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This is what I meant that there is a limit to the need for precision. While all systems would be accurate the precision of that accuracy may not need to be that small in a range. I would intuitively imagine that +/-0.5mm would be sufficient to over kill, +/- 1mm might be reasonable especially when we consider that the foot morphology will change over the stance phase. Presumably we would like a best fit range thru out the stance phase and being at its best in mid stance and resting stance.
Is the fit that is the most comfortable also the most functional and is functional accuracy a funtion of machine accuracy limitation or human design limitation?
Dave
David,
You need more data points in those areas where there is greater contour change but you could have fewer data points in those areas where there is less contour change. For example, there is significant contour change around the perimeter of the heel but far less on the plantar aspect of the heel. There is significant elevation change over a short distance around the perimeter of the heel, so the data points need to be close together to capture this information.
In terms of commercial scanners, there seems to be quite a range in terms of accuracy. Not only are data points significant, but the following issues must be considered: scan distortion, ergonomics, orientation, anatomical landmarks, and economics.
One problem with in office scanners is the loss of data. By this I mean that there is always a loss of some of the surface that would otherwise have been present in a positive cast. There is a loss of the posterior surface of the heel, which is essential for heel bisection and determining the forefoot to rearfoot relationship. Conversely, with our in lab scanner we bisect the heel prior to removal of the upper aspect of the negative cast. This allows use to determine the proper frontal plane orientation of the cast for scanning purposes. With in office scanners, you have to rely on the practitioner to orient the foot to the plane of the scanner. This is part of the ergonomic issue I mentioned.
You also lose any information (contour) beyond the vertical tangent to the plane of the scanner. If you invert or evert the cast (physical or scan) this changes the surface area that is used for correction. So with any scan you lose some of the data that exists in a physical cast.
There is likely to be a difference in the end product depending on whether the scan is done in office off the actual foot or in lab off a negative cast. The question becomes how significant is this difference when it come to patient outcomes.
There is no doubt that scanner have the ability to adequately replicate the plantar contour of the foot. It’s these other issues plus the correction software and the quality of the technicians doing the corrections that are most significant.
In spite of everything, in office scanners will be the way of the future.
Re: Using scanners to capture images of the foot for orthoses construction
Quote:
Originally Posted by Simon Spooner
Back on topic. This looks good: http://www.rob.cs.tu-bs.de/en/resear...cts/3dscanner/ follow the links to read the paper these guys published and to their website. Really interesting- the sort of thing Kirby knocks up in his garage!
Christmas Challaaaaaaange! Lets see if we can all make scanners as outlined at this site and scan a foot or cast using this technique and then post the results back here.
I've just purchased a couple of lasers from e-bay. One a 532nm 5mW green line laser for £40, the other a 650nm 10mW red line laser for £12. I've also purchased a logitech 9000 pro webcam- £50. When they arrive I'll update y'all on my progress.
BTW, I'm not planning to go into business or to be a competitor, Joe this is just a bit of fun to see what you can achieve with a few quid over Christmas- like you were worried anyway
Anyone else up for the challenge? Joe, your not eligible btw, we'll organise a pro-celebrity category later in the new year that you can enter.
Re: Using scanners to capture images of the foot for orthoses construction
Quote:
Originally Posted by Jeff Root
One problem with in office scanners is the loss of data. By this I mean that there is always a loss of some of the surface that would otherwise have been present in a positive cast. There is a loss of the posterior surface of the heel, which is essential for heel bisection and determining the forefoot to rearfoot relationship. Conversely, with our in lab scanner we bisect the heel prior to removal of the upper aspect of the negative cast. This allows use to determine the proper frontal plane orientation of the cast for scanning purposes. With in office scanners, you have to rely on the practitioner to orient the foot to the plane of the scanner. This is part of the ergonomic issue I mentioned.
Jeff, This whole subject is tied up in so many other threads here that I'm not even going to attempt to try link them all (admin step in at your leisure). I use weightbearing casts/ foot impressions/ scans rarely. However, I know many people here are advocates of weightbearing foot impressions/ scans. While weightbearing impressions appear to be more repeatable, the uncompensated forefoot to rearfoot alignment is lost in this process and while some methods, i.e. the mass technique, allow for some manipulation of the forefoot within the weightbearing impression, in general it is more difficult to manipulate the foot into a position using weightbearing than it is using non-weightbearing. I guess where I am going with this, it's slightly off-topic but since we have your attention here and I value your opinion- do you think it necessary to determine uncompensated forefoot to rearfoot relationship in a scan? What do you think is the clinical "loss" in weightbearing scanning/ foot impressions?
Also, in your opinion is it better to scan casts or feet?
