Can Botox Help Laminitis?

Botox for the equine hoof sounds like a punchline until you learn the science behind it. We sit down with Dr. Kali Slavik and repeat guest Dr. Andrew van Eps to explore a simple but high-stakes question in equine biomechanics: what happens when you inject botulinum toxin into the deep digital flexor (DDF) muscle, the muscle-tendon unit that helps control the rotational forces acting on the horse’s foot and distal phalanx (P3)? 

We walk through the anatomy in plain terms and then get into the study design, using healthy horses with one treated limb and one control limb to reduce variability. Kali explains how they used wireless pressure sensor membranes to quantify ground reaction forces at different hoof regions and track center of pressure during stance and at the walk, a powerful alternative to traditional pressure plates when you want more real-world movement data. Andrew shares what he expected to see and what surprised him once the numbers came in. 

Then we dig into the findings that matter most for equine laminitis: reduced toe force during breakover and a meaningful palmar shift in center of pressure, including changes seen even when the horse is just standing still. We also cover the practical realities, including the short-lived effect (about two weeks), who this may best help (think acute onset laminitis tied to SIRS or hyperinsulinemia), why it is less suited to chronic or support-limb cases, and the big barriers of cost and technical ultrasound-guided injections. We close with study limitations and the next research step: a blinded placebo-controlled trial that also looks at P3 rotation outcomes. 

If you care about laminitis treatment options, hoof biomechanics, and how veterinary research turns measurements into better decisions, listen now and share this with an equine colleague. Subscribe, leave a rating and review, and tell us what question you want answered next.

AJVR article: https://doi.org/10.2460/ajvr.25.12.0452

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Transcript

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Lisa Fortier 0:31

Welcome

Welcome And Research Question

Lisa Fortier 0:32

to Epic Award-winning Veterinary Vertex, the AVMA journal podcast where we delve into behind-the-scene look with manuscript authors. I'm editor-in-chief Lisa Fortier, joined by Associate Editor Sarah Wright. Today, I'm happy to have another equine issue with our friends from New Bolton. Today we're discussing the effects of botulinum toxin injection into the DDF or deep digital flexor muscle on foot biomechanics and healthy horses with Callie Slavic and Andrew Van Epps. Callie and repeat guest Andrew, thanks again for being here with us today.

SPEAKER_01 1:06

Thank you.

Lisa Fortier 1:06

Thanks for having us. Thanks for joining us, Callie and Andrew.

Why The Deep Flexor Matters

Lisa Fortier 1:10

All right, Andrew, start us off here. Can you explain the role of the DDF tendon and why it's so important in equine hoof biomechanics?

SPEAKER_01 1:17

Well, the um the foot of the horse, the center of pressure on the ground is not in line with the uh the center of force that comes down through the axial skeleton through the joint. And so what it means is that there's a tendency to want to rotate or tip. There's a um there's a moment of force that's constantly acting on the weight bearing foot, and that is balanced by the deflexor tendon. So uh the deflexor tendon has some uh uh tension on it in the standing position, and it's also important for uh for push-off, um, you know, particularly uh towards uh towards breakover uh in in the ambulating course as well. And it's the only tendon that is acting upon the the the distal phallix.

Lisa Fortier 2:10

Just take us back a second, like tell the on the flex aside. Give give a visual for listeners who might not be veterinarians of where this whole muscle starts and ends. I think that's just fascinating when you think about that.

SPEAKER_01 2:25

It's originating up in the uh in the antibrachium, but there's a connection between the uh uh the um uh the bone, I guess, the the uh uh the ligaments of the the back of the carpus, the palmer aspect of the carpus, and the tendon via the inferior check ligament. So um the lower half of the tendon, I guess, um uh below the carpus is almost acting like a like a ligament, um uh uh with sort of some some bone-to-bone uh attachment. And then you've got the deep flexor uh muscles themselves up in the antibrachium that are um capable of applying uh extra tension uh to that tendon during locomotion in particular.

Sarah Wright 3:20

Yeah, someone who has not thought much about equine anatomy since like first year, I appreciate that graphic as well. So thank you very much. So, Callie, what sparked your interest in using botulinum toxin?

