Ever Heard of: Top of Sacral Vertebrae Fused S4/S5?

As part of a lengthy lameness investigation which I won’t get into here, I ended up with an X-Ray of my horses’s sacrum that shows the “top parts” of her S4/S5 vertebrae fusing. Those two vertebrae lean together, fused at the chunky top parts, while the rest curve gently towards the tail as normal, spaces in between the top parts.

I realize the sacrum itself is fused, which makes googling “fused equine sacral vertebrae” or similar an exercise in futility. I will post X-ray when I get the CD. Anyone have experience with or heard of this type of abnormality?

I haven’t heard of this…do you mean the top of the sacral spines are fusing? Like kissing spine of the sacrum?

“Hunter’s Bump.” Not necessarily an unsoundness if it’s “old.”

The S4 is leaning the wrong way, so the top is squished against the S5. I drew a circle and little arrow in the image. :slight_smile:


South of where a “hunter’s bump” would be. It is not visible on the rump. Count four vertebrae up from the tail.

I have a horse with something visible at about that spot out in my field right now, and he’s sound as a dollar. Is this just an incidental “finding,” or do they think it’s the source of his lameness?

I should imagine that might depend on whether it’s fully fused, or in the act of fusing. Why do they think it decided to fuse?

This is not visible to the eye - shows only on X-ray.

Source of lameness is still unknown. The vets have not seen this particular abnormality before, which was curious.