Section: CME Category: Biomechanics Foot Conditions

Pes Cavus

Marc Benard, DPM

Marc A Benard, DPM discusses the etiology, symptomatology, and biomechanical problems associated with Pes Cavus. Dr Benard examines and recommends radiological techniques and orthotic corrections. He briefly touches on surgical correction.

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Goals and Objectives
  1. Define Pes Cavus
  2. Understand the etiology of Pes Cavus
  3. Recognize common patient symptoms
  4. Discuss biomechanical and radiological findings
  5. Understand the recommended procedures for correction
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  • CPME (Credits: 0.75)

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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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    Marc Benard that he is an employee and officer of American Board of Podiatric Medicine.

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

    Male Speaker: Next speaker, Marc Benard who has been with the Baja Crippled Children's Project for many, many, many years is now the executive director of the American Board of Podiatric Medicine. Marc was from Southern California. He now lives in North Carolina, that's why he's got a little bit of a southern accent I can detect in his voice now. But I think you'll find his approach to cavus foot interesting and he can make a complicated subject far, far more understandable. So, let's welcome Dr. Marc Barnard.

    Marc Barnard: Thank you, my friend. Okay. What I hope to do, it's very, very difficult to do this in 25 minutes. We could spend a whole day on cavus foot. But what I want residents in particular to be able to do when we're done with this is have some conceptual framework of understanding what it is you need to know to make salient decisions about management of cavus foot. And in the 25 minutes, hopefully, if I can hit some key points and give you some clinical pearls, that's where I'd like to go with this. Okay. Now, it's easy enough to say that cavus foot is a high arched foot but understand that the etiology of the cavus or the prime location of the cavus, and some of this is pretextual information to where I really want to go with this for you. But it can be primarily located in the hindfoot or the midfoot or the forefoot and often at multiple levels. Typically, the cavus feet, and I almost dislike the word cavus, because cavus is a single plane deformity and 90% of the feet that you're going to be seeing in your practice careers are triplanar deformities. It's truly in 90% of the cases at least cavo adductovarus foot type. Though it’s it triplanar in forefoot, hindfoot, and midfoot. And though yes, it can be sagittal only such as a calcaneal cavus or forefoot cavus, that's not what you're going to see. Typically, they are more rigid and we see a lot of children as Bob was talking about. We, for the last 40 some-odd years I've been co-director of the Baja Project for Crippled Children, and there is some plasticity, a greater plasticity in young children that have cavus feet. And it becomes more and more progressively rigid with time. One of the things I do want to spend some time if time permits, I want to talk about a flexible anterior cavus. Which is a completely different entity and has to be managed both surgically non-surgically utterly differently. But to the untrained person or the person who is less observant or less caring than they ought to be, they may lump a flexible anterior cavus along with the cavo adductovarus. And that's a clinical mistake that you will pay for and so will your patient. Let's talk about just for the sake of completeness covering some of the common associated deformities with cavus foot. You have a functional equinus. And for those of you who may have been trained with the word pseudo-equinus, is pseudo-equinus still taught at the colleges of podiatric medicine? Is that – speak up, please. Pseudo-equinus, do you know that word? All right. That's a functional equinus. What does it mean? There's no true limitation of ankle joint dorsiflexion. What happens is, because the forefoot is plantarflex relative to the hindfoot, it loads prematurely in the gait cycle. And in so doing the talus is therefore kept more parallel relative to the ground. Then if the talus is parallel and therefore rocked further back in the mortise then when the leg comes over the planted foot it's limited as to where the body can be relative to the planted foot before the heel comes off the ground. So there's no frank limitation of the ankle joint but it functions as though there is an equinus component to it. So be clear on that. Plantarflex first ray is common. It's not always present, it's almost always present with cavo adductovarus foot type which is the most common that you're going to see. Forefoot valgus, it's in most cases a one through five valgus because of the plantarflex first ray. Very often, two through five is parallel to the position of the hindfoot. If the fifth ray is subluxated which happens a lot because of chronic overloading on the lateral column of cavus feet that are rigid, then you will have a two through five valgus relationship as well. It’s very important to understand this when you approach it, when you're trying to control this foot biomechanically. And when I say biomechanics, I don't separate out biomechanics and surgery.

