Veterinary Vertex

Continuous Load, Compromised Flow: PET Imaging of the Equine Digit

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A hoof can look fine while its tissue quietly runs out of blood. We sat down with Drs. Georgia Skelton and Andrew van Eps to unpack new 18F-FDG PET research showing how static weight bearing creates sharp, regional perfusion deficits in the equine foot—the very conditions that can spark support limb laminitis in otherwise healthy horses. The findings challenge old assumptions and make a powerful case for movement, dynamic load cycling, and smarter monitoring before the cascade begins.

We walk through why 18F-FDG PET changes the game by capturing function, not just structure, revealing “no-uptake” zones in the lamellae, sole, and coronary band within minutes of standing still. You’ll hear how medial palmar regions are hit hardest in front feet, why lifting the opposite limb shifts deficits laterally, and how the hoof’s intricate anastomotic network lets blood choose the path of least resistance—bypassing vulnerable capillary beds under pressure. These insights tie directly to what clinicians see first in the field: sole pain, growth issues at the coronary band, and rapid decompensation when motion is restricted.

From here we get practical. Andrew and Georgia outline emerging strategies to keep perfusion alive: enforced micro-movement, intermittent offloading with robotic slings, and dynamic orthotic devices that rotate pressure points across the sole. We dig into how mobile PET systems can guide personalized shoeing and support plans, and how tools like pressure mats and targeted near-infrared sensors could bring stall-side monitoring to the danger zones identified by imaging. The goal is simple: reintroduce safe variability and prevent any one region from being starved for too long.

If you care for at-risk horses after fractures, abscesses, or surgery, this conversation offers a clearer map of the problem and a toolkit for early intervention. Subscribe, share this with your care team, and leave a review to help more equine professionals find evidence-based strategies that keep blood flowing and horses sound.

AJVR article: https://doi.org/10.2460/ajvr.25.07.0268

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Lisa Fortier:

Welcome to Veterinary Vertex, the AV Made Journal's podcast where we delve into behind-the-scenes looked with manuscript authors. I'm editor and chief Lisa Fordier, joined by associate editor Sarah Wright. Today we're discussing the role of weight-bearing-related perfusion deficits that are detectable using PET in the development of support limb laminitis with Georgia Skelton and repeat podcast guest, Andrew Van Epps. George and Andrew, thank you so much for taking time out of your busy schedules to be with us here today.

SPEAKER_04:

Thank you.

Sarah Wright:

Happy to be here. Yeah, thank you for joining us, Georgia and Andrew.

Lisa Fortier:

Georgia, let's start with you. Uh, what clinical research question motivated this study on digital profusion in horses?

SPEAKER_03:

Yeah, so um supporting limb laminitis is a very um understood um complication that we see is a result of um painful limb conditions most commonly. It's not something that we see terribly common in prevalence, but um when it happens, it's quite unfortunate. And usually these horses are otherwise systemically healthy and um have a painful limb condition, such as a fracture or an abscess, and um then go on to develop supporting limb laminitis in the other limb, and it's just not very well understood. Um, so we um had noticed some differences in um lamellar uptake with positron emission tomography, just anecdotally in the clinic. And um we were interested in looking at um whether or not there could be a perfusion-based mechanism um based on some previous literature and everything that was out there that could be playing a role in why these horses who are otherwise systemically normal could be developing this condition.

Sarah Wright:

Andrew, why is digital blood flow such a critical area of interest in equine medicine and lameness research?

SPEAKER_04:

Well, traditionally, laminitis was thought to be, uh, regardless of the underlying cause, was thought to be a vascular problem. Uh these days we know that in the majority of cases, it's it's a problem with insulin and it's not got a vascular mechanism, it's not an ischemic problem. Um in sick horses, that also doesn't seem to be an ischemic problem, but there's um some evidence from uh previous studies and from our group that ischemia does play a role in this supporting limb laminitis uh uh form of laminitis. And the foot of the horse is interesting because you've got uh a very vascular tissue, the lamellae, that are richly um vascularized between two hard spaces. So you've got a hard bone and a and a hard hoof. So it is set up for uh compression, focal compression, and focal failure of perfusion and um and things like uh compartment syndrome as well. So uh it is uh definitely something that that likely plays a role in supporting limb laminitis early in the piece, and vascular compression also seems to play a role in the progression of laminitis, particularly as they become more chronic and as that bone moves inside or displaces inside the hoof capsules.

