The Method of Casting is Not Important?

Eric, this was intended to represent a historical perspective of Dr. Root's thinking. He believed that STJ motion was critical to gate and that an orthotic device needed to allow about 4 degrees of frontal plane motion of the heel in order to facilitate normal tibial rotation. His methodology used a neutral cast usually corrected to heel vertical, and a rearfoot post with a lateral grind-off so at heel strike the plantar plane of the post would encourage up to 4 degrees of inversion but resist further inversion; and then allow the heel to evert with pronation but resist eversion of the heel beyond vertical. In other words, he wanted the device allow heel motion for shock absorption but he wanted to prevent excessive motion. He wanted to prevent the heel from becoming everted because he believed that it was difficult to control the heel once the posterior surface of the heel (ie heel bisection) became everted beyond vertical. Again, please bear in mind that this part of the article what an attempt to explain Dr. Root’s theory of orthotic therapy.



2) It was important to capture
the plantar, non-weight-bearing
contour of the heel, so that the orthosis
would conform to the
anatomical shape of the heel and
capture it in all three planes (triplane
heel cup).

Does water in a cup conform to the shape of the interior of the cup? If our goal is to influence the postion of the heel we can do it by using a flat surface to apply a force or we can use a more complex shape. The triplane heel cup is one aspect of a functional orthosis. You can pour your shot of whiskey on a flat surface and still drink it, but I prefer mine, single malt, in a cup.

This is why Root Lab has additional heel expansion as an option on our Rx form. Only the practitioner can determine if the patient may need more expansion. On occasion, it is necessary to modify the orthosis or re-make it to eliminate heel irritation. Not a common problem at my lab. Some practitioners like to give us a heel width measurements to go by. Too many orthoses are manufactured for comfort, not control. Practitioner's don't return orthoses if the patient doesn't get better but they do when they are not comfortable. So what are labs inclined to do? Satisfy their customers by making orthoses comfortable! Not the best policy for resolving symptoms.


3) Fully pronating the forefoot
on the rearfoot would capture the
midtarsal joint in a position of osseous
stability so the orthosis will
support this relationship and resist
compensatory motion (forces) at the
midtarsal and/or subtalar joint.

The issue is not absolute support of the foot by the device or the absolute stance or functional position it assumes. The issue is whether the device, by virtue of the application of the theory, reduces pathological forces and relieves the patient's symptoms. History shows that functional orthoses manufactured following Root theory do this very well. This is not to say that other treatment paradigms might not work. The primary problem is getting good evidence to support one method over another or to know what to use when.

4) Casting the foot with the midtarsal
joint pronated and the subtalar
joint in neutral was clinically reproducible
among similarly trained practitioners utilizing the same technique.

I wrote an article that appeared in this month's Podiatry Management about that very subject. You are preaching to the choir!

Regards,
Jeff

 

Eric,

Take a look at this picture. I cut this orthosis sagitally and removed the medial section about one centimeter from the medial edge of the device. The heel cup has a significant influence in the sagittal plane because it continues anteriorly and supports the medial and lateral columns of the rearfoot. Although the calcaneal inclination angle is supported, look at how much this device supports the head of the talus in the sagittal plane. The shell at the black mark is 22 millimeters higher than the supporting surface and the heel seat is 2 mm thick, for a net increase of 20 mm at the black mark.

I like to look at the sagittal plane contour of the foot and cast. If I took a pronated cast, the foot would be flatter and the black mark would be lower. This would result in less orthotic reaction force acting on the talus, and the foot would probably pronate more. So the neutral position cast is a balance between too flat of a cast (pronated) and too contoured of a cast (supinated). But there are some feet that you could cast supinated or pronated and they might do very well. Although I do periodically advocate casting pronated, I generally recommend neutral position casting.

There is a lot more to making a good orthosis than the heel cup or the arch. However, both of these are important components of a good orthosis.

Cheers,
Jeff

 

From the paper that Jeff sited for the reasons that method of casting matters.

I think we're in agreement that having a cupped heel is better. The question of this thread is whether the casting method used matters. When one uses a non weight bearing cast you have to add expansion plaster. When one uses fully weight bearing cast you won't have to use expansion plaster. You can still make a cupped heel for your device from a fully weight bearing cast.

What I was critical of was the notion that a "cupped" heel can significantly control motion.

