Marc A Benard, DPM presents the first of two lectures covering the topic of pediatric pes planus. This session covers the condition's definition, etiology, parameters of normal development, clinical features, and effect on adjacent joints.
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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 Bernard: This is the assessment of pediatric pes planus and will be done in two parts due to the length of the presentation overall. We will cover part one in this presentation. I'm Dr. Marc Bernard, the executive director of the American Board of Podiatric Medicine, as well as co-director of the Baja Project for Crippled Children. I have nothing to disclose with respect to sponsorship. The learning objectives for this presentation include the recognition of the clinical and radiographic features of pediatric pes planus. Recognition of the compensatory mechanisms involved in its pathomechanics and a recall of the proper assessment techniques in the biomechanical examination of the condition. Before we can engage in an understanding and discussion of clinically significant pediatric pes planus, we need to understand normal development. "Heel valgus" decreases with age to an average of 4 degrees by age 7. I put the term heel valgus in quotes because we will cover the details of what heel valgus truly is further on in the discussion. When we review medial archrite over a large population of children, on average, there's a marked increase in the medial archrite between ages 3 and 6. This is as the fat pad on the bottom of pediatric foot diminishes. Then there's a slow increase in archrite between ages 6 to 10 and it's rather insignificant thereafter. Part of this is due to the cosmesis present when the fat pad in the pediatric foot gradually starts to diminish. Part of it is actually due to positional changes in the foot over time. There's a fair amount of literature available reviewing the normal development of the pediatric foot. I've chosen one by Glen Pfeffer that was done in 2006 because there was a rather large number of children evaluated. As you can see here, 835 children with so-called pes planus in which an assessment of the prevalence of the "flat foot" was made. The study was about 50 percent male to 50 percent female and they were looking at ages 3 to 6. And they were taking about rear foot angle as they defined as the upper Achilles by section relative to the distal extension of the rear foot, which we would talk about in terms of calcaneal bisection. The parameters reviewed were age, gender, weight, and body mass index. In reviewing the spreadsheet, we can see that the parameters evaluated were a rear foot angle as defined in the previous slide of greater than or equal to 20 degrees and they were looking at it in terms of its prevalence at age 3, as well as its prevalence at age 6. In each case if you look at the rows below, they're looking at girls of normal weight, overweight and obese and likewise, boys of normal weight, overweight and obese. And we can see that for every cohort group, the dimension of the rear foot angle decreased from age 3 to age 6. Of significance, is that the more obese or overweight the child, the higher the prevalence at age 6. So there's very strong correlation between a child's weight and the persistence of an overly everted -- a hindfoot. The conclusions drawn in this particular study was that, the risk of flat foot is greater than 2 to 1 in boys relative to girls that as previously mentioned, weight is a significant factor in the prevalence of the condition. [00:05:00] And the probability of flat footedness decreases by approximately a little more than a third per year between ages 3 and 6. The conclusion was that physiologic flat foot decreases naturally with age. And recommendations in that study were that, no treatment was required for physiologic flat foot. And that if treatment was rendered, it was indicated in pathologic flat foot, which by definition in their study was greater than or equal to 20 degrees of heel eversion or in children with symptoms. We'll talk about this further as we go through the presentation.
In this presentation, we'll be concentrating on flexible pes planovalgus because that is, by far, the most common entity that is going to be encountered on a day-to-day basis by the general podiatric physician. But for the sake of completeness, it's important that you understand that there are many ideologies of pes planus in children. Commonly, an equinus condition, be it ankle and/or gastroc-soleus would be one of the major entities that would cause the condition.
Limb length discrepancy could cause a unilateral pes planus, most often present on the "long limb." There is a condition called talipes calcaneovalgus, which is a congenital condition in which there is a pathologic position of the heel relative to the talus and this is typified by extreme pronation both in weight bearing and non-weight bearing situation. There are forefoot, midfoot influences that can contribute significantly to pes planus, such as forefoot varus or forefoot supinatus which is a flexible condition in which the relationship with the forefoot is inverted to the hindfoot. And specifically, I'm referring to those which are compensated or partially compensated so that in order to get the forefoot on the ground, the hindfoot needs to move into an overly pronated attitude. There are also feet in which there is excessive transverse plane mobility of the midtarsal joint. And these are feet in which the pes planus is not so obvious at heel contact but becomes obvious as the forefoot lodes and the midfoot compensates in an abnormal direction due to the instability of the midtarsal joint. Compensated metatarsus adductus cannot be ruled out. And in this scenario, the practitioner needs to evaluate the foot in a neutral position as well as a compensated position because the neutral position would show that the hindfoot is, otherwise, normal and would expose the adducted metatarsus to lesser tarsus relationship. Whereas the relaxed calcaneal stance position might show the metatarsals to be in a relatively rectus attitude, but the hindfoot by way of kite's angle would be pronated and kite's angle would be increased. So in this particular condition, the practitioner needs to, once again, compare neutral to relaxed radiographs. Skew foot is a complex deformity in which the forefoot is adducted on the midfoot and the midfoot is AB, as in boy, abducted on the hindfoot and it's a rather uncommon condition and I will not be covering it in this presentation in any detail.