    [05:03]

    It's all one thing to me. It relates the functional restoration and it's a matter of what tools you have in your tool box to be able to improve foot function whether you're moving anatomy around surgically are you're moving anatomy around or controlling it with some type of foot or foot-and-ankle orthosis. Hindfoot is another misnomer. Because very rarely do you have an isolated frontal plane deformity in the hindfoot. It's a hindfoot supinates because it's a triplanar deformity and I'm going to show you on x-ray what I'm talking about and it will make it more clear to you. Hammer toes, though not always present in a rigid cavus are often present and are almost always present in a flexible anterior cavus. They can be one through five, meaning hallux hammer toe versus lesser hammer toes. Or you can have a global hammer toe development. And of course, because it's triplanar, in cavo adductovarus you're going to have some adduction component typically at the tarsometatarsal articulation. Okay. Patient's symptoms, just for the sake of completeness, metatarsalgia [just comma] [06:12]. Lateral ankle or sometimes lateral subpatellar instability which you hear less of. Digital irritation would be following hammer toe formations. So, DIP joint dorsally, digital pulp plantarly. Although, I must say and if time permits I'll go into it, the reason that hammer toes form in cavus feet is entirely different than the reason they form in pes planus or hyperpronatory feet. And unless you know the difference, and if time permits I'll go through it, unless you know the difference you're going to be choosing the wrong procedures surgically on these toes. So you'd better know hammer toes form in cavus versus hyperpronatory feet. Medial plantar fascial pain can occur if you have a flexible anterior cavus. And many times, what happens is you get bow stringing of the medial strip of the plantar fascia. And it's the medial strip that is painful. It's generally not the central or lateral strip. Plantar keratosis, if it's rigid will generally form sub one and five. But as I alluded to or mentioned before, if a cavus foot has been longstanding, what often happens is the fifth metatarsal or the fifth ray I should say subluxate on the cue board. And that doesn't take the peak pressure. And where you'll get peak pressure is a sub one and sub four. Occasionally, sub one, four, and five. But the point is, that's where you should be looking for your pressure points to develop. And consequently, think about that in your management of these feet when you're using orthosis or if you're going to intervene surgically. Okay. Etiology can be varied. I disagree with the literature that says, I think it's an old paradigm, a literature that says every cavus foot has some component or neurologic underlying component. I completely disagree. I live in a world in the third world when we do the Baja Project. When you see neurologic patients it's clearly a different entity. And the rigid cavus feet there behave differently than what we see as the rank and file pes cavus that's going to come into your practices. I think the vast majority of the ones that you're going to be seeing and that I’ve seen for years in practice are idiopathic. That's the genetic underpinning of that foot type. All right? But for sake of completeness, a lot of neurologic patients and far more neurologic patients have cavus or cavo adductovarus foot types than they do pes planus foot types. No question. It could be CMT, CP, congenital issues such as talipes equinovarus, things like that. Post CVA on seniors, those of you that are in VA environments may be seeing patients that have had strokes and very, very often it's equinovarus posturing. And that leads to a cavus foot type. Trauma, of course, anything that's going to move the hindfoot or the forefoot into an abducted position is going to create mechanical advantage of the muscles around which those joints are affected and it's going to pull it into that attitude. And of course – not of course, you wouldn’t necessarily know unless you're doing club feet. A lot of overcorrected club feet in the hindfoot particularly TAL, where the hindfoot, in order to get to the posterior ankle and subtalar joint, you need to do an open TAL and get to it. If you don’t have sufficient tension when you reanastomose or if you do have sufficient tension and the patient hasn't been appropriately rehabbed, then that will relapse not into a clubfoot, but into cavo adductovarus foot type.

