15/08/2020
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Radiographs and the Pre-purchase Evaluation
Brian S. Burks DVM, Dipl. ABVP
Board-Certified in Equine Practice
Radiographic studies (x-rays) have become an integral part of the equine pre-purchase evaluation, and many apparently normal, sound horses undergo a pre-purchase examination prior to sale. Potential horse buyers commonly request, and veterinarians often recommend, radiographs as part of the veterinary inspection process. Commonly chosen areas include the front feet, stifles, hocks, fetlocks, or carpi, depending upon the breed. The purpose of the pre-purchase examination is to determine if the horse is suitable for the intended purpose, which can be easier said than done.
Many horses have “failed” examination based on radiographic findings, such as bone spurs in the hocks or enlarged synovial invaginations in the navicular bones. But have you ever wondered exactly what information radiographic studies provide the horse buyer?
Radiographs reveal only one small part of the whole picture. This imaging modality provides 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, problems that affect tissues such as tendons, ligaments, muscles, synovial membranes, etc. cannot be evaluated effectively. Therefore, a normal radiographic study cannot identify abnormal soft tissues.
The true source of pain and lameness (i.e. inflammation) is radiographically invisible- inflammatory cells cannot be visualized with radiographs. What we can see is the damage inflammation has on bony structures; 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, the two most commonly requested areas to be radiographed during a pre-purchase exam.
Stress-caused damage detectable on radiographs includes:
1. Increased bone density (sclerosis), which appears whiter on radiographs than normal bone.
2. Remodeling changes, particularly around joint margins. These can represent either adaptive changes, which are necessary to strengthen bone, or maladaptive changes (harmful ones such as bone bruising). A proportion of horses with maladaptive changes might either be lame at the time of examination or at risk of developing lameness.
It is not to say that radiographic examination does not provide valuable information and that taking radiographs 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 radiographic study- especially when assessing low-motion areas.
It is important to understand that breed differences can affect radiographic findings, whether the horse is lame or sound. Warmbloods and draft horses may have bone remodeling around the pastern joint, which should not be confused with osteoarthritis. They can also have modeling of the bony attachments of the collateral ligaments of the distal interphalangeal (coffin) joint. This would be cause for concern in a light breed horse.
Degenerative changes such as sidebone or chips off of the navicular bone might be apparent, but they have little to do with age. There may also be degenerative, age-related remodeling of the distal phalanx and navicular bones.
All radiographic findings should be interpreted in light of complete clinical and lameness examinations. The exam should consider foot shape, overall conformation, and hoof quality. The lameness exam will render clues as to which limb or limbs and to which part of the limb is involved. When a horse with navicular disease has a PD nerve block placed in the lame limb, the lameness will switch sides. Small changes can be present that indicate a number of things, but when correlated with hoof tester, flexion, palpation, and motion findings, those changes may be more problematic.
Fox Run Equine Center recommends pre-purchase radiographic evaluation under the following conditions:
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 five 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 accurately assess pathologic conditions in bone and joints through the process of image comparison. By taking images at the time of purchase, we assure ourselves 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 dissecans (OCD). Since many OCD lesions are subclinical (i.e. do not result in swelling or lameness), the veterinarian may not be able to detect their presence based on clinical evaluation alone. In these cases, radiographic examination is indicated to determine if such lesions exist. Since DOD lesions can eventually become clinically apparent (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, two-three most commonly affected areas are chosen to radiograph.
3. If inflammation is evident in a high-motion joint.
There is much better correlation between clinical and radiographic impressions of high motion 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 is important to the client.
Abnormal radiographic studies have and will continue to adversely affect the sale of horses. Even though not every radiographic abnormality means poor performance and not all radiographic normality 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 a radiographic study provide a lot of information... we just need to be careful how we interpret the information.
Fox Run Equine Center
www.foxrunequine.com
(724) 727-3481
Your horse's health is always our top priority.
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