Section: CME Category: Biomechanics

Musings on the Midtarsal Joint - Clinical Implications

Jeffrey Cusack, DPM

Jeffrey Cusack, DPM discusses functional anatomy, current debate regarding biaxial vs monaxial orientation, and treatment protocols to effectively manage abnormal midtarsal joint mobility.

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Goals and Objectives
  1. Describe the functional anatomy and implications of the midtarsal joint as a separation between the forefoot and rearfoot
  2. Review the current literature regarding biaxial vs monaxial orientation and the clinical consequences of each
  3. Compose useful treatment protocols to effectively manage the clinical consequences of abnormal midtarsal joint mobility.
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  • CPME (Credits: 0.75)

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    Release Date: 06/07/2018 Expiration Date: 12/31/2020

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

    Dr. Trepel: Our next talk is a lecture – I don't think you're going to hear too many other places, not only because of the nifty title of it, because I think of the greatly the subject matter of it. Jeff Cusack is a classmate of mine. I've known him for a long time. I'm delighted he's with us at the college and he's a professor of biomechanics. You can always tell when he's around because there's always – he's like the Pied Piper with a bunch of students following him around there trying to pick his brain, and then to see what's going on. He runs our gait lab at the college. If any of us want to know what's wrong with our foot biomechanically, he's our go-to guy.

    He has a real kind of a nifty topic here. He's going to talk on musings on the midtarsal joint and its clinical implications. Jeff, come on up.

    Dr. Jeff Cusack: All right. Thank you, Dr. Trepel, and to the audience. I walked in just a few minutes ago just doing a little bit of updating on the lecture based on some of the comments that were made yesterday that I think I'll tie in. And believe me, it wasn't intended, but it's going to fall into place.

    I looked at the crowd and I said, "Wait a minute, CME scanning was two hours ago or something like that." And I said, "Hmm, we now have the truly interested participants here." And then, I said, "Oh damn, boxed lunches in a half hour, so maybe it's what folks will do to sit down and get that free lunch." So hopefully this doesn't make it too difficult for that to occur.

    Last year's topic, any of you that were here was exploration of the consequences of equinus on the foot, and it was nice because we had an awful lot of titles that last year lectures on Charcot breech and so on, and it tied in nicely.

    [02:01]

    This year, I was given kind of a free range so to speak on title selection so I thought I'd expand a little bit, and work even backward as to how we got to the clinical consequences I guess we could summarize last year's lecture, and look at the implications of where a lot of these problems arise. And as I said in the context of a couple of lectures in particular that I'll reference, and I'm just going to be paraphrasing a couple of quotes that I heard from the speakers yesterday that I think might help bring this through.

    Financial disclosures as always, damn it, nothing to declare, unfortunately. But, all right, we'll move ahead here, and this will probably the most verbiage you'll see on any of my slides, so do not panic. But I needed to list what we hope to cover in a very short period of time we have here this morning, which is obviously we're going to look at the midtarsal joint.

    And I'd like to look at it a bit more functionally for you as an interesting joint, not just one that we teach the students that divides the forefoot from the rare foot, but let's look at its function. I would like you to become aware of an increasingly interesting debate, if you will, or discussion on the axial orientation of the midtarsal joint, and we'll talk about that in just a minute.

    The one thing that is probably the heaviest bullet we'll go over this afternoon, this morning, whatever, I'm on the cusp here, is the fact that the midtarsal joint is a very convenient replacement joint. No other way to describe it, and it is very susceptible as we all know in our practice, being used as a replacement joint for mobility that just doesn't exist at the right time, and at the right place elsewhere in the lower extremity.

    [04:01]

    And of course try and leave you with some useful information that you can bring home to your practice, and it is certainly treatment-wise but maybe even as far as evaluation.

    First quote from yesterday, Dr. Mike Troiano's lecture on total ankle. Here we go, Webster's dictionary, challenging, requiring much time, effort or careful attention. Mike had a quote, and hopefully I'm close here, something to the effect, medicine in the year 2018, "Thereabouts, it seems like we know more and more about less and less." If there's no better way I think to describe our current understanding, true understanding of the midtarsal joint.

    It is something that is a difficult joint for many reasons, none the least of which is it is classified as what we call an unconstrained joint. So think of it as a shoulder or a hip joint. It responds to the applied force, depending on which direction the force is applied. And of course in a weight-bearing foot, the predominant forces of the interest to us as podiatric docs, is the dorsiflexion moments that are applied to this foot during specific parts of the gait cycle.