Re: Using scanners to capture images of the foot for orthoses construction
Quote:
Originally Posted by Simon Spooner
I've just purchased a couple of lasers from e-bay. One a 532nm 5mW green line laser for £40, the other a 650nm 10mW red line laser for £12. I've also purchased a logitech 9000 pro webcam- £50. When they arrive I'll update y'all on my progress.
For future reference, I buy mine from apinex. Between the laser and camera, I spend $40.00 USD. On a different note, and seeing as I'm not allowed to own guns, I'm thinking of buying a YAG laser. You see, there's this church bell accross the street, and it rings... ever... hour... on... the hour...
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BTW, I'm not planning to go into business or to be a competitor, Joe this is just a bit of fun to see what you can achieve with a few quid over Christmas- like you were worried anyway
Naw, but if you need equations, I'd be happy to help. For simplicity, parametric equations are much easier and straight forward.
[quote]
Anyone else up for the challenge? Joe, your not eligible btw, we'll organise a pro-celebrity category later in the new year that you can enter. [/quote
And in case I forget, happy boxing day to you too.
Re: Using scanners to capture images of the foot for orthoses construction
Quote:
Originally Posted by Simon Spooner
Jeff, This whole subject is tied up in so many other threads here that I'm not even going to attempt to try link them all (admin step in at your leisure). I use weightbearing casts/ foot
Supportable casting methods should be compatible with a potiential scanner customer. In my own case, I support directly, supine scanning, semi and non weight bearing. With little design work, I should be able to support prone semi and non weight bearing. However, even these two basic methods have various preferred angles of scanning, which adds yet again to the number of itterations and while typically prone scanning assumes the patient is on their belly, it's not always the case. While the design allows for customization, am I meeting all of the needs of the customer or potential customer yet? Probably not. Probably never. Some doctors insist on holding an area of scan on the plantar surface that is necessary to produce an orthotic. For cases like that, casting it in plaster is the best method, at least so a technician can grab their mallet and pound the fingers out. That problem wont ever be my headache, thankfully.
Quote:
impressions/ scans rarely. However, I know many people here are advocates of weightbearing foot impressions/ scans. While weightbearing impressions appear to be more repeatable, the uncompensated forefoot to rearfoot alignment is lost in this process and while some methods, i.e. the mass technique, allow for some manipulation of the forefoot within the
Ed promised to send me specifications on the MASS technique so I could review it. Until I look at the document(s) I'm apt to not try to support that casting method. I'm also inclined to think that something might be amiss somewhere to cast that way, but that is something I'll personally think through, listening to people on the technical merits of that method and decide for myself if it's an option I would support. I'm really concerned about instability or fractures that can occur from overly pronating or supinating the cast though, which is my first though of that any casting method that attempts to deflect from subtalar neutral. I might be thinking of a different method, however. By one discription as well, distortion of the lateral arch leaving no support because the orthotic is flat along the lateral column is probably not a good idea either and I'm pretty confident that it messes with the midtarsal joints too, causing a longitudinal shift proximally on the medial side, and ultimately distally as it crosses over from medial to lateral. That's my uneducated thoughts, anyway. Casting methods could be a seperate thread, but then again, as it relates to scanning I think is important. When I'm done making training videos for my customers, I'd be more than happy to accept criticism from anyone to make sure I'm teaching it right.
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weightbearing impression, in general it is more difficult to manipulate the foot into a position using weightbearing than it is using non-weightbearing. I guess where I am going with this, it's slightly off-topic but since we have your attention here and I value your opinion- do you think it necessary to determine uncompensated forefoot to rearfoot relationship in a scan? What do you think is the clinical "loss" in weightbearing scanning/ foot impressions?
Technical merits: I prefer non-weight bearing because most of the anatomical reference points are much easier to find in software making this stage mostly automated in terms of scanning. When the foot flattens out, the distortion in the surface makes it not so intuitive even through human standards when looking at raw 3D data. For that reason alone, I prefer non-weight bearing. However, at least one customer wants both semi and non-weight bearing for each patient, to best serve the patient's needs. I've yet to implement his request, but see his point. While one can estimate the expansion under weight bearing conditions, it's probably better to have both, because each patient is different to some degree.
Quote:
Also, in your opinion is it better to scan casts or feet?
oooh! Trick question. I'm dodging that bullet. ;-)
Re: Using scanners to capture images of the foot for orthoses construction
Joe,
I note that some commercial systems use a linear tracking while others use a revolved. If we wanted to scan the inside of a plaster of Paris cast, would it be better to use a turntable to revolve the laser line around the cast or a linear track to pass it over the cast? Is the answer the same when we are scanning directly from feet?
Re: Using scanners to capture images of the foot for orthoses construction
Quote:
Originally Posted by Simon Spooner
Jeff,
I guess where I am going with this, it's slightly off-topic but since we have your attention here and I value your opinion- do you think it necessary to determine uncompensated forefoot to rearfoot relationship in a scan? What do you think is the clinical "loss" in weightbearing scanning/ foot impressions?
