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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: Assessment of pediatric pes planus part two. Marc A. Bernard, DPM, executive director of American Board of Podiatric Medicine, co-director of the Baja Project for Crippled Children. I have nothing to disclose with respect to sponsorship. The learning objectives include recognizing the clinical and radiographic features of pediatric pes planus, recognizing the compensatory mechanisms involved in its pathomechanics and a recall of the proper assessment techniques in the biomechanical examination of the condition. We're going to go through some of the key radiographic parameters to be assessed in pediatric pes planus or for that matter, any pes planus. Bear in mind, however, that radiographs in this kind of a condition are strictly adjunctive. And the most important aspects of assessment of pediatric pes planus is going to depend on a thorough clinical, including biomechanical examination of the patient. The reasons for that are that in the younger child, many of the areas that one would be assessing are radiographically silent, which is to say that the midtarsus is not fully ossified in the young child. And so you are looking at a lot of empty space or visually empty space. Obviously, it's there and in terms of its cartilaginous precursor to the ossification. However, it's less well defined. So you're going to rely primarily in the younger child on a clinical assessment and the biomechanical assessment. In an older child, of course, it becomes easier to get the standard angles and relationships. So let's take a look at this foot and the illustration on the right. We're concentrating on talar adduction and plantar flexion on the planted forefoot because dynamically, as we said in part one, the forefoot and the hindfoot are captive on the ground. And what is moving is the leg by way of internal rotation and external rotation and the talus is following the leg because it's captive in the ankle mortise in the transverse plane. So when we are looking at a weight bearing assessment, we're really talking about a medial deviation and plantar flexion of the talus relative to the rest of the foot. And of course, that takes the calcaneus with it even though kite's angle will open and close it with pronation and supination. So you have to bear in mind that that's what's going on. That's why looking at static two-dimensional images can be deceiving because it doesn't give you anything close to the entire picture.
Let's take a look at the weight bearing AP radiograph. The two most important angles to evaluate are kite's angle or the AP talocalcaneal angle and the talar first metatarsal angle. Kite's angle is important because it's a reflection of the amount of medial deviation of the talus with weight bearing. Recall that with weight bearing and particularly with gait, the leg internally rotates and because the talus is captive in the ankle mortise, it follows the internal rotation of the leg. The calcaneus is held on the ground by frictional forces. So when kite's angle opens, that's a reflection of subtalar joint pronation. Where that deviation is significant and we have an enlargement of kite's angle, it's telling you that there's a significant amount of range available to the subtalar joint to allow that amount of divergence. The next important angle to look at is the talar first metatarsal angle. And this is significant because as the hindfoot is captive on the ground, so is the forefoot. So this will tell you how much medial deviation the leg is created on the planted foot. And you look at the bisection of the talar head and neck and the bisection of the first metatarsal and you can see that it's [00:05:00] projecting while medial is the talar head and neck to the forefoot. It tells you that there's a significant transverse plane compensation of the midfoot on the forefoot and the hindfoot.
Looking at the weight bearing lateral radiograph and the most important angles are the calcaneal inclination angle, the talar declination angle, and the talar first metatarsal angle. With normal subtalar joint pronation, there is medial deviation and plantar flexion of the talus relative to the calcaneus as was previously discussed. When the calcaneus drops, the medial longitudinal large [phonetic] flattens. And so the talar declination bisection falls well below that of the bisection of the first metatarsal. Be aware that in a very young child, say, one year to approximately three years, the talar declination will not necessarily fall into the bisection of the first metatarsal because young children are abducted and pronated to create a stable platform for stance and early gait. And so the normal physiologic development to the foot is such that it is a flatter foot, so that there is more surface contact on the ground. So when we're looking at very young children, you would expect that the talar bisection to fall below the bisection of the first metatarsal.
Once we get into children that develop a heel to toe pattern, however, which would be age 4 and up on average, then the angular relationship start to look more like those of an adult. Now, the talar calcaneal angle is going to be increased, meaning, the talar declination angle relative to the calcaneus, even though the calcaneus is dropping as well as you can see in the lateral radiograph that talar plantar flexion exceeds that of the calcaneus so that the convergence of the talar bisection and aligned paralleling the calcaneus forms a more acute angle.