Why Try Botulinum Toxin

SPEAKER_04 3:32

Yeah, so um at the beginning of my residency training here at New Bolton Center, I initially became interested in botulism as a disease process in horses. It was something that I hadn't seen previously when I went to veterinary school. And I wound up taking care of a horse with clinical botulism that was down for a prolonged period of time. When I started researching the pathophysiology of botulism in horses, I came across some literature that described the use of botulinum toxin for various purposes in horses, including some anecdotal evidence that it could be used for laminitis cases to help reduce rotation and improve comfort in these horses. So that research really intrigued me because laminitis is also something I've always been interested in and trying to help these horses that have such a debilitating disease process.

Lisa Fortier 4:23

Yeah, there's a lot of good uses for it. I I've tried it in a long time ago, we tried it in the same similar, but uh we didn't have all the great measurements that you guys did. Uh, and in your study design, Callie, you had a group of healthy horses in which in what which in one leg was treated and the other was control. Uh walk us through that model and why you chose that.

SPEAKER_04 4:44

Yeah, so um, as we mentioned, even though there's been some studies that advocate uh botulinum toxin as a treatment for laminitis, nobody's ever demonstrated the true biomechanical effects that it has. Um, so we use normal healthy horses in this preliminary study to help reduce some of the variables we were dealing with versus using clinical cases initially. Um, we used one limb as a treatment limb, the second limb as a control to help us again reduce variation in our measurements and be able to really see the individual effects that these horses were having from the botularinum toxin to determine if there was true biomechanical benefit to this treatment.

Sarah Wright 5:26

And

Measuring Forces With TechScan

Sarah Wright 5:27

Callie, how did you measure changes in hoof biomechanics, particularly ground reaction forces and center of pressure?

SPEAKER_04 5:33

Yeah, so we use this really cool program called TechScan. Um, it is a computer program that connects to wireless pressure sensor membranes that we can custom fit to the foot of each horse. And then as the horse walks around, there's a wireless transmitter, and we can see in real time the pressure that the hoof is exerting on the ground as they're walking or in stance. Um, this is an alternative to um pressure plates for measurement, and it allows us to have the horses move in different directions or over longer distances compared to pressure plates. And the cool thing about the sensor membranes is that it allows us to custom map different areas of interest on the horse's foot, to look at the peak ground reaction forces at the toe versus the heel or other portions of the foot, and also to look at where the center pressure of the foot is at any given point.

Lisa Fortier 6:30

Andrew, uh given all your other experience in this area, what were you hoping or thinking you were going to see when you designed the study?

SPEAKER_01 6:37

Well, it's actually pretty funny because when Callie um Callie mentioned that she wanted to do this, I um was pretty sure we wouldn't really see much effect of uh botuline up television. So I was very skeptical that we would find anything. Um, and mostly because, you know, because of just in my mind and and from doing quite a bit of cadaver work in mechanical test stands, I felt like the the sort of passive connection of the deflex attendant to via the accessory ligament to the the uh carpal ligament, palma carpal ligament was going to be responsible for most of that standing um flex attention. Um and that, you know, I thought maybe we might see something at sort of midstance to break over, but we wouldn't see anything in the static standing horse. So I guess um I was quite surprised that um there was a uh bona fide consistent effect on on biomechanics of the foot, even when they were static still. Which you know, for eliminated courses, that's what they're doing most of the time.

Lisa Fortier 7:53

Yeah. Yeah. Well done, Kelly, to prove prove the skeptic wrong. Thank you.

Sarah Wright 8:00

So, Andrew,

Toe Force Drops After Injection

Sarah Wright 8:01

at say seven, you observed a reduction in force of the toe. How significant is that from a biomechanical standpoint?

SPEAKER_01 8:08

The peak forces at the toe, uh, in particular at when they're walking, each time they break over, uh, they are they represent kind of the the peak rotational force, the peak moment um uh on the uh on the distal on the on the distal thorax, which is kind of a proxy for the peak uh radial uh strain that's occurring on the dorsal lamellae, which is kind of what we're interested in. If we could measure lamella strain, we would do it, but we we can't easily do that, particularly in a in a uh live horse. So that peak force on the toe um uh rationally should equate with that uh peak strain on the dorsal lamellae, which is the important measurement when you're considering whether they're going to uh get uh damage to those dorsal lamellae at rotation of the bone uh away from the hoof wall.

Lisa Fortier 9:14

Then, Andrew, why is that you alluded to this a little bit, why is reducing force at the toe particularly important in conditions like laminitis?

