Is the upper surface of the foot orthosis the required shape

Funny thing if you think world wide orthotic production what would the % of impressions be taken using the Root technique as described by the authors

My guess probably way less than 5% of all devices made

 

Mike,

A large percentage of the devices made in the U.S. use the Root casting technique or very a similarly technique utilizing non-weightbearing casting and positioning the STJ, MTJ, ankle joint and other joints in an intended position. I suspect most of those on the PA have at least experimented with the technique. Regardless of the percentage that use the technique world wide, I'm not sure what that has to do with anything I said. However, perhaps more practitioners world wide should be using it based on the benefits I described since contour of the superior surface and the stiffness of the orthotic device are probably the two most critical aspects of a foot orthotic.

Jeff

 

that's my point if the greater majority of devices are made using different techniques yet patients are still getting better.

I don't disagree that device contour and stiffness are very important.

10 000s of devices made 1000s of different ways everyday. You just don't need standard casting techniques

 

Although "patients are still getting better" we don't have sufficient evidence to say what method is more successful or best for any given patient or group of patients. Success rates (success takes many different forms: practitioner's assumption/opinion, patient satisfaction, patient compliance, symptom resolution, performance, oxygen consumption, etc., etc.) can't really be compared between different individuals or groups. One reason is because one practitioner or one group of practitioners using "the same approach" may actually be practicing substantially differently than another practitioner or group of practitioners who are supposedly practicing the same approach. If the treatment approach is not identical, then how can one compare results? For example, if you and Joe Blow both practice "tissue stress theory" and yet your interventions are different and your definitions of success are different, then how can you compare results? It seems that everyone claims to be getting "good results" or that "their patient's get better". But treatment failures do exists and to some degree, are unavoidable. The number of variables that occur when these theories are put into practice just can't be ignored and as a result, it makes it virtually impossible to determine the "best" approach. What we are left with is the reality of "this is what seems works best in my hands".

Jeff

 

The above makes the assumption that the shape of the cast, that the orthotic is made over, is perfect. When you place an imperfect shank dependent orthotic in a shoe with a shank shape that does not match the inferior surface of the orthotoic, the shank of the shoe could cause a deformation that could make the top surface better, or it could make it worse. Without cutting the shoe and orthotoic it's hard to know how well the inferior surface of the orthotic matches the shape of the shank of the shoe.

Eric

 

You don't need a standard technique across practitioners. However, an individual practitioner should have a limited number of casting techniques. As you learn to modify casts/ prescriptions it is best to eliminate some of the variables.

Eric

 

I can think of one way to test if one method is better. Second try orthotics. If the first orthotic is a failure, you evaluate how well the second orthotic does. Under tissue stress you would change a design variable in the face of an orthotic failure. For example if the patient's problem was related to a high supination moment from the ground, and there was insufficient pain reduction, then you could increase the amount of lateral heel skive in the second device. The generic idea is that if your device did not reduce stress enough you increase, or decrease, the amount of a particular design feature of the orthotic, to alter the stress on the anatomical structure in question. Some protocols would have you just repeat the same orthotic over again.

Eric

 

Eric,

Since I first got involved with the lab back in the mid 1970's practitioners have been modifying their orthotic devices for improved comfort or function when the original device didn't product the intended result. Some of these modifications include but are not limited to:
1. inverting or everting the entire orthotic shell with extrinsic posting
2. increasing or decreasing motion in the extrinsic rearfoot post
3. increasing or decreasing the height of the medial arch of the device
4. adding or reducing a heel lift
5. grinding in a plantar fascia or other type of accommodation
6. reducing the height of the heel cup
7. adding or modifying extrinsic pads, wedges, etc.
8. adding plantar filler to stiffen a device
9. thinning the orthotic shell to increase the flexibility of a device
10. manufacturing a different device with a different Rx when other attempts have failed to produce the desired result

No matter what protocol the clinician uses, they need to be able to think logically in order to modify their treatment plan when necessary. This is not something unique to any one theory or approach.

Jeff

 

I agree and I now do many of my " modifications " during the casting, by dorsiflexing or plantarflexing usually the 1st or 5th MTPJ?s . By doing that I have found an increase in comfort. I think by manipulating the foot it reduces lab error in arch medial or lateral height.

But that is me and I might be the only 1 doing it this way.

And yes Jeff I get errors as well we all do

 

Let's take only the problem of designing a shoe last but not starting from an existing one. How the shank' sagital profile of the last should be designed in order for the footwear manufactured on that last to be comfortable (considering that in the simplest case there is no need to put an orthotics inside). Which are the involved biomechanical principles who will lead to design of the shank sagital profile? We can see in Dananberg's patent an example of some principles but are those Ok / enough/...?

Daniel

 

Eric, I disagree with your statement that it makes the assumption that the shape of the cast, that the orthotic is made over, is perfect. The assumption that it makes is that we want the shape of the dorsal surface of the finished orthotic to replicate the contour of the positive cast that it was made from as closely as possible. And that shape is influenced more by the shoe in "shank dependent" devices than it is in devices that are not as shank dependent.

