It’s a story we’ve all heard. A new horse is found; he suits the rider, has a track record of competitive success and has passed the five-stage veterinary pre-purchase exam (PPE). All that remains is to run some optional radiographs (X-rays) to check nothing is amiss.
All too often, this is the step that ends the process. Perhaps there is evidence of osteoarthritis in a fetlock, a developmental abnormality or kissing spines. Whatever the issue, the findings are enough to cast doubt on the future soundness of the horse. The sale is off.
This sounds black and white, but is it really that simple? Surely the horse either has a problem, or he doesn’t?
The reality is that there is a poor association between radiographic changes — sometimes termed X-ray findings — and the clinical signs that a vet may identify upon examination.
What this means in practice is that a proportion of horses performing well can be expected to have radiographic changes. These changes could even be moderately severe, and have perhaps been present for a considerable period of time.
This fact is the basis of the veterinary approach to the lame horse. Methodical examination, where the lame leg is subject to nerve blocks, is the only accurate means of localising the site of lameness. An owner may request that we simply X-ray, yet a diagnosis based on radiographic findings alone may well be wrong and can lead to unnecessary and perhaps detrimental treatment.
The take-home message is that there are horses working from the lowest to the highest levels with a range of radiographic abnormalities that are of no significance — and do not result in lameness.
So why would we X-ray an apparently sound horse?
Breed societies, insurance companies or individual purchasers may ask for different areas of the horse to be imaged, or for a range of radiographic projections of the same area but from different angles.
The more images obtained, the larger the cost to the client and the greater the dose of radiation for the veterinary personnel — the risk to the horse is minimal, as most horses are only radiographed occasionally in their lifetime.
With a lame horse, a series of projections of the affected area is obtained, based on evidence from scientific study, so that the entire region can be reviewed. Pre-purchase radiographs are typically fewer in number, further complicating the interpretation of any abnormalities.
It is often noted that more emphasis is placed on radiographic changes found in horses due to be exported to other parts of Europe or North America. This may be because the risk is perceived to be higher, as the horse is less likely to have been viewed and the purchaser may not know the examining vet. Changes to the dorsal spinous processes seem to be of particular concern to some American purchasers.
Pre-purchase radiographs may reveal radiographic changes that are very important and have a high probability of resulting in lameness in the immediate or distant future. When interpreting these images, it is useful to correlate findings to the clinical exam.
Consider, too, the horse’s work history, his current activity and his intended use, as certain equestrian disciplines can be more — or less — forgiving of a particular radiographic abnormality.
In some cases, the same radiographic findings may cause lameness in one horse but not another. The developmental disease osteochondrosis, for example, causes the formation of bone and cartilage fragments within a joint in early life. These fragments can stick to the joint surface and remain clinically silent, causing no issues, but may lead to effusion (joint swelling) that ultimately results in arthritis and lameness.
If a horse has been in work for some time and has no clinical signs, the view of most specialists would be that the fragments are of little significance and do not merit removal.
We are often asked to remove a fragment from a joint because of the potential for arthritic change and future lameness, despite the horse being sound and performing effectively.
There is a risk in these cases of treating the image, rather than the horse. Inevitably, the client wants a “clean X-ray” that will enhance the horse’s resale potential and value.
The veterinary world now operates a system of evidence-based medicine, where intervention and treatment are based on the results of rigorous scientific study involving large numbers of animals affected with the same problem.
This system is gradually being applied to our interpretation of X-rays. The ideal would be to study 2,000 horses, each sold with a 3mm bone chip in the front of a fetlock joint as a result of the developmental disease osteochondritis dissecans (OCD), as they enter training and throughout their careers.
If it is found that none, or very few, of these horses suffer lameness that can be localised to that joint, then it could be concluded that such developmental abnormalities are unlikely to be a significant cause of lameness.
If, on the other hand, a large proportion go on to develop arthritis of the fetlock, the opposite may be true — and evidence would support the removal of these chip fragments early in life.
The bigger picture
Any discussion on the merits of pre-purchase radiography inevitably generates more questions than answers.
Is there a value to obtaining radiographs before buying? In many cases, yes, because important abnormalities may be identified. It is important to appreciate, however, that some of the potential changes identified will have been present for a long time and carry little or no risk for the development of lameness in the future. Equally, perfect radiographs are no guarantee of future soundness.
Consider any radiographic changes alongside the results of the vetting procedure and take into account the horse’s competition record, his current level of work and what you plan to do with him. Remember that X-ray findings form just part of the picture — and that ultimately you are buying a horse, not a set of radiographs.
Ref Horse & Hound; 29 August 2019