Board Review Diabetic Foot

Insole Therapy for Managing the Healed Diabetic Foot

Denise Freeman, DPM

Denise Freeman, DPM reviews the importance of off-loading pressure areas and discusses the roles of peak pressures and shear stresses. Dr Freeman analyzes three case studies of different types of insoles looking at pressure and shear forces and relates the difference between standard insoles and shear reducing insoles.

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Goals and Objectives
  1. Recognize the significance for the reduction of foot pressures in healing the diabetic foot
  2. Explain the difference between pressure and shear stresses
  3. Examine the benefits of the novel insole design
  4. Compare standard insoles to shear reducing insoles
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  • CPME (Credits: 0.5)

    PRESENT eLearning Systems, LLC is approved by the Council on Podiatric Medical Education as a provider of continuing education in podiatric medicine.

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    Release Date: 03/16/2018 Expiration Date: 12/31/2018

  • Author
  • Denise Freeman, DPM

    Associate Director and Professor
    Arizona School of Podiatric Medicine
    Midwestern University
    Glendale, AZ

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    Denise Freeman has nothing to disclose

  • Lecture Transcript
  • Host: And keeping with the theme this morning with John, I'm just so thrilled about because we spent so much time looking at disease that we really don't get to concentrate much on health. And our next speaker is going to at least help us to approach the subject once we have treated the disease to keep our patients healthy in two of her lectures. This current lecture is Insole Therapy for Managing the Heel Diabetic Foot. Dr. Denise Freeman is a good friend. She is a professor at the Western University College of Podiatric Medicine, right?

    Dr. Denise Freeman: Midwestern

    Host: Midwestern, I'm sorry. Midwestern. Yeah. This is Southwestern. So you'll understand my confusion. And she has taught for many years. She's also the chairman of the Council of Faculties for the American Association of Colleges of Podiatric Medicine and they have just completed a very comprehensive curriculum for Podiatric Medicine and without further ado, Dr. Denise Freeman.

    Dr. Denise Freeman: Thank you very much. I'm very pleased to be here. With this interesting topic for you, hopefully it will be interesting. All right. Well, we all know that we have to do a lot of things to take pressure off of the diabetic foot, but what we might not understand is many of the things that we do, the total contact casts, the half shoes, the custom insoles, there's very little literature out there to really support some of these things and their efficacy. The other thing that we have issues with is that many of the times when we prescribe these therapies for our diabetic patients, they tend not to wear them or to use them even though they know it will benefit them. Well, we also know that we need to take pressure off of the diabetic foot and I think all of us are really familiar with that concept and the literature has done well to support that concept. There are plethora of articles out there telling us that we need to take pressure off the foot if we want it to heal.

    More recently, what's been coming into the light in the literature is more information about shear and shear forces. And if you look at this, I think that you can see that shear forces are becoming more and more prevalent or our understanding of them and the reason we haven't seen much of this in the past is because these studies have been extremely difficult to do. Most of them are down with mathematical models and they're hard to reproduce clinically, but some of the literature that we're seeing are telling us things that shear stresses do not occur at the same time that pressure stresses occur. The shear stress does occur more often in the foot than pressure stresses occur. And that when you combine both pressure and shear, you have increased the risk of a patient receive �getting an ulcer.

    So keep that in mind is that both of these will come to light and what I'm going to do is present three studies to you and they're both going to look at pressure and shear in a little bit different way. First one is by Lavery. Now, this study was designed to measure pressure and shear reduction in a novel or unique insole design. All of the subjects, and this is important to note, were not diabetic patients. They were healthy. They had no sensory neuropathy. They looked at three separate types of insoles and the three insoles that they've looked at were the same materials with the unique design and without the unique design. So I'll show you more specifically what I mean.

    This is a representation of what that insole looked like. All of the insoles were made of the same materials. They all had a firm density Plastazote base and the only thing that varied were the uppers. They either had that firm density Plastazote base with the Plastazote upper, an EVA upper or a Poron upper. And then they looked at those same materials and they used the same materials. The only difference was is they changed the design on those materials. And they did that by introducing fiberglass thin woven material with a Teflon coating. The Teflon coating gave that design an ability for the top layer to move over the bottom layer thus creating the shear forces between the two layers of material rather than between the patient's foot and the shoe. And here were the results. With the results of shear, the novel or unique insole design showed the two-and-a-half fold reduction in shear compared to the other three insoles but vertical pressure, really wasn't a statistical difference. So their conclusion was is this unique design demonstrated a significant reduction in shear while maintaining equivalent pressure reduction compared to the standard insole design that we're all presently using.

    Lavery took this one step further. He wanted to evaluate the effectiveness of a shear-reducing insole compared to the standard insole that we're all using to see how well this insole did at preventing re-ulceration in patients with diabetes. This was a rather large study. They had 299 high risk individuals and the primary clinical outcome, what they were looking for is did these patients develop ulcers or did they not or at what rate did they develop ulcers? Now, something else to keep in mind with this study is that all the patients were seen by a physician every 10 to 12 weeks, they were well managed and all the insoles were changed every four months which is typically what we do anyway. The patients were followed for a year-and-a-half in this study. Their inclusion criteria, all of the patients had diabetes and they accepted patients between the years of 18 and 80 years of age. They were all able to provide informed consent. They all had a history of foot ulceration or a presence of sensory neuropathy or foot deformity. According to this study, they didn't see that there was any difference in the patient's demographics between their age, their previous amputation or previous ulcerations. Here are their results.

