Section: CME Category: Podopediatrics

Pes Planus Mechanical and Surgical Considerations

Marc Benard, DPM

Marc A Benard, DPM explains the biomechanics of Pediatric Pes Planus, its etiology and the keys to remember on clinical and radiographic exam.

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Goals and Objectives
  1. Understand the etiology of Pes Planus in children and adults
  2. Review pertinent anatomy as well as considerations of levels and planes of compensation
  3. Describe effects on the foot from muscle and joint malalignment
  4. Understand gait events from heel contact to mid-stance to propulsion
  5. Review and understand closed chain function
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    Release Date: 03/16/2018 Expiration Date: 12/31/2020

  • Author
  • Marc Benard, DPM

    Assistant Executive Director, American Board of Podiatric Medicine
    Co-director, Baja Project for Crippled Children
    Hermosa Beach, CA

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


    Male Speaker 1: Our next speaker is Dr. Mark Bernard who is the executive director of the American Board of Podiatric Medicine. He is co-director of Baja Project for Crippled Children. He is the executive director for, as I have stated, American Board of Podiatric Medicine, co-director of the Baja Project. He has done extensive work with children. And Mark and I go back a long time in our proponents of this concept of biomechanics and how important it is. So we've always acknowledged one another saying what can we do for this profession to get them to understand the significance of it. Whether you're surgeon or not, you better know your biomechanics. So today, Mark is going to share his thoughts on a very interesting topic and it relates to pediatric flatfoot, biomechanical and surgical considerations. Please welcome Dr. Mark Bernard.

    Male Speaker 2: See if we can this working. And there we go. We're going to expand this a little bit so that we can bring in the adult flexible pes planovalgus as well because most of the population, podiatric population, sees adults rather than what I pretty much and Harold in large part see which is almost exclusively pediatric, but a lot of these concepts are very similar and it's critical that you --I know it's late in the day -- but it's critical that you pay attention to what I'm covering so that you can understand the context in which you need to approach a flexible flatfoot deformity. Again, this is the kind of deformity that we're looking at, but what concerns Harold and I and others that are well grounded in biomechanical basis of much of what we're operating on or treating conservatively is the fact that if you're not well grounded and that the tendency is to have a hammer and then the world becomes a nail, you tend to look at things statically rather than dynamically. You tend to skip steps in doing your assessment of these pathologies or these clinical entities and miss a lot. And then on top of everything else, you're relying on two dimensional static images that are taken in bilateral stance, which tell you absolutely nothing about what's happening in the real world with that foot. The only feet that develop symptoms that are in stance tend to be insensate feet. Vast majority of patients regardless of the foot type develop their symptomatology in mid stance and propulsion with single limb support. So there are some key things I'm going to ask you to want to take away from this lecture, which you're going to apply not only to flexible flatfoot, but many other conditions that you may encounter during the course of this conference or future conferences. Let’s talk about pes planus specifically. Etiology; there are several causative factors that will cause the pes planus condition, equinus for sure. Within that context by far the most common if there is an equinus is going to be the gastroc equinus. Occasionally, you'll get a gastroc-soleus, but it's rather a rare bird. Gastroc equinus, which we will cover in more detail later, very important when it's present as a causative factor. So you need to rule it in or rule it out. Limb length discrepancy; if you encounter a patient that's got asymmetric feet, which happens often enough by the way that though it's the exception to the rule it happens often enough and you'll see this at the tail end of this lecture. It's essential that you assume that the patient is asymmetric until you find out otherwise and I'll show you very keen example of that. Congenital conditions, talipes calcaneovalgus, which usually resolves spontaneously, sometimes doesn't. And so you've retention of a hyper-pronated foot type if it does not resolve. So if you happen to see pediatric patient population, you want to follow it rather well to see if in fact it’s taken its normal course.

