FAI October 2024 Podcast: The Role of the Flexor Hallucis Longus in the Treatment of the Painful Hallux Metatarsophalangeal Joint

Summary

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Podcast Summary

Overview

Episode Title: The Role of the Flexor Hallucis Longus in the Treatment of the Painful Hallux Metatarsophalangeal Joint
Podcast: Foot & Ankle International
Host: Dr. Charlie Saltzman, Editor, FAI
Guest: Dr. Jim Mickelson, Professor of Orthopedics and Rehabilitation, University of Vermont
Air Date: October 25, 2024

This episode features an in-depth discussion with Dr. Jim Mickelson about his team's 10-year study on the flexor hallucis longus (FHL) and its pivotal role in diagnosing and treating pain and pathology in the hallux metatarsophalangeal (MTP) joint. The conversation challenges traditional approaches, highlights often-missed diagnoses, and explores nonoperative and operative strategies with practical, evidence-based recommendations.

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Key Discussion Points and Insights

Study Background & Main Findings

• Clinical Inspiration:
  Dr. Mickelson recounts seeing patients with unexplained big toe (hallux) pain, ultimately realizing overlooked FHL pathology was significant.

  "It's like a lot of other things … everyone kept saying it was medial deltoid injury until [Ken Johnson] identified it. And then all of a sudden you could see it." — Dr. Mickelson [02:52]

• Study Overview:

  • 10-year review of patients with painful hallux MTP joints at the University of Vermont [00:56].
  • Identified FHL stenosis as a major, underdiagnosed cause.
  • Most patients improved with nonoperative, targeted FHL stretching.
  • Of the small subset requiring surgery, isolated FHL release (not at the toe) led to nearly universal resolution.

  "18 out of those 20 people completely cured. One person got a little worse, one person stayed about the same." — Dr. Mickelson [03:46]

Biomechanical Link Between FHL and Hallux MTP Pain

• Cadaver Study:
  Collaborated with Neil Sharkey to show, through biomechanical cadaver modeling, that minor FHL restriction (as little as 2mm) significantly increased damaging dorsal joint forces at the first MTP.

  "…even if you restricted the motion by as little as 2 millimeters, that it increased the forces inside the first MTP joint significantly." — Dr. Mickelson [06:27]

• Clinical Relevance:
  Provides a mechanistic explanation for isolated arthritis at the first MTP joint—no similar findings at other MTPs [07:42].
  • Suggests FHL stiffness contributes directly to pathogenesis.

Reframing Surgical Thinking

• Traditional Surgeries vs. FHL Focus:
  • Explains that surgical procedures like shortening osteotomies, or dorsal cheilectomy, may inadvertently alleviate FHL tension [08:46].
  • Emphasizes that explicit FHL lengthening or release may be the real reason many traditional surgeries offered relief.

  "…doing the shortening, osteotomies, all the other fancy stuff, basically, functionally are lengthening the FHL." — Dr. Mickelson [09:28]

Prevalence and Patient Assessment

• Bilateral Presence, Unilateral Symptoms:
  • About 50% of all patients showed evidence of FHL tightness, half of them bilaterally, but most had symptoms on only one side [09:58].

  "…50% of everybody had evidence of tight FHLs without symptoms… of those 50%, 50% of those were bilateral. …the majority of them, it's just the one side." — Dr. Mickelson [10:20]

Imaging and Diagnostic Tools

• Role of MRI:
  • MRIs rarely reveal FHL pathology, even when present—radiologists often miss it [13:19].
  • MRIs primarily used to rule out alternative diagnoses (e.g., ganglion cysts) or when clinical findings are ambiguous.
  • Plain films are essential to assess for os trigonum involvement [13:58].

Nonoperative vs. Operative Management

• Isolated FHL Stretching:
  • First-line and highly effective; standardized stretching protocol provided in the published study [18:11].
  • Key is patient compliance—education and demonstration are vital.