I prefer my malt be made into beer and in a tall glass. :drinks

That is a good research question. Does a "tighter" heel cup provide better outcomes. I would predict that it doesn't, because "control" does not come from gripping the heel.

I agree up to a point. The issue is whether the device by reducing pathological forces relieves the patient's symptoms. Where I'm disagreeing with you may just be semantics, but important sematics. I differ when you said by application of the theory.... It is really the prescription writing protocol. This is slightly different than application of the theory. Applying the theory is that you are supposed to support the foot in the correct forefoot to rearfoot relationship. If that were true you should use the forefoot to rearfoot relationship in the position that the STJ stands in on top of the device. On the other hand if you use the protocol as described by John Weed you would balance the heel to vertical (most of the time) and use the neutral position forefoot to rearfoot relationship. (John Weed's protocol is the one I'm most familiar with. I wonder whether it diverges from Mert Root's?) The orthotic writing prescription protocol does not match the theory. As it said in the article that you posted they formulated their prescription writing protocol through trial and error, so it might be better to follow the protocol than the theory.

I can give an example of where John Weed's protocol doesnt' work. If you have a foot with a high degree of forefoot valgus and a high degree of rearfoot varus where the heel just gets to vertical and has no further eversion range of motion of the subtalar or midtarsal joints in stance. Balancing this cast to vertical would create an intrinsic forefoot valgus post that would be attempting to evert the whole foot beyond its normal range of motion.

John Weed's protocol actually was trying to address this but only looked at the heel and not the forefoot. If you broke down his protocol into different parts you would see that one part was don't atempt to evert the heel farther than it could go. A good idea, but you should look at the whole foot when you do this. This is what led me to look at what I call the maximum eversion height measurement. (In stance you have the patient evert their foot and measure the height of the lateral forefoot off of the ground. Don't make you intrinsic forefoot valgus post higher than this heigt. If you do you will be trying to evert the forefoot beyond its normal range of motion.

The above paragraph illustrates the problem of using non weigth bearing measures like forefoot to rearfoot and SERM and PERM to try to make decisions about a weight bearing device.

Cheers,

Eric

 

Eric and Colleagues:

The deeper heel cup would allow, in a foot with a medially deviated subtalar joint (STJ) axis, to have the lateral heel cup push more effectively medially on the lateral heel of the foot than would a shallow heel-cupped orthosis. The deeper heel cup would therefore tend to increase the STJ supination moment from the orthosis.

In addition, a deeper medial heel cup could allow for more medial heel skive to exert external STJ supination moment. In addition, a deeper, tighter heel cup seems to help relieve plantar heel pain better than a more shallow, wider heel cup, at least in my clinical practice.

Therefore, the heel cup doesn't have to "grip" the heel to alter STJ moments or to alter the plantar loading patterns of the calcaneus. Of course, there are shoe limits to heel cup depth.

 

Jeff,

Now I see a problem in our discussion. I've been defining the heel cup as ending about where the distal end of the rearfoot post is in your picture. It appears that you think that the heel cup extends further distal. For me, the black mark is definitely in the medial arch and not part of the heel cup. I don't believe I've ever seen definitions of these terms. So, neither of us is right or wrong. We've just not been using the same definitions. Using my definition, the heel cup doesn't support the calcaneal inclination.

In regards to casting method and support of the talar head.... A pronated cast with less fill can be the same height as neutral cast with more fill. If you took a pronated cast that had an arch height of 20 mm and you decided that you wanted an arch height of 22 mm you could just carve 2mm out of the positive cast and add no expansion. You would still get the same arch height in the finished product.

For people looking at that picture and think that the medial arch of the orthotic supports the tlalar head, you have to remember that there is usually a big hunk of foot between the plantar skin and the bones of the foot. Most of that tissue gets uncomfortable with prolonged pressure applied to it. I question whether a significant amount of force can be transmitted to the bones through the soft tissue to the bones of the medial arch. Were back to the tack-thotic discussion. (If you place a thumb tack on the top of an orthotic the arch of the foot will raise through pain avoidance behavior.)

Cheers,

Eric

 

Eric, I'm not saying the black mark is in the heel cup. In theory, the heel cup ends approximately at the distal aspect of the rearfoot post. But what if I make my post one or two centimeters longer? Is the heel cup now longer? No. If I don’t use a heel post does that mean I don’t have a heel cup? Obviously the answer is no.