SPEAKER_01 9:22

Well, that that tendency to rotate um when you get failure. Um, if you get wholesale failure at the lamellae, you tend to get distal sinking, and that's because you've got um such bad damage that uh even areas of the lamellae that are under less mechanical strain, like in the quarters, usually, um, they're damaged so badly that they fail as well, and the whole bone just moves distally. Most of the time we we're in a gray zone where we've got some damage um that's not sort of uh fulminant everywhere, and so the areas of the lamellae that are under the most strain, which which are again those dorsal lamelli up near the toe, because of that rotational force, they're the ones that are going to preferentially fail. And uh, you know, so it is significant to be able to reduce that um that uh uh moment of force that's acting, which is equivalent to that peak force at the toe, in terms of preserving those dorsal amilium, which are under the most under the most mechanical strain in uh uh and and are more likely to fail in acute laminitis.

Lisa Fortier 10:38

Yeah,

Center Of Pressure Shifts Back

Lisa Fortier 10:39

very cool. Kelly, another interesting finding was a pump or shift in the center of pressure. Can you explain to the listener what that means in practical terms?

SPEAKER_04 10:48

Yes, this was something uh really interesting that I think neither Andrew nor I expected to happen. Um, as we mentioned, horses spend most of their time when they're laminatic standing still. And so changing pressure when they're moving is maybe less of a priority. But the center of pressure tells us how the horse is weight bearing in their foot and where all of that weight coming down the limb is centered in the foot. When we move the center pressure pulmonarly or towards the heel backwards, that lets us know that the horses are shifting that body weight back towards the heels and lifting weight up off of their toes. And this gives us some evidence that the deep digital flexor muscle is actually engaged even when the horses are standing still. And that paralysis of this muscle with the botulinum toxin can result in the activation of that muscle and shifting of weight back off of the toes and reducing strain on those dorsal lamellae. From a treatment standpoint, then um this is great because we can keep horses stall rested with botulinum toxin treatment and see effects even when they're standing still in the stall.

Lisa Fortier 12:03

I think uh as a rider of a horse that has a DDF tear as it goes over the navicular bone, I also think like this is probably not a great thing. Like you might think, oh, relax the deep and take some of the strain off that area, but that Palmer shift would suggest that's not a great uh treatment protocol.

SPEAKER_04 12:20

Yeah, I think potentially uh, you know, this would have to be something uh investigated for different disease processes.

Lisa Fortier 12:26

Uh did you want to add something, Andrew?

SPEAKER_01 12:28

Yeah, I mean it it was it was fairly you know, you talk about statistical significance and then there's sort of um there's also biological significance. And the the shift in the uh center of pressure it wasn't small, it was at least was it 10 or 15? No, it was actually yeah, 15 millimeters. Is that right, Carolyn?

SPEAKER_04 12:54

Yeah, 10 minute tel 10 millimeters in a stance and then 15 millimeters when they were walking.

SPEAKER_01 13:00

It's actually quite quite a lot. Um and um you know, so I think uh you when you're doing research sometimes you get excited about things that are statistically significant but that are fairly minor. Um but you know, I I feel like that change in um center of pressure was was also relevant from a clinical perspective. Uh and um because horses stand around most of the time, uh if you can make an adjustment um to that to that loading pattern, even when they're standing still, I think that uh that is um you know that is quite advantageous.

Lisa Fortier 13:43

Yeah, for sure. Think of what we can do with shoes that shift the center weight bearing.

SPEAKER_01 13:48

Yeah.

Lisa Fortier 13:49

Kelly,

Best-Fit Laminitis Cases And Cost

Lisa Fortier 13:50

based on collectively all these findings, uh how might botuline toxin be used in managing acute laminitis that wears off, how much is it going to add in cost? How do you see this being incorporated into a clinical treatment?

SPEAKER_04 14:02

Yeah, so um, you know, the botulinum toxin effects were relatively short-lived. We saw return towards their baseline measurements by around two weeks after treatment. Um, so we're proposing right now that this would likely be most helpful in acute onset laminitis cases, such as the SERS or septic-induced laminitis, and also acute hyperinsulinemia cases, where you have a case that you can treat the underlying disease process relatively rapidly and get that under control in the short period of time that the botulinum toxin is helping to protect those dorsal lamellae. It's probably not going to be as helpful in more chronic cases or the support limb cases where you need something that's gonna act for, you know, a couple months at a time. Um, cost-wise, this is uh not necessarily the cheapest treatment. Um, it will likely cost between three and four thousand dollars to do both front legs for one treatment, um, just because of the cost of the medication itself, the botulinum toxin, and the amount that we're using. Um, we do use 200 units per front leg. And in comparison, um, for anybody who gets botulism um toxin or Botox in their face, you usually get about 60 units in your face. So we're using more than three times that amount in each leg of the horse.