    [5:00]

    You've got to check your forefoot to mid foot influences on the foot type, forefoot varus not to insult anybody’s intelligence, but forefoot varus, forefoot supinatus and then you've got to understand you have enough depth of understanding of biomechanics to understand why a compensated or partially compensated forefoot is much more important than a fully compensated forefoot. You also have to be aware of the plane of motion, predominant plane of motion at the metatarsal joint. If you have got increased transverse plane mobility in a foot, then it pretty much doesn't matter how nice the foot looks at heel contact intimate stance, it's not going to be stable into late mid stance and propulsion. You've got to assess all of these things dynamically and weightbearing as well as nonweightbearing and don't just rely on angles and dangles in two dimensional static images. You can have metatarsus adductus, which has been compensated. So what happens is you have a parent that has brought a child later than you otherwise you would normally see the condition where the forefoot is adducted on the hindfoot. Now as the child becomes weightbearing and propulsive and starts to ambulate, if the subtalar joint starts to compensate because the forefoot is adducted, then they have an outgrown the adductus. They’ve compensated out of the adductus and what you think as a pes planus is actually a compensated metatarsus adductus. So many reasons to want to check the hindfoot and the foot in general in a neutral and in a relaxed position. Skew foot, I'm going to bypass for this lecture because it's a rather rare entity. If you're interested, there are many papers on it. I have a paper out on it for some years ago, but you'll probably not come across it. What is important is what you don't want to do is confuse a skew foot for a metatarsus adductus because the treatment of metatarsus adductus be it nonsurgical or surgical is much easier than the treatment of a skew foot. Therefore you don't want to miss the skew foot. Torsional rotational factors, very important. Persistent internal tibial torsion creates a demand in an older child to bring their feet into the plane of progression. So you see many adducted angles of gait in young children, but you very, very rarely see an adducted angle of gait in an adult, why? because if they haven't compensated at the lower leg and spun out with normal development, what they end up doing is they pronate out of the problem. So you need to make sure and you'll be presented with a pes planus when in fact what the original condition was with an internal tibial torsion or an internal femoral position. And then there are other things that are more on the edge of the bell curve. We would see a lot in the environment that I practice or see third world environment, but there are other soft tissue conditions, Marfan’s, Ehler-Danlos, things like that. I bring this into the picture to make you aware that the most important thing is don't assume all pes planus conditions are the same thing. You've got to treat every patient individually and rule in or rule out. Obviously, trauma or ruptured PT, paresis, neurologic conditions can cause pes planus. Now, going back to the big picture. It's generally considered a weightbearing collapse of the medial longitudinal arch. This is a foot that when nonweightbearing pretty much looks like a normal contour. The issue is the motion that it goes through with weightbearing and particularly during gait. In children, although I'm going to not limit this lecture to kids, but this is important; children’s complaints are rarely of pain. When a child complains, it’s I'm tired, I don't want to do this, pick me up at the end of the day things like that, or they fatigue early or they just don't want to do it. It's not that they will say my foot hurts me.

    [10:04]

    You get older children or teenagers into the adult population, that’s when you start getting clinical symptoms that we associate as pain. So if a child presents just because they are not saying it hurts me, don't assume that they are not symptomatic, alright. Typically, what you'll find as a maximally pronated subtalar joint with a quote, quote and I'm going to spend a lot of time with this. It's important that you get what -- this is one of the critical parts of this lecture. Maximally pronated subtalar joint with what is generally spoken off or written off as “everted calcaneus at mid stance or in stance.” I'm going to tell you what that really is to try and if anything dispel some myths or clarify for you what's really going on. The maximally pronated subtalar joint creates a condition called medial malalignment of the leg on the foot. And when that occurs, the talus plantar flexes and adducts on the calcaneus, which exacerbates the offset. I'm going to show you picture of it. In other words, Kite's angle opens in a closed chain scenario. Clinically though if you're dealing with flexible pes planovalgus, the foot will be able to re-supinate in either tandem heel raises or single leg heel raises. This is what I'm talking about. Look at the position of the foot on the left in stance and that’s a rather pronated foot. You can see the bulge of the talar head medially below the medial malleolus. You can see just how medial the medial malleolus is relative to the position of the heel. In young children -- this is not a young child -- but in young children because of the baby fat that is around the heel, you'll get an optical illusion that the heel is actually everted. But it has pretty much been proven that unless you have a traumatically induced situation or true ankle valgus, which I'll show you a picture of -- a radiograph of -- later on. The calcaneus doesn't evert beyond perpendicular. There has been a very elegant study a few years ago by Japanese orthopedists that pretty much proved that the calcaneus doesn't evert beyond perpendicular. So to talk about an everted heel is misleading. You read it in the literature, but it will confuse you as to what's really going on. Hopefully, I can clarify that for you. But here no matter how much pronation you may see here when this person brings the heels off the ground, you see that the heel realigns under the leg, which speaks to the fact that the mid tarsus has a locking mechanism. If you look at the illustration on the left, you will see that if you drop a perpendicular to bisect the tibia and bisect the heel, the calcaneus, they are not necessarily in alignment, but they are coaxial, meaning that they are parallel to one another. Look at the clinical scenario on your right. What you see there is the white line bisects the calcaneus and yellow line is the bisection of the tibia coming through at the ankle joint where it's crossing a line going across the malleoli. You see that below that pretty much horizontal line, those lines diverge. That’s what I'm talking about. You can appreciate here; if that heel is being held on the ground by ground reactive force and the leg is driving the talus into an adducted and plantar flexed position, you get this tremendous offset medial to lateral. I'll repeat what I just said, the heel is captive on the ground. Frictional forces are holding it there. What is moving, as the leg comes over the planted foot and internally rotates, heel contact pronation, not to insult your intelligence, heel contact pronation, leg internally rotates, the talus is captive in the ankle mortise in the transverse plane because the malleoli are holding it.