I was afraid that my comments might be confusing or misleading because I was attempting to address two concepts with one answer. The heel cup is a complex, concave aspect of the orthotic device that ends roughly at the distal aspect of the rearfoot post. In most cases you will see that the heel cup and the rearfoot post occupy 1/3 of the total length of an orthosis. I would be very comfortable calling the heel cup the proximal 1/3 of an orthotic device that ends just proximal to the met heads.

In the sagittal plane, the heel cup incorporates an inclination angle that continues to the apex of the medial and if one exists, the lateral arch of the foot. So the sagittal plane slope of the heel cup is very important.

I drew the black mark as a reference. Supporting the head of the talus and the navicular are critical features of a functional orthosis. The second point I was attempting to make is how non-weightbearing casting of the foot influences the orthotic reaction forces just plantar to the head of the talus and the navicular.

During closed chain pronation of the foot, the head of the talus adducts and plantarflexes relative to the floor. The navicular also adducts and plantarflexes relative to the floor, but to a lesser extent than the talus. As a result, there is abduction and dorsiflexion of navicular to the relative to the talus as the talo-navicular unit adducts and plantarflexes. This occurs due to closed chain stj pronation and simultaneous mtj supination during midstance.

The orthotic shell supports the talo-navicular unit and provides resistance of talo-navicular plantarflexion and to some extent, adduction as well. So non-weightbearing casting captures the sagittal plane inclination angle of the medial heel cup and medial arch so that the resulting orthotic shell will resist some of the weightbearing collapse of the medial arch.

I hope that is clearer.

Cheers,
Jeff

 

Eric and Jeff,

I feel you've got this the wrong way around. The heel cup is not defined by the orthosis as such, it is defined by the foot's anatomy. First you must define anatomically where the heel starts (proximally) and ends (distally). The portion of the orthosis which is in contact with this area of the foot is then the heel cup.:drinks

 

I'm playing Devil's advocate Jeff, but if I use a weightbearing cast and remove plaster from the positive in the talo-navicular joint area, the resultant device should provides resistance of talo-navicular plantarflexion. Similarly, if I invert the weightbearing cast through the forefoot balance, it will increase the height of the medial longitudinal arch section of the orthosis and resist talo-navicular plantarflexion. All of this with a weightbearing cast!

 

Simon,

True, in theory. The non Richie Brace type AFO's that I see and Richie AFO's made from semi-weightbearing casts are much flatter than those made from non-weightbearing casts. So if the goal is to make an orthosis with more contour, why not just cast the foot that way rather than trying to recreate it subjectively from a semi-weightbearing cast? I just feel the advantages of non-weightbearing casting outweigh the disadvantages, if there are any disadvantages. What do you feel are the disadvantages of non-weightbearing casting, especially if you’re using the same casting material?

Jeff

 

flatfoot = longer heel and heel cup
cavus foot = shorter heel and heel cup

Why, because flatfoot = less and shorter arch and cavus foot = higher and longer arch when comparing feet of same lenght. Inverse relationship.

 

You have to add lateral expansion. The amount you need to add varies across people. It can be worked around. Just as the arch height issue can be worked around. I haven't done a lot of weight bearing casts to assess if they need any lateral expansion. In what I have done, I haven't seen the need for lateral expansion.

Regards,

Eric

 

No argument from me Jeff, I use the casting technique which will minimise work on the positive model. So if I want a really high arch profile for my finished device I will manipulate the foot into this position during negative casting because removing plaster from a cast is harder work than putting it on. I rarely use weightbearing casts, just a personal preference as I find it easier to manipulate the foot into the shape I want when it is non-weightbearing than when it is weightbearing and moreover, in weightbearing I can't see the plantar surface contour that is being achieved as well as I can in non-weightbearing.

 

Easy, you get a calliper and measure the width in weightbearing so you know what the expansion is from non-weightbearing to weightbearing. Alternatively, we could look at your paper and use the regression equation, Eric Although if I were being highly critical and if memory serves correctly: you plotted the dependent and independent variables the wrong way around.


Regardless, it would be great if you could attach a copy of that paper here Eric.

 

Sorry, don't have a pdf version. Paper version??? The paper had its place. I haven't ever looked at the actual outcomes. The questions that the paper does not answer is whether the width of the heel on the ground is the same as width of the heel in a foam box impression and then whether the foam box impression is wide enough to prevent heel irritation.

