Section: CME Category: Biomechanics

The Impact of Biomechanics on Your Surgical Outcomes

Jarrod Shapiro, DPM

Jarrod Shapiro, DPM demonstrates the relationship between surgery and lower extremity biomechanics. Dr Shapiro also discusses how specific biomechanical principles factor in the choice of surgical procedures.

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Goals and Objectives
  1. Understand the overlap between surgical and nonsurgical biomechanics.
  2. Apply specific biomechanics principles to choose procedures.
  3. Appreciate the evidence behind certain surgical procedures.
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    Release Date: 11/20/2018 Expiration Date: 12/31/2020

  • Author
  • Jarrod Shapiro, DPM

    Associate Professor, College of Podiatric Medicine
    Western University of Health Sciences, Pomona, CA
    Associate Editor PRESENT Podiatry Online

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    Jarrod Shapiro Dr. Shapiro has nothing to disclose

  • Lecture Transcript
  • TAPE STARTS – [00:00]


    Speaker: So I am going to talk about biomechanics in surgery and I have no disclosure. I don't own on a podiatry lab, so maybe that's a positive. So what I would like to talk to you about really is about thought process and how you determine what you're planning to do surgically. So it's kind of really what we are going to talk about. When I was originally trained, there was a disparity in biomechanics between orthotic therapy and surgery. I was taught that biomechanics equals orthotics and surgery was something totally different and the two never seem to meet. I think that's a completely wrong way to look at things and I think we need to change that. So what I think it really makes more sense is that both of these things are aspects of the same continuum of care for your patient. They are tools that work together as opposed to being something completely separate. So whether or not you believe in custom foot orthotics or whatever theory of mechanics you might be interested in, the two's biomechanics and surgery are really are going to work together. I am going to kind of show you how that might look. So what I think makes us unique in podiatry is our understanding of foot function and that is different from a lot of other specialties. So one of the places I trained vascular surgery would do a foot amputation or partial foot amputation and they would guillotine it and then send it to podiatry for the wound care. We know that the vast majorities patients, they really don't need that. You can have a better mechanically planned amputation, for example.

    [02:01]

    So this is a transmet amputation and you know why would you maybe do a tendo-Achilles lengthening for an amputation. We know that that is to decrease plantar pressures in the forefoot and prevent recurrent ulcerations like this one. So what we are really looking at then is pressure. No one is saying you know where is this located in space and all that type of things. So if we do this with our diabetic patients so much better than everyone else, why don't we just approach how we determine what we do with our other surgical procedures from the same way. So it's not necessarily just about where the bones are and the positions of the foot and that type of thing, but it's really about pressure re-distribution and having better function. In the past, what we have seen in the research as well as in many of your private practices was a goal in making the foot straight. And I am going to spend most of this discussion on flatfoot sort of related conditions. What we were really emphasizing are measuring ankles on x-rays looking at the positions of joints, finding neutral position and then determining maybe a planal dominance for say flatfoot deformities. But there is another way to look at this. So being flat doesn't equal better. Even back in '87, people were talking about this that you know the goal of an operation is to completely correct the deformity. And I would argue with you that it is not to completely correct the deformity, it's to get rid of a patient's pain and if I can do that and maybe the foot is slightly flat or someone's cavus foot is not completely prefect and the patient is doing better, then that is what matters. So it's not really about getting a straight foot. If that were the case, I could just fuse all kinds of joints and who cares about function.

    [04:03]

    It's straight and it must be better. We know that that's not true. So if you have this kind of thing coming to your office, you know, pes planus patient, maybe PTD, some issues, you might treat this with orthotics and your various menu of options for modifications for your orthotics. So that's relatively easy. You know you write your prescription. Why do we make surgery so complicated? That was my question. You know why does it have to be a really complicated situation? And in fact, there's really no difference between what you do surgically and what you might do whether orthotics or other kinds of therapies. So there is a real overlap in what these things are doing. So if you consider this as your orthotic therapy adjusting forces around the foot or pressures, you're manipulating the way the foot works, that's often times similar to what you are doing surgically. So the example here I have is a Kirby heel skive. The idea of it is to increase the orthotic reactive force medial to the subtalar joint axis to cause supination around the subtalar joint. Well, part of the job of a medial calcaneal displacement osteotomy is the same thing, right? You are trying to move the calcaneus medially so that it causes more material, more stuff, more calcaneus underneath the kind of medial to the subtalar joint and the cause that same type of thing. Now, we know it's also for medializing the Achilles and that type of thing so it's a bit more powerful per se as an individual kind of treatment option, but they are basically doing the same thing. I think there is a better way to sort of look at your choice for surgical procedures and that's this kind of three-step approach. So you determine the damage you know what anatomical part is damaged.