    [15:03]

    So if the leg internally rotates, they are going to take the talus with it medially. What does that do, that opens Kite’s angle. That’s why you see in the clinical photo, the bulge below the malleolus, that’s the talar head. Look at where the talar head is and look at where the plantar aspect of the heel is. We will develop this concept a little further. Also notice that when the foot is in this attitude -- now remember this is showing a single limb and this is what you're going to be seeing. This is when the patient develops pathology. They are in single limb support at this point. Swing phase limits doing its thing. This is where the stance phase limb is, in mid stance and inter-propulsion. Look at the offset between where the tendo-Achilles is and the back of the leg. You see what I'm talking about. Where the tendo-Achilles is relative to the back of the ankle joint. You see how it's much closer to the fibular malleolus than it is to the medial malleolus. I want you to look at -- and we're going to come back to that. I want you to look at one other thing because it's important that you understand what this really means. When I ask residents and I probably lecture maybe 300 residents a year at various [Indecipherable] [0:16:39] around the country. I said tell me what too many toe sign means and almost uniformly they will tell me that it's the forefoot is abducted on the hindfoot. The forefoot is abducted on the hindfoot, well is that true? If the hindfoot is captive on the ground at contact and the forefoot is now captive on the ground at mid stance, the forefoot can't abduct on the hindfoot. What's moving? What's moving is the mid foot. Internal rotation of the tibia and external rotation of the tibia is what moves the talus medial and lateral over the calcaneus. It's what opens and closes Kite’s angle. So when you see a patient that has got concavity on the lateral border of the foot in stance or in gait, what you're looking at is the mid foot moving medially relative to the hindfoot and forefoot. You see what I'm getting at? Because the hindfoot and forefoot can't move. They are held on the ground by frictional forces. And it's important that you understand this because when you see a foot type like this and in a nonweightbearing situation, you're going to cup the heel, hold the subtalar joint in neutral. And when you check midtarsal joint range of motion, you're going to find that mostly you're going to get transverse plane motion instead of frontal motion. Why is that important? Because it has tremendous implications on your ability to control that foot with either an orthotic or through the surgical procedure or procedures that you choose. Biomechanics is not about orthotics. It's about understanding how feet works so that you're going to apply what you need to apply in your clinician’s tool box to get that foot to function better. It may be some combination of surgery and/or orthotics. It may be one or the other, but the bottom line is you still have to understand how feet work. And this is showing -- look at Kite’s angle and how it is broadened, bisection of the talus on the right or the left, but the lines are on the right, projects way medial to the first metatarsal. And another thing that you are often heard and here lecturers talk about and I go, you know, you're misleading people. They talk about uncovering of the talus as though the navicula moves out of the way and uncovers the talus. That’s not what happens. What happens is the hindfoot is captive on the ground, the forefoot is captive on the ground and when the tibia internally rotates, it's pulling the talus or rotating the talus medially. So what's uncovering the talus is the fact that Kite’s angle is opening and the talus is adducting and plantarflexing. The fact that the navicula becomes abducted on the talus is passive. The active motion is the talar head is moving medially and plantarflexing.