I always had difficulty with that dependent/ independent stuff. Anybody have a suggestion for a good book on statistics.

Cheers,

Eric

 

I think you have exposed a common issue (problem?) in how custom orthoses are frequently manufactured. Why does the heel cup of an orthosis need to be as wide as the total width of the heel when the plantar fat pad is compressed? I don't believe it does.

When you measure the width of the plantar fat pad, you are measuring the distance between the vertical tangents at the widest part of the heel. The heel cups of most orthoses are not high enough to reach the vertical tangent point. As a result, the heel cup is and should be narrower than the total width of the weightbearing heel of the foot. Just as the foot does on the floor or in a shoe, it is acceptable for the plantar fat pad to become displaced. The fat pad can over ride the cup of an orthosis and this is perfectly acceptable. Heel cups become wider when you make them higher. The lower the prescribed heel cup, the more the fat pad will tend to over ride it.

One of the most common problems I see with custom orthoses is excessive heel expansion. At Root Lab, our default heel expansion is none medially, and laterally it is up to a millimeter or so wider than the vertical tangent. In other words, we try not to make the heel of the positive cast significantly wider than the width of the non-weightbearing negative cast. I have included two pictures of a cast to show the frontal plane sections through the heel and at the apex of the arch as per the lines on the cast. Note the slight amount of additional lateral heel expansion (perhaps 1 mm) and no medial heel expansion at all in the heel area.

Periodically, we do need to added additional lateral heel expansion. But this is far from the rule. We due use extra lateral heel expansion on inverted orthoses and with heel skives in order to restore the width of the heel to that which is measured at the widest point of the heel perpendicular to the bisection of the heel. We also add extra expansion on request.

Jeff

 

I haven't tried multiple heel width orthotics on a single individual. It would be an interesting question to explore. What is the most distance that the heel cup is narrower than the measured width of the widest point that a subject would find comfortable. A related question would be is there any difference in efficacy of the orthotic with changing only heel cup width.

However, I have seen irritation of the skin from heel cup. What prompted me to perform the study that I published was one patient who was a severe outlier in the amount of change of the heel width from non weight bearing to weight bearing. I had to make three different pairs of orthosis before the patient could wear them because of heel cup edge irritation.

The heel cups of most orthotics are not high enough to reach the widest point of a non weight bearing foot. The widest point of a weight bearing foot is easily close to the top of most heel cups.

You get callus and heel irritation when the fat pad overides the heel cup. Imagine running, and every step the edge of heel cup rubbing as your heel compresses into the cup. Yes, there are degrees of irritation. A way too narrow heel cup will hurt more than a just too narrow heel cup.

What is the rationale for making the heel cup as narrow as tolerable. I can see the "containing" of the fat pad argument, but wouldn't the heel cup have to be up arround 20 mm to make this effective?

The lateral heel expansion in the picture will create a valgus wedge effect. Is that the effect you want?

Eric

 

There you go gents-

 

Which brings me to something which I consider maybe a positive of scanning over any method - if it´s possible I´ve not asked.

Why don´t 2 scans get taken - 1 semi- weightbearing of the heel and the other non-weightbearing so that the foot can be manipulated and viewed during scan - or even cast and then cast scan.

so now we have the persons weightbearing heel and the scan or cast how we want the foot to be.

then remove the non weight bearing heel and add the semi-weightbearing heel once these2 are connected begin the design process.

in this we will capture the true fat pad expansion - remove the guess work , and in theory the heel should not cause irritation.

 

Try Douglas G. Altman: Practical statistics for medical research. Chapman Hall
http://www.amazon.com/s/ref=nb_sb_n...-keywords=altman practical statistics&x=0&y=0

 

Skin irritation can also be the result of not placing the cast in the proper frontal plane position. This can result in excessive pressure on one side of the heel or the other. Skin irritation can also be related to casting. Our goal is not to design orthoses to prevent skin irritation; our goal is to design clinically effective orthoses. In order to get optimal clinical results, we are willing to deal with the occasional case of skin irritation at the heel. In order to eliminate heel irritation, we would have to add more heel expansion on all of the orthoses we manufacture. That would mean that some of them would get poorer clinical results. I am very comfortable with Root Labs standards with respect to cast modifications. As a commercial lab, we would add more expansion or seek to find another solution if our customers were complaining about excessive heel irritation. Eric, all I can tell you is it seems to work very well for us. What motive do I have to change something that works well?