Other ideologies of pes planus, [00:10:00] torsional and rotational factors. This is where the super structure is positioned. It forces the leg to hold the talus in an adducted position relative to the line of progression. This would be true in internal tibial torsion where the talus is captive in the transverse plane in the ankle mortise. And if the tibia is internally rotated, then the talar head is facing medial relative to the line of progression, compelling the foot to be pronated. Femoral anteversion would have the same ultimate influence, though it's occurring higher up. Certain pathologic conditions, such as Marfan's or Ehlers-Danlos and others cause a soft tissue problem where the connective tissue is so lax that the ligaments are lax as well. And in weight bearing scenario, the foot moves into a hyperpromontory attitude as a result. Obviously, traumatic conditions which would rapture the soft tissues and muscle tendon complexes that would hold the foot stable could cause a unilateral condition of the pes planus and neurologic influences such as paralysis. Again, most likely, tibialis posterior paresis would, likewise, cause a positional change over time.
Let's take a look at some of the specifics relative to pathology in flexible pes planovalgus. Definitionally, it is generally considered a weight bearing collapse of the medial longitudinal arch whereas the arch appears normal when non-weight bearing. This is an overly simplistic definition because pes planus is a tri-planar problem which affects not just the medial longitudinal arch, but the hindfoot, midfoot and forefoot. It's typically considered asymptomatic, but I put this in asterisks because the practitioner needs to understand that in children, symptoms are not necessarily pain. More commonly symptoms in children are fatigue or a lack of desire to participate in sports or run around. Young children may want to be picked up by their parents as time goes on during the day because they are "tired." So symptoms needs to be interpreted in a different way when we're speaking about children versus adults. In the condition, the subtalar joint is maximally pronated with a so-called everted calcaneus at mid-stance. I'm going to be talking about this in some detail as previously indicated because it's somewhat of a misnomer. It is this eversion, however, which creates medial malalignment of the leg on the planted foot. And that's the more clinically significant aspect of this as we will show. This medial malalignment results in the plantar flex in medially deviated talus which exacerbates the offset of the leg on the foot. What is important to know in flexible pes planovalgus is that the subtalar joint does have the ability to resupinate on active heel elevation, which is to say, if you were evaluating the patient in bilateral stance or for that matter, unilateral limb support and ask the patient to pull their heel up off the ground or heels off the ground, you would see that the subtalar joint does move from a pronated to a neutral or supinated position. That's clinically very important to distinguish this particular condition, flexible pes planovalgus from other planovalgus conditions.
It is, therefore, more prudent to talk about [00:15:00] medial malalignment versus heel valgus when one is talking about pediatric or for that matter, adult pes planus. In fact, there are relatively few and far between feet that truly are clinically in an everted position, meaning that the calcaneus itself is truly everted to the supporting surface. Much more often, what is occurring is that the bisection of the leg is far more medial as you carry it down towards the ground than is the bisection of the heel. So if you look at the depiction on the left, you would see that in an ideal neutral situation, the bisection through the tibia passes down through the talus and the calcaneus and if you look at the bisection of the calcaneus, those two parallel lines are not too far apart. If you look at the clinical situation on the right, you would see that the bisection of the leg is represented in yellow. If you project that all the way down to the ground, it would fall well medial to the white line bisecting the heel itself. The heel itself, if you palpated the medial lateral boarders of the calcaneus, it would be close to perpendicular. So the significance of medial malalignment and again, what this relates to is the medial position of the leg relative to the planted foot, is the calcaneal bisection relative to the bisection of the ankle joint. Those two lines influence the position of the tendo Achilles on the posterior ankle and subtalar joints. Take a look, again, in the upper right of the position of the tendo Achilles relative to the position of the ankle joint as shown on the relatively horizontal yellow line. You will see that the Achilles sits much closer to the lateral malleolus than it does to the medial malleolus. And consequently, if you look at the bulge below the medial malleolus, that's the talar head. And the reason that it's that far medial is because the talus, as previously mentioned, is captive in the ankle mortise in the transverse plane. So as the ankle mortise moves medially on the planted foot is taking the talus with it, and you see there's significant offset of talar head to calcaneus, which if you were looking on a radiograph would be an increased kite's angle. This position in turn influences the ability of the swing phase limb and the gastroc-soleus