    [20:02]

    Alright so uncovering of the talus is due to motion of the talus, not due to motion of the forefoot. I want to build on the concept of gastroc-soleus influence on the subtalar joint in mid stance and propulsion. The main function of the soleus -- I don't have time to get into, to ask you questions and answer to make you think about this a little bit more. So I'm just going to give it to you. The soleus is the prime muscle that delays anterior motion of the leg on the planted foot, why? Where does the soleus originate? Proximal tibia, little bit of the fibula but proximal tibia, below the knee, yes? Where does it insert? Through the tendo-Achilles into the calcaneus. So in the closed chain environment when the leg moves over the planted foot, tension develops in the soleus to delay rapid anterior motion of the leg on the foot because if tension didn't develop in the soleus when the gastroc contracts, it buckle your knee. You've got the gastroc contracting, which is getting ready to pull the heel off the ground. The soleus is contracting below the knee, which is delaying rapid anterior motion of the leg over the planted foot. There is a reason I bring this up. So let’s develop this. By the way, the tibialis posterior is assistive in delaying pronation at this point in the gait cycle. Tibialis posterior is not a primary resupinator of the foot in closed chain. It is in open chain. If I had you sitting and I asked you to plantar flex and invert your foot where it's dangling off the end of a table, that’s tibialis posterior, open chain. Closed chain, that’s not what it does. What it does in closed chain is it's a decelerator of pronation. As it contracts, it's resisting heel contact, ground reactive force to rapidly pronate the foot. So you get a gradual smooth pronatory moment. I want to take a look at these three pictures. First of all, look at the image on the left. That’s the soleus. As you can see it, it originates below the knee and inserts into the calcaneus. Look at its position relative to the subtalar joint access. What happens is we thinks of the gastroc-soleus as having its primary function at the ankle joint, which is true in the sagittal plane. But what is also true is because the insertion of the tendo-Achilles is actually below the subtalar joint. If that foot is pronated when it should be neutral, the contracture of that muscle is going to maintain that foot in a pronated position. Look at the clinical photo in the middle. That’s a neutral foot and look at where the tendo-Achilles is relative to the posterior aspect of the leg. You see that it's centralized. That will tell you whether the foot is clinically in neutral position in mid stance or propulsion. Look at what happens in a foot, upper right when a foot is pronated. The muscles stayed in the same position, the tendo-Achilles position didn't shift, what shifted?, the leg. Because Kite’s angle opened, the leg moved medial relative to the planted foot. And conversely, we're not going to talk about cavus feet at this time, but the reverse happens when the foot is overly supinated as you see in the lower right. But as you see in the upper right if that foot is hyperpronated, when it should not be, once that soleus muscle contracts to delay anterior motion of the leg over the planted foot, it's going to maintain that foot in a pronated position because the gastroc-soleus taken together is the second strongest muscle in the body, the gluteus being as a group, the strongest.

    [25:00]