  "Two things we do for everyone is give everyone an instruction sheet … and then I walk through it with them personally and show them…" — Dr. Mickelson [18:12]

• Open vs. Endoscopic FHL Release:
  Dr. Mickelson strongly favors open, above-tarsal-tunnel approach:
  • Faster (3 min tourniquet time for standard, 6 min with os trigonum removal), supine position, fewer complications (notably, avoids sural nerve injuries more common in endoscopic).
  • Comparable recovery, lower complication rates, and cost.

  "It is a slam dunk. So I wholeheartedly vote for open. I love the scope. I do scopes for other things, but not for this." — Dr. Mickelson [17:24]

Stretching Protocol Details

• Described Protocol:
  • Place a small book (~½ inch) under big toe, just distal to MTP joint, passively dorsiflexing it.
  • Foot flat, knee bent, perform Achilles stretch while keeping ball of foot and heel on ground.
  • Hold for 30 seconds, 3 reps, several times daily [19:20].

  "…foot flat on the ground and you do an Achilles stretch with your knee bent. …hold it for a count of 30, stand up straight three times in a row, a couple times a day." — Dr. Mickelson [19:28]

Unrecognized and Delayed Diagnosis

• High Frequency of Missed Cases:
  • Average diagnostic delay originally 7 years per patient; has improved, but still up to 30% experience a delay of two years [20:09].
  • Emphasizes importance of clinician awareness and early, simple intervention.

  "…It's an easy diagnosis to make and an easy diagnosis to treat." — Dr. Mickelson [20:49]

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Notable Quotes & Memorable Moments

• On Eye-Opening Nature of FHL Pathology:

  "It's seen me, but I haven't seen it, as you said." — Dr. Saltzman [09:39]

• On Shifting Paradigms:

  "If we can get in front of this, we potentially have… a way to prevent [progression]. So I think that's pretty cool." — Dr. Mickelson [20:56]

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Important Segment Timestamps

• [00:56] – Dr. Mickelson’s summary of the 10-year study & clinical observations
• [05:18] – Biomechanical data linking FHL tightness to increased MTP joint forces
• [08:46] – Explaining why some traditional surgeries likely work: role of FHL
• [09:58] – Data on prevalence and bilaterality of FHL tightness
• [13:19] – On (limited) use of MRI and reliance on clinical assessment
• [14:40] – Open vs. endoscopic FHL release: technical and practical considerations
• [18:11] – Detailed description of patient FHL stretching instructions
• [20:09] – Impact of missed diagnosis and evolving clinical awareness

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Takeaways

• FHL stenosis is a common, underdiagnosed cause of hallux MTP joint pain, often mistaken for primary joint pathology.
• Nonoperative management with directed FHL stretching is highly effective and should be first-line.
• Simple, open FHL release is effective in refractory cases—often superior to endoscopic methods.
• Early recognition can prevent unnecessary surgeries and potentially halt arthritis progression.

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Further Reading

The study as discussed is published in the October 2024 issue of Foot & Ankle International. Supplemental materials, including the FHL stretching protocol, are available with the publication.

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“It’s an easy diagnosis to make and an easy diagnosis to treat.” — Dr. Jim Mickelson [20:49]

Transcript

[A]

Foreign.

[B]

This is Charlie Saltzman, editor of Foot and Ankle International. Today I have the distinct honor of talking with Dr. Jim Mickelson, who is the lead and senior author of this month's lead paper in Foot and Ankle International papers entitled the role of flexor Hallucis longus in the treatment of painful hallux Metatarsal Phalangeal joint. This is a really provocative study that should encourage all of us to reassess how we approach patients in clinic and decide on their treatment management. Dr. Mickelson is a professor of orthopedics and rehabilitation at the Larner School of Medicine at the University of Vermont, which is in Burlington, Vermont. A beautiful place. Welcome to the program, Jim. I would like to start by asking you to give a brief summary of your paper and its minimum major findings.