While, it's hopeful to understand the nature of these angles as we're learning about the pathomechanics of pediatric and/or flatfoot, it's important that you understand that there are significant limitations that are inherent to static images that are taken in bilateral stance and are two-dimensional. If you think about it in the normal development of pathology and with normal motion, never is the foot attitude as it is here where it is in static bilateral stance. The leg on the lateral side is shown directly over the planted foot. And this occurs in only a fraction of a moment in the normal gait cycle. So the best these radiographs are capturing on the AP view is a mere approximation of these relationships because in gait, the foot is central under the superstructure, particularly in a gait that is heel to toe in an older child. Not a toddler, but an older child. And so what we're looking at in a bilateral AP view is only a rough approximation. And again, when we look on the lateral, we're looking at it, as I said, with the leg perpendicular to the planted foot. And in gait, that only occurs at a very small amount of time as the leg is moving over the planted foot. That's why clinical assessment and biomechanical assessment is so much more critical than radiographic assessment.
When we do a radiographic analysis as well as a clinical analysis, bear in mind that the concept of planal dominance has to be considered. What is planal dominance? Individuals vary with respect to the orientation of the subtalar joint and midtarsal joint axis. Yes, they are all [00:10:00] within a certain range, tri-planar and therefore, the motion around them is obligated to be pronotary and supinatory. They don't function purely in one of the cardinal planes. But because people vary and children vary in terms of the orientation of those axes, then they will exhibit some variance from patient to patient in terms of the ability of the foot to compensate while it is pronating and supinating. So that if the axis, for example, is slightly more vertically oriented than the "average axis," then it will favor transverse plane compensation capability. And if that's the case, then on radiograph, you would see a relative increase in the AP talar calcaneal line or kite's angle. You would see an increase in the cuboid abduction angle and a decrease in the percentage of talonavicular congruency.
Let's talk for a moment about the last two bullet points. Recall that I said before that the hindfoot and the forefoot is captive on the ground. And what's moving is the midfoot as it's taken by the leg’s internal rotation with pronation and external rotation with supination. So that when we talk about a cuboid abduction angle, what we really need is a calcaneal adduction angle because it's not the cuboid that is actively abducting, it's the anterior calcaneus that's moving medially on it. Likewise, the talonavicular joint is not the navicular that's abducting on the talus. It's the talar head and neck that is adducting as it's carried by the leg’s internal rotation on the navicular. So it's important that you understand the nature of the motion so that you know how to control it, clinically or surgically.
Feet that exhibit frontal plane dominance are those whose axes are oriented more parallel to the supporting surface, so that the predominant motion around those axes while still tri-planar is also largely present in the frontal plane. Accordingly, you're going to see a widening of the lesser tarsus on the DP view or AP view, the normal amount of metatarsal base overlap that you would see in an otherwise neutral foot will be decreased and you'll see the metatarsal bases more individually and less stacked visually. And you will see a decrease in the first metatarsal declination angle on the lateral view. Likewise, the height of sustentaculum tali will be decreased because of the rotation of the hindfoot in the frontal plane, and this is seen on a lateral view.
In feet whose axes tend to be oriented slightly more in the transverse plane, you will see them exhibit primarily sagittal plane dominance. And the clinical and radiographic features there would be an increase in the talar declination angle, oftentimes the navicular-cuneiform breach, and due to talar plantar flexion, an increase in the lateral talocalcaneal angle. Supplemental radiographs can and often are very helpful in the assessment of the condition. Though, standard AP and laterals are used most of the time, there are good reasons to get the supplemental radiographs in a given patient. Stress views can be helpful to rule out an equinus condition. A bone block or otherwise, a radiographically silent limitation due to the fact that [00:15:00] the ossification centers at the distal tibia and the talus in a young child may not be fully appreciated. So that if you take a stress view and the leg doesn't move forward as much as you would expect on the planted foot, there may, in fact, be some reason for that that is radiographically undetectable due to the young age of the child. Likewise, a flattened talar dome can be seen in a child that has got adaptation to excessive stress on the talus due to an equinus condition.
