Guido LaPorta, DPM, FACFAS, MS gives a unique look at rearfoot and leg deformities by reviewing how to plot and interpret the angles of the foot. Dr LaPorta shows a host of foot radiographs and how to correctly find and interpret the important angles of the foot. He concludes by showing how these angles can be used to provide your patient with optimal surgical correction.
Guido LaPorta, DPM, MS
Director Podiatric Medical Education
Community Medical Center
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�planting angles and then showing how it actually applies to something that we do rather frequently in the forefoot hallux valgus deformity. Okay, so we�re going to look at this particular foot, and what I like to do with my residents and students that are visiting is, we�ll do a clinical exam, we�ll watch somebody do a gait analysis, and then we�ll throw up the X-rays, because I think you need all three. I think an exam is not complete unless you do the non-weight-bearing range of motion exam, look at them walk, and then evaluate their X-rays. And we�ll look at the X-rays of this particular person and point out some things that I think are important, and it�s what I want our residents to report when they�re evaluating X-rays.
First one would be, the relationship of the forefoot to the talus. Now, in the literature, and certainly when I was growing up, the talar first metatarsal angle was always the important angle. Unfortunately, if, whether or not you have a bunion, with an increase in the metatarsal angle, greatly influences what that angle is. So if you have an increase in the metatarsal angle, then you draw a talar first metatarsal angle, that range is going to be within normal. It doesn�t really give you the breadth of the deformity. So Michael Graham and colleagues just published an article within the last year the talar second metatarsal angle. And interestingly enough, this is a far better predictor of the relationship of the forefoot to the rear foot, and that normal angle should be around 17 degrees, and as it enlarges, then you have on the pronatory side of the deformity, and as it decreases, you get to the supinatory side. So what we ask for is the talar second metatarsal angle, and we think this is more reflective of what�s going on that particular foot.
Another angle that I think is important, especially if you evaluate deformity from a planal dominance standpoint, is the talar calcaneal angle. Now, the way it�s shown in most recent articles is to draw a line, which is the solid red line, which indicates the lateral wall of calcaneus, and your talar bisection line. And you will get an accurate angle if you do that. The only problem with that is that that does not represent a bisection of the calcaneus, and having been brainwashed by the Baltimore group, there�s really only two ways to plant a deformity. You could either use a mechanical axis which goes from joint to joint, or you can use an anatomical axis that bisects a bone. So obviously the solid red line doesn�t bisect a bone. But using the three-line technique, you can then just move that line and draw a parallel one right through the middle of the calcaneus so that it exits that distal medial corner of the anterior calcaneus. And now what you have is a line that really bisects the calcaneus but more important, represents a longitudinal axis of the foot. You get the same angle, but now when you go to plan deformity, you have a much more accurate representation. And when you have that line, then you can compare it, if you will, to your other structural angles which show where the deformity is. So for instance, if this solid red line that bisects the calcaneus were back out where the lateral border is, it wouldn�t even cross the line that�s the forefoot abduction angle. So you would not be able to get an apex of deformity. You would get a correct angle measurement but not an apex of deformity. So now that I have that line, if I draw the bisection of the tarsus and extend it forward, where the purple and red lines cross is, measures the angle of forefoot abduction or adduction. And that�s another pet peeve of mine. I get a lot of students who come into the residency program who really don�t know forefoot abduction from their elbow. And I�m not sure why, �cause I know it�s taught. I�m just not sure why, and it�s possible that what gets taught in the classroom may not work its way down into clinic. And I think it�s so important, when we�re especially considering whether or not we�re going to reconstruct a particular deformity, to know where the center is, to know where the apex is, because that is going to influence where you do your osteotomy and what it should look like.
So there�s forefoot abduction, as measured using the lesser tarsus bisection. And then you can bisect the second metatarsal and see metadductus. And all of these are in fact very important, because if it�s a metadductus, the core for that deformity is in a different point than forefoot abduction or forefoot adduction, so it at least tells you where you need to place your osteotomy. When you�re trying to explain a surgical procedure to a resident, you really need, I think, a system that, although not perfect, will explain the surgical intervention.
