Foot orthotic device and plantar topography of the foot

Re: orthotic device and plantar topography of the foot discussion

Got to agree.

When prescribing orthoses for my patients - whether they are casted/scanned or OTC - I do a hierarchy of importance in the following order -
1. Compliance - will they fit the shoes
2. Will they treat the primary pathomechanical plane I need to reduce tissue stress without impairing 'good' function
3. Can I facilitate function in any way - can the insole stiffen up the patients ridiculous floppy shoes, can I get the windlass moving better etc
4. Cost and durability - are these important to the patient or to the long term treatment approach

I don't really see the point of having a close topographical fit when I only really need a heel raise. However if the patient has a 'flexible foot type' with a history of symptoms related to this type of foot, then I prefer to use a closer fitting device that can be modified to do all of the above.

Phil

 

Re: orthotic device and plantar topography of the foot discussion

He's fun.

We take a pre fab shell, something like a thermoshell. Put three covers on it, 1mm eva, 1mm eva and 3mm poron and 1 mm eva / 6 mm plasterzote. Stick it in half a dozen subjects and checksee if the kinetics of gait are different between the 3 states. Null "The topcover makes no difference to the kinetic effects of an orthotic.

 

Re: orthotic device and plantar topography of the foot discussion

Too late. I'd already read it.

 

Re: orthotic device and plantar topography of the foot discussion

I am the only person in our hockey club never asked to be the captain. does that tell you anything about my reliability/organisational skills

 

Re: orthotic device and plantar topography of the foot discussion

Hi Robert,

Didn't mean that covers alter kinetics. Just that material stiffness and covers may effect percieved comfort and that this is subject specific so it will be hard to predict.

When Simon finishes his work on supination resistance testing we should hopefully know that a certain variable will alter forces by a certain amount. (I think that's right?)

Applying the Evidence based variable might not suit everyone with that pathology due to comfort though?

Thinking out loud. Happy to be told it is nonsense so I can learn.

BTW many thanks for the excellent 4 days you taught on our masters module a few months back. really enjoyed it.

Now I'm off to join the witness protection scheme...

 

Re: orthotic device and plantar topography of the foot discussion

Masters module hey? So, if your doing a masters degree, you'll probably have to do a project at the end of it- right? I might have a little job for you too young man.

 

Re: orthotic device and plantar topography of the foot discussion

If you are serious about this and have the necessary equipment to carry out such a study it would be helpful to the cause if you could look first at variation in friction co-efficients of the top-covers. So, rather than varying the thickness of the materials employed, use thin splits of materials with different friction coefficients.

Let me know if you are serious, have the time and equipment (in-shoe pressure measurement) and we can talk about methodology. That goes too for anyone who might be reading this that would like to help out and get involved with these series of investigations.

 

Re: orthotic device and plantar topography of the foot discussion

When you're playing, do you listen to your captain/ coach and try to do what they ask of you?

 

Re: orthotic device and plantar topography of the foot discussion

Fair enough.

Do the words 'brokeback mountain' appear in the job description?

 

Re: orthotic device and plantar topography of the foot discussion

No, but the words "foot orthoses" and "load/ deformation" do.

 

Re: orthotic device and plantar topography of the foot discussion

Simon,

I'm ready to start when you are so let me know what you need done? Another little human due in September so might fall off radar for a bit. But otherwise good to go.

Cheers,
Athol

 

Re: orthotic device and plantar topography of the foot discussion

Send me a pm with your phone number and we can talk about it.

 

Re: orthotic device and plantar topography of the foot discussion

Sadly, I am Mr Team Player. I'm rubbish on my own. I need the fear of letting others down to do anything.

I'm not sure I have much to offer but I would be willing to help if I can.

Robin

 

Re: orthotic device and plantar topography of the foot discussion

What you got? Kit? Patients? Enthusiasm? Can you tick yes to any of the above? Seriously, it's kind of a mission of mine to get people that I believe have potential to publish, to publication. If you are not interested tell me to 'Koff. If you are interested lets move it forward.