Daniel, we need to make sure we have our terminology correct. A shank is a part of a shoe that is placed in the shoe to stiffen it. It is often made of steel or fiberglass. The shank helps maintain the sagittal plane contour of the shoe. The shoe gets its sagittal plane contour from a combination of the shape of the shoe's last and the shape of the shank. We often use the terms "shank" and "sagittal plane contour of the shoe" interchangeably but technically they are two different things. For purposes of this discussion I assume we are using them to mean the same thing however from a shoe design standpoint, we should probably be talking about the sagittal plane contour of the last which is supported by the addition of a shank within the shoe. The shape of the last determines the entire shape of the shoe because it is designed for a specific heel height and shoe type.

I assume you want to focus on the sagittal plane component of the shape of the last (shank if you like). A shoe without a shank or sagittal plane contour would be a wedge. Most shoes that are called wedges are not true wedges because they typically have some amount of sagittal plane contour in them. If we look at the sagittal plane contour of the last it typically has two basic transitions. One transition in contour occurs just anterior to the heel and the second occurs in the area of the MPJs. The heel transition tends to plantarflex the forefoot at the midtarsal joint and the second transition tends to dorsiflex the digits. The higher the heel, the more pronounced these transitions will be except in a wedge type of shoe.

One thing a functional orthosis does is change the transition in the heel area. That is one reason why we tend to get heel slippage with orthoses in high heeled shoes unless we modify them to function in a shoe with a more pronounced sagittal plane contour. Many shoes are designed to achieve a desired look and not so much a desired influence on the biomechanics of the foot.

Jeff

 

Yes, it is right. From a technological point of view the shape of the shank is close related with the shape of the sagital plane contur of the shoe last, which pass through long axis of the last. As the length of the shank is shorter that the length of a "shank dependent orthosis" I think, technically, the term "shank dependent orthosis" is inappropriate as for example the shank length doesn't cover the digits area. But is convenient to use it !
Dananberg is describing in its patent the mathematical relations between the angles of sagital plane contour in those 2 transition points you've described and heel height.

In order to design the sagital profile of the last (which will be identic with the bottom sagital profile of an orthotics) how much plantarflexion is required in the heel transition point and how much dorsiflexion is required in the second transition point for a comfortable walking/foot functioning ?
I think this is the ideea of Insolia: to change the midtarsal joint plantarflexion in the heel transition point.

Daniel

 

It isn't just the degree of plantarflexion in the reafoot of the shoe that matters. What is very important is where that transition takes place and how long or short the transitional curve is. From the standpoint of fitting an orthotic in a shoe, I can tell you that the further anterior the transition is, the more pronounced it is and the longer it is, the more difficult it will be to fit an orthotic in the shoe because the apex of the transition point will act as a fulcrum and the orthosis will rock in the sagittal plane within the shoe. This is a common problem with high heel shoes.

A shank dependent orthosis will bend in the sagittal plane to accommodate the contour of the shoe. This will tend to enable plantarflexion of the forefoot on the rearfoot. So I think one of your biomechanical questions should be, does a shoe decrease dorsiflexion moments on the forefoot that encourage plantarflexion of forefoot in the shoe and if so:
1. is this desirable?
2. how much is desirable?
3. why is it done and why is it desirable (comfort, style, function, etc.?)

Root Lab manufactures a lot of hybrid devices that are a combination of a functional orthosis and an accommodative orthosis (for example our Cushion-Flex device). It has a thin, flexible high density polyethylene (HDPE) shell which is filled plantarly with EVA foam. If the practition sends us the shoe, we sculpt the bottom to match the shape of the shoe in the sagittal plane as best we can. This maximizes the contact surface between the device and the shoe and reduces the bending moment of the device in the sagittal plane. Since the plantar contour of each custom orthotic device is unique, the plantar contour of the foam is dictated by the shape of the shoe and not the shape of the shell of the device. If we don't have the shoe, then the foam is left thicker (fuller in the midfoot area) so that the practitioner can reduce it to fit the contour of the shoe, it if necessary.

I know that last design is more of an art than a science and that shoe manufactures guard their lasts closely because of the proprietary significance of each last design.

Jeff

 

Putting any shoe material plantar to the forefront will increase the dorsiflexion stiffness at the MTPJs
But then you would also need to consider the shoe "drop" or heel to toe pitch before looking at the significance

 

"Putting any shoe material" I suppose doesn't mean only to add some material but also to look at the sagital profile of the footwear (or better to its last). I think shoe drop give only basic information. For example a longer heel seat combined with a short rearfoot post of orthotics could increase dorsiflexion of the midtarsal joint or orthotic instability. The same when we have a high than normal (whatever this means) last' sagital profile in the forefoot area.
If I've to "think like an engineer" then the upper surface of the foot orthosis is the Tower of Pisa and the sagital profile of the footwear last is its foundation ( https://en.wikipedia.org/wiki/Leaning_Tower_of_Pisa )
This is why I think the "bottom surface" of foot orthosis is important and worth some design principles

Daniel

 

Read your posts again, good stuff; as for buzzcock's it gets me down, always has and i'm long in the tooth; got to go, off to protest! so many wrongs, injustices in this world but that doesn't make any one of those wrongs, those injustices any less wrong, any less unjust ...