Section: CME Category: Diabetic Foot

Amputation Principles for the Diabetic Foot "Decision Analysis"

Stephanie Wu, DPM, MSc

Stephanie C Wu, DPM, MSc gives a concise look at the difficult decision of lower extremity amputation. Dr Wu provides a detailed look at the WIFI system to aid in the amputation decision analysis, as well as patient factors to consider when determining level of amputation or possibility of limb salvage.

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Goals and Objectives
  1. Identify factors that would favor amputation vs. limb salvage
  2. Understand the WIFI system and how it aids in amputation decision analysis
  3. Discuss how to determine the appropriate level of amputation
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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: 12/31/2020

  • Author
  • Stephanie Wu, DPM, MSc

    Associate Dean of Research, Professor of Surgery
    Dr William M Scholl College of Podiatric Medicine
    Rosalind Franklin University of Medicine
    Chicago, IL

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    Stephanie Wu Stephanie C Wu, DPM, MSc has nothing to disclose.

  • Lecture Transcript
  • Okay. We’re switching gears again back to our surgical management of a diabetic foot. And since we’re in the Chicago area, I could think of no one other than our next speaker to give us her overview on amputation principles for the diabetic foot, a decision analysis or at least a decision analysis that she uses. So, Dr. Stephanie Wu is the Associate Dean of Research at the William Scholl School or Rosalind Franklin University here. Stephanie has published quite a bit. She’s a popular lecturer and professor. And I’m really very happy to have Stephanie joining us on the podium today. So, let’s welcome Dr. Stephanie Wu. Thank you.


    Dr. Stephanie Wu: Thank you Dr. Friedberg. First of all, disclosures, I have nothing to disclose for this lecture. Now, when we talk about diabetic amputations, let’s first take a look at the trends. In the rates of diabetes-related complications for the past two decades from about 1990 to about 2010 in US adults diagnosed with diabetes. And if we concentrate on lower extremity amputation which is the denoted by this dotted dark green line, I can’t really point it, there you go, you can see that from about 1990 to about 1995, there was a slight increase. However, from 1995 on, you can see this gradual decrease in the rate of amputation. Now, this decrease actually correlates really well with some of the other diabetes complications including heart attack which is denoted by the dotted orange line, stroke which is denoted by the solid green line, kidney failure denoted by the dash blue line here, slight decrease, same thing with this secondary to hyperglycemia. Now, all these can be attributed to all the limb-salvage work that we’re doing. When we look specifically at lower extremity amputations in the diabetic patient, you can see from this pie graph here that toe, foot, as well as ankle amputations consist of over half of all the lower extremity amputations that’s performed. However, as commonly as we perform these amputations, it’s important that we remember that we have to have extreme diligence in the decision analysis or our reasoning to support these amputations. As you can see by this old newspaper clipping here, this angry legless patient end up killing his doctor. I can’t tell you the number of cases I’d actually have come across my desk. In lawsuits, nowadays they may kill but a lot of times, you see lawsuits in patients who are angry and they’re suing their doctors because they lost their leg. In fact tomorrow, I have a deposition for this nursing home patient who’s suing the nursing home because she ended up with a below-knee amputation. So when we’re deciding looking at the amputation decision analysis, what are some of the factors that we should consider whether the patient should receive an amputation or whether we should try limb-salvage on the patient? One of the factors of course is the presence of gangrene. When you see gangrene present even if the patient is revascularable, the chances are it’s a high likelihood that this patient is going to end up with some form of amputation. Another factor to consider is nonrevascularization. If these patients are nonbypassable, if there’s nothing that we can do for these patients arterially, more or less likely, this patient is going to end up having some form of amputation. Another factor to consider is the infection, the severity of it, the greater the severity of infection, the greater the likelihood of the patient requiring amputation. Oftentimes though, it’s really not just one individual factor. It’s really a combination of these factors that’s involved in the patients. And it’s also important to remember patient selection because as dedicated as we are to saving salvaging these limbs, saving these feet, we have to make sure that the patient is going to be compliant, the patient has the mental capacity, the social capacity as well as the physical capacity in order to tolerate or endure the long processes that’s often associated with limb-salvage in this patient population.