I didn't say nor imply that the heel cup of a non-weightbearing cast comes out as wide as the heel. Unless you use a very high heel cup, the cup of the orthosis will often be narrower than the heel and the fat pad will override the rim of the heel cup. Some patients will develop a little asymptomatic callous in the heel. If it is symptomatic, then it needs to be addressed.

We try to retain as much of the normal anatomical contour of the heel as possible, unless we are intentionally modifying it as you would in the case of a heel skive. The more expansion you add, the more that plaster tends to cover the plantar surface of the heel as well. I see labs run their heel expansion around the entire heel and flatten out the heel in the process. If I can, I will try to find a picture of typical excessive expansion and post it later. So far we have limited this discussion to heel expansions. But combine this with excessive medial arch fill, excessive lateral expansion, fill to obliterate any intrinsic ff varus or valgus, and you have a very flat, generic orthosis. There are a lot of them out there!

We like to slightly cup the lateral border of the foot since the lateral aspect of the foot is round, not flat. The deeper the heel cup, the more this is necessary and beneficial. This tends to prevent the sensation of the foot sliding off the device laterally. None the less, sometimes an orthosis does adduct under the foot. This can be resolved by adding a medial buttress to prevent adduction of the device.

Regards,
Jeff

 

Why do you think you would get worse results if too much expansion is added? My idea of too much expansion is that the heel cup of the orthotic does not fit into the shoe.

Sometimes heel irritation and fitting in the shoe cause conflict. In those cases I will tend to make a flatter heel cup so that the edges of the cup are less vertical and hopefully cause less irritation. Of course you can't do this if you do a significant amount of heel skive. Many competing variables.

[/QUOTE]


Why is it important to retain as much of the normal anatomical contour of the heel as possible?

Think about this in terms of Kevin's anterior axial projection paper. The countour of the skin is not the same countour of the bone. Also think about this in terms of the goal of the orthotic. If the goal is to shift the location of ground reaction force then it should be ok to alter the countour.

Jeff, I used to do this type of lateral expansion because this is what you taught us in biomechanics class in 1984. As a student I got orthotics with this type of modification. They helped my foot. I then had the chance to place a emed in-shoe sensor on top of that orthotic and then stood on it. Compared to barefoot there were higher pressures on the lateral heel. I didn't have the opportunity to check the location of center of pressure, but higher pressures laterally is not what you want if want to decrease pronation moment from the ground. After that I stopped doing the lateral only expansion.

Jeff, If you look at the picture you posted, if that cast's balance platform is parallel with the floor, then when that orthotic is made the lateral half of the heel cup will be elevated higher off of the ground than the medial half. This is essentially a valgus wedge. This would explain the findings of higher pressures on the lateral part of the heel cup with an orthotic made with this kind of lateral expansion plaster.

Jeff, you have been using the "it works for me" arguement. Those orthotics worked for me. However, for my medially deviated STJ axis foot, a heel cup with a varus wedge effect works better for me. The reason why they work better can be explained by thinking about shifting the location of center of pressure relative to the STJ axis.

Regards,
Eric

 

I've got to say casting is very important. I've worked with students alot and other podiatrists and I've had to throw a lot of casts out and start again because they were so crap. it is definitely possible to take a bad cast. It's so important the patient is relaxed and that the cast is moulded to the shape and ontours of the foot. It is just the starting point of the process but important nonetheless

 

I approach heel pad expansions slightly different.
We ask customer to measure the inside heel counter width of the shoe (A certain protocol is required). This measure then over rides the actual width of the foot.
It does seem a strange approach but auditing has shown that returned orthoses are virtually zero.
I think the main reason being that the orthoses doesn't migrate during gait and also doesn't force the shoe upper to gape.
The main issue is when the insole has to go into multiple shoes but there are few trick to get round this.

Phil

 

Yesterday I had a practitioner return an orthosis because he had ordered a 25 degree inverted Blake device with a request for a 65mm fat pad expansion and a 21mm heel cup. When we originally made the device, we complied with both requests. The 21mm heel cup request happened to make the heel cup of the device too narrower for the foot. The 65mm fat pad expansion happened to occur at a point above the 21mm heel cup. The device was made on a CAD/CAM system and there is no way to predetermine the heel width at 21mm. As a result, these two Rx variables happened to be in conflict. We are re-making the device and the practitioner opted to have it manufactured to a heel width of 65mm, which require us to use a much deeper heel cup in order to capture the width of the heel.