Also, in your opinion is it better to scan casts or feet?
Simon, I believe it is important to capture the uncompensated forefoot to rearfoot relationship in a cast or scan provided the lab who uses the model to manufacture an orthosis actually utilizes that contour in their cast correction process. I believe there is a compelling argument to support this opinion.
An everted forefoot to rearfoot relationship is by far the most common type of forefoot condition we see in the foot. If the negative cast or scan captures this relationship and if the resulting orthotic shell supports it, then we can assist the windlass mechanism. However, if we use a semi-weightbearing or full WB cast or scan which via compensatory action has allowed ground reaction force to dorsiflex the 1st ray or the medial column, then the resulting orthosis won’t support the forefoot with the medial column plantarflexed relative to the lateral column. So, an intrinsically corrected orthotic shell that is made to capture the medial column plantarflexed relative to the lateral column (ie captures the everted ff to rf relationship) will encourage the windlass mechanism. Conversely, if weight bearing forces are allowed to dorsiflex the medial forefoot during casting, then the shell shape will not act to promote relative plantarflexion of the 1st ray. Therefore I believe intrinsically posting an everted forefoot angle will do much to improve the mechanical efficiency of the windlass mechanism.
I would love to be able to offer my customers an in office scanner that would give the lab the same quality file that we get when we scan their negative cast in our lab. This would save the practitioner and the lab a significant amount of labor. Unfortunately I’m not aware of a commercially available scanner that will do this. Until then, I feel we can produce a better orthosis if we scan the negative cast in house.
There don’t seem to be a lot of labs who actually incorporate true intrinsic forefoot correction in their orthoses. This is because they use too much filler in an effort to reduce any “radical” contours in the orthotic shell. For these labs, semi-weightbearing scans might be adequate for the forefoot but they still tend to reduce arch height and flatten the plantar surface of the heel, which many labs do required based on their cast modification protocol. If there’s a good in office scanner out there, then I’m sold. If so, please sign me up!
Re: Using scanners to capture images of the foot for orthoses construction
Quote:
Originally Posted by Simon Spooner
Joe,
I note that some commercial systems use a linear tracking while others use a revolved. If we wanted to scan the inside of a plaster of Paris cast, would it be better to use a turntable to revolve the laser line around the cast or a linear track to pass it over the cast? Is the answer the same when we are scanning directly from feet?
I've made both styles you're referring to, and knowing more about the original design of my product, I might have made a successful implementation of the design. A problem I discovered after I abandoned the design was that the stepper controller for the mirror that rotated the laser was that it needed a delay on a direction change prior to sending steps to it. Error magnifys at the end point of the laser when it rotates radially, much like a fraction of a degree on a cue stick will represent inches on the other end. I took an immediate direction change because of the instability and unrepeatability of a radial motion of laser in my implementation to make a scanner that was a more sound design. Then again, if I had moved the sensor away from the mirror even an inch, it would have probably worked much better. The advantage of a radial travel is that precision of manufacturing is not as critical, and while both methods use LPi to determine location, a linear travel is more consistant and for my implementation, as the machines are nearly identical from one to the next, calibration is too.
The original product had a static laser, which was reflected off of a mirror, and on the circuit board was a photo transistor designed to sense where the laser was, radially, which probably helps you see why I named it. Ironically, it cost more in materials, was a significantly taller box due to the FOV (Field Of View) of the camera (22"x5 1/2"x16"), and required calibration. Here is the implementation, which, while produced accurate 3D data, was a product I chose not to bring to market because of reliability issues and delivery issues, both of ambient lighting and quaity of workmanship. (I'm lousy with hand tools) I am, however, using the original circuit board I designed for the parallel port interface, but likely in the future will go with a USB interface design a different board to take the cpu clock out of the equation, and make it more up with the times, technologically speaking.
My own personal preference, thanks to inexpensive inhouse built technology for manufacturing is to make a linear travel system, which in comparison is significantly less expensive, and is now in production. Here is a picture of what is pretty close to the final base product (24"x10"x15", being reduced to 12" in height in the next revision) that is actually in production, which is much more attractive and accurate than the original, in part because both the camera and laser move along the same linear travel. Henry ford proved one concept, that it has to be an an efficient assembly line to keep the costs low, and well, he is still right. It currently costs approximately $125.00 per unit in labor, which is probably unheard of in this industry for a device of this quality.
For any economy, good money management, quality of workmanship and service, and knowledge of the industry are key components to success. There are some really good shoulders I'm standing on, but there's always room for more opinions and already some of my customers are asking for customizations, because they have good ideas too, which is exciting. While I have confidence that the unit will be generally accepted, I still have much work to do and look forward to criticism because it makes for a better product and also keeps my own ego in check. I sincerely hope this implementation encourages other competitors to bring the price of their own products in line with what the doctor can afford, but that is in fact what competition is about, encouraging quality products at reasonable prices.
