Radiographs at the Sales: Know Your Subjectivity
Full disclosure: For the last dozen years, I have spent about three weeks annually reading radiographs for buyers at public sales. My goal is to provide buyers with part of the information they use to decide whether to purchase a horse and how much to pay.
Since the beginning of the sale radiograph repository, reports describing radiographic abnormalities have been generated by the veterinarian taking the radiographs for the consignor. The original purpose of the report was to make consignors aware of any abnormalities on the images before potential buyers or their agents reviewed them. Despite disclaimers written on most reports that the information is for the consignor only, it has become common practice for the reports to be used by consignors as a marketing tool. This practice has resulted in pressure on veterinarians taking repository films to generate as ‘clean’ a report as possible. Because there is considerable latitude in how abnormalities are described (more on this in a bit), some consignors’ reports may not contain all the information a buyer wants or needs.
The utility of a report describing radiographic images in the repository is dependent on several factors. First, image quality: this has improved substantially in the last 10 years partially due to the shift to digital imaging; however, poor positioning, motion and exposure errors still result in the occasional non-diagnostic image. This can result in the need to take additional images. Secondly, radiographic interpretation is largely subjective. Some findings are objective, such as yes/no as to whether there is a chip. But most of what we describe is categorical (responses are given names, not numbers). An example is: Do I describe this as sesamoiditis? And is it mild, moderate or severe?
Finally, additional subjectivity is added by the interpretation of the significance of an abnormality: yes/no/maybe it will bother the horse. The significance of an abnormality with respect to athletic performance is largely determined by a readers’ experience, and is an opinion. Very nice horses can and do perform well with abnormalities (sometimes with treatment, sometimes without) and perfect radiographs don’t make a fast horse. What a good reader will tell you is their experience with this finding in training and racing horses, and you decide if you can live with that risk.
Consistency between evaluators of many kinds of clinical data has been studied extensively – often in regards to imaging. Most assign a value of “almost perfect agreement” when evaluators assign the same grade or score more than 81% of the time. Substantial agreement is considered to exist if readers agree 61-80% of the time. So, you can disagree on the interpretation 39% of the time and be considered to have substantial agreement. This is not to scare the hell out of you over what your radiologist is saying, but to illustrate how frequent differences of opinion occur when reviewing images. Lack of agreement is part of the process.
Keeneland has this right when they say “veterinarians can, and do, disagree.” Additionally, people make honest errors. On busy days I can read over 1,000 separate images, sometimes under serious time pressure. Can I make a mistake? You betcha. Hopefully, it’s not one that will materially affect a horse’s value or performance.
This past year, to allow comparisons between reports from buyers’ readers and consignor reports, those reports were placed in the repository. When I found what I considered to be an abnormality of a magnitude to exclude a horse from purchase, I checked the consignors’ report. In each case, some finding was mentioned. However, the description was always far less critical than mine, and of course did not include an interpretation of significance. Other veterinarians have told me their agreement with consignor reports is worse, with the “softer” report always being the consignor’s.
This suggests that buyers that rely on consignor-generated reports will sometimes not get a complete evaluation of the radiographs. It has been suggested that consignor reports should be excluded from the back walking ring or from the sales grounds. That would be fine, but I don’t see how enforcement would work, and what would the penalty be? In a perfect world, veterinarians taking the radiographs would be free to write a comprehensive radiographic report for the consignor, who would use it to determine fitness for sale and influence the reserve price. However, buyers would still not get any personalized report considering their intended use of the horse or their risk tolerance.
The amount of information the consignor (especially if they raised the horse) and the buyer have about an auction horse is asymmetric; the buyer knows far less about the horse than the seller. Radiographs attempt to provide buyers with a little more information about a potential purchase. Due to the subjectivity in both the reading and the interpretation of radiographic abnormalities to performance, buyers are best served by getting an objective reader to evaluate the images rather than relying on consignor information, and there are many very experienced and knowledgeable veterinarians to choose from. Let whomever you choose know what your intended use of the horse is, and how comfortable you are with risk. Getting your own radiographic interpretation of repository films is important to getting the best information possible before deciding to bid on a horse.
Dr. Santschi is Clinical Associate Professor of Equine Surgery at The Ohio State University. She trained at Peterson and Smith Equine Hospital in Ocala, Fla., is board certified, and has been a surgeon for 25 years. Her interests include orthopedic conditions of young racing stock, and she has been a consulting veterinarian at Equine Medical Associates in Lexington, KY for 12 years.