Posted in  Understand Hoof Health  on  7 March, 2014 by  Debs Crosoer

It’s what’s on the inside that counts… right? How do the distortions in the hoof capsule affect the internal structures of the foot?

So we had a look at what was happening on the outside in Part 1

There’s a few things that happen to the pedal bone when the heels underrun. First lets look at what it’s supposed to look like, with the aid of my seriously impressive graphics skillz…

Underrun Heels Explained Part 2 01

The pedal bone is roughly at a 3-5 degree angle (I’ve exaggerated it a little if I’m honest as it makes it easier to see) and I’ve put a funky little extension out the back which you don’t see on most diagrams. You’ll see why in a minute. But this is the palmer process.

The blue line represents the ground reactive forces. Not massively significant here – but it will be when we compare in a minute so hold on to you hats!!

If you haven’t seen a pedal bone in person – well! You don’t know what you’re missing!! Let me introduce you…

Underrun Heels Explained Part 2 02

Doesn’t look much like a triangle there does it? It does in x-rays and cross sections, which is why it’s most commonly represented as a wedge shape. You can see here the palmer processes are little bits sticking out the back.

Underrun Heels Explained Part 2 03

At the risk of appearing like an over proud parent, posting way too many photos of their child on their facebook profile… Here’s another photo from another angle. I’ll stop and go back to dodgy graphics. But hey! I’ve moved on from crazy felt tip pen scribbles (for the moment anyway…)

What happens when the heels collapse? (or underrun)

Underrun Heels Explained Part 2 04

The heels underrun, which makes them shorter in terms of vertical height, even if the actual length of the heel is the same. (it’s all trigonometry, I can go in to more detail as I loved maths at school… and college… and uni… or you could take my word for it and I won’t bore you. If you want an explaination, ask in the comments section)

The heels being shorter, reduces the angle of the pedal bone, causing a ground parallel or in very bad cases a negative angle on the pedal bone. That’s bad for many reasons. The one I’m pointing out here, is what happens to the ground reactive forces.

See how the blue arrow, indicates that the pressure from the heel landing is getting very close to the back of the palmer processes. In many dissections I’ve done, the heels purchase (ground bearing surface of the heel) is in fact pressing directly on the palmer process.

Underrun Heels Explained Part 2 05

You can see in this photo where the heel surface is much further forward than it should be. Look at how the laminae are angled forwards. They’re exactly how the tubules of the wall were angled forwards in last weeks post.

Underrun Heels Explained Part 2 06

What I’m pointing out here is that the underlying structures have underrun. Yes the hoof capsule has gone with it, but the corium that grows the heels has moved forwards not just the hoof capsule.

If the corium that produces the heels and wall, has moved, then how can you possibly expect a trim to correct the problem. Wouldn’t it make more sense to stimulate the internal structures to regain their strength, and the hoof capsule will follow?

In part 3, I’ll be covering common ways of addressing underrun heels, and how I think they affect the internal structures.

Is this an internal or external problem? Well clearly it’s both, but which comes first? Does the hoof capsule hold the internal structures in place, or do the internal structures that produce the hoof horn, dictate how that hoof horn grows?

Have these pictures changed the way you think about underrun heels?
Did you already know what the pedal bone looks like?
Does your horse suffer from underrun heels?
Tell me what you think in the comments below


Want to read the first in the series?

Underrun Heels Part 1

Underrun Heels Part 3

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About the author

Debs is a practicing Equine Podiatrist with over 15 years experience, author, and educator.

She’s here to show you how to simplify your horse’s management painlessly so you feel in control and have a straightforward system that works for you.

When she’s not working you can find her playing with her own horses, watching geeky sci-fi or baking epic cakes.

    • Yes, absolutely. The pain can be simply from the soft tissue in the foot being weak and squashed which tends to sort itself out pretty quickly when given a chance, or it can be due to the extra strain on the tendons and ligaments, which can take a little longer to get right.

  • I don’t care how old these posts are or how many folks have seen them before I did, I truly appreciate the depth and clarity of information.

  • Hi, this is really interesting. Has Part 3 been written yet? I need to know how to help my toe-first landing horse (4 weeks into barefoot with good nutrition, ridden in boots with pads and daily short walks on tarmac without boots). Looking at your photos, I realise his heels must be underrun and we have a problem… 🙁

  • You really explain things well! Took a little bit of brainwork but not impossible to understand – really enjoying your articles, good job! 🙂

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