Re: Using scanners to capture images of the foot for orthoses construction
Quote:
Originally Posted by Jeff Root
An everted forefoot to rearfoot relationship is by far the most common type of forefoot condition we see in the foot. If the negative cast or scan captures this relationship and if the resulting orthotic shell supports it, then we can assist the windlass mechanism. However, if we use a semi-weightbearing or full WB cast or scan which via
Could you elaborate on the windlass mechanism? I agree with you completely in terms of knowing the rearfoot to forefoot deformity.
Quote:
I would love to be able to offer my customers an in office scanner that would give the lab the same quality file that we get when we scan their negative cast in our lab. This would save the practitioner and the lab a significant amount of labor. Unfortunately I’m not aware of a commercially available scanner that will do this. Until then, I feel we can produce a better orthosis if we scan the negative cast in house.
There's no reason that same scanner couldn't be designed to scan casts and feet, and as a matter of fact, it would be best if it did, to cover feet that can't be scanned easily. Scanning casts and feet, and climbing up the calcaneous on feet, however, is difficult for a single camera implementation, but still possible. It is extremely easy to scan the plantar surface and calcaneous in cast scans.
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There don’t seem to be a lot of labs who actually incorporate true intrinsic forefoot correction in their orthoses. This is because they use too much filler in an effort to reduce any “radical” contours in the orthotic shell. For these labs, semi-weightbearing scans might be adequate for
the forefoot but they still tend to reduce arch height and flatten the plantar surface of the heel, which many labs do required based on their cast modification protocol. If there’s a good in office scanner out there, then I’m sold. If so, please sign me up!
I see this problem with competitors, and suffice it to say that most of these problems are a combination of a rush to bring a product to market, and the demand for that product. I almost made that mistake with my first scanner, which would have ruined me. As it stands now, and thanks to automation I can send out retrofits easily and it's not nearly as critical as scanners past. As for my own product's growth, I'm finding that I have an immediate need to deligate tasks to people so I can have time to continue development and have to identify a personal weakness there, but I'm adapting to these new challenges. Sometimes, for financial reasons, it happens as a matter of survival, but a properly maturing system will grow to meet the customer's needs and it will be evidenced only in part by the developer's customer base growth. If you raise the bar of your expectations, we as the developers for your product will have to meet them or be left at the curb. If you don't raise that bar, the down side is that all you'll get is the same product, which is degrading fast because of cheaper and inadequate products entering the marketplace and the podiatric community accepting them.
Re: Using scanners to capture images of the foot for orthoses construction
Joe made an excellent point, regardless of scanner the software developing the foot orthotic is critical. In 1992 I started developing a system to manufacture custom foot orthotics. The system utilized a 3-D scanner, intelligent software and CNC machine. I was able to develop the prototype software but unable to develop or find a functional scanner that made economic sense. In 1992 the technology for scanning was poor. In 2008 I'm sure it's improved. I still have an interest in moving this project forward. If anyone has an interest, scanning technology and engineering skill I would be interested in collaborative efforts.
Re: Using scanners to capture images of the foot for orthoses construction
Quote:
Originally Posted by Jeff Root
An everted forefoot to rearfoot relationship is by far the most common type of forefoot condition we see in the foot. If the negative cast or scan captures this relationship and if the resulting orthotic shell supports it, then we can assist the windlass mechanism. However, if we use a semi-weightbearing or full WB cast or scan which via compensatory action has allowed ground reaction force to dorsiflex the 1st ray or the medial column, then the resulting orthosis won’t support the forefoot with the medial column plantarflexed relative to the lateral column. So, an intrinsically corrected orthotic shell that is made to capture the medial column plantarflexed relative to the lateral column (ie captures the everted ff to rf relationship) will encourage the windlass mechanism. Conversely, if weight bearing forces are allowed to dorsiflex the medial forefoot during casting, then the shell shape will not act to promote relative plantarflexion of the 1st ray. Therefore I believe intrinsically posting an everted forefoot angle will do much to improve the mechanical efficiency of the windlass mechanism.
Jeff, I agree with your comments above, but I guess if we were to use a first ray cut out this may help in reducing dorsiflexory forces on the first met from the orthosis shell, also a 2-4 valgus forefoot extension may help. Dave, how do you get around this using the AMFIT scanner?
Re: Using scanners to capture images of the foot for orthoses construction
Jeff
Quote:
You need more data points in those areas where there is greater contour change but you could have fewer data points in those areas where there is less contour change.