    [06:03]

    You figure out why? Why that's happening and then you fix it in whatever way you choose to do that. So the first step of that again is to determine the damage. So look at the pathoanatomy. Neuropathic ulcers or foot ulcers, they are pretty easy to determine sort of what's damaged. You know kind of there is a hole in the particular part and that's pretty easy. Plantar fascia, you know that the problem is in the plantar fascia. It's insertion on the calcaneus. That part of things is pretty easy. You do history and physical and you do exactly what you are doing now but you are identifying what exact anatomical structure is the problem. That was the first step. The second step is a little bit more complicated and you are kind of clarifying for yourself why the person has that particular problem? So you are going to look at a couple of things. You are going to look at the pathomechanics and the forces that that act on the foot. So you are going to do that of course by doing an exam. And you know for the residents and the audience, I know we kind of you know talk about biomechanical exams and how many you have to log and that kind of stuff. But in reality, most of these are simply exams. They are not biomechanical exam. They are just examination so that you understand what's happening with the patient's foot to help you to treat them. So for me, I tend to start with a standing exam first. Most of these patients have problems when they are standing. So I look at the overall appearance, patellar position, you know the super structural problems that have a genu valgum varum, their resting calcaneal stance position and then the overall reducibility of whatever their deformity is. So you could see these are both different types of things. You have kind of picture the middle fellow with -- you know he has limb length discrepancy and he is compensating by contracting the gastroc in order to put the toes on the ground. So I am figuring out, okay, what is it about this that's you are causing the problem that the patient came in complained about?

    [08:01]

    My second thing tends to be a gait exam. I am looking for all the things that you are taught. This is nothing different really you know so far than what you already know. Are there limb length discrepancies, whether their heel strike, are they maximally pronated and staying there, are they re-supinating correctly, does this swing leg have any problems? And then like everybody else I do my seated exam. You know in practice, I try to be relatively quick. I don't want to take three hours to do a biomechanical exam. So I tend to look at few main things. I am looking at sort of rear foot to the leg. I am looking at the forefoot to the rear foot. Are there calluses so I know what pressures is being distributed and then any special or provocative test. So there is a variety of those related to specific diseases. Things like forefoot and then measurement of the location of the subtalar joint axis. So one of those kind of provocative methods might help you to determine what's the problem and this is for patients with posterior tibial tendon dysfunction or maybe dysfunction of flatfoot and this is called the neutral heel lateral push test and you are looking to see the integrity of the spring ligament. So you hold the heel essentially in a rectus. If you want to call neutral, go ahead. So a rectus position and then you are attempting to abduct the rest of the foot. And you can grade this by how severe abduction you are able to get and this helps you to determine the integrity of the spring ligament. So we know that for the patient's with PTD the spring ligament since it's a major arch stabilizer, this may be something that you need to address. So you will know, okay, well, my patient has PTD, they have pain along the posterior tibial tendon at whatever various points and then I know that some of the pathomechanics behind this would be an unstable mid tarsal joint with very poor ligamentuous support.