 

Re: orthotic device and plantar topography of the foot discussion

Do you get the coaches award at the end of the season as well?


I´ll be off then.... Taxi.

 

Re: POP casting vs Impression box casting

Robin:

There are an infinite number of shapes that could be put into someone's shoe, if you still think that orthosis shape doesn't matter much to the comfort and function of foot orthoses. To truly understand this thought experiment, don't let your imagination be constrained when you consider possible orthosis shapes.

Just imagine taking a tool box full on screwdrivers, wrenches, saws, drill bits, hammers, chisels, etc and putting one of these tools, that each have specific shapes, into your patient's shoes to see it is true that shape really doesn't matter when one is considering custom foot orthosis comfort and function.

Now when you have tried that and open up your mind to all the possible permutations of shapes that a foot orthosis could have, tell me, Robin, which shape do you think would be most comfortable and have the greatest ability to improve the function of the foot, one that has the shape of a screwdriver or a bolt or a crescent wrench, or one that is shaped to resemble the plantar surface of the foot??

 

Re: POP casting vs Impression box casting

Shape and congruence in foot orthoses are important since by having good congruence to the plantar foot a more even and uniform distribution of plantar pressure during weightbearing activities for the patient is allowed. Also, better orthosis congruity allows for a baseline shape in the orthosis by which further small modifications in orthosis shape may be used (i.e. medial heel skive) to precisely redistribute the plantar pressures with less chance of discomfort to specific areas of the foot in order to accomplish the goals of foot orthosis therapy.

 

Re: orthotic device and plantar topography of the foot discussion

With respect, I made it quite clear that the orthosis shape is critical to the outcome

If you are genuinely asking this question then, of course my answer will be one that is shaped to resemble the foot.

However, if you asked whether I thought my outcome would be significantly different with an orthosis plate that is shaped to resemble the foot or one that is essentially flat but with the correctly prescribed modifications, my answer would be that I would struggle to answer that question.

You use the "term resembled the plantar surface of the foot."

I suppose I don't really disagree that the device should resemble the plantar shape of the foot, I just don't think that closely matching it is that critical. Thus I can't see the point in spending the extra time casting.

Regards,

Robin

 

Re: orthotic device and plantar topography of the foot discussion

Robin:

If you don't cast the foot, then how do you make a thin, durable orthosis for a patient, one that may last the patient 5-10 years, such as one made from polypropylene?

 

Re: orthotic device and plantar topography of the foot discussion

Here's something that bothers me about "congruence": it doesn't tell us anything about the interface forces.

Take for example two orthosis: one is a sponge, the kind you might wash your car with, it's highly compliant. The other is a stiff 6mm polprop shell moulded from a cast of the foot. When I stand on the sponge the sponge deforms lots, my foot relatively little and congruence at the interface between foot and sponge is achieved. When I stand on the polyprop it deforms little and my foot deforms relative more and congruence is achieved. Thus both devices are congruent with the foot, yet the manner in which this congruence is achieved and moreover, the kinetics/ kinematics that occur at the foot-orthosis interface to achieve congruence are very different.

It's also a problem similar to the pushing against a wall. I can lean against a wall with my hand flat and congruent with the wall, I can push harder or with less force, my hand stays congruent regardless.

 

Re: orthotic device and plantar topography of the foot discussion

Simon:

When I use the term congruence in regard to custom foot orthoses, I am also assuming the foot orthosis is made from a relatively non-deformable material (ie. shank dependent or shank independent) such as that would commonly be used by most podiatrists for their orthoses, and not made from a sponge.

 

Re: orthotic device and plantar topography of the foot discussion

I used two extremes in my example. The point being that in the presence of some orthoses, congruence between the foot and the orthosis is achieved by relatively greater deformation of the orthosis than the foot, and in the presence of other orthoses, congruence is achieved by relatively greater deformation of the foot than the orthoses. Both result in congruence, but they do not result in the same kinetics.