This is a problem of resolution and range and in principle I agree with you, this is one reason why high flanges and deep heel cups are not really possible with the Amfit system. Since the pins have a limited vertical displacement they cannot capture data that requires greater displacement than 30mm. The next limitation related to range is that the blanks are only 30mm thick so even if you could scan a vertical displacement greater than 30mm you couldn't mill it anyway.
Fortunately, in reality the resolution is not such a problem since the curve of a heel or arch or whatever is fairly predictable in terms of interpolation and is unlikely to change shape by very much within the difference in displacement of two pins. Even if it does the soft tissue can attenuate this discrepancy in the charactreisation of the curve.
So you could look at the displacement of shape as the magnitude of signal and the rate of change in shape as the frequency of signal and the pins or data points as the sample rate. As long as you can estimate the maximum frequency you can be fairly sure of the sampling rate estimate giving a reasonable characterisation of the change in shape. How often will the real frequency be far outside the estimated one? Not often by my experience.
The Amfit pin array has 8mm between pin centres and I would guess that Amfit have estimated that this is a usefull resolution and that thinner pins closer together may be more prone to damage and to cause trauma to the skin.
I have seen that another manufacturer of a simmilar scanner does have a greater pin resolution (can't think of the Name at present) So I guess its a case of designer discretion. Eight pins / squ centimetre will give a better characterisation of the foot shape than 4 pins / squ centimetre but will it be any more useful.
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For example, there is significant contour change around the perimeter of the heel but far less on the plantar aspect of the heel. There is significant elevation change over a short distance around the perimeter of the heel, so the data points need to be close together to capture this information
The problem is you can't predict where the most data points will be required when you design a machine so you would have to settle for your estimation of the optimum / most useful number. More data usually also means more headaches in the collection and processing and expense, in both finance and time. And at the end of the day is it any more useful?
That's a good point about orientation and reference however the Amfit has the advantage of a built in reference system ie the box you stand on.
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The question becomes how significant is this difference when it come to patient outcomes.
Quite
All the best Dave
__________________
Descartes seems to consider here that beliefs formed by pure reasoning are less doubtful than those formed through perception.
Re: Using scanners to capture images of the foot for orthoses construction
Quote:
Originally Posted by joejared
There's no reason that same scanner couldn't be designed to scan casts and feet, and as a matter of fact, it would be best if it did, to cover feet that can't be scanned easily. Scanning casts and feet, and climbing up the calcaneous on feet, however, is difficult for a single camera implementation, but still possible. It is extremely easy to scan the plantar surface and calcaneous in cast scans.
So why aren't the vast majority of scanners using multiple cameras? I don't want to keep going back to the past, but the scanners I worked on "back in the day" used 4 cameras to capture the whole foot, if memory serves- it may have been two- I really can't remember. Is it so difficult to write the software to integrate data from multiple cameras? Clearly the hardware cost isn't the limiting factor...
Re: Using scanners to capture images of the foot for orthoses construction
Quote:
Originally Posted by Simon Spooner
So why aren't the vast majority of scanners using multiple cameras? I don't want to keep going back to the past, but the scanners I worked on "back in the day" used 4 cameras to capture the whole foot, if memory serves- it may have been two- I really can't remember. Is it so difficult to write the software to integrate data from multiple cameras? Clearly the hardware cost isn't the limiting factor...
One system I worked on used 2 cameras, but not for any other reason than stereovision, meaning that the cameras were the eyes. For a LPi Camera/laser plane based design, only one camera is necessary, as the other eye is the laser itself, effectively. As to other surfaces, I see it as possible to capture a volumetric scan of the foot, simply by projecting the laser off of mirrors, creating a complementary plane and anterior surface scan, but it is significantly more complicated.
v-mirrors- v
/ foot \
|
|
laser
camera
The drawback to this concept is that the scanner height would become an issue, the projected plane relative to the camera would be more complicated, but accuracy and performance probably would not suffer much as a result. Also calculating an optimal reflection angle would need to allow for latitude when it comes to non-weight bearing implementations, and would probably increase overall cost and maintence issues.
Using multiple cameras means extra time for scanning from multiple sources and additional potential failures, and practicioners don't want a device that is slow. I've seen one scanner that used 8 stationary cameras, and to me that was an attempt to create a low profile device and suffered from ambient lighting issues. That unit was over $20K in cost.
Re: Using scanners to capture images of the foot for orthoses construction
Quote:
Originally Posted by Simon Spooner
I suspect that Joe is probably your man here. But I'd be interested in getting involved too, for the European end.