    [05:11] And when we look at the causal factors that’s present in lower extremity amputation cases, really a lot of it is what we discussed earlier. You’ve got gangrene as well as ischemia, you’ve got the infection going on, we have nonhealing ulcer secondary to faulty healing. However, in a meta-analysis that was just published in February of this year where they looked at all the diabetic foot ulcer classifications out there and they try to correlate it with the risk of amputation, the meta-analysis found very little evidence to really support it. So in response to this, the Society for Vascular Surgery came up with this lower extremity threatened limb classification system. Now what this is, is really an amputation risk system that involves three components, wound, ischemia, as well as foot infection, hence the term WIFI for this name of this system. And what this system, unlike some of the other system, is it’s a synthesis of multiple previously published classification system schemes. So what they do is they kind of merged the system that’s really focused on diabetic foot ulcers, as well as pure ischemic models. And as you can see, this actually gets a little complicated. Now, in this WIFI system, it’s based on a scale from zero to three for each of the three components, the wound, ischemia, as well as foot infection. And for this, the scale zero represents none, one represents mild, two, moderate, and three, severe. So take the ischemia portion for example. You can see here that in a patient whose ABI is greater than 0.8 which many authors deem it okay for healing and that, chances are, you don’t need revascularization, they actually scored these patients with an API greater than 0.8 of zero. Conversely, for a patient whose API is less than 0.39 and whose toe pressure or transcutaneous oxygen pressure is less than 30 millimeters of mercury, they got a score of three. And as you can imagine, the higher the score, the greater the likelihood of the patient requiring an amputation. Now, the wound portion of this gets a little complex because unlike previous wound classifications that really looks at the depths, this one actually adds in a portion of gangrene. Now I know that previously if you look at the Wagner classification, they talked about gangrene but it wasn’t really as utilitarian as this one. The other component that they included in this is really how difficult or how much effort it requires to heal the wound. So for class zero here, there is no wound. For class one, it’s a superficial or small type of wound, usually bones shouldn’t exposed unless it’s really by the toe area, and it requires either some skin coverage or the application of the advanced bioengineered type of tissue replacements to heal it. And if necessary, maybe a toe amputation is required to close it. Grade two is a deeper type of wound where more extensive type reconstruction is required. And then by grade three, I went too quickly there, didn’t I? There we go. In grade three, this is extensive type of deep wounds or those deep heel ulcers, these type of large tissue deficits may require a free flap. And if amputation is required, it actually requires amputations that’s more proximal to the transmetatarsal joint, so meaning Lisfranc or Chopart type of amputation. Now the infection component of this classification correlates very well with the Infectious Disease Society of America classification, where zero correlates with uninfected, one correlates mildly infected, two correlates with moderately infected, and three correlates with severely infected. And the idea is the classification was validated by Dr. Lavery who you just heard from. And you can see from this graph here, in this longitudinal study where they looked at over 1666 patients, you can see that from where there is either no infection or mild infection, there’s barely any hospitalization required or amputation required all the way to moderate to severe where you have anywhere between 50% to 80% of these patients require hospitalization as well as amputation in these population. So with its correlation, it seems to do very nicely.