Now, here�s another angle that I think is important, and this deals with the obliquity of the metatarsal cuneiform joint. Larry D. Domenico will be here in a while, you know, always says, you know, like, �Why are we cutting the first metatarsal? It�s a straight bone.� And consequently, he�s right, and therefore what�s the indication for obliquity? Well, if you measured this angle, I can tell you that at least in our unpublished study, that obliquity retrospectively was a 22 degree angle or greater. Okay? That angle measures 22 degrees or greater. And when we looked at all the procedures that were done without lapidus type approaches, the angle isn�t even close. It�s down around 15 to 13. So there�s a big range there and when it�s 22 or greater, that classifies in our institution as an oblique joint, which may be an indication for you to do a lapidus procedure.
How about looking at the lateral view? I asked a resident to evaluate a lateral view. It�s amazing what you�ll get as what they think is important or what they remember from the lecture. And that�s my first clue that they�ve never used it in clinic. When the first thing out of their mouth is, �I have to remember what I heard in the lecture,� that means they never drew the line in their life when they were down in clinic. But I�m going to tell you what I think is important in the lateral view, and the first one is the angle of the articular surface on the distal tibia. Conceptually, you and I � or at least I � thought it was always at a right angle to the tibia. It�s not. In fact, it�s angled up 10 degrees. And if you look at the knee, which I�m not going to talk about now, that articular surface is angled back 10 degrees. And there�s a very functional reason for that. In mid-stance, single lane support is flexed 10 degrees and your angle is dorsiflexed 10 degrees. Both joints are horizontal to the ground. Okay? So that is the moment during the gait cycle that has the most stress and at that time the normal alignment is such that those joints are horizontal or parallel to the weight-supporting surface.
Now, what�s the other thing we look for? What happens if that angle measured distally is less than 80 degrees? Well, that joint has an overly tilted ankle joint, and is susceptible to shear and osteoarthritis. As that angle approaches 90, then you have literally an osseous equinus. So when we look at an X-ray and we see jamming anterior ankle, and see all of the reactive spurring that occurs, that�s really secondary to the fact that that angle only measures 90 degrees, not 80. All right? And in many deformities, and how do I know? You know, I was always interested into why I could do a posterior muscle group lengthening � whatever, gastroc recession, whatever, and get more than adequate dorsiflexion on the table, and then post-operatively, some of the patients functioned like they had no dorsiflexion whatsoever. And when we went back and looked at them, those patients didn�t have the 10 degree slope of the ankle. You need that to allow the 10 degrees minimum amount of dorsiflexion that�s necessary at the ankle in order to function relatively normally.
Now, what�s the other important thing about this line? Oh, it does work? Okay. The other important thing about this line is that when you bisect the tibia, that line should pass through or just posterior to the lateral process of the talus. Okay? So that�s just drawing
that little angle tells you a couple of things about this particular foot. We would ideally like to see it here, in the lateral process, but it�s posterior to it. So that immediately tells us that even though at first glance this foot looks rather healthy, remember what the clinical picture looked like � this foot was flat as a pancake. And when you look at this, you can see that that talus has migrated distally within the subtalar complex, so that it shows the signs of pronation.
Another angle I like the residents to look at is the latter talar calcaneal angle. Why do I do this? Well, I frequently hear everyone say the talus is plantar flexed. And my question is, to what? Is it plantar flexed to the calcaneus, or is plantar flexed to the floor? Okay? And in this particular case, this lateral talar calcaneal angle measures between 48 and 54 degrees in a normal foot. It�s a pretty tight angle. And consequently, when that angle is normal, it means that there is no sagittal plane deformity between the talus and the calcaneus. Now, if you look at this, you and I know that a line that bisects the talus should pass through the first metatarsal. All right? And obviously that�s not going to happen here. And consequently, if there�s any plantar flexion of the hind foot, it�s the hind foot as a whole, and not the talus or the calcaneus.
So when I hear people talk about arthroereisis and they�re going to prop the talus up, that�s really not the goal of an arthroereisis in my mind, because in most of the feet that I see it used on, the talus is already propped up. It�s not a sagittal plane deformity within the subtalar joint � it�s usually transverse and frontal
Now, it should strike you as interesting that I don�t use the bottom of the heel for calcaneal inclination angle. And the reason for that is the same reason for the AP view TC angle. Again, if you�re trying to plot deformity, there�s really only two ways to do it: mechanical axis or anatomic axis. And if you use the bottom of the calcaneus, these lines cross out here somewhere. That�s not where the deformity is. When you use the bisection of the calcaneal body, then you get the true cora or apex of the deformity. So I bisect the body here, and my distal point is the end of the posterior facet of the subtalar joint. That gives you the accurate bisection.