[A]

The paper is basically a 10 year study of the patients that we've seen in our foot and ankle clinic at University of Vermont and specifically looks at patients who presented with pain in their hallux MTP joint. And the reason for it is I had seen a patient years ago, literally 25, 30 years ago, who had presented to me with posterior medial ankle pain and big toe pain and had been actually seen by several other very good foot and ankle folks who I know, you know, they're great docs, but no one could figure out what the hell was going on. And so I said, oh, I know it's his posterior tip. So I did a posterior tip sinovectomy and he got 10% better. That was it. And then he still had pain and most of his pain was in his big toe. And finally I just said, all right, what else could be causing this? And I went back to basics. What's behind the medial ankle that can also affect what happens at the big toe? And then it became clear it was the fhl. I'm like, oh, that's interesting. So I'd never seen it before. Ended up doing an FHL fibrosis tunnel release, and all the symptoms went away completely. And I'm like, oh, that's pretty interesting. I'll never see this again. But what happens is, it's like a lot of other things, like with, with Ken Johnson and his posterior tibial tendon stuff. Everyone kept saying it was medial deltoid injury until he identified it. And then all of a sudden you could see it. You know, it had been seeing us, but we hadn't seen it. And that's exactly what started happening. And so over the years, I've ended up seeing a ton of folks who have had years of pain. And a subset of them, a substantial subset, had pain in the big toe. And you know, no evidence of clear how excitedus or minimal how excitedus, normal motion, but tenderness and along the FHL and stenosis, you know, you couldn't move the toe the way you should. And so we realized that these people really had stenosis of the FHL causing pathology in the first MTP joint. And so this is our 10 year study of all these patients who we looked at. And it's a substantial number of folks who, most of them responded actually to non operative treatment, which is just isolated stretching of the FHL using a protocol which we published. And most patients got better, their big toe got better, and then a few of them didn't, not 20 of them. And for those folks, we just did a release of the FHL at the fibrosis tunnel, nothing at the big toe. And 18 out of those 20 people completely cured. One person got a little worse, one person stayed about the same. So this is what the study, sort of the bare bones of the study shows, but I think it speaks to a larger question about the etiology of arthritis and pain in the first MTP joint.

[B]

Thank you. That's a great summary. In your mind, how do you link this FHL stenosis or tightness to pain in the hallux MTP joint?

[A]

So we did a study, and by we, I mean Neil Sharkey, who was at Penn State at the time that ended up winning the Nat Gould Award, if you remember years ago, where he had this really cool cadaver modeling system where basically all the muscles were attached to cryo clamps and control them with computers and, and you could literally get the cadaver leg to walk. You know, if you got a picture just looking at the cadaver leg, it looked like a normal foot walking, you know, push off the whole thing. And we did that and then instrumented the first metatarsal with strain gauges so we could measure how much forces were acting across the first MTP joint. And then mimicked stenosis of the FHL by restricting how much that FHL could move because it was all computer controlled. And what we found was even if you restricted the motion by as little as 2 millimeters, that it increased the forces inside the first MTP joint significantly. And where it increased, it was on the dorsal part of the joint, which is of course exactly where you see the initial lesions in hallucritus. You know, Bingham and a bunch of folks back in the 50s had done surgical studies looking at early how to treat it, and that's where all the initial delamination of the. Of the cartilage occurred. So once I saw that, it gave us a biomechanical linkage between the stenosis of the FHL and change in the biomechanics at the first MTP joint. And, you know, as you know, arthritis in the first MTP joint is the most common arthritis in the foot, you know, and it doesn't occur in any other MTP joint at all. And I remember medical students and residents asking me, well, why? And I look at them, I go, I don't know. You know, it just is. Everyone knows it. But this gave us potentially a rationale. And so armed with that, I then started when I started seeing patients with MTP joint pain, but no real impingement, you know, no big dorsal osteophytes or anything. I'm like, and. And they're tight with their fhl, like, well, the data shows that that's causing it. So let's. And I explained this to the patients, and they said, sure, makes sense. So we did the stretching. Most of them got better, and the ones that didn't, we just did an isolated release, and they got better. So it was a really nice translation of basic science to the bedside.

[B]

Boy, is that interesting to me. And I've watched, and all of us have watched our colleagues do shortening osteotomies of the first metatarsal head in different kinds of ways. And all fits in with the general theory of a tight fhl, doesn't it?