 

Would't it be easier to adjust or align the patient as they stand? Then there's no need for guessing... how much expansion, MLA height, forces required on R/F, Mid/F and F/F, but only if the shape matters! :bang:

Neil

 

Phil makes a good point. I was hugely impressed with the protocol, and although I prefer a different type of caliper, I will now often measure the internal dimensions of the shoe so the orthotic fits it snugly if I'm fitting away from the lab.

I think this is also a good habit to get into for the leading edge of the orthotic. A device which fits the foot perfectly but slops around in the shoe cannot be accurate.

Sorry Phil. I nicked that idea. Hope you don't mind . You'd not patented it or owt had you?

Pax

 

Does this really help considering the variability in footwear?

 

Depends on the variability in the footwear.

Like most such things, its never going to be perfect in all shoes. But at least it will fit firmly in at least one. For Paeds (where I work mainly), for fitting to surgical footwear, fitting to running shoes and such its well worthwhile IMO.

 

Robert

Share and share alike!!!
Another trick we sometimes use in more difficult cases is to reduce the heel cup height to 0mm high and over lap the top cover around the heel. If the shoes are narrow then the softer top cover rides up the edge of the heel counter. If the shoes are wide, then the top cover flattens out to stop transverse plane sliding.
However this does bring us back to the question of whether it is the shoe or the insole that resists excessive transverse plane movement from the ORF.
I prefer to rely on the shoe counter to do this as it must be more effective than even a 40mm heel cup - but only if the construction etc is up to the job - the great conundrum of shoes and insoles!

Phil

 

It might be easier, but that doesn't make it equal to or better than other techniques. The patient stands in a compensated position due to the influence of grf. Picture adult acquired flatfoot. We don't want the orthosis to support the foot in an abnormal, compensated position. We want the orthosis to move the foot away from a maximally pronated position to a better functional position. This is what the concept of functional control is about. When you make an orthosis to conform to a compensated position, you are supporting the foot in that position. While this might tend to resist further deformation to some degree, it usually takes more anit-pronation influence from the orthosis to get satisfactory clinical results.

 

Sorry Jeff, I think you mist my point.
I'm talking about applying vertical, translational and rotational forces on the plantar surface of the R/F, Mid/F and F/F while the patient is being cast.

The shape you get is of a corrected or aligned weight bearing foot.
All three segments can be aligned at the same time or seperately. You can also individually raise and tilt each heel to compensate for L/L and shoe shank.

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.

I will be at the National Pedorthics Conference in Orlando Florida from the 18th to the 20th November if you want to come and test the device. I can even cast your feet so you can make a pair from the moulds, at your lab.

I hope you or anyone else in the Podiatry field can come to booth 601 and see if there's any merit in it.

Cheers
Neil

 

Phil- Not sure I agree with you on this one.
While I believe that the heel counter is an important component in resisting transverse ORF, but I do not think it is more effective than a high heel cup orthosis (assuming we are talking about a shell device).
Back in Melbourne it is commonplace to not have a heel cup at all 'to prevent heel irritation' in wedge type orthoses (it is one of those regional orthosis types seen due to widespread use of a particular ortho lab and their development of the technique). At the same time it is recommended to have good footwear to help control lateral translation of the calcaneus.
This works very effectively when the shoe is new, however I regularly saw cases where the liner of the shoe would rapidly wear significantly around the lateral border of the heel before the heel counter would then crack and the upper of the shoe would shift laterally. I saw many instance where this led to pathology- particularly in athletes.
The orthosis is very effective while the shoe is new, but there is a problem when it wears. If the orthosis fits as if it part of the shoe, it would not have the wear problem.

 

But is the shape which the foot adopts on top of the orthotic the same shape as the "corrected" foot?

If I might use a baking analogy, the cast is a bit like the shape of the cookie dough when it goes in the oven. Certainly it affects the shape of the cookie (the position of the foot atop the orthotic) but it is nowhere near the SAME shape. The cast / shape of dough you have to end up with to get the position of the foot / finished cookie shape you want may bear little or no resembelance to the end result.