Sarah Wright 15:32

Callie, what are the potential advantages or limitations of this approach compared to current treatments?

SPEAKER_04 15:38

Yeah, so I think um right now there's no other treatments out there for laminitis that are very similar to the deep digital flexor muscle, botulinum toxin. Other treatments aim to either reduce lamellar inflammation, like icing the feet or various systemic medications, or to externally alter the angle of the foot, such as with wedges that help reduce the deep digital flexor tendon tension by elevating the heel. Now, one concern with heel elevation and changing the external alteration of the foot is that we change the orientation of the forces on these lamellae. Normally the lamellae are under a tensile strain, and when you elevate the heel, you put them under more shear strain. And there are actually multiple studies out there that show that the dorsal lamellae are weaker in shear strain. And so this heel elevation may actually predispose already inflamed and partially damaged lamellae to further damage. Um, in contrast, the botulinum toxin doesn't change any of the angles of the foot. Um, it just works to change the intrinsic forces internally, um, which should limit those negative consequences. Limitation-wise, I think we have um two big limits here. Um, the first is that this is a relatively complicated procedure and probably something that would be hard to do in the field. Um, it does require five separate ultrasound guided injections in each leg that you're treating. Um, and this is not a standard muscle intramuscular injection that um most veterinarians do. Um, and it's not a standardly ultrasounded area either. It took us probably about an hour to get ourselves oriented the first time. Um, secondly, is again coming back to the cost of this. This is um not a cheap procedure and could potentially limit its utility for some clientele.

Lisa Fortier 17:39

On

Study Limits And Next Trials

Lisa Fortier 17:40

the research side, Kelly, what are on the study design and all those things, what are some of the limitations of the studies that clinicians should keep in mind when they're considering implementing this?

SPEAKER_04 17:50

Yeah, absolutely. So I think um our main limitation in this study was that we didn't control um or treat the control limbs with a placebo injection. Um, one thing that you have to consider is whether the physical act of injecting um a substance into this muscle caused any type of inflammation or pain or lameness in these horses that artificially changed our um pressure sensor readings. Now, what information we do have is that there was a previous study done with the exact same procedure of botularinum toxin injection, and they performed gait analysis on these horses with a control limb, and they didn't see any induction of lameness. And in the horses we used, we saw no pain, lameness, swelling associated with the injection. So we think that's unlikely to be a problem. The other limitation, as Andrew already mentioned, is that we didn't directly measure the strain on the dorsal lamellae. This is really hard to do in vivo in live horses. Um, and so we're using a proxy measurement with the toe pressures.

Sarah Wright 18:58

Kelly, what are the next steps for this line of research?

SPEAKER_04 19:02

Yeah, so we're really excited with the um results we got from this preliminary study, and we're very grateful to have received a grant from the Foundation of the Horse Innovation and Discovery Grant to continue investigating the use of this treatment in laminitic horses. And we are currently conducting a blinded placebo-controlled study on horses with acute onset laminitis that have SIRS to determine if we see the same biomechanical effects. And we're also adding in evaluation of rotation of the distal phalanx of P3 to see if there is a difference between the placebo horses and the treated horses in their propensity to actually rotate, which is what we all really clinically care about in the end.

One Takeaway And How To Follow

Lisa Fortier 19:49

So much good information, you guys. Thank you for sharing this with us and with the listeners. And we're gonna wrap it up with Andrew. If the listeners had one takeaway from this that you'd like to share, what would it be?

SPEAKER_01 20:02

Well, I think um, in a nutshell, there there are um favorable biomechanical effects that you can that you can achieve by injecting the deflux of muscle with with botulinum toxin. Whether that translates to uh clinical benefits, I think is um you know it's too early for us to really know. So uh hopefully we can we can gather some more information on um whether it makes a clinical difference.

Sarah Wright 20:31

Well, I sure learn a lot today, especially as someone who's not an equine person. So it's really, really, really cool stuff. Really appreciate you guys being here today. Just a special thank you to Army Major Callie for serving, and then Andrew for joining us.

SPEAKER_01 20:43

Thank you.

Sarah Wright 20:44

Thank you. And for our listeners and viewers, you can read Callie and Andrew's article on AJVR. I'm Sarah Wright here with Lisa Fortier. Be sure to tune in next week for another episode of Veterinary Vertex. And don't forget to leave us a rating and review on Apple Podcasts or wherever you listen.