Harris Beath views can be very helpful to measure the calcaneal tibial offset, also known as medial malalignment that I referred to in part one. And this is done by bisecting the calcaneus and bisecting the tibia and projecting that bisection down parallel with the bisection of the calcaneus and seeing how much offset there is between the two lines. Also in a Harris Beath view, if you take the angle correctly, you'll be able to look into the middle facet clearly. And in some cases, you'll see that the middle facet is not parallel to the posterior facet and that eversion of the middle facet can be indicative of a potential hyper pronotary position or can be the ideology of the broadening of kite's angle. And of course, overt abnormalities of the middle facet or posterior facet by way of subtalar joint coalition.
Neutral weight bearing films compared with relaxed weight bearing films can be very helpful if you suspect that the patient may be compensating for an, otherwise, adductory condition that is perhaps not well detected with a standard AP view. By comparing the relaxed AP view, for instance, to a neutral AP view, you can unmask or uncover a metatarsus adductus or a skew foot deformity. And it's critical that you know this so that you understand what the ideology of the compensation is leading to the hyper-pronotary foot type.
Patients with an excessive amount of medial malalignment in which the leg is significantly medially offset relative to the planted foot, on occasion, it's not common, but on occasion have a condition known as ankle valgus in which the distal epiphysis at the ankle joint is in actual valgus relative to the bisection of the tibia. And so in these cases, it's important to understand that there's yet another level of deformity and that impacts your ability to treat the patient. It may be the difference -- if in a nonsurgical scenario, the difference between a UCBL type device or a deep foot orthosis versus an ankle foot orthosis, that goes up high enough to stabilize the ankle position.
Let's move on to clinical evaluation. Typically, pediatric pes planus is of flexible nature. And with it, we see an unstable subtalar and an unstable midtarsal joint. Now, when I speak of an unstable subtalar joint, I don't mean that the joint itself is innately unstable. What I'm speaking to is its functional stability in stance and in particular, in gait. When a subtalar joint is over pronated in an older child where there is an active heel to toe gait, the swing phase limb coming through and externally rotating the stance phase limb cannot, even with muscle contracture on the medial side of the stance phase limb [00:20:00], bring that subtalar joint into a neutral or slightly supinated position preparing it for a propulsion. And in that scenario, the subtalar joint can be deemed to be unstable or hypermobile.
Likewise, the midtarsal joint in these situations is unstable because it is in a supinated position relative to the hindfoot rather than in a locked pronated position. This is often hard to visualize. And what I'm talking about is, the forefoot is captive on the ground. When the hindfoot normally moves from a pronated to a neutral to slightly supinated position with the forefoot captive on the ground in a normal situation, there is a relative eversion of the midtarsus on the tarsus, the so-called locked midtarsal joint. But if the hindfoot is hypermobile with a pronated subtalar joint in late mid-stance and inter-propulsion, the ground reactor force is holding the forefoot in a position that it cannot achieve stability relative to that pronated hindfoot. And so we have a pronated foot in mid-stance and it remains pronated inter-propulsion because the midtarsal joint can't lock.
Bear in mind that with very young children who are not yet heel to toe, they have a more broad base and abducted gait and they are toddling. They are toddlers. And so in this scenario, the feet are normally pronated and should be pronated to maximize the amount of medial longitudinal large and foot contact on the ground for stability for the child who's developing and learning to walk.
With pronation of the subtalar joint, the talar head and neck are medially deviated and plantar flexed. This has been covered And with that, you have the collapsed or the flattening of the medial longitudinal arch. Though, by no means common, an equinus is not infrequent in children that had a hyper-pronotary condition of the foot for an extended period of time. So it's important that you always, always evaluate the ankle joint for an equinus condition. If present, it's typically a gastrocnemius equinus.