Lisa Fortier:

Yeah, it's such an important area for equine surgeons. People just don't understand that we can fix the bone. It's the other dang leg that gives out on us sometimes. Uh, I remember years ago, too, many like 30 years ago, Jeff Watkins made the observation that when he would do, especially pastor and Arthur DCs on horses and they would be sore. The horses that moved around in the stall or weaved even were the ones that did not founder. So we were all, you know, you're cringing because you're looking at all the stress and cycle on your repair. But uh he made that observation that those horses that kept moving were the least likely to get support limb laminitis. But anyway, um, Georgia, what makes dynamic uh pet CT valuable for studying this perfusion in the equine foot?

SPEAKER_03:

Yeah, so um the beauty of positron emission tomography is particularly FDG scanning, is that it is a functional imaging modality for us. So basically, our radio tracer is a um uh radioactive labeled glucose analog that we give intravenously, and um that's of great advantage to us because um just something like CTR um arteriography can be quite painful, um, even though we can do it. Um, getting horses to stand quietly for it can be difficult, and um, it also is still only giving us structural information. Whereas by using a glucose radio tracer, we can look at um essentially functional, what is going on in the hoof in terms of how are the lamellae um not only uptaking it through the vasculature, but how are they utilizing it and retaining it within their foot or not in the is the concern um for these supporting limb laminitis cases. Um another great um benefit of positron emission tomography over something, say, like nuclear scenigraphy, is the fact that we are getting a 3D multiplanar um picture of what's going on in that limb versus just a 2D umaging. So when we combine that with our CT imaging, we have not only a functional picture from the positron emission, we um also get structural information from the CT.

Sarah Wright:

Very cool. And Georgia, what differences in digital perfusion did you observe during prolonged standing compared with post-ambulation imaging?

SPEAKER_03:

Yeah, so um when we just stood the horses in the detector and didn't allow them to move around, um there were these discrete regions throughout the foot that developed what we essentially call uh perfusion deficits in the paper. And um particularly these were developing in specific locations in um different feet in different horses, and the severity of them was quite different. So um we were thinking that just the way that the horses maybe particularly stand individual to individual um and put pressure on their feet could be playing a role. Um, but even though they were different, um, some specific patterns came out for us.

Lisa Fortier:

What were those patterns, Georgia? I think that's fascinating. I mean, we all stand differently, so it's not surprising, but what were the patterns that you noticed?

SPEAKER_03:

Yeah, so we particularly started to notice that the medial aspect of the horse's foot was more affected than the lateral aspect and particularly more um palmerly, because we only scanned front limbs in this study. Um, but the coronary band and the lamella and the sole specifically um were developing these deficits more immediately, and the exact severity of them would vary again between individuals. But um, yeah, the sole and coronary band were very significantly affected in multiple animals.

Sarah Wright:

Andrew, did the presence of perfusion deficits in healthy horses surprise you?

SPEAKER_04:

Yes and no. I I think that different groups and our group uh over the years have looked at the effect of load on perfusion in feet and noticed that there are uh uh definitely deficits associated with weight bearing that you can see. Um we see it artifactually on venography, um, which is contrast under pressure injected uh retrograde into the foot. We've also seen it with um arteriography of cadaver limbs, but we haven't published that in the past just because we we felt like it wasn't uh we were worried it didn't apply to to live animals, I guess. And there was a study from a farrier, actually, um guy called Levant Cranberg in South Africa many years ago uh showing uh that there were arteriographic deficits to stop plain X-ray that could be noted um in horses that were load-bearing. Uh I guess what surprised us is just how extensive these regions of no uptake were in healthy horses in the medial quarter region in particular. Um, they were in some animals really extensive. And for 20 minutes those horses stood there with uh weight bearing on that foot, and there was no evidence of perfusion in quite extensive regions of the lamelli, the sole and the coraly band of the medium side. And so to us, I guess it um you know, it explains to some extent why some horses would have much more detrimental effects associated with standing still, uh, let alone having increased load compared to others if they had a fracture or another prop wall that was inhibiting their ambulation.