I have no problem sharing ideas with other companies, even competitors. While it isn't often reciprocated I see my participation as win win. Building a 3D scanner is easy, especially with bar lasers. If one understands a ccd pixel as a 3D line, and the laser as a plane, the rest is simple identification of camera characteristics, laser plane relative to camera, and about 5 lines of code, coupled with assorted filters. The real trick is implementation, of which, I'm now in my 3rd revision, ergonomics. There is a tradeoff with a single camera implementation in terms of accuracy of the profile, and making it user friendly for the doctor. The next version of my device will be 12 inches high, and probably slightly uncomfortable for a doctor to have it between him/her and the patient, but a scanner that has an extremely low profile is most likely a simple page scanner, and not the direction I'm thinking appropriate. Most likely, the doctor or technician will still have to be off to one side. Most important I see of all of this now that some level of maturity in my product is acheived, is to make the system as friendly as possible for the user, making available every possible casting method a technician could use, naturally of course, that is biomechanically correct for casting. Leaving the business end out of this forum, I don't see why more people can't be involved, discussing what sorts of implementations they would have on their wish list, and hopefully even competitors would be willing to participate also.
While I already have developed a complete fabrication system in place for manufacturing of orthotic devices, I'd rather share concepts and get the slackers up to speed on what needs to be in place to produce orthotics than watch our overall product quality degrade. Even now, one competitor made it into my network on at least one customer site, busted up a jig, and isn't anywhere close to ready to produce prescription devices, conventionally speaking, and yet at least one lab in the states is using them for prescription devices. I've already created one thread on cast corrections, focusing on the rearfoot, and as it develops, hope to cover all aspects of orthotics manufacturing, including any and all concepts related to providing a quality product to the end user. It would be nice to see professionals from both camps participating (Labs and podiatrists).
Re: Using scanners to capture images of the foot for orthoses construction
Jeff, Simon
Yes a NWb POP cast can capture a forefoot deformity and commonly that is a forefoot valgus. This can of course then be balanced intrinsically and the resultant orthotic may assist the function of the 1st ray/MTP
But taking a POP cast takes time and cast modifications take time. The question is do you need to capture the deformity be able to add the valgus post? Semi-weight bearing casts eg foam are oft criticised for the obliteration of a flexible forefoot valgus but does this really matter? As long as you note it during assesment and add posting (extrinsic) accordingly is there then any difference?
Re: Using scanners to capture images of the foot for orthoses construction
Quote:
Originally Posted by Lawrence Bevan
Jeff, Simon
Yes a NWb POP cast can capture a forefoot deformity and commonly that is a forefoot valgus. This can of course then be balanced intrinsically and the resultant orthotic may assist the function of the 1st ray/MTP
But taking a POP cast takes time and cast modifications take time. The question is do you need to capture the deformity be able to add the valgus post? Semi-weight bearing casts eg foam are oft criticised for the obliteration of a flexible forefoot valgus but does this really matter? As long as you note it during assesment and add posting (extrinsic) accordingly is there then any difference?
I would think it the same on the AMFIT
Lawrence,
In short, the answer may well be no. There are many ways to skin cat's. However, do those methods really result in the same outcome? If the interaction between the foot and orthosis is significant, and if the mechanics of that interaction are, in part, determined by the mechanical behaviour of the orthoses under load, then I believe the differing methods would result in different mechanical properties of the resultant orthoses. The real question is, how do these differences influence outcomes? I don't know.
Re: Using scanners to capture images of the foot for orthoses construction
Quote:
Originally Posted by Lawrence Bevan
But taking a POP cast takes time and cast modifications take time. The question is do you need to capture the deformity be able to add the valgus post? Semi-weight bearing casts eg foam are oft criticised for the obliteration of a flexible forefoot valgus but does this really matter? As long as you note it during assesment and add posting (extrinsic) accordingly is there then any difference?
Quote:
Originally Posted by Simon Spooner
Lawrence,
In short, the answer may well be no. There are many ways to skin cat's. However, do those methods really result in the same outcome? If the interaction between the foot and orthosis is significant, and if the mechanics of that interaction are, in part, determined by the mechanical behaviour of the orthoses under load, then I believe the differing methods would result in different mechanical properties of the resultant orthoses. The real question is, how do these differences influence outcomes? I don't know.
If you take a nw cast of a foot with an everted forefoot condition (ie ff valgus or plantarflexed 1st ray) and place the positive model with the heel vertical, you will see that the entire lateral column back to the cc joint is elevated off of the supporting surface. If you cast the same foot in biofoam, the medial column will be dorsiflexed by vertical grf and the lateral column will not be elevated off of the supporting surface to the same degree as it would in a nw cast. A forefoot valgus extension would not replicate the contour of the orthotic shell, since it is placed on the distal aspect of the orthosis and on the top cover's distal extension. To get the same influence as the everted forefoot captured in the cast, a valgus extension would need to be placed on top of the orthotic shell starting proximally at about the cc joint. It would need to have a valgus angle as well be wedged in the sagital plane with an anterior angle of inclination. We sometimes place wedges like these on top of existing orthoses to increase the valgus support.