    They found that the standard insole group had three-and-a-half times more likely to develop an ulcer during the year-and-a-half that this study went on. So their conclusion, the results of this study suggest that the insole with the ability to reduce shear can improve prevention compared to the standard insoles that we're presently using.

    Well, so we had an opportunity as well to do a similar study with a little bit of a different twist on it. And we wanted to see to look at, again, a different design being that unique design with kind of another caveat to it and to see how well it did at reducing pressures.

    So this is the insole that we used, the shear-reducing insole. It was a unique combination in this case of five materials. The anti-microbial top cover, the next layer was a Plastazote layer so we could make nice, firm contact with the foot. Then it was followed by a shocking�a shock-absorbing layer. And then between that that same Teflon sort of coating layer and this base was EVA and not a firm density Plastazote. Again, if you look at it, the top layer and bottom layer are adhered with these elastic band so they can move on each other, very similar to the previous Lavery Study but a little bit different in that this is a composite of different materials, so that when the diabetic patient walks, that top layer can move proximally and distally so again, so that all of that shearing forces occur within the insole and not against the foot.

    So we wanted to look at the plantar forefoot pressures of this particular insole and we were convinced that this insole was going to reduce the plantar pressures in the forefoot and that's what we were looking to see. This was a prospective study, self-controlled. It was a pilot study so we had a small end. We only had 20 patients in this study. All of these people were capable of ambulation and we were going to look at this particular insole against multiple footwear conditions.

    Our inclusion criteria, if you look at this, was similar to what Lavery did. They are all diabetic. They were all able to provide informed consent. The age groups we accepted were between 20 and 80 years of age and the average age group for this particular study was 65.2 years. They all had a history of peripheral sensory neuropathy or loss of protective sensation or they had a previous ulcer or both. We excluded any patient that had an open ulcer or amputation, that had Charcot arthropathy, that had an ABI of less than 0.7. We did not accept anybody who had a TMA amputation or more proximal. Two of the patients in here did have toe amputations but none of the other patients had any amputations. None of these patients had active foot infections. None of them were impaired cognitively or at least we hope not and none of them had a history of drug or alcohol abuse within the last year, okay�or any other disorder that might affect their ability to walk.

    So all of our patients were recruited from the VA here in Phoenix, Carl T. Hayden and we collected the data, again, under three conditions � We had the patients walk in just their shoe, whatever shoe they had, their shoe plus the standard insole, and then their shoe plus the shear-reducing insole which is what we were looking at and we measured pressures in all three conditions.

    We used a computerized insole sensor system to evaluate pressures and this is very similar to what we did use in our study where the insole was placed within the shoe and then the patient just tethered to the computer and needs to walk. Each patient walked where we did a minimum of three trials on each patient. In some cases, it was more and we averaged the best results. And here are the results on that.

    Now, when you look at them carefully, what we see is if you're looking at the pressures in the forefoot within the shoe, they're high compared to the pressures within the standard insole and the shear-reducing insole, so not much difference there. And especially when we looked at the standard insole versus the shear-reducing insole, there was not a significant difference in pressure reduction.

    So our conclusion was that the shear-reducing insole provided significant reduction in peak planar pressures against the shoe alone but when we compared it to the standardized insole, the shear-reducing was comparable at reducing the pressures.

    Now, I need to explain some limitations of this study to put it into perspective. Number one, we did have a small end. It was a pilot project so we only had 20 patients. We did not control for the type of shoes that they had. All of the patients received their shoes from the VA System but not all of the shoes were identical in this. Some of them looked like an athletic-type of shoe. Some of them were the typical extra depth shoe that you see and the other caveat is we did not control for the age of the shoe or the age of the insole which means that some of these shoes that patients came in were right out of the box and some of those patients had been wearing that shoe for a certain amount of time.

    So I know what you're thinking � you're thinking, Denise, this is all great but you know, what does this mean to me when I go back to my practice and I see my patients? Well, I always have to do a comparative chart before I can make a decision by taking the literature and saying, what �what does this mean for me? And what am I really going to do with it? So I've listed a list of variables that I tend to do when I'm looking at do I want to use a product or do I not want to use a product and how will it benefit my patients? And if you look at that, both the standard and the shear-reducing accommodate well to shoe gear. They all come in a wide range of sizes and they're both for the most part depending on how you look at it, cost-effective. Do they both reduce pressures? Well, we've seen that no in two studies so they do both reduce pressures and do a good job with that but look at the last two lines. Durability is maybe an issue because the standard insole lasts approximately four months. This is why with the shoe bill, we usually replace or prescribe three insoles to our patients. With the shear-reducing insole is advertised to last between 12 and 18 months depending on the wear, and of course, with shear reduction, if you look at the bottom, we have the standard insole which is not proven to reduce shear and the shear-reducing of course which is. I don't know about you. When I'm looking at that, if I believe that pressure is the only thing I need to worry about in my patient, then maybe it doesn't matter which insole I prescribe. But if I am convinced and the literature is pointing that way that both shear and pressure are going to be critical in improving our patients' outcomes, then I think the way that I'm really going to want to go, is to give a patient something that offers both to them. So I want to leave you with this thought, and thank you.