    [10:10]

    So how about your bunions? So understanding the pathomechanics also becomes important for this. So you know we typically tell everybody that Lapidus is for hypermobility, maybe a wide IM angle, that type of things. But what if you think about this in another way? Maybe a Lapidus is for something else. How about that there is an actual variety of motion that occurs in the medial column? So first ray motion has actually been shown to be multiple joints, so we only get about 41% of motion through the first metatarsal cuneiform joint. So when you do that first ray excursion test, you're really looking at the entire arch and how it's moving. So if you are to a Lapidus procedure, you are removing somewhere closer to 50% of the motion of the medial column and that's an important thing if you're considering a patient who has a bunion and maybe it's caused by excessive pronation causing the hypermobility. If you fuse that, you are doing something besides just fixing the bunion. We also know that an everted first metatarsal and when it sits that way it tends to be in a sort of what's called closed pack position you know where the met and medial cuneiform are in line with each other that makes for a much tighter joint, which holds together well. So again another benefit of Lapidus procedure and when you do those things, you are re-establishing the function of the peroneus longus to evert and plantar flex the first ray. So the Lapidus if we understand sort of the mechanics that go behind the problem, we know that this is also an arch stabilizing procedure in addition to fixing the patient's bunion.

    [12:03]

    So how about plantar fasciitis? We have heard this argument is a plantar fasciitis or plantar fasciosis. Your treatment might change depending on your kind of view of this. Lamont sometime ago did project where they found that this was really a chronic degenerative problem with myxoid degeneration and not an acute inflammatory problem. They have also found that mechanical forces like an everted calcaneus and the presence of equinus are both really significant risk factors for patients having plantar fascial or heel pain symptoms. If you believe that type of thing and you know that this is a chronic degenerative condition at least for those patients who've had it for sometime, then you may not necessarily inject the heel with a steroid. That might be an argument perhaps against it and then the steroid then becomes more of a symptomatic treatment and not necessarily something that you are trying to use to cure it. So I mentioned about looking at forces. I am not a mathematician and I am not a physicist. I can barely count, so math is not my thing. So I like kind of simple things. Kevin Kirby came up with the idea of the rotational equilibrium and basically if you find where the subtalar joint axis is sitting in a transverse plane, then you can understand how the rear foot is functioning and then use that information to help treat your patients. So in these pictures, you can kind of see on your left that sort of normal subtalar joint location kind of runs between the first and second toe and when that happens, when you strike, the ground is allowing an eversion or supination moment to occur at the subtalar joint and the patient will function better. If the subtalar joint is medially deviated, then you are going to get excess forces on the lateral side and that's going to push the patient into pronation.

    [14:03]

    So the ground works on the foot in those ways, but we also have tendons that are doing all kinds of things, right? So if we have in the middle picture there, that's a normal subtalar joint axis location and you can see that the Achilles insertion is medial to the subtalar joint axis. So when the person fires his gastroc, it will cause not just the plantar flexion but an inversion of the subtalar joint. All good stuff, right? That's what we want. But if they are deviated medially, then the Achilles insertion is now sitting lateral to its insertion and it becomes a pronator. The same thing is true for a lot of the other tendons. So we might think, okay, we'll find no where the subtalar joint is sitting. I can use that information whether it's surgically or non-surgically to help to realign this and have better forces functioning around the foot. So the examination for this is actually pretty easy. What you are doing is you are basically placing the forefoot kind of parallel to the end of your chair. So that's kind of what you are using to line up. You are making sure that the knee is straight, orthogonal, up and down and you are just going to load the fifth metatarsal head. You are not putting the subtalar joint into neutral position. You are just simply essentially holding the foot and then you are going to palpate medial and lateral and when you hit the spot where the subtalar joint axis is, that's the spot that will not move because you are right on the axis. You mark that with a pen and then you are going to get aligned that's going to go somewhere on the heel to somewhere on the forefoot and the optimal is that that line is running about to the second toe or to just between the first and second toe. That would be normal. So that would give you some information.

    [16:00]