    And Dr. Schoenhaus in his lecture yesterday on first ray, mentioned the fact that moving through midstance and certainly into propulsion, is when you're going to start to see these dorsiflexion moments applied to an unconstrained joint manifest in sometimes a very challenging way. So functionally, what is the midtarsal joint? What does it do?

    [06:00]

    Yeah. It's what we teach our students and we know it divides the forefoot from the rearfoot. The key to understanding it is to step back though and not just mnemonically memorize and spit these things out, but ponder, if you will, a couple of things. It is permitting independent movement of the forefoot from the rearfoot. That's a very heady statement to make again in an unconstrained manner, responding to ground reaction force in a way that is sometimes very difficult to appreciate until the manifestation appears in your office.

    It does allow this foot and this is the emphasis on that word selectively, to alter its stiffness. And you'd heard Dr. Richie once or twice during his lecture yesterday, start to talk about the stiffness of the first ray, rather than the term we always hear, which is the hypermobile first ray, stiffness being a resistance to a strain moment applied to the foot. Well, this midtarsal joint is something that enables this foot to at times, as needed, to selectively alter its stiffness, which in turn is what allows it to function both as I say here, something that allows it to adapt to the ground and stabilize it to enable efficient push off across the ground.

    The other thing which we're just starting to appreciate now is the fact that the arch structure, through the midtarsal region, enables the foot to actually store and release elastic energy much like the glued hamstring complex, which is something we go over with the kids at school, how the hip flexion is initiated, all of us appreciate. And there was another lecture yesterday alluding to the physiologic changes of the Achilles tendon in diabetics, and certainly in the aging population that the mechanism of heel-off requires movement of the ankle in a dorsiflexion direction.

    [08:05]

    So we have yet another side of storage, and therefore, release of this elastic energy, which is always much more efficient than muscular input.

    So what is the buzz? And those of you that are interested, if you have never visited the Podiatry Arena forum which is online, it's a free site. You sign up, you put your name in, pick out a password, but there's no moneys involved. But this is the secret site where all of the folks, the heavy biomechanical hitters, so to speak in our field right now, kind of hangout. It's their area of I guess relaxation until you start reading the discussions that become quite lively, by the way, and various topics are discussed. And if you go on to it and have a look and you can pretty much type in, a search engine, name of anything you'd like to see, discuss, and I guarantee it's been talked about.

    And right now, the hot area of discussion is the monaxial versus biaxial nature of the midtarsal joint. And everyone of us in this room, everyone of us were taught that classically based a lot on the work of Manter and Hicks, which by the way if you look at the dates, and the method that was employed, which we'll talk about in a second, taught us that it is a biaxial joint consisting of two axes, one launched totally orientated, that favors pronation, but favoring the frontal plane component. Meaning inversion, eversion, and an oblique axis, because of its orientation, favoring transverse and sagittal plane mobility.

    [10:05]

    And yeah, although it is purportedly easier to explain foot function, I think Dr. Trepel will agree. We sat there with Dave [Squire 10:16] as freshmen, moved on to Dick Schuster as sophomores, and Joe Wernick, sophomore. I don't know if it was all that much easier because we sat there and had to listen to it pronating around one axis while it's supinated around the other, and I suppose it was easier. But it does help to explain many things that we see in the foot but there's a problem with it and the sciographic method that was used early on is somewhat questionable because not the fact that it was a cadaveric study, which is in and of itself not a problem, but the fact that these pins were inserted by eye based on a guess, best guess method, and possibly introducing some predetermination of those axes.

    But more importantly, here's the problem. In engineering and true mechanics, there's a problem and you can't rotate one rigid body about another rigid body, about two axes at the same time. The analogy would be this door over here that I always tell the students, would be open that door, which is clearly an example of transverse plane motion. As you open that door, one degree, as you open that door, it's going to fall toward you a degree at the same time. And of course, it's absolutely impossible to do that.

    So we have an issue right off the bat about that problem. So fast forward into the '70s, '80s and more recently, Nester's work in 2001 and his paper was published in [indecipherable] [11:58] using a more sophisticated.

    [12:01]

    Because remember, the technology when the regional axes were determined, back in the '50s, they did the best they could with that they had available, and using more sophisticated insertion of small steel balls in either side of various joints throughout the foot, was the basis by the way of the [indecipherable] [12:18] and [Sheriff 12:19] study looking at dorsiflexion stiffness of the various MC joints throughout the foot, as well as a TN and NC joint.