    [10:09]

    I want to spend a little bit of time on radiographs. And I don’t want to – you can read in a book most of the common findings on the lateral view. I want to give you a clinical pearl because it is essential that you understand it and do it when you do an assessment. I'm not a big fan in the first place of static two-dimensional images to understand the way feet work. And the problem you have with radiographs, though you can get a lot of information, one of the things you can't get out of radiographs is out feet work. That you must assess biomechanically during gait. And I'm going to show you some gait videos. And getting your hands on the foot and measuring them or evaluating them in stance and on weight bearing. The only way you’re really going to understand how feet work. But from the perspective of radiographic imaging, aside from what you see here with all the salient features, calcaneal pitches increase, patellar declination is decreased et cetera, et cetera, you can read that in a text book. But you're not going to get, and it's critical, is I want you to look at the top image. Here and look at the position of the fibula. And look at the image below it. Do you see how the fibula is posterior in the way this is projected to the posterior aspect of the talus? Here you see it much better aligned. The reason is that in a cavus foot because the forefoot is adducted on the hindfoot, when you order a lateral, we all know that the medial border of the foot is up against the plate as a weight-bearing lateral obviously. If the medial border of the foot is up against the plate and the hindfoot is supinated then the ankle mortise is externally rotated to the plane of the foot. Why is that important? Because if you run the x-ray beam across it, it's going to show that the fibula is posterior to the tibia. And less so in an adult, but if you're dealing with children or even young teenagers where the trochlear surface of the talus is not fully expressed radiographically, what you will get is a spurious impression that there's a flattop talus there. And that's going to drive you to conclusions that are incorrect about what you might have to do if you intervene surgically with that patient. It is much better with cavus feet and much safer to don't order a lateral, order a medial. In other words, put the lateral border of the foot against the plate so that you true up the position of the malleoli relative to the x-ray beam so that you will be getting this. And when you get this, you'll get a more true representation of the talus. If in that scenario you see that there is flattening of the talus trochlear surface, you’ve got flattening of the trochlear surface. And you need to intervene and do something surgically if the patient merits it as a result of it. All right? So clinical pearl number one. That's a major takeaway for you. Position the patient properly on lateral view. All right? Otherwise you’re going to get wrong information. All right. AP view. Again, nothing here that you don't already know. There is tarsal stacking. [Tights’] [13:36] angle is going to be very narrow because of the hindfoot supination. And as a result, you're going to get probably an increased forefoot adductus angle. You may in severe cases get talonavicular subluxation as you see right here. Okay. Here's the other clinical pearl that I want you to be aware of. The reason the hindfoot varus is a misnomer with respect to cavus foot is it implies to you that it's a uniplanar problem. Varus being in the frontal plane. That's definitely not what occurs in cavus feet. It's a hindfoot supinates, supinates is triplanar. So this is a weight-bearing calcaneal axial. And what I did was I bisected the heel of the calcaneus. Excuse me. And I bisected the tibia. And what you're looking at here is a significant adduction, AD-duction of the posterior heel relative to the posterior aspect of the leg. The significance of the heel position in cavus is more important relative to the transverse plane than it is the frontal plane and I'm going to show you why. Okay? So here if you look at the upper right-hand image you see a neutral foot. And in a neutral foot type you notice that the tendo-Achilles is centralized relative to the back of the leg.

    [15:04]

