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Background: Existing techniques of taking foot impressions for producing foot orthoses are static, while walking is a dynamic process. Objectives: The aim of the study was to evaluate a newly developed dynamic casting method for foot orthoses in comparison with static casts.
Study Design: Double-blind, randomized two-period cross-over trial. Methods: Twelve healthy volunteers (six women, six men) were randomly assigned within gender to two groups. The first group wore orthoses made from static casts for two weeks and then orthoses made from dynamic casts for two weeks, and the second group vice versa. The orthoses were worn during work in sports shoes. The outcome measure was coefficient of variation (CV, defined as standard deviation/mean) over seven measurement spots on each foot.
Results: Foot orthoses produced by a dynamic casting system redistributed plantar pressure (reduced CV) more effectively in the first period on both feet. In the second period, carry-over effect and/or treatment wearing off was observed.
Conclusion: The dynamic casting procedure is simple, low-cost and appears promising, but further research is needed to introduce it into clinical practice.
Re: 'Dynamic' casting leads to better foot orthoses
If our only clinical aim when issuing foot orthoses was to redistribute plantar pressure more effectively (however that is defined) in asymptomatic patients whilst they are at work then I suppose it may be time to get excited about dynamic casting...but as it isn't... I'm not.
Re: 'Dynamic' casting leads to better foot orthoses
I often wonder the same thing. Why do so many studies try to measure the function of foot orthotics with plantar pressures when none of us are trying to change plantar pressures with functional foot orthotics clinically?
I can't get the paper, what do they mean by dynamic casting? Its not what I think it might be is it?
Re: 'Dynamic' casting leads to better foot orthoses
Not sure exactly what they mean, as I can't get the full text either. I guess whether this sort of negative model production gets ones pecker up will come back to the value one places on kinematics/visual alignment.
The concept of kinetically quantifiable casting is more exciting in my opinion.
Re: 'Dynamic' casting leads to better foot orthoses
Outcome of coefficient of variation??? We don't even know if that is a good thing to reduce. A plantar pressure could be very high in a particular location. Patient symptoms could get worse if that high pressure didn't change.
Re: 'Dynamic' casting leads to better foot orthoses
Quote:
Originally Posted by davidh
Twelve healthy volunteers?
Quote:
Originally Posted by Robertisaacs
I know! Where on earth did they find 12 healthy volunteers?!
12 is not an unusual sample size in the biomechanics literature. If you are doing a between groups comparison you need a bigger sample size. If you are doing a within groups/subject comparison (ie each subject acts as their own control)(which is what this study did), you can get away with a smaller sample size, but 12 would be close to the lower end of what is acceptable. Need to look closer at the subject subject responses - if the response was systematic, then I have no problem with 12.
The "healthy" bit could be problematic, as there is no indication that the subjects even needed foot orthoses..... ie I hope they report something like the FPI, so we can make a judgement on the foot types.
I have not had a chance to look at the full paper yet.
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Re: 'Dynamic' casting leads to better foot orthoses
Quote:
Originally Posted by Craig Payne
12 is not an unusual sample size in the biomechanics literature. If you are doing a between groups comparison you need a bigger sample size. If you are doing a within groups/subject comparison (ie each subject acts as their own control)(which is what this study did), you can get away with a smaller sample size, but 12 would be close to the lower end of what is acceptable. Need to look closer at the subject subject responses - if the response was systematic, then I have no problem with 12.
The "healthy" bit could be problematic, as there is no indication that the subjects even needed foot orthoses..... ie I hope they report something like the FPI, so we can make a judgement on the foot types.
I have not had a chance to look at the full paper yet.
Beat me to it re: sample size. Regarding fpi and foot types- how does that predict whether or not a subject needs an orthosis?
Re: 'Dynamic' casting leads to better foot orthoses
Quote:
Originally Posted by Robertisaacs
I know! Where on earth did they find 12 healthy volunteers?!
I'd love to know more about the dynamic casting. I'm getting a sniff of a formthotics type system here. Could be wrong.
There is a system capable of obtaining dynamic digital scans of the foot. I can't remember the name and I'm about to board a plane. Phil wells will tell you what it's called.
Re: 'Dynamic' casting leads to better foot orthoses
There is a 3D volumetric scanner from Lion Systems in Luxembourg- uses scattered light at (I believe) 30fps.
So the question would be- what would you actually use it for?
Do you choose a particular frame to base your orthosis on? Would you combine information from multiple images? What information would you use?
Just thinking out aloud...