    And then, using some very interesting imaging techniques, we're able to determine what is and what isn't moving. And so, well yeah, the foot needs to be kind of thought of a little bit differently, and the feeling seems to be now that we look at the talus and calcaneus as one rigid body, and navicular and the cuboid as a second rigid body. And the movement occurs between those joints. So you have one rigid body relative to the other moving about one singular axis that, and here's the problem with this as far as understanding.

    The top right hand GIF file that's rolling there is an example of what's called helical movement, sort of conical, if you also look at it in a static photograph. The point being that midtarsal joint appears to function around this helical, pivotal axis, which changes all the way through stance. So once the foot contacts the ground, the orientation of this axis constantly changes throughout stance, which makes it even a little bit more interesting, so to speak.

    The point is that its orientation of the axis still comes up and favors a medial direction so that the vast majority of the movement seem still is seen in the sagittal and transverse planes.

    [14:01]

    Okay. So let's bring it back one more time. What does the midtarsal joint permit? It permits movement of the forefoot relative to the rearfoot, okay? And these are some videos from Dr. Kirby's YouTube sites and it's just him placing this foot through a range of mobility.

    Right now, there's a real heavy interest in trying to quantify and kind of tighten up this theory, but in the interim, what has been offered is to perhaps discuss midtarsal joint mobility using our three cardinal planes, and establishing three axes of movement, a vertical axis about which you'll see of an abduction of the forefoot. Okay, we see that and we'll see that in just a second. A medial laterally-orientated axis, which will enable dorsi and plantar flexion movements of the forefoot, and an anterior, posterior axis, which will give us our inversion, eversion axis of the forefoot. Bottom line, it is truly an awful lot more complex even than what we were taught and appreciate as students.

    The dilemma that we're all seeing at the various schools of podiatric medicine, and you'll see a number a number of editorials that have been put out there about the fact that we continued to teach the biaxial model. But we are kind of in the evolutionary stage of migrating toward this monaxial orientation and it's something that you can look up and see what has been done in this direction so far, but be aware that you will hear more and more, and more discussions about the monaxial orientation of the midtarsal joint. What they consider this to be now, this being the two axes model, is what they often refer to as this instrumentalist theory.

    [16:00]

    It's somewhat useful for understanding in teaching but clinically might have a bit of a problem and challenge. But I can see from even in the darkened area here, I've lost probably three quarters of the office. The heads are exploding and the same thing I had, the reaction when I started getting involved with this is, "Okay. What do we do with the information?"

    For the remainder of this lecture, let's talk more about the why of what it is that we see in the office as far as the midtarsal joint, its presentation to us, and generally speaking, it will not present to us until the joint is put under duress.

    Let's start this way. Consider, if you will, its relationship first to not only the ankle, which it often is very often compared to, and we spoke a lot about that last year. The first metatarsophalangeal joint, and then more importantly for this morning, I'd like you to also ponder the relationship of the midtarsal joint to the knee and hip recognized that roughly speaking, they're all parallel to each other. That's very important point to keep in mind.

    Another reference to the door over here that we use for the students, and this is very important point when we treat our patients as I'll show you in just a minute, and that is concept of so-called biomechanical leverage. If you ever pondered why, except it never works here, because we always have these emergency push bars, but a door that has a doorknob, ever ponder why the doorknob is located where it is on the door relative to the hinge? Because when you talk about rotational movement, rotational movement always occurs much easily as far as a force applied when you push the force against the axis of rotation as far as away as you possibly can.

    [18:01]

    Closer you get to the door, and I do with the kids all the time when they first come into clinic, there's a couple of the doors that are perfectly hung, and they're solid outdoors. And as I have the kids run their fingers closer and closer toward the hinge, and try and close and open door, it's amazing how the expression on their face when they appreciate how much more difficult it is to close that door as you move closer to the axis.

    Well, take it the opposite way. As you move further from that door, it requires less force to induce a breech moment. And that becomes critical when you have patients with midtarsal joint issues. Specifically, the further away you are imparting a force that may impact the midtarsal joint, the manifestation through the foot maybe devastating.

    Midtarsal breech is often a reflection of pathology, specifically a lack of movement, mobility elsewhere in the body. It often is a very interesting clinical and functional picture of problems within not only the foot, or else the midtarsal joint wouldn't be in trouble, but somewhere else in the body. And the areas that you need to ponder occurs certainly the ankle. We evaluate for equinus influence is with our Silfverskiold test. And if we still release the gastroc and we have no movement, a lateral X-ray to rule out an osseous block at the ankle.