Forefoot supinatus as has been alluded to in the first bullet, forefoot supinatus is present in a hyperpronated hindfoot because the ground reactor force is maintaining the forefoot in a relatively "inverted or supinated position" relative to a pronated hindfoot. In young children, the forefoot supinatus is flexible. And you can tell that by bringing the hindfoot into a neutral position lining the heel up with the posterior leg and then pressing down on the medial column. And the medial column can often easily be reduced down to the supporting surface. With age, over time, this condition becomes more rigid. And so we may actually see true rigid forefoot varus or forefoot conditions in an older child. By convention, when we are evaluating our patients in bilateral static stance, we typically view them from posterior and central. So that we orient ourselves midline relative to their position of stance. And this is important to cover because it's often enough true that patients are asymmetric. That even though it's in the minority of cases, it's true enough that it's important to assess the patients with the assumption that they are asymmetric until you find out otherwise. [00:25:00]
So here is a case where we're looking at one of my patients, one of my kids from directly posterior. And by and large, it's pretty much asymmetric presentation. You would say, possibly there's a little bit more hyperpronation in the hindfoot, a little bit more medial malalignment in the hindfoot on the left than the right. However, moving onto the next slide, when we look at the feet individually -- and this child was not moved, this is the exact same position. The only thing that's changed is the point of view of the observer. So when we move to our left so that we can look directly posterior to the left leg, you see just how much medial malalignment there is on the left side. Conversely, if you look at the clinical photo on the right, you see that the heel and leg are rather well aligned. Yes, the foot is pronated beyond what you would expect, but far less than what is present on the left side. So again, it's very important that you assess the patient from the appropriate point of view so you don't lose pathology that's truly there. You don't miss it, I should say. And thereby, do your patient a disservice by missing that important feature to their condition.
Forefoot to rearfoot relationship is more easily observed than a non-weight bearing situation. And what we're looking at is the relationship of metatarsals one through five and separately two through five to the heel bisection, preferably with the subtalar joint and neutral. So if you look at the clinical photo on the left, subtalar joint is in neutral. And a way to double check that is that the tendo Achilles is central relative to the posterior aspect of the leg and central relative to the malleoli.
Clinically, as you bring the foot through a range of motion, the arch described by the subtalar joint will demonstrate a low point. And it's at that low point that subtalar joint neutral is present. And when you get to that low point, you should see the tendo Achilles centralized relative to the malleoli in the back of the leg. When that's there or when that's achieved, then you low the forefoot and you get an assessment of forefoot to rearfoot relationship. In this particular child, the relationship is perpendicular.
If on the other hand, you look on the clinical photo on the right, you are not appropriately assessing it and you're checking forefoot to rearfoot relationship with the hindfoot pronated, then you will get a inappropriate position of the forefoot to the rearfoot. And the more you pronate the hindfoot, the more you will unlock the midtarsal joint and vary what would otherwise be a normal relationship. So it's important, again, if you're going to assess forefoot to rearfoot relationship that you do it with the hindfoot and neutral.
As was discussed in the part one lecture and I'll repeat it here, in clinical evaluation of the foot in stance, we're interested in the medial malalignment of the leg on the planted foot in a hypermobile flatfoot. And so what you see here is the offset of the calcaneal bisection to the bisection of the middle of the ankle joint. The midpoint between malleoli. And you will see that they are significantly low parallel or offset from one another. Another way of looking at this clinically, is the relative position of the tendo Achilles compared to the back of the ankle and the back of the leg. And here, you see that the leg itself is significantly medially deviated on the planted foot. You see the medial malleolus and the bulge below the medial malleolus is the talar head. [00:30:00]
The heel itself is not everted. It looks clinically everted because of the soft tissues around it and because of the line present from the bulge of the talar head working backwards to the calcaneus. But in reality, unless it's a pathologic, meaning a traumatic condition or a true ankle valgus is present, you will almost never see significant true calcaneal valgus. It's medial malalignment that's really what's going on.
A key feature of flexible pes planovalgus is that the midtarsal joint is not innately unstable, which means that with the forefoot captive on the ground when the heels are raised off the ground, the subtalar joint will, in a vast majority of cases, resupinate. And it's able to resupinate because there's enough intrinsic stability to the midtarsal joint to allow that to happen.
