Radiographs – Know What They Can and Can’t Tell You

With many lameness situations, veterinarians take radiographs as a first line method of diagnosis. Some radiographs are relatively easy to decipher in that the average horse owner can make out which bone is which, and generally conceptualize where they are on the horse. Yet other views look like a Picasso painting – and it they leave many scratching their heads wondering, “What on earth is my vet looking at?”

Credit: g.-miller-photo Subtle findings like the bone chip indicated by the red arrow in the fetlock joint can be easy to miss, but can cause huge lameness problems.

Understanding a few basic principles as well as keeping some tips in mind when communicating with your vet about what he or she sees in your horse’s bones will help you take away more for your money when it comes to radiographs.

Radiographs and the Digital Age

In the horse world, radiographs are used to look at bones. In special circumstances, they look at lungs, but that is rare. Radiographs generate pictures of bones by passing a radioactive beam through the patient to project an image on an imaging plate. In some parts of the country, the imaging plate is still a good ol’ fashioned piece of X-Ray film.

But with the advent of digital processing technology during the past 15 years, the film is becoming a thing of the past – just like with normal cameras! Digital imaging offers several advantages over conventional analog films, not the least of which is a significantly more detailed image. In addition, if a shot is blurry or not quite at the right angle, it can simply be erased on the spot and taken again, versus having to be manually processed and then retaken days later.

That means, with digital technology, veterinarians can adjust the brightness, contrast, and hue of each image, as well as zoom in to get a closer look on suspicious lesions. Digital radiography has become a standard in equine practice. Of course, these advancements come at a cost to the owner. On average, you can expect one digital image to set you back about $50 or so. When you consider that a standard set of views of a foot is five images, and a hock and stifle are both four, it doesn’t take long to do the math.

The “Art” of Radiology

Veterinarians are trained to the nth degree when it comes to reading and interpreting radiographs. Deciphering them takes an intricate knowledge of the anatomy of each bone, and qualifying abnormalities on the images takes a blend of expertise and experience. Kind of sounds like an art, right? Well, it sort of is.

No two veterinarians will have the exact same assessment of a given set of radiographs because reading radiographs isn’t just about spotting a lesion. It is also about watching patients over time live with those lesions and then using those observations to make predictions about how other horses with similar lesions will fair.

Credit: G.Miller Photo Red arrows point to a classic osteochondrosis lesion in the stifle.

In the same vein, something may look really scary on a radiograph and lead one to believe that the horse should be crippled… but then when we see the horse running around in the pasture, there is a new light shed on the situation. On the flip side, sometimes a radiographic lesion can appear insignificant, but for the horse, it is debilitating. Therefore, each veterinarian who evaluates radiographs is doing so in the context not only of the horse that they are assessing, but all of the horses that they have known before that have also had similar lesions. In a word, they are using experience.

So, What Is The Vet Looking For?

No exaggeration here – there are literally dozens of things that the veterinarian evaluates when viewing radiographs. Most commonly, of course, we look for evidence of osteoarthritis. If a joint is inflamed for long enough, the bones will start to change by either dissolving away or laying down more (aka “bone spurs”). Sometimes, they do a mix of both. These are called destructive or productive lesions but are more commonly known as osteoarthritis.

But productive/ destructive lesions are the easy stuff. Many other issues can faintly show themselves on radiographs! We find them by spotting things that deviate from the normal anatomy of the bone. In a pinch, we can also compare the radiograph to known “normals” (these are published in a book), or by looking at a shot of the same bone in a different leg. We are trained to spot subtle clues – like a flattened bone edge, a dark spot, or a bump where it shouldn’t be. Sometimes, all we see is a fuzzy bone surface, but that can be enough to make a diagnosis. Even the density of the bone is evaluated when we look at radiographs. And these are just to name a few.

When veterinarians look at radiographs – many apply a systematic, methodical approach using a mental checklist to keep us thorough. Although we all do things a little differently, most of us follow some basic general rules:

1. We take “standard” views. For instance, if we are radiographing a hock, it is common to take a front to back picture, two side to side pictures (one with the hock flexed and one with the hock in standing position), and two diagonal pictures.

2. With each of those views, we try to take a specific angle (45 degrees, 65 degrees, etc.).

3. We strive to take a complete series when we are looking at a bone. This is a big deal because many owners feel “pain in the pocketbook” with click of the camera. Sometimes owners try to talk the vet into “just taking a few shots”in an attempt to make the ordeal more financially palatable. The problem is that taking radiographs is like shining a flashlight at a garage door. You can see part of the door but not all of it with the flashlight beam. Therefore, you have to move the beam around to all the different parts of the door, and then piece together the images to make the “whole.” Your vet cannot provide you with complete information without a complete series of radiographs for the same reason that you cannot tell someone that their garage door is OK by just looking at one part of it.

Credit: teaching-crop Digital images means a bad picture can be retaken immediately.

4. If we see something suspicious, we try to visualize it on more than one view before we declare it to be real. Radiographs are famous for having “artifacts” on them. An artifact can show up in the form of a shadow or an apparent mass that is not actually part of the bone. Sometimes artifacts can be from mud on the skin or air underneath the frog that shows up as a black line on a radiograph of the hoof. In order for us to determine if what we are seeing is real or fake, we try to see the suspicious image on more than one view. If we can see it on several views, we can approximate its location and improve our confidence that it is indeed real.

