A friend of mine called his vet out because his horse had some swelling near the hock.

A small, less than finger-sized, swelling and the horse was not lame.

The Vet xrays and says, “The horse’s hocks are fusing. Let’s give Osphos and see what happens.”


Here’s my opinion on Osphos:  Osphos and why it’s bad

But what does “Fusing hocks” actually mean?

By definition, hocks are called “fused” when the xray shows bone growth (aka arthritis) covering up the joint space.

Here is a normal hock xray:

The hock has 4 joints, and lots of little bones. The bones are the white areas on an xray. The black areas are where the joint space is supposed to be. That space is where the joint fluid lives.

Here is the xray of my friend’s horse:

There is definitely less black space. And in a few areas the black space appears “covered over” with white bone.

Often vets assume this shows a process of “fusing”. That is, where one or more of the bones are fusing to become solidly stuck together.

But they’re not fusing like we assume

What looks like fusing on an xray, ONLY shows the EXTERNAL area of the hock joint.

Studies show that 80% of “fused hocks” on necropsy (name for horse autopsy) are not fused internally. They are only fused on the outside of the joint.

So, for example, if you placed your hands on each side of your ankle, your hands would be where the xray “fusing” is located. NOT on the inside of your ankle.

But you can still move your ankle even with your hands tight on each side, right? Because the inside of the ankle can still move, even if the outside is held tight.

What’s really going on?

We have to keep in mind that the horse is not surprised this extra bone is there. The horse’s body put it there on purpose.

Why would it do that?

Several reasons: Lax ligaments, decreased or assymetrical muscle, wrong angle of trim, sacroiliac issues, pelvic misalignments…just to name a few.

The point is, there is some reason that the horse is putting more bone on the outside of a joint(s). Typically, horse’s add more bone to the outside areas of a joint for stability and support.

If you remove the cause(s) of the instability, the horse will — over time — remove the additional bone.

Why does “fusing” sometimes seem effective?

I’ve known lots of horses where fusing was tried. Some were put out to pasture for a year. Some were put on Bute and ridden for a year.

In some cases, this seemed to work. The xrays show additional bone “fusing”, and the horse became sound.

This is simply the horse having time to completely build all the stability and support it needed for the hock to function acceptably.

This is not ideal, because the real underlying cause has not been addressed.

But I’ve also known people who have tried to “fuse hocks” for 10 years! And it never worked.

I’m sure you’ll hear lots of different stories and opinions. I’m just sharing what I know to be true.

The horse puts the bone there for a reason, and if you find the reason and correct it, the bone can be reabsorbed over time.

Why do vets give joint fluid products when they see “fusing” happening?

This really does not make sense. If the vet believes the bones are fusing together, giving more joint fluid would be contraindicated.

But sometimes people just want to try everything.

So if giving products to increase joint fluid (via oral products, or intramuscular/intravenous shots, or joint injection) helps your horse, that is a sign that your horse wants to move the joint. And also that your horse needs help moving the joint, rather than “fusing” it.

Check out my podcast that delves deeper into this here: Do joints really fuse, and would Osphos help?

There’s always a reason, and a way to fix it. Don’t give up on finding the cause.

Best of luck,
Renee Tucker, DVM

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