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Fascia Accommodation

Discussion in 'Biomechanics, Sports and Foot orthoses' started by sspod2001, Oct 22, 2012.

  1. sspod2001

    sspod2001 Active Member


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    Hi Guys,

    I have recently began working in Ontario and the clinic i'm at uses 3 labs to manufacture their custom orthotics, the thing that i'm questioning is when I prescribe Orthotics with fascia accommodation these labs are grinding clean through the shell!

    This seems to be effecting the strength and integrity of the MLA of the device even when they provide arch fill. My understanding is that a fascia accommodation should be ground out but not completely through the shell, am I wrong? is there a new technique that i've missed?

    thanks
    Steve
     
  2. efuller

    efuller MVP

    Grinding all the way through the shell is a new one for me. It does sounds like it would be easy to get potential problems in terms of shell breakage or irritation at the edge of the hole. I've seen either plaster or cork added to the positive cast so that when the plastic is pressed there is an accommodation in the finished orthotic that leaves the orthotic full thickness. This accommodation will tend to make the device even more rigid for a given thickness of material. Of course, I've got no problem with grinding part way through the shell.

    Eric
     
  3. sspod2001

    sspod2001 Active Member

    This is exactly what I was thinking Eric, thought I was going crazy.

    And your absolutely right from what i've seen the highest point of the MLA on the device seems to depress leaving a nasty looking crease in the material which would feel awful, not to mention provide very little support.

    cheers
     
  4. Talk to your labs, tell them what you want. Personally, I don't find the need for fascial accommodations too frequently. I'm not a big fan of putting an addition onto the positive cast as this creates a rib in the device leading to a longitudinal stress riser and increased stiffness in a highly specific area of the shell (never done an FEA analysis of this- perhaps someone should?). Obviously, when grinding the addition into the shell, the depth is limited by the thickness of the shell material. I will often use a 3 mm thick high density EVA top-cover, which allows me to grind 3mm of material away without penetrating the shell at all (I press the shell with an offset sheet between the cast and the poly-prop to accommodate this). If a deeper grind is required, then obviously you can then go into the shell too.
     
  5. sspod2001

    sspod2001 Active Member

    Grinding the accommodation into eva sounds interesting does the 3mm eva plus the shell fit to footwear well Simon?
    I see your point about the increased stiffness with the addition of the longitudinal ridge, maybe the shell thickness could be reduced if indeed the rigidity increases (following your FEA analysis :)

    cheers
     
  6. Don't have too many problems with shoe fitting; the vast majority of my devices are constructed with a relatively thick EVA top-cover, but then I'll typically use a 3-4mm polypropylene in concert. I like this approach because it gives me the "best of both worlds".
     
  7. Mart

    Mart Well-Known Member

    In line with Simons suggestion; in those with need for plantar aponeurosis accomodation simply use EVA without any rigid thermoplastic sheet - the stiffness of the device can be tuned according to material durameter and shape of its space filling volume.

    I have had success doing this for many years in those with distal chronic plantar fasciosis or plantar fibromatosis when it seems important to avoid compression from ground reaction force against degenerated zone. I find intolerance to foot orthoses use a common finding in those patients who I see when this has not been thought about.

    hope that helps

    Cheers

    Martin


    Foot and Ankle Clinic
    1365 Grant Ave.
    Winnipeg Manitoba R3M 1Z8
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  8. RobinP

    RobinP Well-Known Member

    If I know that a plantar fascia accommodation is required, I will probably opt for an EVA device that the groove can be ground into after milling(greater accuracy of placement than adding it into the cast - in my opinion). Leave the device thickness fairly substantial under the MLA and at the fitting stage increase the stiffness as required by making the EVA thicker or thinner.

    If I find that I require a PF groove after, I will add a 3mm LD EVA top cover and create groove or in some cases, I have ground out the black rubber on a piece of Spenco in order that when it is mounted on the shell, the groove is correctly positioned.

    Definitely would not cut through the shell although in principle, if the MLA were infilled under the shell, It probably wouldn't be such a big deal so long as the EVA/polyprop interphase were smooth enough
     
  9. Mart

    Mart Well-Known Member

    I agree with Robin regarding milling the groove at fitting stage; not only because of error in trying position the groove whilst capturing foot topology by whatever method but also the arbitary nature of how deep to cut - I find best results by doing this empirically and tuning volumen at foot orthoses fit. A counfounding factor I have found is interpreting pain to palpation. Bear in mind that the medial plantar nerve tends to be located within compression distance of the plantar aponeurosis and many people with pain to palpation may simply reporting pain associated with nerve compression. Gold standard is to use US to examin for degenerated zones and if you have a US machine at hand map the zones if ambiguous for palpable location.

    Cheers

    Martin

    Foot and Ankle Clinic
    1365 Grant Ave.
    Winnipeg Manitoba R3M 1Z8
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
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