The Convergent Talus Part 1: Idiopathic Non-Neurologic Adductocavovarus

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Clinical Summary

Concept Overview

• Convergent talus represents a biomechanical state of closed kinetic chain supination (talus dorsiflexion/abduction, calcaneal inversion).
• Many clinicians recognize open-chain mechanics but underappreciate closed-chain supination and its role in deformity development.

Idiopathic, Non-Neurologic Adductocavovarus Deformity

• Considered an end-stage arthritic deformity without neurologic cause.
• Presents as a subtle cavus foot with associated conditions: peroneal tendinopathy, 4th/5th metatarsal stress fractures, anterolateral ankle impingement, and ankle instability.
• Neuromuscular exam, EMG, and nerve conduction studies appear normal despite deformity.
• Radiographic findings:
  ◦    Calcaneal pitch elevated (~30° vs normal 20–25°).
  ◦    Meary’s angle apex often at the first metatarsal–cuneiform articulation.

Physical Exam Findings

• Foot may look biomechanically normal, but subtle signs include:
  ◦    Peekaboo heel sign: heel visible from anterior view in weight-bearing stance.
  ◦    Heel varus position observed posteriorly.
  ◦    Silfverskiold test often positive for gastrocnemius equinus.

Diagnostic Workup

• Coleman block test helps distinguish flexible vs fixed deformity:
  ◦    Fixed heel varus suggests a rearfoot-driven problem due to abnormal subtalar facet orientation.
• Assess midfoot and forefoot contributions for surgical planning.

Surgical Considerations

• Gastroc recession (Strayer) indicated for equinus related to fixed heel varus.
• Dwyer osteotomy ± Mitchell modification: correct calcaneal varus and reduce elevated calcaneal pitch.
• Forefoot correction:
  ◦    If first metatarsal corrects with hindfoot/soft-tissue procedures → no further intervention.
  ◦    If flexible plantarflexed first metatarsal → consider peroneus longus to brevis transfer.
  ◦    If rigid plantarflexed first metatarsal → consider first metatarsal dorsiflexory wedge osteotomy or first metatarsal–cuneiform dorsiflexory fusion.

Clinical Implications

• Failure of procedures for peroneal tendon tears, Jones fractures, or ankle instability may reflect unrecognized cavovarus deformity.
• Patient selection is key: not every peroneal or lateral ankle pathology requires cavus reconstruction, but in recurrent/obese/high-demand patients, restructuring the platform of the foot should be considered.
• Recognizing gastrocsoleus contracture as a deforming force is essential, even in cavus feet, contradicting older teaching that Achilles procedures are contraindicated.

Key Takeaway

• Subtle cavovarus deformity can underlie common lateral foot and ankle pathologies. Proper recognition, biomechanical assessment, and targeted reconstruction are critical to preventing recurrence and optimizing surgical outcomes.

Transcript

Jennifer Spector, DPM: Welcome back again to Podiatry Today Podcasts, where we bring you the latest in foot and ankle medicine and surgery from leaders in the field. I'm Dr. Jennifer Spector, the Assistant Editorial Director for Podiatry Today, and we're thrilled to have with us Dr. H. John Visser to share with us the first of several episodes that will discuss a really dynamic topic having to do with the convergent talus. He was the president of the St. Louis Podiatric Medical Society and he is also a past president of the Missouri Podiatric Medical Association. He has served as an examiner of the American Board of Podiatric Surgery and served on the Missouri State Board of Podiatric Medicine over several governorships. He has served as the director of residency training as well for several hospital systems in Missouri and has trained countless residents under his leadership role. 
 
Okay, so Dr. Visser, we are so glad to have you here with us today to talk about a really interesting take on a complex scenario associated with cavus deformity and that is the convergent talus. Why don't you give us a little bit of an introduction to the concept of this, and then we'll get into some great topics of discussion related to it. 
 