to resupinate the hindfoot in gait. So this is a closed-chain phenomenon and this medial malalignment syndrome of the malleoli on the foot is much more significant than static heel valgus. And notwithstanding the extent of medial malalignment of the leg on the foot, you can see that in this patient when the heels are brought off the ground, the hindfoot resupinates rather well. And so definitionally, as flat or as significant the pes planus is in this case, it is nevertheless considered flexible because of this ability, of the patient to reduce the deformity. It's important to know as well that not all flexible pes planus is going to demonstrate an excessive amount of medial malalignment or in the other terminology heel valgus. There are many feet that simply do not have the range of motion in the subtalar joint to place the leg to foot position in significant malalignment. [00:20:00] On the other hand, these feet may clinically have an unstable midtarsal joint or a midtarsal joint whose access of motion is predominantly vertical. What that means is that if there's a verticality that the midtarsal joint access, the motion available to it is predominantly transverse plane as opposed to a more tri-planar motion that would be present in an access that's oriented and less vertical. And in these feet, what one can clinically see either in stance or gait is the so-called too many toes sign and what we're looking at is transverse compensation at the midfoot. It is not that the forefoot is abducting on the hindfoot. Let me repeat, the forefoot is not abducting or abducted on the hindfoot because the forefoot and the hindfoot are captive on the ground and are held there by frictional forces. What is able to move is the midfoot. So what we're looking at is, the heel that's captive on the ground, a forefoot that's captive on the ground, but the talonavicular joint complex and the calcaneal cuboid joint are moving medially and are driven that way by internal rotation of the leg in stance and in gait. So again, we're talking about closed chain abduction of the calcaneus and the cuboid relative to the navicular and the talus in stance and in gait. In order to understand foot mechanics, it's necessary to understand the influence of the superstructure on the foot itself. In this particular case, we'll discuss how heel off normally occurs. Simplistically, we have anterior momentum of the superstructure which includes the swing phase limb moving the leg forward on the planted foot. While that's occurring, we have gastroc-soleus contraction in mid-stance and propulsion. Those two factors cause the knee to extend and with continued momentum and muscle contractor of the gastroc-soleus complex, we achieve heel off.
Now, if you look in the lower left-hand illustration to review your anatomy, you'll notice that the gastrocnemius muscle originates above the knee and through the tendo Achilles, inserts into the back of the heel. While the soleus originates below the knee and again, through the tendo Achilles, inserts to the same place on the heel. So you can understand that as the swing phase limb and momentum bring the superstructure through on the planted foot. When the gastroc- soleus complex contracts, the soleus is holding the tibia back against momentum, so you have a smooth transition of the leg moving over the planted foot. That causes the knee to extend and with continued contracture of those two muscles and advance of the superstructure over the planted foot, the heel comes off the ground.
Let's take a look at the relationship of the tendo Achilles to the ankle and subtalar joints and especially in the context of medial malalignment as I discussed previously. If you look at the illustration on the left, we have a depiction of the calf muscle or at least the soleus muscle which inserts via the tendo Achilles into the posterior calcaneus. And take a look at the two axes that I want to draw your attention to. The ankle joint axis is essentially horizontal to the supporting surface and is in the transverse in the frontal planes [phonetic], meaning that the motion of the ankle joint, as we all know is pretty much purely sagittal. The subtalar joint, on the other hand, has an axis that roams from inferior, posterior lateral to superior, anterior medial. [00:25:00] And that axis is oriented so that any motion around is tri-planar. Bear that in mind when you take a look at the position of the insertion of the tendo Achilles, so that when the calf muscle contracts, there is a strong moment to resupinate the foot if there's not excessive medial malalignment. In other words, when the foot is in neutral position as is depicted in the photo immediately to the right, you can see that the tendo Achilles is lined up pretty much central to the back of the ankle joint and the posterior third of the leg.
In a pronated scenario, as you see in the upper right-hand corner, the closed chain effect is that when the subtalar joint pronates the superstructure deviates medially. Therefore, the tendo Achilles is laterally placed relative to the posterior aspect of the leg and it's lever arm is closer to the subtalar joint access. Conversely, if you look in the lower right-hand corner, the clinical photo shows a supinated foot where just the opposite occurs. When the subtalar joint supinates, the leg deviates laterally on the planted foot and you can see that the tendo Achilles is displaced medially with a larger lever arm to the subtalar joint access.