Take two relatively non-deformable orthoses say 6mm polprop shells, one moulded from a full weightbearing cast of the foot without modification of the positive cast, the other from a neutral suspension cast with modifications to the positive. When we stand on both devices the foot is congruous to each. Yet in order to achieve congruous interface with the suspension casted device the foot has deformed more than on the fully weightbearing casted device. The two devices will not have the same biomechanical effect, yet they are both congruent and both stiff devices.

Further, within one orthosis there will be areas at the interface in which the foot has deformed more and areas where it has deformed less in order to achieve the congruence.

 

Re: orthotic device and plantar topography of the foot discussion

I had not though about the kinetic difference when I made a similar point about comfort earlier.

tis a tangled web

 

Re: orthotic device and plantar topography of the foot discussion

I basically agree with your analysis, Simon. However, in the clinical setting, if the clinician doesn't have a pressure analysis system available by which to assess plantar pressure at the orthosis-foot interface, how might they be able to determine the effective fit of an orthosis to the patient's clinically, if not by congruence?

Of course, there are differing levels of congruence and maybe this is a sticking point within this discussion. It all comes down to what is the tolerance level of incongruence in order for an orthosis to still be considered to be a "congruent orthosis"? Is an orthosis that gaps away from the medial arch 10 mm still a "congruent orthosis"? In my book, no. However, an orthosis that gaps away from the medial arch by 2 mm may still be considered "congruent" by many clinicians. Each clinician may have a different tolerance level for what they consider to be "congruent" in a foot orthosis, and this may also depend on which area of the foot that the "tolerance perfect congruence" is being measured.

Certainly, the ability of the plantar fat pad of the human foot to undergo significant compression deformation at relatively low magnitudes of applied compression force to effectively shield the less compressible osseous structures of the plantar foot allows for some tolerance of incongruity in a custom foot orthosis before plantar pressure levels start to cause pain or discomfort. The medial heel skive technique is just one example of where the plantar heel fat pad is used to effectively distribute more plantar pressure to the medial heel with a change in plantar heel contour from perfect congruence, and without causing plantar medial heel pain and injury. These are just a few of the unknowns of how foot orthoses can best be designed to produce not only improved comfort, but also improved function and certainly this area of orthosis-foot interface biomechanics is quite ripe for further research and mechanical analysis.

Now, off to Conwy Castle and more of the work of Longshanks......

 

For me, the question still hinges on the simple question, congruence to what?

My WB arch is about 8mm. But If I stick a 6mm arch cookie in, I can feel it during gait. So its congruent... at some point.

By the same token, my nwb neutral arch might be 14mm. But if you take a fully WB cast and give me the 8 mm insole, My foot will be in contact (congruent) with it for most of the gait cycle.

Congruent to what and when is the question which needs answering before we talk about whether it's important or not.

 

Re: orthotic device and plantar topography of the foot discussion

Worthwhile visiting Conwy Bistro - great food although it is 2 years since I was there. Great authentic Welsh dishes and some great little complementary nibbles are always given with the meals.

have a great time - Conwy is lovely place

 

Re: POP casting vs Impression box casting

Does an orthosis made from a cast made without a medial heel skive resemble the plantar contour of the foot more than an orthosis made from that same cast with a medial heel skive?

It's the adding or subracting of a few milimeters here or there that can make the difference between a successful device and an unsuccessful device. It's the finished shape that matters and there are many pathways to that shape.

Eric

 

Re: POP casting vs Impression box casting

Agreed. Anytime I talk about my own experience with the clinicial effectiveness of custom foot orthoses, I assume a baseline of a properly performed negative cast. This properly performed negative cast should produce a congruent foot orthosis.

Then when modifications are made to the positive cast such as the medial heel skive, the orthosis may be less congruent than it would have been with no modificaitons, but less congruency may produce the necessary therapeutic mechanical effect to relieve the patient's pain and make them function better during gait.

Of course, there are many pathways by which to produce a functional orthosis. However, it is important to keep in mind that consistency in the chain of events that produces a custom foot orthosis is the key since, without consistency in the orthosis process, it will be difficult for the clinician to have a basis by which to modify the orthosis in a positive fashion for the patient