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Podiatrist ASPETAR-
Qatar Orthopaedic and Sports Medicine Hospital
Doha
QATAR http://www.aspetar.com/
Re: 'Dynamic' casting leads to better foot orthoses
Depends on what you do at work, but if these healthy volunteers had desk based jobs then it would occur to me that a static, semi weight bearing plantar capture of the foot may well be preferable if they are looking at plantar pressure redistribution
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Re: 'Dynamic' casting leads to better foot orthoses
Finally got the paper. Here is what they did for the dynamic casting:
Quote:
For dynamic casting, special shoes were made in two sizes (Figure 2). They had room for a 10-mm layer of plasticine. Hardness of the plasticine was chosen on the basis of an unpublished pilot study by the same authors, in which subjects walked using plasticine of three different hardness and the one with which impressions of medium depth were obtained was found to be the most appropriate. Subjects walked with the special shoes for 10 metres, so that the dynamic foot impression was obtained (Figure 3). Plasticine was then put into a model for foot orthoses and filled with plaster of Paris to get the model.All casts were minimally modified in the area of transversal and longitudinal arch by the same orthotist. All foot orthoses were made from the same material: 2 mm of viola on top, 6 mm of polyphorm beneath it, and 5 mm of thermo cork at the bottom. In the area of the longitudinal arch, 10 mm of thermo cork was added. Layers were glued together and vacuumed on the model.
__________________ Craig Payne
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Re: 'Dynamic' casting leads to better foot orthoses
Quote:
Originally Posted by Craig Payne
Finally got the paper. Here is what they did for the dynamic casting:
I really don´t know what to say. But why was this paper published and why did it even need to be written.
1 step forward 10 steps back
EDIT :
Read the full text thank you Sir - still really don´t get why but anyway.
Quote:
Conclusion
In the studied healthy subjects, the redistribution of plantar pressures tended to be better with foot orthoses made from dynamic measurement than with those made from static measurements, but the study limitations do not permit a definite conclusion.
Anyone care to explain this to me
we have healthy patients and the plantar pressure changes when we introduce a device - ok not problems with this
But we conclude that the redistribution is better - how can they be if the patient is healthy or symptom free
Re: 'Dynamic' casting leads to better foot orthoses
Quote:
Originally Posted by Simon Spooner
The "cast" method captures the lowest heights from the supporting surface that each contact point of the foot achieves. Probably very comfortable.
Its bizarre; the casting method is really going to capture the foot in its worse compensated position!
__________________ Craig Payne
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Re: 'Dynamic' casting leads to better foot orthoses
Quote:
Originally Posted by Craig Payne
Its bizarre; the casting method is really going to capture the foot in its worse compensated position!
Like I said, probably very comfortable because it's only going to attempt to arrest motion at the end of range of the motion envelope; its not attempting to change anything in terms of kinematics.
Re: 'Dynamic' casting leads to better foot orthoses
My experience from seeing quite a few approaches from around the world is that the aim of practitioners 'prescribing' orthoses is incredibly variable. Having said that, there must be some apparent benefit or they wouldn't keep making them (or so I would hope).
Pressure redistribution is certainly one aim that is recurrent...
__________________
Craig Tanner
Podiatrist ASPETAR-
Qatar Orthopaedic and Sports Medicine Hospital
Doha
QATAR http://www.aspetar.com/
Re: 'Dynamic' casting leads to better foot orthoses
Quote:
The outcome measure was coefficient of variation (CV, defined as standard deviation/mean) over seven measurement spots on each foot.
Results: Foot orthoses produced by a dynamic casting system redistributed plantar pressure (reduced CV) more effectively in the first period on both feet. In the second period, carry-over effect and/or treatment wearing off was observed.
The only reason that you would choose coefficient of variation over peak plantar pressure or even mean plantar pressure was that those other measures were not significant. I don't see how this variable proves that pressure "redistribution" is better.
I would hope the casting method would reduce peak plantar pressure. Was that even reported? If it didn't reduce peak pressure better than a foam box then it is worse than a foam box because of the degree of dificulty
Eric
Re: 'Dynamic' casting leads to better foot orthoses
Quote:
Like I said, probably very comfortable because it's only going to attempt to arrest motion at the end of range of the motion envelope; its not attempting to change anything in terms of kinematics.
Agreed on what they aim. I'm not convinced that's what they will get though.
I wonder. If you had someone whose COP is medial of the midline, would that mean the medial area on the heel and forefoot would be more squashed and give you a lateral wedge?
'Dynamic' casting leads to better foot orthoses
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