondly, you have stated that there is nothing magical about the shape we have captured the foot in. I find the post by Mr. T to be quite telling when looking at the wireframe view of the difference between positioning, just from looking at the image it's very obvious that the end orthotic will have very little resemblance to the 3D scan. Virtually everything will be subjective. When I manufacture an orthotic the anatomy of the foot is machined with reference to a NWB scan. I make relevant adjustment to the wireframe mesh of the negative to give the force correction required. This may be a heel skive, medial wedging, intrinsic valgus wedging, etc. However these additions/subtractions to the orthotic negative are all based around a 3D scan that is measured and has a defined starting alignment in multiple planes which gives rise to an orthotic negative that closely resembles the foot shape prior to these additions/subtractions.

    So essence I'm trying to ask you the following question...Do you believe capturing a scan utilising a methodology that allows for good clinic -> lab correlation and in essence results in a higher degree of correlation at the foot-orthotic interface between intial 3D scan and final orthotic is better for quantifying changes to the orthotic prescription? Because to me this makes logical sense and is a vital element to orthotic manufacture.

    Thanks.
     
  10. CraigT

    CraigT Well-Known Member

    Hello All
    Just catching up on this discussion- lots of good points.
    Some quick questions-
    What software are you using for design of foot orthoses?
    What options are there currently for allowing the design of true custom foot orthoses? ie- different materials and truly flexible design parameters... Delcam has been bought out by Autodesk and they have killed Orthomodel which I have been using for the past 5 or so years...
    Any thoughts appreciated.
     
  11. Craig Payne

    Craig Payne Moderator

    Articles:
    8
    http://www.lasercamorthotics.com.au/
     
  12. Lawrence Bevan

    Lawrence Bevan Active Member

    Craig

    what do mean killed? they've discontinued the selling/supporting software?
     
  13. Craig Payne

    Craig Payne Moderator

    Articles:
    8
    yep; they dropping the product and all support. I think from March next yr (but stand to be corrected on that one)
     
  14. Lawrence Bevan

    Lawrence Bevan Active Member

    wow I'd imagine all those who've made a sizeable investment will be quite annoyed!
     
  15. Daniel Bagnall

    Daniel Bagnall Active Member

    Hi Craig,

    I would also highly recommend the Lasercam creation suite. I've been using Lasercam to model and manufacture custom orthoses in-house and commercially (on a very small scale) and I haven't looked back.

    Thanks.
     
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