By Matt Randall, DVM

navicular webRadiography is the most common imaging modality used in veterinary medicine, second only to visual inspection of the animal. While “x-rays” allow us to see within a horse’s body, they don’t always tell the entire story. Here’s a short sampling of what radiographs can and cannot tell you.

While radiographs are primarily used to look at bone, or calcified structures within the horse’s body (like enthroliths in the case of colic), you do get a little information on the soft tissue structures. Some of the soft tissue problems that might appear on x-ray include effusion, enthesiopathy and soft tissue swelling.

Effusion is the presence fluid. For example, you might see “bulges” on an x-ray of a coffin joint that may indicate effusion. Enthesophathy is a disorder of an attachment sight of a ligament or tendon. For instance, where the suspensory ligament ties into the sesamoid bone, a roughening or fractured-appearance at the attachment is an enthesiophathy. Swelling is generally visible as “gray areas” or shadowing on x-ray.

However, radiographs are generally limited when it comes to diagnosing straight soft tissue injuries. For instance, the horse with navicular symptoms that x-rays clean but still nerve blocks sound to the heel may have more complex soft tissues injuries within the hoof capsule.

Also, radiographs aren’t infallible when it comes to diagnosing fractures. It takes the perfect angle to see a non-displaced or hairline fracture. You also can’t see bone contusions (bruises).

Some areas are just difficult to get proper imaging. Most areas above the distal limbs, i.e. legs, become very challenging. With shoulders and stifles, you’re limited in the images you can take because the rest of the horse gets in the way. The head and neck can be challenging because there are so many curves and folds that it creates a lot of artifacts—basically something on the x-ray that’s not real.

Here’s an example of an artifact. When shooting navicular x-rays, if you don’t pack the play dough into the crease between the frog and the sole of the hoof very well, the air trapped in there will appear as fracture line right through the navicular bone.

Another down side to x-rays is that you usually need multiple angles to make a proper diagnosis, as a single shot may not tell you the whole story. This is one of the big benefits of digital radiographer over traditional film x-rays. With digital, the image is instantaneous so you know if you need a better shot or more images right away.

A last word of caution on x-rays: it used to be common practice to delay treatment of joint pain in the absence of changes on radiographs. Veterinarians have learned through the growth of the sports medicine field that the trick is to prevent those boney changes from ever appearing. By the time you see the spurs or decreases in joint space, you’re already late to the party. The damage has already occurred. It’s far easier to prolong a horse’s athletic career through pro-active maintenance than to repeatedly patching up an advancing case of osteoarthritis.

Next time, we’ll discuss one of my favorite modalities—ultrasound.

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