    When you have a cavus foot, and the same would be true in hyperpronated feet in the other direction. The foot is captive on the ground. When the hindfoot is supinated as you see here, then the superstructure, meaning, the distal aspect or the leg, the entire leg relative to the planted foot is displaced laterally as you see in the lower right-hand image, clinical photo I should say. So look at where tendo-Achilles is relative to the posterior aspect of the leg. You notice that it's medially displaced on the leg or more correctly, the leg is laterally displaced on the planted foot. Now, look at the illustration to your left. That's the soleus. Soleus and gastroc taken together are the second strongest muscles in the body. The strongest being what? The glutes. The second strongest muscles in the body are the gastroc-soleus. So they have a profound effect on foot function. And what happens is if you look at, let me see if I can get this right. Got it. All right. Here's the subtalar joint axis here. When the hindfoot is supinated, the relative leverage that the soleus has relative to subtalar joint is significant. Now, you are taught and it's correct that the main function of gastroc soleus primarily is at the ankle joint. It's true. But if the foot is in a supinated position, then because of the insertion point of the soleus which is distal not only to the ankle joint but it's distal to the subtalar joint, come on. As you see here. All right. Here's functional insertion of soleus at the back of the calcaneus. True? Here's ankle, here's subtalar joint. It’s distal to that. Why is it important? If the foot is supinated at heel contact and midstance, then when the leg moves over the planted foot and tension builds in the soleus as the swing phase limb is coming through and as the leg moves over the planted foot, tension builds up in the soleus. If the hindfoot is already supinated, you've got an enormously powerful muscle that's going to contract at that point and keep the hindfoot supinated. Understand? By the way, that's not part of this lecture primarily. But the reason we are built this way is the soleus originates distal to the knee, the gastroc proximal to the knee. So as the superstructure is coming forward and tension builds up in these two muscles, soleus the lace anterior migration of the leg so that the knee can extend by slowing this down. As the as the superstructure moves over, the forward motion of the tibia is slowed then gastroc and soleus continue to contract, the knee is extended and the heel comes off the ground. That's how it works. And you ought to know that if you're going to be intervening with patients doing TAL's gastroc recessions, Murphy's, partial recessions, percutaneous TAL’s however you want to do it. We get a lot of residents in there and I lecture to residents all over the country, about three hundred a year. And most of you, unfortunately, I don't know why, it's certainly not your intellect, it's what's not coming through to you or not emphasized in your programs, cannot tell me coherently how the heel comes off the ground. Then don't take a knife to the structures that are going to pull the heel off the ground if you don't understand it. The takeaway is, I'm not yelling at you. I just want you to be great at what you do. Just be great at what you do and know it better than anybody else. All right. Peroneus longus and tibialis posterior are both stance phase muscles that function concurrently. Although tibialis posterior fire sooner than, to stabilize the hindfoot it is not a supinator of the foot. Tibialis posterior is a decelerator of hindfoot hyperpronation at contact and at stance. They keep the hindfoot neutral. Why? Because with a neutral hindfoot you have a transverse torso arch forming and peroneus longus via its insertion as you see here. No, don't do that. Right here into the base of the first metatarsal maintains the first ray against the ground, stable against the ground as the superstructure comes over the planted foot.

    [20:08]

    So peroneus longus and tibialis posterior work in concert with one another. Now We’re going to talk about gait findings. I'm going to show you this both in real time and in super slow motion, same patient. So let's concentrate on the right foot. If you look at the right foot, you see that the hindfoot hits supinated. Watch. Watch how it contrasts, supinated and supinating. Because as soon as you get into mid stance which is quickly in this kid because of the plantarflex forefoot, what you'll see is a lateral rocking of the ankle joint. See it? Now. Now. Did everybody see that? Yes? We're going to show it in slow motion if you can. One more time. And I want you to look at the position of the hallux. Notice that the that the hallux never purchases the ground and that's the busy young child. And it's the beginning of the hallux hammer toe. And the reason the hallux doesn't, excuse me, purchase the ground is because of the declination of the medial column. All right, let's move on to the next slide. We're going to show this in slow motion and we're going to freeze frame this for you. Watch what happens. Heel contact, rock laterally. I want to show you the position of the tendo-Achilles. We're going to freeze this soon, soon, soon. Now. All right. Do you see the position of tendo-Achilles right here? You got it? Can everybody see it? Thank you. All right. This is what I'm talking about in terms of functional position of the soleus on the hindfoot. If the hindfoot is supinated at contact and through mid-stance, when the gastroc soleus complex contracts, the soleus has such leverage on the subtalar joint axis that even in swing phase it's going to maintain that foot supinated. When the foot is maintained supinated in swing, watch what happens. Continue. So swing phase predicts stance phase. And now you have a vicious cycle of supination all the way through. Now watch what happens when the patient comes towards you. It was a little tough to see in real time. But with the foot supinated, you then develop a dynamic imbalance between the tibialis and the muscles that are in the swing phase relative to the subtalar joint axis. So what happens is, watch. Watch it toe off. Do you see the foot snaps medially? One more time. Watch what happens at toe off. When this toe comes off, the other foot snap medially. All right. That's due to the fact that in a cavus foot because of the position and space, tibialis anterior has a mechanical advantage over extensor digitorum longus. EHL is pretty much neutral because it runs right over the first ray which is pretty much in alignment with subtalar joint axis. So you have a dynamic imbalance between anterior tib and extensor digitorum longus, which in swing phase on a cavus foot is now going to snap that foot medial. And now the foot is adducted in space, and when they place it on the ground the adducted position is then going to maintain the hindfoot supinated at contact. So it becomes a vicious cycle. And you need to understand this if you're going to approach a correction of this foot, especially a surgical correction on this foot. All right? So just to reiterate quickly, because I covered a lot of it. Peroneus longus. Oh, I didn't cover this. And you'll say what is he talking about? They're out-of-phase muscles. Peroneus longus overpowers tibialis anterior. Well, you say, well how could it overpower tibias? One is land stance phase muscle and one is a swing phase muscle? What happens is the peroneus longus has a mechanical advantage in stance. It holds the first ray down in greater declination. When that occurs, and you go into swing, the EHL and the EDL because of plantarflex forefoot have a phenomenon called extensor substitution to try and get clearance of the forefoot.