    So it that a valid method of examination and it turns out that it is. So this has been studied and they found that the interradial reliability was relatively high. So that's a good thing. We like that. So then moving on your next step, you have done your history, you have done your physical. You know what the problem anatomical structure is and you know what the mechanical forces going on behind it are causing the problem. You are then going to fix it in whatever way you decide. So how you do that is going to be looking at this as I am adjusting the forces inside and outside the foot and then you have to understand exactly what your procedures of doing. That's why you have to kind of sort of look at the research literature to know that for sure. So this is a patient of mine who some years ago, she has classic hammertoe deformity. She had an ulcer. We did very simple. We just essentially straightened her toe out and that got rid of her ulcer. That's really easy. We adjust the forces that were on that skin by straightening the toe out and that part of things is pretty easy. That's an inside sort of adjustment. So what about orthotics, if you compare orthosis and surgery. So if my goal is to increase subtalar supination, I can do that with an orthotic with maybe a medial heel skive or any variety of things and medial phalange, high medial arch or you could do surgery. You could do a medial displacement calc osteotomy as an example. What if I wanted to medialize the Achilles? Same thing, rear foot varus post will do that to some extent and maybe to a little bit greater if you have gotten to the point where you are going to do surgery that you do a medial displacement calc osteotomy and you can even varus it a little bit if you want it. There are of course other options available for that. So you are thinking instead of making something straight, I am trying to adjust the forces that are acting on the foot.

    [18:04]

    I think this is a little easier way to go. If I want to stabilize the medial arch, I have an orthotic method and I have a surgical method. Maybe I want to fuse the joint or something. Varus supinatus and forefoot varus. You have got a Cotton osteotomy or you have first ray cut out or valgus posting for your orthosis, really simple kind of things but you will notice that in all of these cases, the surgical procedure is doing exactly the same thing that the orthotic therapy is doing. It's just that one is essentially inside and one is outside. If you want to get rid of forefoot abduction, you know that's not the easiest thing to take care for with orthotics. A lot these patients end up with an Evans osteotomy and then maybe before that you try adding a kind of longer lateral clip, which will prevent the forefoot from abducting. So in all of these cases though, I would say that the surgery is generally a more powerful way to go because those have much more significant interactions with the body. So you know have to know what those procedures are doing. It's not just the matter of, I have a transverse plane deformity, I am going to pick this procedure but in fact these procedures do a lot more than what you might think. We know the Evans osteotomy is good for transverse plane but it also re-establishes midtarsal joint function. It allows the peroneus longus to work better and those types of things are important because it does more than simply just the transverse plane issue. So there has been some research that's gone on about these and what these do. Most of it is still kind of early stages as far as you know they are doing them on cadaver. It's hard to do these things on actual human beings. What they found with this particular study that looked at the Evans, they found that it decreased the forces at the talonavicular joint.

    [20:00]

    Here is a medial displacement calc osteotomy, very similar type of things. So if you have a patient with posterior tibial tendon dysfunction, these research projects are proving to us that we can reduce the stress on the particular you know like it's a PT tendon in this case, we can reduce the stress on this by doing these procedures. So I am not aiming at a straight foot per se. I am aiming more at trying to adjust the forces to reduce the stress. Same thing for an arthroereisis. It's been found to decrease the moments or the pressures or the forces around the talonavicular joint. So this is one of the ways that we can start to learn about what these procedures are really doing for us. So how about this one. Now, for quite sometime, I would do my flatfoot reconstruction and I would add gastroc recession, that would be the first thing I would do when I did my flatfoot reconstruction. But then you actually have to wonder if that's really the best way for us to go. So this study looked at two versions of a medial displacement calcaneal osteotomy. The first one is where they adjust slit it over in a pretty standard fashion and the second one is where they put a bone graft in to both slide it medially but also add length to the calcaneus. They found that that one was a more effective way to decrease forces on the PT tendon as well as decrease the amount of work that the Achilles had to do in order to plantar flex the foot. So that's pretty interesting. I wonder, do we really actually need a gastroc recession for our flatfoot reconstructions? So this is a patient of mine. This patient had surgery on both feet at different times. So the first one was the right side. So she had sinus tarsi syndrome.

    [22:02]