Now, if you look at this foot and say, �Well, that lateral looks pretty good. How could that be the lateral of that foot we saw clinically?� Well, if you compare the talar bisection to the first metatarsal bisection, you can see that there�s a significant angle here. So that angle means that the forefoot is elevated or the hind foot is plantar flexed. You got to figure out which one that is. And you do that with any one of a number of different angles. For instance, what�s the normal metatarsal declination angle? The normal one is somewhere around 22 degrees. So if this measures 22, and you have that big a difference between it and the talus, you have a hind foot deformity. Okay? If this angle is not 22, and in fact is very high, so that it measures in and around 18 to 15 degrees, then you know you have forefoot contributing to that particular deformity. So by process of elimination, you can figure out where the deformity is.
Here�s an angle that I don�t see many people draw, and it�s the fifth metatarsal calcaneal angle, and I consider that the representation of the lateral column of the foot. And isn�t it interesting, then, following Paley�s principles, that if you�re looking at a cavus lateral column, and you want to reduce it, then actually the best place to do that is with your calcaneal osteotomy, �cause here�s the apex of that deformity. So you can do, in most cavus feet, a
Dwyer type displacement osteotomy dorsally and reduce the lateral cavus without having to do an additional osteotomy in the mid foot. That to me becomes a very important aim.
The other thing I like residents to talk about is the facets. And facets are joints, you know, so what I tell the residents are that if you are looking at the subtalar joint, you have to be able to see both facets � the posterior and the middle. They should be clearly visible; they should be symmetrically open; they should form an angle between 45 and 30 degrees with the weight-supporting surface. So you�ve got to treat that as you would treat any joint.
If you look at these angles, this is a xxxx approach [17:45] to the foot, and you can see here that if you measure these angles, if you have a normal calcaneal inclination, and you have a normal metatarsal declination, and these three angles are normal, then the pathology is in the hind foot. It�s the red triangle, not the blue triangle, �cause the blue triangle measures all the normal numbers. So then your job, when you�re correcting a flattened foot or a hyperpronated foot, is to make both of those triangles overlap.
Let�s look at the AP view of the ankle. Again, we think that this is at a right angle, and most people, if they use 90 degrees, would probably be correct. But if you look at the numbers in all the studies, it has a tendency towards valgus. And population normal is 88 to 89 degrees, although it ranges from 87 to 93. The population normal is considered to be on the valgus side. And this is the long leg calcaneal axial. I started taking these about eight years ago, and it�s completely changed what I do for various foot deformities. This has taken like a Harrison Beith view � patient stands on the X-ray; X-ray beams 45 degrees from the back; he accidently cracked the knees; and you take the view. And you can see the relationship of the calcaneus to the lower third of the leg. So as you bisect the calcaneus, and bisect the leg, you get to see what this relationship is.
Now, if you extend this blue line proximally, it�s not going to cross anywhere in the foot. It�s going to cross in the distal third of the tibia. So I know just from seeing that, that whatever procedure or osteotomy I do on the calcaneus needs to be translated so that the blue line and the red line become the same line. That�s why Koutsogiannis osteotomies work so well. It�s mechanically an accurate osteotomy.
Now, look at these areas here also. Here are those same facets that we saw on the AP view, I�m sorry, on the lateral view. Again, when you�re looking at this view, these facets should be fully visible, symmetric, parallel to each other, and parallel to the ground. So when you look at that, you look at those facets, that�s the relationship you want. If you have that relationship, then basically the subtalar joint�s fairly healthy. If you don�t have that relationship, for instance, if this angle angles down 15 degrees or more, if you don�t have a coalition, the foot�s going to function like one. It�s going to be rigid and it�s not going to be able to reduce back into its neutral position.
All right. So I will now just finish off with plotting hallux valgus deformity, and this is the intermetatarsal angle. And if you look at this intermetatarsal angle, it measures about 18 or 19 degrees. This is anatomic planing, is it not? We�re bisecting the bone. So it�s anatomic planing.
But one thing I want you to consider, after you draw your hallux valgus angle, is that there is a center point on the phalanx, and there is a center point on the metatarsal, and in the normal foot, they should be opposite each other. So you can, by doing a very complex
analysis of this triangle, figure out how much of that bone you need to shorten to get it back in its anatomical position, or if you�re using calibrated digital X-rays, you simply measure the distance between these two lines, and it will tell you if you need to shorten that first metatarsal somewhat in order to get a smooth-fitting joint. And we have to remember that this is going to travel in an arc, and much of the reason why there is jamming post hallux valgus correction is that I think we might pay too much attention to not shortening the metatarsal significantly, and we probably need to reconsider that. I�ll leave that up to your own investigation.