    First MTPJ, which we'll explore in a second, Dr. Schoenhaus referred to in his first ray lecture, the importance of being able to allow for plantar flexion of the first. And Dr. Richie did confirm, thank goodness I sat in the back and held my breath. Yes, the first ray axis is dorsiflexion with inversion plantar flexion, eversion. But the bottom-line is, plantar flexion of the first ray is required to achieve arthrodial rotation of the first, the so-called good stuff in gait.

    [20:07]

    And as I said, hip and knee, we'll look at that right now, but main thing keep in mind during gait, if there is a restriction of motion at any of those joints at any one time when that motion is necessary, the least susceptible or the most susceptible, least stable joint, will be required to provide that mobility. And we're doing all this by the way, keep in mind, the average walking speed. We got about a second worth of time from heel-strike to toe-off for all of this to be satisfied.

    So being the unconstrained joint that it is, midtarsal joint and its relationship, and orientation to those joints that we've been speaking about, hip, knee, ankle, first MTPJ, it does become a very convenient go-to joint in the face of lack of movement elsewhere.

    As we move forward across the supporting surface, there is an increasing need for both hip and knee extension, as well as ankle dorsiflexion. We could probably throw in there as well, first MTPJ movement, rotational movement, specifically dorsiflexion as well.

    When you look up in the superstructure, the two areas that we've learned, but unfortunately sometimes fail to evaluate in the context of what is sitting in front of us podiatrically, is the effect of a [indecipherable] [21:37], and more important the psoas group on hip extension. Look over here on the right, induces a forward tilt of the pelvis, as well as the effect of the hamstrings to provide or enable adequate knee extension.

    [21:56]

    I can't tell you how many times, and Dr. Trepel certainly backed me on this, we were probably the last class that had Dr. Schuster formally as a professor. And then, I was able later on to spend an awful a lot of time with him privately in his office and in his laboratory. But certainly, when he would evaluate patients in his office, runners and Dick's practice was primarily runners, those of you that knew him, which followed his pediatric practice.

    But it was always interesting to watch his reaction when he had a runner in the office with a recalcitrant fasciitis and the runner was very proud of the fact that he would tell Dr. Schuster that, "But I stretch my muscles, Dr. Schuster. I don't understand why this is a problem." And he would laugh in his little way. He had a chuckle about him and he would say, "But you've told me that you stretch your calf muscles and what else do you stretch?"

    At the time, generally the answer was, "Well, what else is there?" type of an answer, and Dick would always say to these patients, and then to lots of students, and it was hard at first to appreciate this. But Dick would say, "You could have 15 degrees of ankle dorsiflexion, through dorsiflexion, not midfoot break." And in the face of a five-degree hamstring contracture and a 10-degree hip flexion tightness, which is not that difficult to achieve, and this was back in the late '70s by the way when I was hanging out with him.

    And certainly nowadays with the way jobs are set up where the folks spend an awful lot of time at a computer terminal with hip and knee bent, which is allowing for adaptive shortening of these muscles, it is not difficult for that 15 degrees at the ankle to be completely nullified by the five-degree knee flexion contracture and the 10-degree hip flexion contracture. Point being, we've got to start looking above the ankle for these influences, because again, the axes of these joints are roughly parallel to the midtarsal joint.

    [23:58]

    Another point, and this was made a couple of times yesterday, and that is that the way the foot is designed, and thank goodness we're past the minimalist phase in running, which had the mid strike forefoot strike based on the Born To Run book. But the foot is designed to work proximal to distal, which means that proximal alignment is going to be key to this. And again going back in the day, we were taught that the blocking mechanism of the midtarsal joint occurs when you have obliquity between the axis of the subtalar midtarsal joint, pronate the subtalar joint, the axis become parallel, and therefore, permit more mobility.

    Well, not quite. A good deal of the stability at least of the calcaneocuboid joint, the lateral portion of the midtarsal joint, was found in a nifty paper that [Ross Mueller] [24:50] did, his cuboid compaction theory that he developed, is that he found that a slightly inverted position of the calcaneus is necessary in order to stabilize it. And therefore, enable the little overhang, the little roof, the dorsal roof that the distal part of the calcaneus shelf, if you will, provides as, and that is what enables the true compaction of the cuboid into the calcaneus.