Here's a clinical [indecipherable] [00:31:22] when evaluating ankle joint dorsiflexion in open chain. The clinical photo on the right is taken with the patient prone and the knee flexed 90 degrees and the ankle joint, therefore, dorsiflexed. The reason this is important is that, most patients, adults as well as children will, if being assessed in a supine position where you're lifting the leg off the clinical table, get tension in their hamstrings. And when they do, they automatically, subconsciously, will clutch and resist in anticipation of that stretch. And when they do so, not only will the knee not fully extend but the gastroc and soleus or gastroc in particular will develop tension. And so when you then dorsiflex the foot on the leg, it's met with a certain amount of resistance. You can eliminate all of that by keeping the patient supine. And with the patient supine, flex the 90 degrees and he stretch off the gastroc and then you dorsiflex the foot on the leg as you see on the right.
This is exactly the same photo that you see on the left, but I've rotated the photo 90 degrees so that you can appreciate the position. Then when the patient is in the flexed position, you gradually extend the knee and keep tension on the foot so that you're dorsiflexing the foot on the leg as you see clinically on the photo on the right. So now, you've taken the patient from a knee flexed position with the foot maximally dorsiflexed to a knee extended position with the foot maximally dorsiflexed. And as you can see, again, using the photo from the previous slide, which was rotated 90 degrees, so you can compare apples to apples, you see that there is decreased dorsiflexion with the knee extended then there is with the knee flexed as shown on the left.
And again, I find this to be a much more repeatable and clinically competent way to assess this. It's also very helpful with children because of the cognitive processes with young children. If they are not looking at you, they are less intimidated. So for a variety of reasons, both clinical and patient management wise, it's more prudent to assess ankle joint dorsiflexion this way. I'm not saying it can’t be done the other way, but I think you have more variables to have to deal with the other way than this way.
I need to emphasize the importance of assessing a child's shoes. Parents will tend to bring their children in with newer shoes because they don't want the doctor to think that they are, somehow, neglecting their children by not having them wear current and new shoe gear. However, that doesn't tell you very much with respect to the way the child has been functioning. [00:35:00] Much better is to ask the parents to bring in, if they have them, shoes that the child has been wearing for a while. And there are certain clinical features that you're going to notice. If you look on the left side, you'll notice that the upper is broken down medially compared to laterally. You also look posteriorly at the heel and you notice that in this scenario, the medial side on the right is much more worn in the lateral side on the right.
So shoes tell a story. Just as tire tread tells a story when you're being evaluated for tire rotation or tire alignment. It shows where the pressure points are over time and with motion. If you look at the clinical photo on the right, you see the wear pattern on the sole of the shoe. So if you look on the right, you'll see that the left foot on the right clinical photo, you'll see that the heel wear pattern is central. And as you come out towards the forefoot, you'll see that it's under the first metatarsal head and going out under the hallux. If you look at the right foot, then you'll notice that the heel wear is more medial than it is central and stays more medial. So that the wear pattern on the first metatarsal head is under it and medial to it and actually off to the medial side of the hallux. So again, shoes tell the story. They don't tell you what's happening dynamically as you're watching the child walk, but they will tell you the summative forces on the foot overtime and gait. It's true for adults as well as children.
But it's important because you're relying on the parents to cooperate with you so that you can fully assess the child properly, that they bring in shoes that she'll wear and that they retain the shoes once you've treated the child. Let's say you've treated them with orthosis or whether you've done surgery on the child, make sure that the parents don't throw the shoes away. You always want to see the old shoes as well as any new shoes that they're wearing, so you can tell how they have been functioning over time.
In summary, if I had to come to the most salient parts of this lecture and what I feel to be the most important takeaway from this lecture, obviously, in addition to the aspects of pediatric pes planus that I've discussed is the following, radiographs capture only a portion of the information required. You cannot expect it to capture more than that because they are taken in the best of circumstances in bilateral static stance. In addition, they are two-dimensional. So if they are two-dimensional and are taken in bilateral static stance, you can only get a very small piece of the information that you require. Furthermore, most patients that develop pathology or have a problem develop that dynamically in gait and you're not going to be able to pick that up in bilateral static stance radiographs. They cannot substitute, therefore, a thorough clinical and biomechanical assessment and they, therefore, cannot be relied upon for the conservative and especially for the surgical management of the patient because they don't give you a feel for the actual ranges of motion innate to the ankle joint, the subtalar joint, the midtarsal joint. Thank you.