Here is distal metatarsal articular angle, proximal set angle. If you drop a perpendicular from that, you see that it crosses right here. Consequently any osteotomy that is going to correct the angle of this joint to the metatarsal should be done right there. That�s called osteotomy rule one, and that�s the apex of the deformity. And it�s all over � it�s never in the same place in every case. But we do our procedures the same way every time, and kind of wonder why we get variable results. And I think it�s because we�re not really evaluating them appropriately. So if I did a lapidus to correct this, this is what a lapidus has to look like. It can�t be just angular � you also have to translate it. That�s the only way you can get the bisection of the metatarsal down to what you want it to be. Every procedure that we do to correct the intermetatarsal angle is distal to cora. Here�s cora � the apex. Therefore, we�re not doing a procedure here � we�re doing it at a distance from cora. Every procedure has to be angulation translation. All right? And here is the reduced angle if you look at it.
Now, let me just finish with mechanical access, and I�ll give kudos to Paul Ofada who�s in the audience, who I coerced into measuring a significant number of X-rays to find out what this normal angle will be. And this is the way I plan intermetatarsal angle correction. If you draw a line from the center of the head of the talus to the center of the second, center of the head of the talus to the center of what was the joint, the phalanx, that angle ranges between 9 and 13 degrees in the normal foot with the average being 11. Now, I want you to look at this.
When I draw that same angle in this deformed foot, it also measures 11 degrees. How is that possible? It�s possible because the hallux doesn�t go anywhere. The metatarsal moves. All right? And this I call the mechanical axis of the medial column, and if I draw a line from the cuneiform to the middle of the metatarsal head, that�s the mechanical axis of the first ray. The first ray and the medial column mechanical axis should be the same line. Here�s the cora, all right? So the area between these two lines is the amount of deformity. And if I want to correct it, you see it plots the same way as the anatomic axis, but it�s kind of easier to understand. If you take that wedge out and move the bone, that�s the deformity. If I do a closing wedge or if I start my xxxx [26:25] there, that�s what it has to look like � it can�t just be rotated and angulated � it has to be translated. All right? If you do a xxxx [26:36] and you don�t translate it, here�s what happens: look how far apart these two blue lines are. They�re parallel, so your angle measures good, but you didn�t restore the mechanical axis. You need to move this line to that line and you can only do that by translating the bone. All right? That�s what you need to do. So that�s a normal mechanical arrangement.
Open-wedge osteotomy does exactly the same thing. It�s got to look like that. Okay. So let me finish with this statement, and I�m going to � this is a quiz, okay? And whoever gets these answers right, Dr Schoenhaus is going to buy a drink right after this session. Why does hallux valgus form? Anybody want to venture a guess? Two reasons. Pardon? Hypermobility pronation. I won�t argue with that, but that�s, that�s an observation that
occurs with the formation of hallux valgus. That�s not why. All right? Here�s what a simpleton from Scranton says. All right? �Hallux valgus forms (1) because it has to and (2) because it can.� Now what the hell does that mean? It has to because there�s limited range of motion at the first MTP joint. How does it get increased motion? The intermetatarsal angle increases, uncovers the sesamoids, and now the hallux moves any way it wants to. You know that when you examine patients � you examine them in the deformed position, they�ve got all the motion in the world. You straighten the bunion out, and all of a sudden it�s limited, because you covered the sesamoids. So it�s no different in the foot pronating when there�s an equinus. It�s got to get motion somewhere else. All right?
Why does hallux rigidus form? Pardon? Almost. Exactly. It can�t form hallux valgus. And what do I mean by that? Well, the same biomechanical deformities cause hallux rigidus and hallux valgus. There�s no mystical difference. So what�s the difference in what forms? The difference is the first ray motion. In hallux valgus, the first ray can get out of the way � it can uncover the sesamoids. In hallux rigidus it can�t � it has no transverse plane motion, it�s only sagittal plane motion. So the sesamoids never get uncovered, and the joint jams. Okay? And therefore the intermetatarsal angle is a critical part in correcting hallux valgus deformity, but it always has to occur with some shortening or you will jam the joint and not get the appropriate range of motion that you need in order to have a good result.
So I�m not sure if any of that was helpful, but maybe it�s food for thought.
Thanks a lot.