    So proximal alignment of the subtalar joint, meaning, a somewhat inverted attitude to reflect that's generally it's acquired or congenital rather, varus position, is necessary to provide the lacking mechanism to the calcaneocuboid joint. And again, excuse me, in Dr. Schoenhaus' lecture yesterday, the key to P longus stability or function rather, is a stable cuboid around which it can exert its influence. It's the final fulcrum as it changes direction to insert into the foot.

    So we end up with a two-stage lift. If it is not stable, the calcaneus is here. That is the calcaneocuboid joint versus a one stage.

    [26:02]

    When you look at clinical pathology associated with instability, early instability, the midtarsal joint, what a shock. Fasciitis, dorsal midfoot compression syndrome, cuboid, sinus tarsitis, these are all consequences of midtarsal joint instability. Of course the end stage, rocker bottom, Charcot breech, we're all well familiar with it.

    Dr. Schoenhaus, here it is, yeah. The great results that occur in the OR theater as I say to students, you know, it all looks great on the OR table. However, true measure, whether you're doing headwork, midshaft, scarf, invert the scarf, flip the scarf, it doesn't matter, lapidus. There was a discussion yesterday about it. Point being, if the proximal alignment is not there, none of those procedures are going to work.

    And by the way, another paraphrasing Dr. Schoenhaus for those of you who were at that lecture, if faulty biomechanics got you into the OR in the first place, they're still going to be there after the surgery has been achieved. Many years ago, he gave a lecture at the New York Clinical Conference, and I believe he was talking about implants. And, you know, he's a favorite of the implants. And I went up to him afterward. He had this line. This is a quote and I gave him full credit. I said, "Someday I'm going to use this because it's great." Elevatus outcome killer, and elevatus oftentimes occurs as a result of the proximal breech of the midtarsal joint, hindfoot pronation.

    Reconstruction, flatfoot recon, sure, procedural choices Dr. LaPorta, a couple of years back at the Schuster seminar, had a few things to say about the seemingly explosive use of subtalar arthroereisis in the face of a subtalar dominant flatfoot versus what is really a midtarsal dominant deformity.

    [27:58]

    Back in the '80s when Dr. Richie started to use the term, the adult-acquired flatfoot in the context of posterior tibial dysfunction, we started talking about an Evans foot, the cuboid notch. This is an example, again, the way this might be described now as what you're seeing, is an illustration of vertical midtarsal joint movement of an abduction.

    Management of this. First, why is the joint failing within the foot? This is an interesting concept. You can look up the work that Fuller and Kirby have done on subtalar joint axis plot. Remember, to stabilize calcaneocuboid joint, the calcaneus must be maintained in a somewhat inverted position by our varus rearfoot posting.

    Here's the problem. As the foot drops down and starts to pronate, the inclination angle drops. The axis plot of the subtalar joint shifts medially. If you look at that lower left hand sketch, everything in red, if you apply dorsiflexion moment, push up on any part of that foot in red, it will pronate the subtalar joint. So it becomes this devolving spiral that as the axis plot shifts further medially, you're running out of real estate, so to speak, to control that hindfoot, but control it you must.

    Dananberg in the '80s when he talked about the retrograde pronation effect of a functional hallux limitus, elevate the first, lock it, and keep lifting the heel. The dorsiflexion moment has nowhere else to go but proximal. And the first joint of ease is the midtarsal joint, and of course extra pedal influences as well. Are we going to intervene, speaking now conservatively, is it a correctable joint? Can I maintain this in a weight-bearing position versus something like that that's already failed?

    The goal with orthosis will be very simple. You're going to reduce the abnormal pronation, a stiff shell. You will modify the device to take advantage of the transverse component by the addition of a long lateral flange.

    [30:09]

    Again, Dr. LaPorta talked about a non-surgical evidence. Long lateral flange, it blocks the transverse component of that. In the '80s, the use of the pitch came on. And lastly, this is something that is very easy for you to discern. If you fail to recognize the adequate or rather the influence of where that midtarsal joint is compensating from, and the patient complaints of transverse arch pain backed by the rearfoot post, you fail to neutralize what is present, and simply need to apply adequate lifts to maintain the foot in a more plantar flex attitude. Shoe gear as well, positive heel drop, running style shoes.

    And with that, I'm going to stop right here and I thank you for your attention.

    TAPE ENDS - [31:02]