H. John Visser, DPM, FACFAS: Yeah, so basically the idea that convergent talus is conditions that basically create what we call closed kinetic chain supination. Interestingly, with the residents and begin discussing various topics with them, I find quite a bit of weakness in biomechanics, and I try to accentuate that to all these surgical principles that we are going to talk about. And basically oftentimes they don't even know what closed kinetic chain supination is. Basically, that's what the foot does while it's sitting on the floor. Talus dorsiflex and abducts and the calcaneus inverts. And yet a lot of people don't really understand that. They're a little bit more with open kinetic chain, but not so much with closed kinetic chain. And what we're going to try to do is take various disease conditions that you probably have heard about, but maybe not had a really good understanding about and basically how this concept is manifest. And we're gonna go and get into the surgical perspective, but we're also gonna really accentuate a lot of the biomechanic that go to developing these various types of deformities. And that's what we're gonna try to accentuate and hone in on. 
 
Dr. Spector: Well, great. First, a great place to start, I think, would be for you to share a little bit with us about idiopathic, non-neurologic, adductocavovarus deformity. 
 
Dr. Visser: Yes, this is a condition that has gotten a little bit of print here in probably the last four or five years, but prior to that, there wasn't really anything really mentioned about it. It kind of represents the very end stage of arthritis from a non-neurologic standpoint. Basically the patients present with a very subtle high arched foot, but there's a lot of conditions that we see clinically such as peroneal tendinopathy, stress fractures of the fourth and fifth metatarsal, enterolateral ankle impingement problems and ankle instability. These are very, very common conditions that we see amongst patients in our practices. And we tend to just kind of hone in on them as an isolated issue, where we don't really take a good look at the platform of the foot. And the platform of the foot can represent idiopathic form of a cavus deformity, and basically, if you do neuromuscular examination on this, you do an EMG, you do a nerve conduction study, it'll all be completely normal. Yet, you'll take a lateral X-ray and you'll notice that the calcaneal pitch seems to be a bit high. Normally, it's around 20 to 25 degrees, but in this instance, it'll peak out at about 30 degrees. 
 
The other thing is that Meary's ankle, which is a very useful angle that we use in cavus foot, but we obviously use it in flatfoot too. If we do this and we bisect the talus in relationship to the first metatarsal, we begin to find to see that we have an apice forming. And in this case, it's usually at the first met-cuneiform articulation. 
 
Dr. Spector: So what can one expect from physical examination of a foot like this? 
 
Dr. Visser: What happens is sometimes this foot basically gets looked at as a normal foot. It looks pretty much normal biomechanically. But we have these subtle things that show up, that indicate it's really not normal. It's at the end stage of normal, basically because of the fact that the neuromuscular exam is perfectly normal. 
 
Another interesting thing is the clinical exam. If we take a look at these patients, and this is a good thing to always do, when you're dealing with any of these patients with the things that we just described, possible peroneal tendinopathy, you're gonna do a peroneal brevis repair for a split tear. You should take a look at the patient straight on, look at them while they're standing, and you will notice that the heel will peek out around the rest of the foot. This is referred to as a peekaboo heel sign. And if you look at a patient who is standing weight-bearing, you should normally straight ahead never see the heel. It should never be visible to you. So if you notice this, you should be aware that potentially this is what could possibly and indicate a peekaboo heel sign, which is typical of this idiopathic form of a cavovarus deformity. 
 
Now further examination begins usually from proximal to distal, usually the way you would look at a flat foot biomechanically and try to determine what maybe procedures you would perform. 
 
Dr. Spector: Are there any other particular findings that stand out to you in these cases? 
 
Dr. Visser: The first thing and the thing that you usually don't equate with cavus is equinus. You know, back in the day when I was a student, cavus basically it was a no-no to consider anything to be done with the Achilles tendon. But what we tend to find in this particular instance is that if we do a Silfverskiold exam on the patient, oftentimes we will have the presence of a gastrocnemius equinus. And when we also look at the patient standing from behind, we will notice that the heel is in a varus position. 
 