    When I was originally trained, we were taught to do sinus tarsectomies and just remove a bunch of stuff and the patient is okay. And this patient was a little different. So she had her painful right sinus tarsi and then subsequent to that later about a year later, she had PT tendon dysfunction on the other side, so we treated that left side later. You can kind of see how she is standing inverted on that left side and you know she is clearly flat, she is dysfunctional, she has that increased pressure on the medial side. So I try to clarify why that was happening, so this patient obviously she is pronated. She has immediately deviated subtalar joint axis. She has increased arch strain especially on the left side for that PT tendon type. So we then looked at her and I think this one is a video, if you guys might hit that. So if you watch this, I have asked her to keep her feet stable and just externally rotate and you will kind of see in a second there she is starting to externally rotate and you could see that she is pretty flexible. She straightens back out and she collapses completely once she gets into her relaxed calcaneal stance position. So this is telling me that her medial support structures, her spring ligament is really not working particularly well. So I have adjusted the forces. We tried non-surgical and that didn't work for this patient. So then she proceeded to surgery. This is the post-op and what we did with this patient, just sinus tarsi on the right side, we did a medial displacement calc osteotomy and I did at that time do a gastroc recession. So what we did was not particularly try to straighten her out. I wasn't trying to increase her arch height or do anything cosmetic in that sense.

    [24:01]

    All I want to do is try to get her to supinate more so she has decreased lateral pressure and she is not getting that jamming into her sinus tarsi. Well, that was pretty successful. So then on the other side was a little bit different. So she had PTD, so we approached this one a little differently. This is her post-op by the way for the right side, so we did a calc slide. You can see I came just a little close to air balling the medial screw, not particularly happy with that but it worked okay. She feels fine. You can see how far we moved her over. So that decreased the forces on the lateral side of her hindfoot and she was now a slightly more, if you want to call, inverted or she supinated, so that removed the pressure from the lateral side in her sinus tarsi. So the left, this was her pre-op. Now, if I were to look at this with my students and I ask them what plane is dominant, they might say a transverse plane dominance. You can see that really significant talar head uncovering and the CC joint abduction. She has got a lower calc inclination angle. My problem with planar dominance has always been that every patient seems to have multiple planes that you could say might be dominant and it's hard to pick out exactly one plane all the time. So instead of that, I think while this patient has PTD. Her posterior tib is a problem. So what can we do to decrease the forces around that? So what we did was a double calc osteotomy. I wanted to medialize the calcaneus so that we increase the forces on the plantar medial side of the heel. We did the Evans of course as part of this double calc osteotomies. I am trying to abduct the forefoot, but I want to get that peroneus longus to restart its function again.

    [26:01]

    And then we also did a spring ligament repair, so not the old fashion desmoplasty but an actual spring ligament repair where we used an allograft to fix this. Looking at this critically now, looking back, I want to actually include the navicular cuneiform joint in this. I think I would have liked that better. But you can see she is a little bit better than she was before. So there is her pre-op and her post-op on the side that we did that double calc osteotomy. By the way, I didn't do a gastroc recession at all. So by medializing the calcaneus, I have increased the pole of normally functioning muscle. So instead of being a pronator, it's now a supinator and here you go, she has a foot that's a bit more normal in function. So five weeks out after the surgery, she is fully walking and she is pain-free, fabulous. We got rid of the forces that were causing problems with it. This woman is about 250 pounds. So she is not really small. I think I was a little brave not doing an arch fusion procedure given her weight, but I guess in 10 years from now we will report back on whether or not she was successful. So there is her post-op for the other side, pre and post. If you looked at this, yeah, she is straighter. But what matters is not how straight she is but whether or not she is pain-free. Straights not that hard. So last example here, this is a patient, obvious, it's neuropathic ulcer. He has a cavus foot. He has a rigid first ray. He had previously had his medial, his tibial sesamoid removed but he continued to have this ulceration, came back. So what we did was there we go, his post-op. So we did essentially a dorsiflexory Lapidus procedure. We got rid of the pressures on the plantar surface. We did include a gastroc recession into this because I wanted to decrease the pressures in the forefoot.

    [28:04]

    This patient is fully ambulatory and doing well. I didn't elevate the first metatarsal so much that I am worried about transverse lesions to the second. These are small amounts of elevation. So to kind of end this off here, I think if you want to make better decision surgically, you are going to first look at the damage. What's damaged, what anatomical structure is the problem. You are going to clarify why looking at your pathomechanics and what forces are acting on the foot and then you are going to fix it in whatever kind of way you feel is best based on the evaluation that you have done and when you do that, you are going to be addressing forces. And if you understand the way the procedures what they are actually doing, you have tools that will be more successful for you. Okay, thank you very much.



    TAPE ENDS - [28:54]