    [25:09]

    When the hallux and the other digits are pulled up, it has a retrograde force to drive the medial column even further. So the preposition of the first ray being plantarflexed and supported by peroneus longus predicts that the proximal phalanx of the hallux and lesser digits sometimes is now dorsiflexed on that metatarsal and you create a scenario where that creates a dynamic imbalance. Okay. The other stuff I have covered, so I want to move on. We’ve covered a lot of this. Let's briefly talk about the Coleman block test and a nuanced through that test. Coleman block test is useful in trying to determine whether it's a primary hindfoot supinates or a primary plantarflex first ray that's causing the hindfoot position. It's good prognostically because it helps you determine what you need to do with an orthotic or surgically on that foot. You don’t need to – If it's the first ray, that's plantarflex and causing retrograde supination you don't need to do a hindfoot osteotomy. But there's a nuance to this. When you see this on the Coleman block test and you see that by unloading the medial column you still have a significantly supinated hindfoot, here's a clinical pearl, start shimming the heel and bring it up incrementally leaving the forefoot in this position. So you're keeping two to five loaded by the block, unload the medial column, and then shim up the heel. Why? Because the posterior aspect of the trochlear surface of the talus is narrower than the anterior aspect of it. And you have a little bit more play when the ankle joint is slightly plantarflex. Why is that important? Because if a patient is not easily controllable in an orthotic with a standard – with the foot flat on the ground, they may be controllable if you do all the right things, by giving them a heel lift and taking advantage of that anatomic scenario where you have more frontal play motion in the ankle joint to get that foot more pronated relative to the hindfoot. Or less supinated, not more pronated. But less supinated relative to the supporting surface. Okay? A lot material here. Primary goals of orthotic management are to use as much surface area under that orthotic as you can to support the midfoot because you want to disperse the weight away from the plantar aspect of the forefoot because you've often got metatarsalgia or plantar lesions there. You want a wide devise with a minimal fill. And we're going over time here, so I want to move very quickly. All right? You want to have a DPO cup on the lateral side or a lateral skive to resist heel contact supination and a wide device if you can. Okay? Moving quickly ahead, because there's just not enough time. There are a lot of procedures that you can use to correct a cavus foot that needs correction where you can't control it with an orthotic. Calcaneal osteotomy is one, posteric calcaneal osteotomy. We like to do translocating osteotomies because it's easier to centralize the Achilles tendon and the on the posterior aspect of the leg which is critical. So you can do angulatory, but you're better off doing angulatory translocating osteotomies. You have more control over the heel. Mid foot osteotomies are fine. I would avoid a [japus] [29:00] if you can. It creates a very stiff foot. We do a lot of cuboid third cuneiform osteotomies and medial cuneiforms. And that gives you a lot of control over it, where you want to put the midfoot and forefoot. Tendon transfers are essential in children with cavus foot deformities because if you prematurely do an osteotomy let alone an arthrodesis, it’ll iatrogenic deformity. So you better understand phasic activity of muscles so that you can do split anterior tib transfers, split posterior tib transfers, Murphy procedures, and so on and so forth to understand – to be able to neutralize that foot until the kid is skeletally mature enough to if you need to go in and do an osseous procedure. But you can do a lot of good with targeted muscle transfers. And I don't have time to go through that. And thank you.

    TAPE ENDS - [30:05]