If you’ve been around horses for any length of time (usually measured in minutes), you’ve probably heard that a horse needs X-rays (hopefully, it wasn’t yours). And while you probably have some idea of what X-rays are, I thought it might be fun to talk a bit about them, and to give you some resources so that you have a little bit better idea of what you’re in for when you hear that a horse – or your horse – has had, or needs, X-rays.
A VERY BRIEF HISTORY OF X-RAYS
First, a bit of history. X-were discovered way back in 1895. By way of reference, that was the year that Tschaikovsky’s ballet, “Swan Lake” first appeared, the year that volleyball was invented, and the film/camera projector was patented (among many other things – if you want to see what else happened in 1895, CLICK HERE). So we’re talking old technology here. The rays were discovered, somewhat accidentally, by German scientist Wilhelm Conrad Ròntgen (which is why X-rays are called “ròntgen” in German-speaking countries, and in Japan, as well). Ròntgen himself called them “X” rays, the “X” being used because the type of radiation that he discovered was unknown. Over his objections, the name stuck; today, most medical folk call them radiographs, which, when you break it down, means, “writing with radiation.” I think the name X-ray pretty cool, actually – much more mysterious and magical sounding than “radiographs,” don’t you think? The wonderful, mysterious rays pretty much captivated the scientific world, and a mere six months after their discovery, X-rays were being used by battlefield physicians to locate bullets in wounded soldiers. And to top it off, for his discovery, Ròntgen won the very first Nobel prize in physics, back in 1901. If you want to read more about the history of X-rays, or X-rays in general, CLICK HERE.
FUN FACT: By 2010, it was estimated that 5 billion X-ray imaging studies had been conducted around the world. This actually seems rather small to me, since that’s roughly the number of X-rays that some people take during a single prepurchase exam on a modestly priced horse, not to mention the expensive ones.
WHAT ARE X-RAYS?
X-rays are basically the same thing as visible rays of light, it’s just that you just can’t see them. And just like visible light rays, X-rays do one of two things. Either they pass through stuff, or stuff gets in the way of them (in a variety of ways, such as absorption, or reflection, which we’re not going to talk about right now). Pretty simple, actually. So, when you shoot X-rays at a horse, mostly, one of three things can happen:
- Some of the X-rays pass right through the horse
- Some of the X-rays get stopped by tissues in the horse, and especially bone
- Some of the X-rays miss the horse altogether (it’s inevitable).
HOW DO YOU COLLECT AND PLAY WITH THEM?
WHAT DO YOU SEE WHEN YOU X-RAY A HORSE?
Well, here, I’m going to direct you to a couple of fun websites. The University of Illinois School of Veterinary Medicine has a website devoted to imaging anatomy of four different species (including horses, of course), which you can see if you CLICK HERE. On this site, you can take a look at the normal anatomy of various parts of the horse’s front and back legs, and the skull, too. Even if you’re not 100% sure what you’re looking at (veterinary school helps with that, of course), the pictures are really great and you can have all sorts of fun with the color highlighting feature that lights up various bones and bumps and holes.
DO X-RAYS HAVE ANY LIMITATIONS?
Yes, well, here’s where things can get a little sticky, diagnostically speaking. Remember how X-rays work, that some x-rays get stopped by tissues, and others pass through? It turns out that the tissues that are especially good at stopping X-rays are bone. Bone is very dense, it has a lot of minerals in it (especially calcium and phosphorus), and when X-rays hit bone, most of them run out of steam. That means that there’s very little X-ray to pass on
Limitation #1 – The problem is that, just like the air, most of the non-bone tissues of the horse (which are mostly composed of water) don’t stop many X-rays, either. Things like tendons and ligaments and blood vessels end up looking pretty black, too. That’s why, for example, when your horse has a tendon injury, if you want to see what’s going on, you use a different imaging technique, such as ultrasound.
Take Home Message #1 – If you want to look at bone, X-rays are a pretty good choice. If you want to look at something else, use something else.
I suspect it’s the same way in horses. Other than studies about the horse’s navicular bone – a real can of worms, as it turns out – there aren’t very many studies that have looked at the correlation between X-ray findings and clinical lameness. I did one way back in 1997 (CLICK HERE) – in fact, all of the horses that I looked at in my flexion test study were sound, even though some of them had some X-rays that were remarkably different from what we would consider normal. And in my clinical practice, I routinely find some pretty odd looking X-rays on some very sound horses.
Limitation #3 – X-rays simply can’t predict the future. That’s something to keep in mind when you’re buying a horse. Lots of people spend lots of money on X-rays in hopes that they’ll be able to get some idea how horses are going to do in the future. On the other hand, lots of people lose lots of money because people offer less than the asking sales price because of supposed X-ray “changes” that actually have no known significance (think back X-rays, or navicular bone X-rays, to name a couple). X-rays can’t tell you how fast a known problem will get worse and they also can’t tell you if a “change” is going to develop into something significant in a horse that is currently sound.
Take Home Message #3 – You have to ride the horse; you can’t ride the X-ray.
X-rays are an extremely useful imaging tool in horse medicine, especially if you’re doing lameness work (which, as a horse veterinarian, you often are). But you have to be a bit careful in interpreting them, because not every “change” is significant, and we don’t always know what those changes mean; they may even be normal for a particular horse. If your veterinarian finds something on your horse’s X-ray, it’s often a good idea to get a second opinion before making an important decision: consider having them sent to a veterinary radiologist. X-rays are old technology – and very useful technology, for sure – but you have to remember to consider them in the mysterious light of the horse.