A traditional valgus extension is typically used to enhance the valgus support at the distal aspect of the orthotic device, not more proximally as described above. A functional orthosis is a complex triplane support, not just a valgus wedge. This is why I'm a big believer in the value of non-weightbearing casting. As Simon said, there's more than one way to skin a cat. We might be talking about the difference between cats and dogs because these devices might be different animals.
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Re: Using scanners to capture images of the foot for orthoses construction
Quote:
Originally Posted by Jeff Root
If you take a nw cast of a foot with an everted forefoot condition (ie ff valgus or plantarflexed 1st ray) and place the positive model with the heel vertical, you will see that the entire lateral column back to the cc joint is elevated off of the supporting surface. If you cast the same foot in biofoam, the medial column will be dorsiflexed by vertical grf and the lateral column will not be elevated off of the supporting surface to the same degree as it would in a nw cast. A forefoot valgus extension would not replicate the contour of the orthotic shell, since it is placed on the distal aspect of the orthosis and on the top cover's distal extension. To get the same influence as the everted forefoot captured in the cast, a valgus extension would need to be placed on top of the orthotic shell starting proximally at about the cc joint. It would need to have a valgus angle as well be wedged in the sagital plane with an anterior angle of inclination. We sometimes place wedges like these on top of existing orthoses to increase the valgus support.
A traditional valgus extension is typically used to enhance the valgus support at the distal aspect of the orthotic device, not more proximally as described above. A functional orthosis is a complex triplane support, not just a valgus wedge. This is why I'm a big believer in the value of non-weightbearing casting. As Simon said, there's more than one way to skin a cat. We might be talking about the difference between cats and dogs because these devices might be different animals.
This thread has become rather interesting and Jeff's explanation here is excellent regarding POP casting, modifications and FF valgus deformities. Early on when I was learning about orthoses it seemed that every orthosis that made its way into my office dispensed by another chiropractor had two common characteristic (okay well three because many were also Foot Levelers inserts and crap if you ask me ):
1. High MLA
2. Extrinsic forefoot varus post
I pondered why I felt more of these patients had FF valgus issues not varus and many complained of 1st MTP pain and MLA and/or lateral column discomfort. Most were cast in biofoam. This perplexed me until I realized that there were more people with FF valgus foot types out there and that recognizing them was not something that we were taught to do.
Am I wrong or at a certain level of training does everyone see supinatus due to correctable muscle involvement as a FF varus? Owning a lab I bet Jeff can answer this question.
Regards,
__________________
"If we all worked on the assumption that what is accepted as true is really true, there would be little hope of advance." - Orville Wright
Re: Using scanners to capture images of the foot for orthoses construction
Jeff, Simon and David
Definately David the mechanism and orthotic failure with foam cast devices that you have observed is a real phenomenon. In my mind the capture of the flexible forefoot valgus with a NWb POP cast or creation of a (relative) supinatus with a foam cast is the crux.
And I would agree with you Jeff that adding a forefoot 2-5 extension of say 3mm flexible material or valgus wedge under the met heads is not the same as a valgus forefoot post in the shell for the reasons you suggest.
However I have found, with foam cast Rx's, if you use a shank dependent material and extrinsically grind it you can incorporate the degree of valgus posting you want and in doing so have a post that extends more proximally in the manner you so clearly describe.
I have tended recently to make these sulcus length and ground through under the 1st met head. I also add some degree of medial heel skive more often than not. (if your interested!). Shank interdependent materials and foam casts are not particulary consistent and if that material is wanted POP NWb impression taking is probably far more consistent. I find this to be due to pitch/elevation problems
This might be a good time for David (Smith) or Bruce Williams to chime in as they both use the Amfit system and prescribe shank dependent device.
Re: Using scanners to capture images of the foot for orthoses construction
Lawrence
Quote:
This might be a good time for David (Smith) or Bruce Williams to chime in as they both use the Amfit system and prescribe shank dependent device.
I generally use a semi weight bearing scan for most of my orthoses. This allows capture of the foot shape as you might see it non weight bearing but also gives enough expansion of soft tissues to approximate the weight bearing shape.
When i want to enhance a certain feature eg a forefoot valgus or a high lateral arch etc I can increase the pin pressure and for instance manually hold down the first ray while dorsiflexing the hallux. The contours captured are readily visible in the 3D characterisation or the 2D contour map of the foot scan. Using the software tools these shapes can then be proportionally accentuated or minimised as required. Of course infinitely variable wedges and posts, positive or negative, can be added to increase the bias of a certain area as required.
Dave
__________________
Descartes seems to consider here that beliefs formed by pure reasoning are less doubtful than those formed through perception.