Now, the next step then is to determine is this is fixed, or is it flexible? In other words, is it being driven by the anterior portion of the foot, primarily the first metatarsal and the medial column? And so we will do what we call a Coleman's book test. And when we do this, we'll drop out the first metatarsal over the edge of the book, and we will notice then that nothing really changes. The heel stays in that fixed varus position. So this indicates that this is a rear foot driven problem. Basically what happens is the facets, the anterior middle facet, the posterior facets have an abnormality. They're abnormally tilted such that they maintain a fixed structural heel varus. 
 
The next step that we want to look at in this particular condition is what the midfoot may be doing here. The midfoot in this situation, since the rearfoot is supinated, is relatively pronated. And when we do this, what we wanna do is when we examine now, as we are potentially performing these operative procedures, a gastroc recession, such as a strayer and a Dwyer osteotomy, and if we do have a calcaneal inclination angle up in the 30s or a little bit higher, we can also do what we call a Mitchell modification with the Dwyer and shift the tubers superiorly to correct some of the calcaneal pitch. 
 
Once we have performed this, we look at the forefoot then and we look at does what happens to the first metatarsal here. In some instances, first metatarsal completely corrects. In other words, its alignment with the metatarsals two through five are all basically on an even platform. Basically, we're done with our procedures. We finish what we need to do. 
 
If on the other hand, we notice that the first metatarsal lies lower than two through five, we then check its flexibility. And if we are able to get the first metatarsal to a level of two through five, this indicates that basically the peroneus, the longest tendon, is overpowering. And in this case, we would consider a peroneus longus to brevis transfer. And if in a situation we cannot get that first metatarsal to move above the plane of mets two through five, then we would have to address it structurally with a dorsiflexory wedge osteotomy of the first metatarsal or possibly a first met cuniconeiform dorsiflexory fusion. 
 
So this is what we would consider to do if we had a patient who had recurrent instability. Let's say that patient had a peroneal split tear performed. The patient failed, they did not get any better. Then the surgeon's wondering, well, why didn't it? I know I did a decent job on it. And then they begin to look into it deeper and find out, you know what, this foot looks a bit of a cavus foot, and they go through the workup. And as we just described, and they indicated we've had a failure here, or we've had a nonunion form on a Jones fracture of the fifth metatarsal base and the fourth metatarsal base. These are then considerations where we may need to consider restructuring the platform of the foot to get a good outcome with the primary problem that we're dealing with. 
 
Now, this is not to say that every particular patient that has a peroneal tendinopathy or an instability of their ankle or a stress fracture or impingement lesions of the ankle joint are going to need to have a cavus foot reconstruction. But there are certainly instances where you indicate maybe a large, relatively obese patient, for example, or a patient that's already had that procedure performed once and fails, then we need to consider the possibility of restructuring the platform. This idiopathic cavovarus foot deformity may need to be addressed, even though it's a non-neurologic status. 
 
One thing to also add about this gastrocsoleus issue and the fact that lengthenings may need to be done, which is kind of contrary to what you usually believe that if you weaken that particular group, you would expect an increase in pitch. Remember here what the problem is. The equinus is because of contracture created by the fixed heel varus. The heel varus is fixed in this position. You cannot reduce it to a vertical position. And in this particular instance, then you would have to consider equinus as a potential deforming force. So that gives us a good scenario about what to look for in a patient that you would have these outcomes on the lateral side of your foot. They have lateral side issues that are very common and that are commonly done in your in your practice and failures that may have occurred because of the fact that you failed to recognize this particular problem.
 
Dr. Spector: Well, thank you so much for sharing this bit of information with us today. There's so much more that Dr. Visser has to share with us on this topic of the convergent talus. So be sure to stay tuned for future episodes, we're going to have several that focus on this particular topic. And you can find this and other episodes of Podiatry Today podcast on podiatrytoday .com and your favorite podcast platforms.