Radiographic studies (x-rays) have become an integral part of the equine prepurchase evaluation. Potential horse buyers commonly request x-rays as part of the veterinary inspection process. And, as you know, many horses have “failed” examination based on radiographic findings, such as bone spurs in the hocks or enlarged channels in the navicular bones. But have you ever wondered exactly what information radiographic studies provide the horse buyer?

First of all, we must realize that radiographs (x-rays) reveal only one small part of the whole picture. Radiographs provide structural information; in other words, they tell us what things look like. More specifically, they tell us what bone looks like. Since soft tissues all have a similar density on x-ray film, we often don’t get a lot of insight into problems that effect tissues such as tendons, ligaments, muscles, synovial membranes, etc. Therefore, a normal radiographic study doesn’t confirm normal/ healthy soft tissues.

Secondly (and more importantly), the true source of pain and lameness (i.e. inflammation) is radio- graphically invisible. In other words, we can’t “see” inflammatory cells on x-ray film. What we can see are potential effects that inflammation may or may not have on associated bony structures. Therefore, the normal radiographic appearance of bone does not confirm the absence of active inflammation. Likewise, the abnormal appearance of bone does not always confirm the presence of active inflammation.

This is especially true in low-motion areas, such as the distal tarsal (hock) joints and the navicular region. Ironically, most horse buyers request radiographic studies of these two areas before anything else!

It is not to say that radiographic examination does not provide the veterinarian with valu- able information and that taking x-rays is a waste of time. It is very important to know what bone looks like, especially in suspect areas. However, since there is poor correlation between what is observed radiographically (i.e. what the tissue looks like) and what is observed clinically (i.e. what tissue acts like), the veterinary examiner must be careful during interpretation of the x-ray study (especially when assessing low-motion areas).

It is not uncommon the hear of a sound horse “failing” a prepurchase exam due to abnormal radiographic findings, only to watch it per- form beautifully for years to come. Likewise, it is not uncommon to hear of a lame horse “passing” prepurchase examination due to normal radiographic findings, only to watch the new owner invest a lot of time and money in trying to diagnose and treat the lameness.

Admittedly, veterinarians tend to be hesitant to make recommendations that conflict with radiographic findings, especially if they are abnormal. This is undoubtedly one of the repercussions of our current legal system. However, it is very important that the horse buyer understand exactly what information is contained within the radiographic study so as not to disregard the veterinarian’s clinical impression.

In our opinion, the horse buyer should have specific reason(s) for requesting radiographic examination of a horse, rather than just to see what “shows up”.

The Atlanta Equine Clinic recommends prepurchase radiographic evaluation under the following circumstances:

1. If the client wants “baseline” studies that will allow for future radiographic comparison of certain areas.
   If a horse develops lameness, for example, as a result of a sore joint 5 years after purchase, it would be nice to know what osseous (bony) changes have occurred in that joint since the time of purchase. Veterinarians can more accurate- ly assess pathologic conditions in bone and joints through the process of image comparison. By taking images at the time of purchase, we are assuring our- selves the luxury of comparative interpretation in the case that a future problem arises. This is better, of course, than passing judgment on a lesion based on a single radiographic study.
   
2. If developmental orthopedic disease (DOD), such as osteochondrosis, is suspected.
   In young horses particularly, there is often concern that a manifestation of DOD is present. The most common manifestation of DOD is osteochondritis dis- secans (OCD). Since many OCD lesions are subclinical (i.e. do not result in swelling or lameness), the veterin- arian may not be able to detect their presence based on clinical evaluation alone. In these cases, radiographic examination would be indicated to determine if such lesions exist. This is sometimes referred to as an “OCD hunt”, since there is often no preconceived notion as to what might show up. Since DOD lesions can eventually become clinically apparent (i.e. eventually cause lameness), their radiographic presence may be considered significant in regard to future performance of the animal. Exactly how the lesion(s) might affect future performance depends on their type, size, and location. It is important to realize that the only way to confirm that there is no evidence of DOD is to radiograph every joint in the horse’s body. Since this is generally not practical, the veterinarian usually selects the 2-3 most commonly affected areas to study.
   
3. If clinical evidence of inflammation is evident in a high-motion joint.
   There is much better correlation between clin- ical and radiographic impressions of high mo- tion versus low-motion joints. Therefore, the presence of radiographic lesions in high- motion joints can provide us with invaluable information concerning both the degree and duration of a problem. One could accurately predict, for example, that if significant bony abnormalities are visible radiographically in a high-motion joint (such as the fetlock joint), that there will likely also be some clinical abnormality (such as a positive flexion test). This is not always the case with lower-motion areas, such as the distal tarsal (hock) joints.
   
4. If resale value of the animal is important to the client.
   As most of us know, ugly x-ray studies have and will continue to adversely affect the sale of horses. Even though we’ve determined that not all radiographic abnormality means poor performance and not all radiographic normal- ity means good performance, knowing what specific joints look like might be important when it comes time to sell the horse. Just remember, the results of an x-ray study provide a lot of information... we just need to be careful how we interpret the information.