Lisa Fortier:

Yeah, it does make sort of sense, right? Like you're at least I was always taught that remotely your weight bearing, whether you're a human, a dog, or a horse is on your medial axis, a medial femoral condyle, medial side of the hoof wall, but it's interesting to hear you say how striking it was in the soul and the coronary band. Um how does that inform our fundamental understanding of constant weight bearing?

SPEAKER_04:

Yeah, I mean, I think um we've come to to sort of um realize that horses need to move. They uh they're not okay with just standing still for long periods of time. Uh but um, you know, I think the other thing that we notice, talking about the soul in particular, is that we notice in a good proportion of these horses that develop supporting limb laminitis clinically that they often break out in the soul initially and they often probably get sole necrosis. I think we we don't um you know, we don't uh a lot of this isn't isn't published in the literature and we don't necessarily um recognize it every time, but it's probably more than just the metal damage that we're seeing in it, you know, if the coronary band isn't perfused well, there may also be uh be issues with with growth over long periods of time, particularly immediately, which perhaps we also do see uh in these in these cases.

Sarah Wright:

So, Andrew, on the clinical side of that question, what potential implications could this research have for monitoring prevention or early intervention in at-risk courses?

SPEAKER_04:

Yeah, great question. I I think we we still need to do some more work, and we are doing some more work looking at how increased load affects perfusion using using that. And we're also um looking at how we can then incorporate this information into the clinical situation. I guess one way we could do it would be to look at individual perfusion patterns under load and and uh work out ways to adjust the load bearing to take away those um those areas of uh of poor perfusion in some of these animals. I I suspect, though, that sort of static orthotic type devices are are not going to be the answer, and they haven't really been the answer in the clinic. I suspect that these animals need to to move uh to have uh uh some enforced or uh intermittent therapeutic load cycling uh or some dynamic alterations of their load-bearing surface to try to prevent this problem. Um but you know, I think PET could be used. It's a little bit cumbersome and it's expensive, uh, but it could be used clinically to uh to monitor these animals um in their opposite limb. But I in in my mind, I think what we may do now knowing where the the focal areas are that that uh the lack perfusion, I think we could try to develop other means of monitoring perfusion specifically in those danger areas uh that you know we know are affected more.

Lisa Fortier:

It kind of begs the question of if something like a vibration plate or something else could be a proxy for enforced exercise so that we're protecting that contrary the the limb with the implants or something, and it not having to walk the horses. Is that on your mind or if it's been done, my apologies, but is that something you've thought about or plan to investigate?

SPEAKER_04:

Yeah, I mean, uh vibration plates or um what we're looking at, and you'll get a you'll get a paper set on this. We're looking at dynamic orthotic devices, so uh uh we are looking at the effect of sort of um of dynamic modulation of of pressure, particularly on the sole, on the frock. Uh and you know it is it is actually a bit promising. Uh the other thing is dynamic alteration of the bearing surface and whether you can you know, I I think you can you probably can't get something for nothing. You're probably always gonna have a portion of the foot that's poorly diffused under load because you can't, you know, unless you take away the load, which is was is is another option. Yeah. With dynamic sling technology, with another thing we're testing, you can take partial load or all of the load off intermittently to try to solve this problem. And traditional slings have the issues with sores, and you know, you're either sort of taking all the load or another load. With robotically controlled slings, you can you can control that and modulate it dynamically or partially. And I think that that's a big deal. But they're you know, uh coming back to to um modifying the load-bearing surface, if you if you're not taking load off the loom, you're probably always going to have some part of the foot that's poorly that's poorly perfused. But can you rotate the responsibility of that uh you know, using some sort of dynamic orthotic device? You know, a vibration plate, maybe, but in my mind I think probably more gross um uh changes now in the load-bearing service might be the place to start. And we do have some encouraging early evidence to suggest that that that that might be the way to go. Yeah. It's logistically a little bit difficult, uh, but not insurmountable.