[A]

Yeah, it absolutely does. And if you look at the, you know, years ago, people were talking about just instead of a hallux chilectomy for early hallux reduce, just. Just taking off the bone spur and see how that did. Well, they did terrible. And it turned out you had to take off the dorsal, you know, quarter, third, whatever of the articular surface. And no one quite knew why. But this gives you an explanation, because what's happening is if you don't loosen the fhl, you're still getting that dorsal impingement. But now with the chillectomy, just take away the bone. So now there's no impingement, and that's why it works. But you're right, doing the shortening, osteotomies, all the other fancy stuff, basically, functionally are lengthening the fhl.

[B]

Boy, that is. To me, that's really illuminating. And it's seen me, but I haven't seen it, as you said. I'd like to get into a little more detail on your assessment and decision making, if I could. So how often do you see bilateral symptoms?

[A]

So it's interesting because that's actually two questions. The first question is how often do we see a tight FHL on both sides? And the answer is fairly consistently. We did a prospective study for another reason, but we were looking at everyone who came in for tightness of the FHL. And what was interesting was about 50% of everybody had evidence of tight FHLs without symptoms. So it's probably pretty common. And of those 50%, 50% of those were bilateral. So that gets to your first party question. So if they're tight on one side, about 50% chance the other side will be tight. The second question is, if they are tight on both sides, how often are they symptomatic on both sides? And the answer to that is not very often. It does happen, but I would say the majority of them, it's just the one side. And why it's one sided and not the other? Because it doesn't seem to have a left, right predilection or anything, or being related to athletics or not. But it's a really interesting problem. I think it's a little bit like the Hagelund's deformity, calcific Achilles tendonitis stuff where if you look at X rays of people with no symptoms, you'll see all these people with Hagel's deformities with no symptoms.

[B]

You see patients who have ostragonums. Do you think that has any impact on the rates of non operative treatment.

[A]

In our data? It doesn't seem to. Both with the general study we did of non operative treatment for fhl tenosynovitis came out about three years ago. Having an ostragonum or not didn't really have an impact on the success of stretching. And the same was true in our, in this current study. You know, the question of whether the astragonum causes this I think is one of these questions that we were never really going to get an answer to. Early folks could pretty clearly link it in displaced ostracom injuries, particularly in athletes, ballet dancers, that kind of thing. And I think now our sense is if you've got enough trigunum, you're going to take it out just because you don't know. And it adds two, three minutes to the surgery.

[B]

Well, maybe two, three minutes to your surgery. And perhaps I can ask you this as well. Do you ever get MRIs? Are MRIs useful in any way to making this diagnosis?

[A]

They can be. I don't normally get them. A lot of our patients come in already with MRIs, because they've had long history of this pain and no one knows what's going on. So the default is, let's get an MRI and see what's going on. The interesting thing is that radiologists almost never pick this up. They're just like, totally blind to it, which is not surprising. About the only reason I would get an MRI in someone I was already seeing would be if I was worried about something else going on. So, for instance, sometimes you get people with ganglion cysts associated with the FHL stenosis, and it can actually cause a tarsal tunnel syndrome because it's nerves right there. And so in people where it's not quite clear, then I'll get an MRI because, you know, you want to see and take care of everything all at the same time. But most people have shown, as have we, that getting an MRI in and of itself doesn't really help a great deal in your decision making. You absolutely have to get plain films because you need to know if there's an ash trigonum.

[B]

Can you also give us your Overview of open vs endoscopic FHL release?

[A]

