Welcome to the Podiatry Arena forums

You are currently viewing our podiatry forum as a guest which gives you limited access to view all podiatry discussions and access our other features. By joining our free global community of Podiatrists and other interested foot health care professionals you will have access to post podiatry topics (answer and ask questions), communicate privately with other members, upload content, view attachments, receive a weekly email update of new discussions, access other special features. Registered users do not get displayed the advertisements in posted messages. Registration is fast, simple and absolutely free so please, join our global Podiatry community today!

  1. Have you considered the Clinical Biomechanics Boot Camp Online, for taking it to the next level? See here for more.
    Dismiss Notice
Dismiss Notice
Have you considered the Clinical Biomechanics Boot Camp Online, for taking it to the next level? See here for more.
Dismiss Notice
Have you liked us on Facebook to get our updates? Please do. Click here for our Facebook page.
Dismiss Notice
Do you get the weekly newsletter that Podiatry Arena sends out to update everybody? If not, click here to organise this.

The Method of Casting is Not Important?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by drsha, Sep 12, 2010.

  1. Visual example. Consider this arm. Held non weight bearing at the desired angle to the table
    [​IMG]

    Say the hand is 5 cm from the table

    So would we expect that if we cast the arm in that position, still non WB, and build up under the hand end by 5cm this would hold the arm at that position when weight was placed on it?

    [​IMG]

    It seems not. Because there is lots of soft tissue at one end of the arm and not the other.

    In fact, when weight is placed on it, the arm can be in the desired position with no "orthotic" at all

    [​IMG]

    The foot is similar. The soft tissue surface does not follow the bony anatomy exactly. Thus there is considerable "slop" between the orthotic and the skeleton, even if the orthotic is in contact with the whole foot...
     
  2. N.Smith

    N.Smith Active Member

    I understand what you're saying but the fatty tissue explination your using and the inconsistancies in the shape it produces, is the exact reason I would like debate on this method. Like I said before: The positive needs no modifications because all corrections are intrinsic to the positive, so the cast taken is only as good as the users understanding of where they want the foot to be and how much force they want to apply to it.

    Thickness of fatty tissue doesn't matter, size or shape along with differences in L/L (greater force on longer leg) and shoe shank. The only problem is the mobility of the foot. But I think this is a good thing, as the foot will only move a certain amount so it's very hard for a clinician to judge shape, especially MLA height. Some will have a lot of mobility and others very little. I've had great success with very rigid feet for this very reason.

    Before I get slammed for trying to preach a different method, I am still learning what this device can and can't do (12 years on), but I do believe that people, like yourself and other experts in the field, would be the best at testing it's merit of whether it's a tool that can give the user the outcomes (with orthotic therapy) they require. I will be in Orlando Florida 18-20 November Pedorthics Conference Booth 601.
    I hope some of you can visit!

    Cheers

    Neil
     
  3. Phil Wells

    Phil Wells Active Member

    Neil

    I understand what you are saying but I wonder how a one off snapshot of the foot and the orthotic shell it produces can in reality reflect the variability of ORF.
    We are pretty sure that an FFO doesn't hold the foot in a fixed position, consequently the foot will slide,roll etc over the surface of the FFO.
    Bearing this in mind, where does your concept really differ from the rest of us?

    Phil
     
  4. I'd say closer to 100% sure!

    Well, we know don't we. Short of bolting the shell to the skeleton it can't!
     
  5. Jeff Root

    Jeff Root Well-Known Member

    A little google search of pfa booth 601 and we find The Foot Alignment Clinic and this system at http://www.footalignmentclinic.com.au/index-2.html for those who want more information.
     
  6. Oh it's the FAS machine!!

    we've trodden these grapes before. Clever idea, clever system. But the fact that one has controlled the foot better does not alter the effect of the insole!

    As I said in the other thread, for me this solves a non existent problem!
     
  7. N.Smith

    N.Smith Active Member

    A little google search of pfa booth 601 and we find The Foot Alignment Clinic and this system

    Ill have to have a look at the site. It not promoting the clinic, just the device.

    I understand what you are saying but I wonder how a one off snapshot of the foot and the orthotic shell it produces can in reality reflect the variability of ORF.
    We are pretty sure that an FFO doesn't hold the foot in a fixed position, consequently the foot will slide,roll etc over the surface of the FFO.
    Bearing this in mind, where does your concept really differ from the rest of us?

    Phil


    I totally get what you're saying. It differs because you are applying Vertical, Translational and rotational forces to the R/F, Mid/F and F/F whilst the patient is standing, with shoe shank, angle and base of gait and L/L taken into account. The mould produced is the orthoses template so, no modifications to the positive. When you cast and align this way you can feel the supination or pronation resistance and determine how much force you want to apply, how much the foot moves when doing it and see the osseous, structural and functional changes as you apply force to the feet. Basically you can only apply force and shape the foot as much as it will allow.

    It's up to the user to determine how much force they apply to the 3 segments, and where. So you can pronate or supinate the foot and raise and tilt the heel, while taking the cast.

    The 2 studies done by Craig Payne show it has more repeatability and less variability than Non-WB casting and has greater comfort than orthoses made Non-WB.

    I know the the foot rolls over the orthoses as the person moves through gait and this would only be a problem if the shape of the job wasn't right and applied too much or not enough force or pressure to particular areas, which tends to be the problem of modifying ie: how high should the MLA be, lateral expansion, Kirby Skive (how much), Blakes inv. (how much) areas that need deflecting, length of orthoses, subluxed bones and overall shape.