Lisa Fortier:

Great. Look forward to reading that. Uh another question would be we're learning so much about the subtleties of metabolic disease in horses and early, early metabolic before they have PPID and other metabolic diseases. In this in this uh study group, did you find any correlation between severity of vascular occlusion uh or decreased perfusion in correlation to metabolic status?

SPEAKER_04:

We didn't look. These were these were generally healthy. Um, Georgia, they were pretty much all healthy thoroughbred standard types, weren't there? But there was the odd, you know, I think one or two metabolic type horses. But did you I didn't think there was noticeable difference in those.

SPEAKER_03:

We had two older standard breads, um, but they were at the time of the study considered metabolically healthy. Um, but we had two that were um more towards the metabolic phenotype, as um Dr. Granops mentioned. Um, but in general, we um just looking at, you know, the limited prevalence data that we have, we were looking at horses that were similar to what has been most commonly reported, which tend to be these um younger race horse individuals that have suffered catastrophic injuries. So um our population probably most closely matches that um in terms of healthy young to middle-age standard breads and thoroughbreds in this particular publication.

SPEAKER_04:

What's really interesting is that when you lift the opposite limb, so we started lifting the opposite floor limb and looking at the fusion edit, and it's just way more dramatic. It's it's unbelievably dramatic. But what's dramatic about it is that it like cuts off there's like this demarcation, and then the whole side of the foot is like black. There's no uptake. But it's the lateral side in the front, we're like, God, what? So what's going on here? Now we're starting to measure um pressure distribution underneath the foot. When you lift the opposite forelim, it most of the load goes laterally. So it seems like the deficits follow the load distribution, and like you were saying, Lisa before, like most of the there's there's higher load medially, uh down the front leg. Um and it seems like when you modulate that pressure, if you put it laterally, or you you know, it follows the the deficits follow the load. So uh that to me is really super interesting, which makes you think that we could dynamically modify it by you know forcing them to posturally change or or just going direct to the foot. Uh it's super interesting. Yeah. Well I'm I'm excited that we can solve this one soon. Um the other thing I wanted to say about the sort of when you asked me about where were we surprised about uh that there were deficits? Um the only other thing I wanted to add to that was that the foot is the foot of the horse is interesting. There aren't there aren't valves um distal to the to the hasten area in the veins, but there are so many connections between the arteries, so arterior-arterial anastomoses, the arteries and veins, arterial-venous anastomoses, and then the veins are interconnected as well. And so what you have is a vascular network, arterial and venous, that's all interconnected, and blood doesn't have to come down and perfuse all of the capillary beds in a in an orderly fashion, like you might expect, or at least that I would expect in my mind. Blood can take the the route of least resistance, the path of least resistance through the foot, and and leave whole areas behind. And that's what that's what we're we're seeing. Um, and we're seeing it very discreetly with with load. It's really interesting.

Lisa Fortier:

Yeah, it is very glad you're in charge.

Sarah Wright:

Yeah, it's fascinating. I've learned so much through this episode. So, Georgia, any comments to add? Any thoughts about the future?

SPEAKER_03:

You know, I think that we could potentially use this technology, as Andrew suggested, for um monitoring these horses over time. The beauty of the uh Panners that we use in our horses is that they are in fact mobile. While it is cumbersome to move them, it is possible to roll out to a stall where an at-risk animal may be housed and scan a limb, um, or use it in theory to monitor um. Changes, therapeutic shoeing that you may have in instituted. And then we can also just use this to guide further research. There are some spectroscopy near infrared technologies out there that have been used in the brain, for example, to look at cerebral tissue oxygenation. And the problem with them is that they have very localized pro placement, but um, knowing what we know about where our deficits seem to um be popping up, at least in static weight bearing, we could um target research with those types of technologies.

Lisa Fortier:

Well, very cool. Uh George and Andrew, thank you again for joining us today. For our listeners and viewers, you can read George's and Andrews' article in AJVR. I'm Lisa Fordier here with Sarah Wright. 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.

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Lisa Fortier, DVM, PhD, DACVS

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Sarah Wright, DVM

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