Short answer. Yes, I can. I was actually asked to give the non endoscopic view at the Foot Society symposium about two years ago, I guess, and pretty much everyone in the audience was a scopeaholic. So, you know, they didn't really get it. So the potential that the scope gives theoretically is faster recuperation. And people say, well, you know, you mobilize on maybe a walking boot, something like that, couple weeks, then can get out, do normal activities, no running or jumping for a little while, and then totally normal at six weeks. That's exactly my protocol when I do it open. Exactly, because I do it not a tarsal tunnel approach, because that takes a long time to recuperate from. We just go above the tarsal tunnel, posterior, medial. And so really the only thing we cut is the skin and the fiber options tunnel, and that's it. So the recuperation is fast. The only nerve we have to worry about is the medial calcaneal nerve, because in 5, 7% it comes down across early takeoff. So sometimes that gets stretched a little bit. Usually I've never seen people get pain from that. Just numbness. In contrast with the endoscopic sural nerve injuries are a significant issue. And I've had people tell me, you know, they're going to stop doing them just because of the sural nerve issues. And the last is time. I mean, I. If I do an open FHL straight FHL my tourniquet time is 3 minutes. If I do it, add an ostragonum to it, add another three minutes, you know, and then add five minutes to close to do a scope. You know, everyone says, oh, it's really fast. All the literature I've seen and talking to folks, it's been 30, 40 minutes minimum. And most of the time, you have to do it prone, which means you have to flip them and all the time. But more importantly, if you have to do anything else, you have to flip them back. Whereas for me, you know, I do them supine, do it. If I need to do a colectomy or do a bunion or do something else, it's not a big deal. I just go do it so it's easier, it's faster. Complication rate is no greater, probably better. Recuperation is no different, and it costs less. So I think you have my position on this, which is clearly a minority position right now, which I find amusing, because this is literally the easiest operation I do. Of all the operations I do, it is a slam dunk. So I wholeheartedly vote for open. I love the scope. I do scopes for other things, but not for this.

[B]

Well put. And importantly to all of us is, can you tell us how you instruct patients to perform, Perform FHL stretching exercises on their own?

[A]

Two things we do for everyone is give everyone an instruction sheet that has pictures, shows the stages of the stretch and how to do it. And then I walk through it with them personally and show them, I demonstrate for them exactly how to do it, and most of the time, have them do it as well. The interesting thing is There are some YouTube videos out there. I actually haven't done one. I keep saying I should, and maybe you'll inspire me to do that, but that also, you know, patients can do that, and in general, it's not been hard to get them to do it or at least do it correctly. Sometimes you run into patients who just aren't compliant, and they come back at six weeks and go, well, yeah, I'm not better, but I only did it for two weeks. I'm like, well, what do you expect? And. But yeah, it doesn't seem to be a big problem.

[B]

Do you have them bend their knee and bend and pull up on the big toe or. I'm just wondering how you do it.

[A]

So in the paper, we actually have a supplement that is the instruction sheet, so that'll be helpful. But basically what it means is you take a small book, about maybe half an inch, stick it underneath Your big toe just distal to where the MTP joint is. So what that does is passively dorsiflex the big toe and then foot flat on the ground and you do an Achilles stretch with your knee bent. And keeping the ball of the foot on the ground and the heel on the ground, go as far forward as you can, hold it for a count of 30, stand up straight three times in a row, a couple times a day.

[B]

I think I could figure that one out. That's great. Was there anything else you'd like to add, Dr. Michelson?

[A]

Well, I think, I mean, I'm glad to do this discussion with you, have this discussion with you because FHL pathology is something that, as you were saying, you know, it's seen us more than we see it. And I've seen a ton of patients. When I first did my first study, the average patient had a delay in diagnosis of seven years. And that was simply because people weren't looking for it. It's gotten a little bit better. The most recent study, 30% were delayed for two years. So that's better. But it's an easy diagnosis to make and an easy diagnosis to treat. So I'm really encouraged. And potentially, you know, in the long run, the biomechanics suggest strongly that this causes Alex Rit. So if we can get in front of this, we potentially have, you know, a way to prevent it from. From progressing. So I think, I think that's pretty cool.

[B]

Agree? Agree completely. Thank you, Dr. Mickelson. I am Charlie Saltzman, editor of Foot and Angle International Today. Today I've had the distinct pleasure of talking with Jim Mickelson from the University of Vermont, who is a lead and senior author of this month's lead paper in Foot and Ankle International entitled the role of Flexor Lucis Longus in the Treatment of Painful Hallux Metatarsal Phalangeal joint. I found this to be really illuminating, eye opening conversation and paper. And I hope everyone will read the paper and will start thinking about this as they work through their listing clinic. Thank you so much for being part of this today, Jim.

[A]

It was my pleasure. It's great seeing you again, Charlie.