I'm hungry now. Mmmmmm cookies.

And lets face it, there is no "correct" position. And the foot does not stay in any one position anyway.

The issue I have with Neil's approach is simply that it seems to infer that the position of cast extrapolates to the kinematic clinical effect. It doesn't.

 

But is the shape which the foot adopts on top of the orthotic the same shape as the "corrected" foot?
If I might use a baking analogy, the cast is a bit like the shape of the cookie dough when it goes in the oven. Certainly it affects the shape of the cookie (the position of the foot atop the orthotic) but it is nowhere near the SAME shape. The cast / shape of dough you have to end up with to get the position of the foot / finished cookie shape you want may bear little or no resembelance to the end result.


There is some minimal spreading of the plaster as it sets (J & J 6"specialist seems to work the best), but I wouldn't say it deforms like a cookie after its been baked, probably the same as spreading in non-WB. As far as resembelence of the foot goes, I haven't seen an orthoses made from one of the casts, not fit the foot like a glove. When you align the foot the cast is very maliable, so as it sets, it takes the shape you've positioned the foot into, so, no guess work as to what shape or force you want to apply to the platar surface of the foot. You can feel the resistance as you reposition (align) the foot so you can only apply as much force as the foot will allow which reduces the guesswork when modifying.

Cheers
Neil

 

Sorry neil. I failed to make myself clear (baking analogies will do that to you). The cookie in the anology was

Not the shape of the orthotic itself.

The point being that the foot does not adopt the shape or form of the orthotic during weight bearing function. The insole may well be shaped to the NWB configuration of the foot in the desired position, but the foot will NOT be shaped to the same position atop the insole in even static wb (much less dynamic function.

In other words, one can shape the insole exactly to the foot, but one cannot expect the insole to shape the foot the same way.

 

In other words, one can shape the insole exactly to the foot, but one cannot expect the insole to shape the foot the same way.

Why not. If the object is to apply a certain amount of of force to a segment of the foot and that force can be applied as the person stands, why won't it take the shape of the foot and to a great extent promote it to be at or near that position when moving?

Cheers

Neil

 

Because the foot is moving, so while it may adopt that position at a single instant in time, it will not be fixed in that position throughout contact. If your device is compliant enough it will deform under loading to match the shape of the foot. But if your device is this compliant why do you need a cast at all?

 

Because the foot is moving, so while it may adopt that position at a single instant in time, it will not be fixed in that position throughout contact.

Thanks for that. I understand now what you mean.
Would the orthoses (in theory) work better, the closer it was to the foot, at the different stages of gait. As long as the forces applied were correct. I figure, no contact or force, no resistance to forces.

Cheers

Neil

 

Craig

I totally agree with you. That's why I put in the proviso about the the construction of the shoes. Some shoes will not lose heel counter strength and some will.
The issue we sometimes have is that customers will send back orthoses due to heel cup irritation and ask for extra lateral expansion. This is done but they no longer fit the shoes - especially if the patient has bought new shoes.
It is sometimes best to concentrate on compliance over function and let the patient take responsibility for their shoes - got to pick the customer well or its just complaint after complaint.

Phil

 

Also because your cast is of surface anatomy, not bony.

Consider the depth of the fatty tissue. When you cast non weight bearing you cast the skin with the fatty padding in a non WB configuration. If the foot was homogenous then perhaps the insole would position the foot consistantly. But its not!

Lets take a minutiae example of the first met, in isolation. In non weight bearing let us say that head of the 1st met has 1mm between the skin and the bone. Let us further say that the base of the 1st met has 10mm of soft tissue.

If we cast the 1st met in a position plantarflexed by 10 degrees (ie higher in the base of the met than the head) would we expect the met to move by that number of degrees? Doubtful, because the extra bulk at the base of the 1st met is pushing into a big squashy fat pad. Conversely, apply the same amount of extra bulk to the head of the met we might expect more change in the position of the bone because it is pressing (more or less) directly on the bone.

Put yet another way, have someone stand up and place your fingers lightly into the arch. Then pull up and see how much your fingers move before they start changing the position of the foot. Quite a bit!

Consider the data we have on the change in position of the rearfoot with wedging. None of it states that a 5 degree wedge repositions the foot by 5 degrees. In the same way an insole cast to X position will not change the position of the foot to X position.