    So not only is the gastroc-soleus, that’s why the gastroc-soleus complex is so influential in a pes planus foot type. It's not that it creates the pes planus, but it maintains the hyper pronated state of the foot. And this is just a clinical representation of the fact that the insertion point of the soleus via the tendo-Achilles is below the subtalar joint. So what happens? Assuming there is adequate range of motion, continued pronation drives the talus plantarly and medially as the leg moves over the planted foot and leg rotates internally. It maintains medial malalignment. And the talonavicular joint as the talus rotates as I said before rotates medially with the leg, the TN joint subluxates in the transverse plane. And then you see the wedged shape navicula on radiographs and other things that you all know from podiatric medical school. The forefoot does not abduct, the mid foot abducts. It's important because you need to understand why you're doing the surgeries you're doing when you're doing them. The naviculocuneiform joint and cuboid subluxates and as they do the mid foot is driven further plantar inter-propulsion. Eventually, in bad enough cases, where you have an unstable mid tarsus, you'll get cuboid fourth, fifth subluxation; in other words, lateral column subluxation. Now, you got to get this because I don't know why this is as hard to understand as it seems to be. When residents talk about supinated feet, they tend to think the foot is supinated relative to the supporting surface, but what happens in a pes planus is you've got a pronated hindfoot, Kite's angle is open, a pronated hindfoot with a forefoot captive on the ground. If the hindfoot is pronated and the forefoot is captive on the ground, it is relatively supinated to the hindfoot. That’s an unstable position at the midtarsal joint. And the when the patient goes inter-propulsion, there are propelling on an unstable mid tarsus and they collapse even further. If that condition is present, neither tibialis posterior contracture nor peroneus longus contracture is sufficient to overcome it. And then the first ray continues to give away and you develop a hypermobile first ray, can't maintain its stability against the ground. Hypermobile first ray doesn't mean a first ray with a lot of range of motion. It's not ligamentous laxity. When we as a podiatrist talk about a hypermobile first ray, we mean the first ray that is not maintaining its position against the ground to resist pronation in late propulsion and heel off. And the effect of the swing phase limb is inadequate to resupinate the stance phase limb. I have the swing phase -- can you hear me? I've got the swing phase --

    Male Speaker 3: Can you go right behind the podium?

    Male Speaker 2: Huh?

    Male Speaker 3: When you are behind the podium, we can hear you better.

    Male Speaker 2: Well, I got to demonstrate this. So can you hear me now?

    Male Speaker 3: Yes.

    Male Speaker 2: Thank you. Stance phase limb. Swing phase limb is coming through carrying the contralateral hip through, yes? My foot is planted on the ground, the leg is externally rotating. In a normal scenario, the externally rotating leg is closing Kite's angle because the talus in the transverse plane has to follow the malleoli. So they go from a pronated to a more neutral and eventually to a supinated position of the hindfoot. But when that foot is hyperpronated to that extent, then the swing phase limb or muscle contracture from tibialis posterior are inadequate to return the foot from a hyperpronated position to a neutral position. I won't spend a lot of time with this because you all know your angle and dangles, but basically you look -- in the AP view, you're going to see a very open Kite’s angle with projection of the talus, talar bisection medial to the forefoot and in the lateral position, because of the dropping of the talus, you're going to see that the talar projection in lateral view is way below the first ray.

    [30:13]

    There are important supplemental radiographs that you need to be aware of. It doesn't mean you're going to take them every time. You take them when you're suspicious of certain conditions. AP and lateral stress views to rule out equinus meaning osseous equinus, other bony blocks or a flattened talar dome. Flattened talar dome is important because it reduces the arc and therefore the ability of the leg to come over the planted foot. It's also indicative of an awful lot of stress coming through that foot in a young child and over time the normal curvature of the trochlear surface of the talus starts to flatten. So if you get inadequate dorsiflexion, think of that. Harris-Beath views can be important because you want to look at the medial malalignment and many of these feet have middle facet eversion. Middle facet doesn't parallel to the posterior facet, so if things don't add up in your biomechanical exam, get a Harris-Beath view and look at the middle facet and see if it's foreshortened or everted or possibly there is a coalition. If you get a young enough child, you may not be able to see the coalition. And compare neutral views to relaxed views to rule out adductory deformities that are being compensated. Am I over time, how much do I have?

    Male Speaker 3: Five minutes.