5. We try to look at radiographs in a dark, quiet room. It’s amazing how much a dark room can bring out new radiographic findings. For those who still use X-ray film, the viewer boxes usually are in a dark room. For those using digital technology, it can sometimes be tempting to read radiographs right there on the farm, but glare from the sun can rob the image of a lot of detail. For this reason, and because we sometimes need our text books or another trained set of eyes, many vets try to sit down in a non-distracted setting and study the images closely.

6. If an image is blurry, we won’t read it. Horses and veterinarians can sometimes move at the precise moment that the X-Ray beam is exposing the bone image onto the plate. With digital imaging, the computer actually senses the blurriness and applies technology to correct the image. If that method fails, the image can simply be erased and retaken. Yet still, we sometimes come across fuzzy images. And of course, with actual film, you never know what you are going to get until it comes out of the processor, so blurry images can survive. The fact is that many lesions can be missed on a poor quality image. For this reason, we tend to turn up our noses at them.

7. With each view, we evaluate the radiograph for bone shape, bone density, abnormalities on or in the bone, and bone angles, among other things.

Credit: G.Miller Photo Catastrophic fractures, such as this one that has been repaired with surgical screws, can be characterized on radiographs.

The “Easy” Stuff

As technically difficult as reading radiographs can be, we get pretty good at spotting some of the more common problems when we see them repeatedly:

1. Osteoarthritis: Mostly this is seen as bone spurs or a roughening of the bone surface, this finding is called bone spavin in the hocks and ringbone in the coffin and pastern joints. Of course, it can occur in any joint, including the vertebrae (discospondylitis), the knees, fetlocks and stifles.

2. Osteochondrosis or Osteochondritis dissecans: Osteochondrosis refers to a defect in the cartilage overlaying the bone. It can occur in any joint in the body but is most commonly found in the stifle, hock, elbow and shoulder. It looks like a flattening of the bone surface and in some cases, a radiolucent bone cyst (shows up as black). Osteochondritis dissecans (OCD) refers to when the defective cartilage lifts away from the underlying bone, thus exposing it and causing it to become irritated.

3. Injuries: As frightening as they sound, some fractures can be helped. Finding them early and intervening is key. Most commonly, we hear about chip fractures, in which a piece of bone comes off and is sitting in the joint. But horses can also have hairline fractures all the way up to catastrophic breaks. Beyond fractures, bones can have deep bruising. Although bruising is more reliably seen with advanced diagnostic modalities such as CT or MRI, radiographs can give up some clues to suggest that they are bruised. Bone bruises are nothing to take lightly – they can be responsible for retiring a horse if they are bad enough.

4. Developmental Abnormalities/ Congenital Deformities: Sometimes if a horse is born at the wrong time, the bones in the carpi (“knees”) and hocks are not fully mineralized when they begin to walk around. As a result, once the bones do calcify, they can be deformed. These cases, along with OC lesions, justify radiographing very young animals during a prepurchase exam.

5. Bone Disease: Infection (osteomyelitis) and metabolic bone disease such as Bran Disease or Silicosis can show up on radiographs. Of course, it takes the presence of concurrent physical signs to help make a complete diagnosis, but radiographs can show very distinct signs when they are diseased.

Some Terms To Know

Credit: G.Miller Photo The red arrow points to a bone spur in the hock, which indicates osteoarthritis.

“X-Ray” is a common term for radiographs. But, in actuality, the X-ray refers to the radioactive beam that comes out of the camera.

“Radiograph” is the actual image that you look at.

“Radiolucent” means that something is showing up as black. Gas and thinner bone mass shows up as radiolucent relative to the other bone around it.

“Radiopaque” or “Radiodense” refers to something that is showing up whiter than the tissues around it. Some foreign objects, and fluid show up as radiodense.

The Rrole of Radiographs in the Prepurchase Exam

Nowhere is the veterinarian’s interpretation of radiographs challenged more than in the prepurchase examination. Surprisingly enough, in many instances, the prospective buyer gives the vet a harder time about the radiographs than the seller. Is this because the buyer really really really wants the horse? One can only speculate.

Keep in mind that the veterinarian is really going to stick to the textbook interpretation of radiographs during a prepurchase exam. For instance, if there is osteoarthritis in a joint space, the veterinarian will point it out, and tell you whether it is mild, moderate or severe. Do not expect your veterinarian to tell you whether or not the osteoarthritis will be a problem down the road. Nobody can know that. All the vet can do is tell you that it is there when the picture is taken – you have to make the informed decision as to whether or not you want to purchase the horse with this information in mind.

Bottom Line

Let your veterinarian take the views that he or she needs to take in order to feel comfortable making an evaluation of your horse. Yes, they are expensive. But, so is missing a radiographic lesion that becomes a lameness down the road because the vet was not allowed to take that one view that could have found it.

Allow your vet to not just take the radiographs but to also thoroughly review them before you ask for the interpretation. Remember, they are complicated, and all parts of the garage door need to be looked at before they can be put together to see the “whole.” When your vet does interpret them, don’t hesitate to stop the conversation if you are not following.

Have the vet use a pencil to point precisely on the image to what is being discussed. If you are unsure of what your vet is telling you, ask him or her to tell you in their opinion about the significance of the radiographic finding. The interpretation of radiographs is as much an art as it is a science because it is based not only on the technical findings, but also on the experience that the veterinarian has with similar past cases.

Finally, remember that nobody has a crystal ball. We do our best to help you make informed decisions based on what we see and what our experience and education have taught us. But never underestimate the horse in that the only thing predictable about them… is that they are unpredictable.