Re: Using scanners to capture images of the foot for orthoses construction
Quote:
Originally Posted by Jeff Root
If you take a nw cast of a foot with an everted forefoot condition (ie ff valgus or plantarflexed 1st ray) and place the positive model with the heel vertical, you will see that the entire lateral column back to the cc joint is elevated off of the supporting surface. If you cast the same foot in biofoam, the medial column will be dorsiflexed by vertical grf and the lateral column will not be elevated off of the supporting surface to the same degree as it would in a nw cast. A forefoot valgus extension would not replicate the contour of the orthotic shell, since it is placed on the distal aspect of the orthosis and on the top cover's distal extension. To get the same influence as the everted forefoot captured in the cast, a valgus extension would need to be placed on top of the orthotic shell starting proximally at about the cc joint. It would need to have a valgus angle as well be wedged in the sagital plane with an anterior angle of inclination. We sometimes place wedges like these on top of existing orthoses to increase the valgus support.
A traditional valgus extension is typically used to enhance the valgus support at the distal aspect of the orthotic device, not more proximally as described above. A functional orthosis is a complex triplane support, not just a valgus wedge. This is why I'm a big believer in the value of non-weightbearing casting. As Simon said, there's more than one way to skin a cat. We might be talking about the difference between cats and dogs because these devices might be different animals.
Jeff:
So good to have you contributing regularly here on Podiatry Arena where you can share your knowledge with many others. Your insights here are extremely valuable to us.
I totally agree with Jeff about the benefit of non-weightbearing casting. Being able to see the dorsal, plantar, medial and lateral aspects of the foot during the casting procedure, I believe, is one of the most positive benefits of using non-weightbearing casting. I will also modify the usual non-weightbearing "neutral suspension casting" procedure to either plantarflex the medial column/first ray, dorsiflex the medial column or position the subtalar joint more pronated than normal. In other words, non-weightbeairing casting gives me the option to either increase or decrease the medial longitudinal arch of the resultant negative cast as I see fit for the patient's biomechanical and therapeutic needs. Then, once the negative cast is off the foot, I can visually inspect the three-dimensional contours of both the interior and exterior of the negative cast to make sure that I have captured the shape that I wanted.
Of course, much of what we do in medicine is a product of how we were trained. I was trained in the plaster neutral position suspenstion casting technique by the originators of this technique, which has probably helped me greatly in my practice career. I have been train podiatric students and podiatric surgical residents on negative casting for nearly a quarter century and still think the non-weightbearing method is the best way to cast a foot for orthoses.
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
Re: Using scanners to capture images of the foot for orthoses construction
Quote:
Originally Posted by Jeff Root
As Simon said, there's more than one way to skin a cat. We might be talking about the difference between cats and dogs because these devices might be different animals.
Agreed!
The puzzle to me is that they all may "work". The question then becomes which is the "best" for each given patient?
Re: Using scanners to capture images of the foot for orthoses construction
Quote:
Originally Posted by Simon Spooner
Agreed!
The puzzle to me is that they all may "work". The question then becomes which is the "best" for each given patient?
This spurs more questions. Any scanner would need to meet specifications that the end user requires to provide a method the practitioner is most comfortable, and the technology used needs to have credibility. To simplify this, let's assume that credibility issues need not be discussed, but rather, that each practitioner would want to document how they cast a patient, according to foot position relative to grown level, supine or prone, technician position and patient position, with enough information to test the method, and then document that they support it or not. For example, many doctors cast in the prone position, with the patient laying on their belly, and the foot locked into a subtalar neutral position, and that they used plaster previously. Obviously, the scanner either supports this method, or doesn't. If the practitioner has to change their practice to meet their needs, I would have to say that the technology was inferior to the in office practice. On this note, I would have to concede that although this is my own favorite method, my product is inferior, but this is only a temporary issue and one that will be resolved quickly.
In layman's terms, if I want that practitioner as a customer, I would have to meet their needs. I also think my reputation would suffer if I claimed to support a method and in reality, either didn't or the implementation of their method was poor.
Re: Using scanners to capture images of the foot for orthoses construction
this is just a bit of fun to see what you can achieve with a few quid over Christmas- like you were worried anyway
This whole subject is tied up in so many other threads here that I'm not even going to attempt to try link them all (admin step in at your leisure). I use weightbearing casts/ foot impressions/ scans rarely. However, I know many people here are advocates of weightbearing foot impressions/ scans. While weightbearing impressions appear to be more repeatable, the uncompensated forefoot to rearfoot alignment is lost in this process and while some methods, i.e. the mass technique, allow for some manipulation of the forefoot within the weightbearing impression, in general it is more difficult to manipulate the foot into a position using weightbearing than it is using non-weightbearing. I guess where I am going with this, it's slightly off-topic but since we have your attention here and I value your opinion- do you think it necessary to determine uncompensated forefoot to rearfoot relationship in a scan? What do you think is the clinical "loss" in weightbearing scanning/ foot impressions?
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