    Male Speaker 2: Thank you. This is what I want to talk about. There are feet that have a true ankle valgus. And so if in a nonweightbearing scenario, your biomechanical exam is not coming up with something definitive, but the foot position to ground in stance is particularly everted or if you've a truly everted calcaneus, then it's not the subtalar joint that’s causing the heel to go beyond perpendicular. Something is happening superior to that. Get ankle AP views, rule it out. It's not common, but if you see a lot of kids, you're going to see it. A couple of key points in the clinical evaluation; hypermobile, unstable subtalar and midtarsal joints, collapse of the medial longitudinal arch, rule out an equinus condition typically gastrocnemius, but not always. Check the forefoot to rear foot position and see if there is a forefoot supinatus or an inverted forefoot to rear foot. It can be a supinatus or a varus. I don't spend a lot of time differentiating between the two. If you treat children, it's going to be somewhat flexible. It's in the older group that it becomes more rigid. So mainly what you want to look for is an inverted forefoot to rearfoot position nonweightbearing. Alright. Remember, I talked to you before about asymmetry. This makes the point. This was just a kid in my practice. Nothing unusual about this kid. Parent brought him in because he had hyperpronated feet bilaterally. I stood him up on the orthoposer, took a picture from directly posterior and you would look at this and say, well, alright, there might be slightly more hyperpronation on the left than there is on the right when you're looking from directly posterior. So what I did was then I moved to my left, shot a picture, moved to my right. Watch what happens. I did not move the kid. When I aligned myself up to get the posterior aspect of the left ankle mortise, look at the position of the degree of medial malalignment on the left. And when I align my point of view to the right posterior ankle, look at the amount of medial malalignment. You see just how much worse it is on the left than the right and this is so common. Why is it important? Because if you are going to order -- if you're going to try and manage this with a foot orthosis or ankle foot orthosis or something like that and you [Indecipherable] [0:35:01] trouble, if you could put this and order some prescription that is bilaterally symmetric, you write something up or lab judgment.

    [35:10]

    There is no way the lab is going to be able to make this judgment. All they get is a shape of the foot. They have no idea where the foot is relative to the leg. You've got to look at both feet independently. Check forefoot to rearfoot, double check the offset as we talked about -- I don't want to beat this to death -- the offset of the calcaneal bisection to the ankle bisection. Check the patient’s ability to resupinate in tandem heel raises or single leg heel raise. Check for equinus. I check for equines, you don't have to do it this way. If you know what you're doing, you can check for this hanging from a chandelier. The fact is you have to know what you're doing. So what are you looking for? It's easier and unless you really know how to do this, to check with the patient supine, keep the knee flexed, which takes the stress off the gastroc, dorsiflex the foot with the knee flexed and keeping the gastroc relaxed as well as the hamstrings and then extend the knee -- remember the patient is prone -- extend the knee and keep the foot dorsiflexed. And if the patient appears to have limitation, when you extend the knee, ask the patient to pull their toes towards their nose. Tell the patient to pull your toes towards your nose. If they have adequate dorsiflexion that way, they have adequate dorsiflexion. The problem is if you check a patient supine rather than prone, they are going to feel the tension in their hamstrings when you pull up on the foot and they're going to clutch and fire their hamstrings inappropriately and they're going to resist you because they can see you. But if you've them prone and they’re looking in the other direction, you really don't know what you're doing and they are much less likely to anticipate. So it's just a clinical pro. You can do it supine if you know what you're doing, but it's a clinical pro. All I ask is that you try it my way and do it that way the rest of your lives. Look at shoes. I cannot tell you how -- you can get so much more out of this than any theoretical goniometer and anything else you want to use. Shoes are like the alignment of your tires. They tell what has happened. So if you look at this particular child's shoes, you can see that the counters are asymmetric. And you can see that the heel wear is asymmetric. Two feet are doing two separate things.

    Conclusions: Understand the basics of closed chain function, understanding osseous relationships are critical, closed chain, understanding when muscles fire, normal muscle firing and what's the agonists and the antagonist, understand the origin and the insertion of the position of muscles and their action relative to the joints that they are influencing, understand the events of gait, heel contact, what should be going on at mid stance and what should be going on in propulsion. And evaluate the patient’s gait for the influence of other factors, meaning torsional and rotational factors, frontal plane issues, genu varum, genu valgum, ability to resupinate. Understand the planes of compensation, not all flat feet compensate the same way. There are certain flat feet that are predominantly frontal plane compensators. They have to be treated certain ways surgically or biomechanically. There are many flat feet that look great at heel contact and at mid stance, the foot collapses. They have unstable midtarsal joints. They may be candidates for completely different orthotics type or an opening Evans with a graft. It's a different approach. You need to understand what cohort of conditions the foot has in order to bring in the right cohort of surgical procedures or orthotics, what orthotic prescription you need to control what you're trying to control, evaluate for equinus, assess for asymmetry, but remember you cannot rely on static bilateral images as a pretext to making any decision about that patient. Did I get on time? Okay. Thank you.

    [Applause]

    TAPE ENDS - [40:01]