    Because the device has so many movements to apply force and pressure to the foot it can take a person, new to the system, a while to get there head around what they're doing, which takes me back to any criticisms people may have.
    It's up to the practitioner to determine what position they want the feet in, not some lab technician or computer model.

    There are many feet out there that can be helped and sorted (if they need orthoses) with an OTC or even a bit of padding. In these cases, if it aint broke, why fix it! It's the tricky ones that this device adresses and less hassel with easy ones.

    Another important thing to realize is that, because the process is done in real time, the patient can be asked questions about how they feel during the casting.
    I tend to think pressure is fine, pain is bad.

    I understand the patient is static when cast but they're still standing and bearing weight. This is a variable as there are a lot of differences between static stance, walking and running but there are far less variables doing it this way than modifying a NON-WB or semi-WB cast.

    This week I'll be taking photos of the movements, casting process, pre and post orthoses fit. If you want a look, give me your email and I'll flick it across.

    I've always been an open book with this device and the manufacture of the jobs so I'm open to critcism because it helps me to understand what I'm doing. Unlike a lot of other methods and manufacturing protocals where it's very secretive.

    Cheers

    Neil :drinks
     
  8. Brahim

    Brahim Member

    Is it fair to state that the benchmark by which the accuracy of all morphological capture tools, including plaster and digital casting, is the direct clinical set of measures taken in a bio-mechanical examination? If so, why bother casting at all? What other information is stored in the cast that is needed to build an orthosis?
     
  9. Graham

    Graham RIP

    NO! Too much inter and intra errors in "measurements" for them to be of any use, plus you have to ask yourself why are you doing these measurements? Does the measurement influence your orthotic Rx and if so why?

    The orthotic is akin to the frame of a pair of glasses. It carries the prescription. The cast allows for the device to "fit" the individual.
     
  10. efuller

    efuller MVP

    There are some measures that are helpful in determining the prescription. Others are pretty much useless and unrepeatable. Well, some people claim that they are repeatable, but certainly not across clinicians. (Forefoot to rearfoot relationship)

    That is an interesting question. What information is stored in the cast? I'd say the sagittal plane contour of the lateral plantar arch when the foot is partially loaded. The length and width of the foot. If marked on the foot, the location of the plantar fascia (It can vary from one foot to another within the same person.) If marked on the foot prior to casting, the location of lesions that need to be accomodated. If casted with the forefoot fully abducted, there is a rough measure of the amount of metatarsus/forefoot adductus. Anyone else think of any others?

    Things that are not captured in the cast. Comfortable medial arch height. A non weight bearing cast cannot predict the amount of spread of the fat pad of the heel. The location of the STJ axis which determines the amount of medial/lateral heel skive to be done.

    What say you?

    Eric
     
  11. Semi WB in foam can ;)

    average 71% of total expansion on first 25% of body mass.
     
  12. OK Robeer, you've said this so many times now that's it's probably time to explore it;). So, we have a study that showed that 71% of fat pad expansion occurred with 25% of body weight, that's still a further 29% unaccounted for. What if the last 10% of expansion occurs with the last 10% of body weight loading onto the foot? Moreover, during dynamic function the force applied to the heel will be greater than body weight; walking approximately 1.5 times body weight; running approximately 2.5 times body weight (rate of loading will come into play too).

    Do we know what proportion of body weight is achieved when pushing down on the knee during a semi-weightbearing cast (you could measure this with a hand held dynamometer- you could bastardise something like this: http://cgi.ebay.co.uk/Hand-Grip-For...essories_ET&hash=item2eb0d115e0#ht_1803wt_997 or maybe just place a set of bathroom scales beneath the casting box as long as you could get a measure of peak force)? Now, you being a big boy and all, it'll be pretty easy to achieve a force equivalent to 25% standing body weight in a youngling, but do you achieve 25% body weight in an 18+ stone rugby player? How much force can you apply to the knee with one hand, while still maintaining the foot in the "desired" position with the other?

    What is the stiffness of the casting foam? How thick is the block of foam in the casting box? In other words, how much load can we apply before the foot will hit the bottom of the box? How is this related to the contact area of the foot, in other words a smaller foot will exert a higher pressure for a given load upon the foam (another simple experiment). Less important, since the foam can still be compressed laterally, even when the foam directly beneath foot is maximally compressed, but interesting none-the-less.

    Have we any studies which show the differences in heel width obtained from a semi-weightbearing foam box cast to those that occur in-vivo in standing, walking or running? Nice easy little study to get you moving along with scientific publication. Measure your foam box obtained positives against static weight-bearing heel widths. Piece of cake. Up for it?

    Yet to put all of this into perspective, what's the average heel expansion on weight-bearing? 3mm, 4mm...?
     
  13. The data tables are in:-

    Vern L. Houston, Gangming Luo, Carl P. Mason, Martin Mussman, Maryanne Garbarini, and Aaron C. Beattie
    Changes in Male Foot Shape and Size with Weightbearing
    J Am Podiatr Med Assoc 2006 96: 330-343.

    Its about 4mm ;). Massive.

    Point taken with the foam resistance. And, of course, an average is made of points either side and some to none on the mean.

    Obviously I'm not saying that I can make 25% body mass accurately. I can't judge to, say, the nearest 5lbs pressure. And we can't say what the change would be if I could.

    What I will say, with some confidence but no data, is that semi wb is more wb than non wb, and that wb causes the fat pad under the foot to spread.
     
Loading...

Share This Page