    [10:12] Dr. Stephanie Wu: So what they do was they combined it all. And as you can see, there’s actually 64 permutations that’s available because this is actually a very complex process. And so what the panel did was they looked at the estimated risk of amputation at one year for each of the combinations and they kind of color code it. And as you can imagine, the wound from having no wound to a big to large deficit, it increases. So as you go down, it increases the likelihood of having an amputation. And of course the severity of infection, having no infection to severe infection, it increases the likelihood of amputation. And same thing as you go from left to right here for the ischemia, the more ischemic the patient, the greater the likelihood for the patient requiring amputation. Now that we decided that yes, amputation is the route to go for this patient, we next need to determine the level of amputation. Now this is first determined by the level of vascular sufficiency which we will talk about in a few minutes. It’s also important when we’re considering in our decision analysis really the aftermath of the patient. After we do this amputation, is the patient going to have transfer lesions that’s ultimately going to result in the formation of new ulcers? If that’s the case, are we truly helping the patient with this type of amputation level selection? What about contractures? Will there be contractures after the amputation? If so, what kind of tendon balancings do we need to do to prevent this from occurring? The other point that’s important is really preserving the functional capacity of the patient. What is the rehabilitation goal for the patient after the surgery? Will the patient be able to ambulate either with a filler or with some sort of prosthesis? What about transfer? You know, transfer is something that a lot of times, we as surgeons kind of ignore a little bit. Why? But however, it’s important because really, it’s not whether the patient is able to ambulate with or without prostheses that keep them in and out of the, that’s not the decision factor in keeping them in a skilled nursing facility. It’s really whether the patient has the ability to transfer on that stump unassisted from say the wheelchair onto the bed or from the bed onto commode to allow them to determine whether the patient can be released to go home or whether they need to stay in a nursing facility. Other factors to consider include nutritional levels. Of course ideally, we want the total lymphocyte count to be greater than 1500 per microliter or the serum albumin level to be greater than 3000 milligrams per deciliter, good glycemic control as well as decreased tobacco use are all going to help facilitate better healing for the patient. The BMI for the patient, studies have found that for patients with BMIs greater than 35, a lot of times they end up being moderate ambulators. They’re not really walking around, so a lot of times we need to kind of keep that into our decision making for the patients because what are they going to do with their amputation stump after. And of course patient compliance is one of the keys to successful amputations in the patient population. As far as the level of vascular sufficiency, in addition to the basics such as palpation of pulses, Doppler’s, ankle-brachial index, gross noninvasive vascular studies such as pulse volume recording, we need to combine them with microvascular assessment. Things like toe pressure, transcutaneous oxygen pressure, skin perfusion pressure, even possibly fluorescein angiography, all these tools can help us really determine the level of vascular sufficiency and hence the level of amputation for the patient. Now this is actually a chart that was adapted from the vascular surgery group. And what it shows is really the hemodynamics and probability of healing of a diabetic foot ulcer. Remember back in the schooldays where we learned like 30 was key, you want the toe pressure to be, anything less than 30 indicates poor healing. Well, this is actually data that was just published in 2014. And it was modified by Dr. Joseph Mills as well as Dr. George Andros where they felt that the healing is less likely if the toe pressure is less than 55 millimeters of mercury. And finally just one quick point on preserving functional capacity for this patient, oftentimes in our quest for limb-salvage to preserve as much tissue as we possibly can, a lot of times with these patients end up with these deformed feet, with bony prominences and ulcerations secondary to these bony prominences.

    [15:10] And in this case, it’s actually would have been easier even though it is a proximal type of amputation to have done a Chopart amputation in this patient. You can see this on reattaching the tendon here, flapping over the skin, the drain, and the patient actually ended up doing well now that he has a functional stump that allows him to transfer and ambulate with a filler. And when we talk about limb-salvage in all these patients, it’s almost like a marriage. And if you think about it, the minute that we actually take these wounds and we start debriding, it’s almost like a courtship. And then by the time we actually perform surgeries on these patients, that’s when we seal the deal, you know, you’re now married to your patient. And a lot of times, this marriage has this bad connotation to it. However, it’s important to remember that if you’re passionate about it, having mutual respect with the patient, having good communication with the patient, it’s all going to be helpful and it can lead to a successful marriage. Yes, things will go wrong on you. However, with mutual understanding, mutual good communication, we can actually help the patient and walk through this together to help with our quest for limb-salvage. Thank you.