Now, let's view the situation from medial and lateral. In the illustration shown, you see that the tendo Achilles is highlighted in yellow. And while it’s clearly appreciated by most people that the insertional point of the tendo Achilles into the heel is inferior to the ankle joint, what's less well appreciated, I think, is that it is also inferior to the level of the subtalar joint. So thinking back to the position of the subtalar joint access, if you have a significant amount of medial malalignment in closed chain, meaning in late mid-stance and inter-propulsion, when the gastroc-soleus muscle contracts as the leg moves over the planted foot, you've got a lateralized position of the tendo Achilles relative to the posterior leg. And therefore, its ability to function to resupinate the foot is compromised because its lever arm is much shortened. And in very significant cases where there's a lot of medial malalignment, because the promontory position of the subtalar joint results in the talus dropping towards the supporting surface, you eventually develop adductive contracture of the gastroc-soleus muscle. And the tight gastroc-soleus, i.e. soft tissue equinus maintains the pronated foot in a pronated attitude because of its positional insertion relative to the subtalar joint axis.
So to emphasize this in another way, when we're looking at the effect of a tight gastroc-soleus and its effect on the foot, dynamically, the leg cannot rotate forward on the planted foot for adequate closed chain ankle dorsiflexion, which again, is the leg moving on the planted foot, not the foot dorsiflexing on the leg. That's an open-chain phenomenon. Therefore, there's a need to take up sagittal motion that's not being met at the ankle joint and it is typically met at the subtalar joint via pronation. Closed-chain subtalar joint pronation causes progressive medialization of the leg on the foot as kite's angle opens and the talus is carried medially and planarly and the leg follows it via internal rotation and anterior rotation. So as the leg moves forward into this position and the foot is pronated, this compromise of the gastroc-soleus function in the frontal plane. [00:30:00] As you can see in the clinical photo on the right, the tendo of the Achilles is laterally deviated relative to the leg. More accurately stated, the leg is medially deviated on the planted foot and the tendo Achilles is just maintaining its position as it inserts into the heel which is captive on the ground.
So as this condition develops, the lever arm to the subtalar joint decreases as I've mentioned previously and the soleus becomes less efficient resupinator of the foot. Eventually, if the condition is severe enough, the lateral tendon position causes that muscle tendon complex, meaning the gastroc-soleus to maintain the pronotary position of the foot in mid-stance and inter-propulsion. And as we follow the chain of events, as far as the talonavicular joint is concerned, as the talus continues to rotate medially with the leg, the talonavicular joint subluxates in the transverse and saggital plane. That occurs when the talus is driven planarly and medially relative to the navicular. And when we look at the navicular cuneiform joint, the calcaneal cuboid joint and the cuboid fourth and fifth metatarsal articulations, with this cascade of events, the midfoot is driven planarly as these joints subluxate with further instability due to persistence subtalar joint pronation at a time when it should be resupinating.
So when we are dealing with the pronated hindfoot in mid-stance, the midfoot is forced to assume an unstable supinated position. Why, the supination in closed chain is mandated by the fact that the hindfoot is captive on the ground and so is the forefoot. So if the hindfoot is pronated and the forefoot is captive on the ground, there's a relative supinated position of forefoot to hindfoot in late mid-stance and inter-propulsion. Now, you can't clinically see that because the foot is captive on the ground and you can't look at the hindfoot to forefoot position as you could if you're examining the foot on the table so that you can see an inverted position. But this is a functionally inverted position of forefoot to rear foot. That inverted position or supinated position of the midtarsal joint is the opposite of what's needed for propulsion. For propulsion in a healthy foot, you need a locked midtarsal joint which means that the hindfoot is supinating on a planted forefoot as you move into propulsuion. But in the hyper-pronotary hindfoot type foot, there is instability in the midtarsal joint because that condition can't be met so much so that neither tibialis posterior nor peroneus longus muscle contracture can overcome that position. Therefore, the first ray cannot maintain its stability against the ground as is normally the case when the hindfoot is resupinating on the planted forefoot. And the inability of the first ray to maintain its functional position against the ground results in it being "hypermobile." And as one moves into propulsion, the medial column then gives way causing further pronation. So when the summation of those forces [00:35:00] place the foot in a hyper pronotary position with an unstable midtarsal joint, over-pronated high subtalar joint and hypermobile first ray, then even the momentum of the swing phase limb as the superstructure is coming through, that would normally and externally rotate the stance phase limb, is inadequate to counter act the pronated position of the foot.
This concludes part one of the discussion of pediatric pes planus. Please refer to part two for a continuation of this discussion. Thank you.