Answers not always black and white with radiographic changes

Veterinarians are commonly asked to evaluate horses for their clients and these "prepurchase" examinations often include radiographs.

A study completed by leading equine researchers and the Equine Orthopedic Research Laboratory at Colorado State has shed some light on radiographic changes in Thoroughbred yearlings and correlated those changes to future athletic performance.

When the horse in question is young and has not been trained, raced or ridden extensively, then radiographic changes can be very difficult to interpret. There may be no clinical history and there is usually very little performance history, so the veterinarian must decide if the changes, usually subtle, seen in his/her films are significant.

Basis for decision

But what is this decision usually based on? Certainly past experience is important, but many times even this does not allow for more than an "educated guess." Guess wrong, and say that the lucency that you see on this horse's films may indicate future problems and your client passes on a great horse, or worse, ends up getting beat by this horse in some future event.

Guess wrong, and say that the small fragment in that joint is not of concern, and your client buys a horse that becomes lame, may need future surgery or may never be a functional athlete. All in all, it is not a good position to be in and with the increasingly litigious nature of the profession, many veterinarians find themselves less and less willing to evaluate young horses.

Clients thinking about a horse for purchase often look to their veterinarian for help in evaluating radiographs. Information that can help predict the relevance of X-ray changes will make such decisions easier.

Drs. Kane, McIIwraith, Park, Rantanen, Morehead and Bramlage may have provided a bit more information for veterinarians who find themselves in this situation.

These researchers, along with the Equine Orthopedic Research Laboratory at Colorado State University, have completed a study that looked at radiographic changes in Thoroughbred yearlings and then tried to correlate those changes to future athletic performance.

Large sample

This study took place over three years and looked at 1,200 horses. Because the evaluation of yearling Thoroughbreds occurs each year at specific sales, this was a natural population to use for such a study.

Positive future athletic performance proved a bit harder to define and quantify but, for these Thoroughbred yearlings, the ability of a horse to complete training and to actually start a race was taken as success.

The authors readily admit that this study may not be easily applied to the future success of horses used for different disciplines because the stresses of racing are different from those of many other sports. It is the first such study of this scope however, and much information can be learned that applies directly to racehorses, and indirectly to other equine athletes. This study was jointly funded by the Keeneland Association, the Fasig-Tipton Sales Company, the Ocala Breeder Sales Company, the AAEP, Barrett Equine Limited, the Jockey Club, and the Blood Horse Charitable Foundation.

Other attempts

Many other researchers have attempted to look for normal variations in radiographs in horses.

This study goes a step further by evaluation films, following these yearlings through their 3-year-old year and looking at their performance. A questionnaire was also sent to the owners of these yearlings and information on training progress, problems and surgical intervention was obtained. The results of the study hopefully give the practitioner some "black and white" information as to the significance or lack of significance of certain abnormalities seen in the radiographs of thoroughbred yearlings.

As Dr. Al Kane stated, "One of the purposes of this study was to perhaps re-introduce the concept of 'incidental findings' ". Not all changes are significant and knowing which are and which are not can make all the difference.

This series of films contain minor changes of little significance to the athletic function of this horse. Other minor changes in different locations, however, can be "red flags" and may mean a future of poor performance, possible surgery or lameness.

The most commonly affect area in these horses was the front fetlock. Abnormalities consisted of flat areas (51 percent) on the distal articular surface or lucencies (17 percent) in the same area. Moderate to extreme palmar supracondylar lysis was also noted in some horses and this finding was significantly associated with lowered racing performance. These horses were one third less likely to start. Flat areas or light areas in the bone (lucencies) associated with the saggital ridge of the distal cannon bone did not correlate to decreased racing performance or other medical problems. Enthesophytes or areas of roughening on specific bones can be one of the more common incidental findings. Such areas on the front of the proximal sesamoid bones were related to problems and these yearlings were one third less likely to start a race.

Vascular channels in these bones, however, were not associated with problems and 98 percent of yearlings had at least one channel while 58 percent had more than two.

Hind fetlock

The hind fetlock was the second most affected area and fragments of the proximal phalynx were more common behind than in front.

Horses with these hind fetlock fragments were half as likely to start a race and 50 percent needed surgical correction. Fragments and lucencies of the dorsal aspect of distal metacarpal III were the most common problems. Remember that these were yearling sale radiographs. These horses were not expected to have significant incidences of trauma or excessive wear and tear. It may be beneficial; therefore, to more closely examine the hind fetlock joints in young horses at prepurchase examinations based on the findings of this study. Supracondylar lysis, while very common in the front fetlocks, was not found in the hind limb.

As expected, changes in the carpas were important to the ability of these horses to run and abnormalities of the intercarpal bones resulted in a one-third less likely chance of starting.

The change related to rounding of the edges of the radial carpal bone, thickening of the cortex of the radial carpal bone and proliferative changes on the radial carpal or third carpal bones. Circular lucencies, however, were not associated with any problems. Carpal fragments or osteophytes were significantly correlated with problems in 75 percent of affected horses and 50 percent of these horses required surgery.

Stifle problems

The incidence of stifle problems was low with only four of 660 horses having flattened areas on the lateral trochlear ridge of the femur. These flat areas were not related to any problems in this study. Thirty four of these 660 had defects or fragments in this area and 40 percent required surgery.

Eleven percent of the study horses had pedal osteoitis, 18 horses had navicular changes, 15 had fragments of the palmar process of PIII, and seven had lucencies or cysts in PIII. None of these changes were correlated with problems in this study.

This study now provides the veterinarian with some specific information to aid in the interpretation of radiographs of young horses, especially thoroughbreds.

It would be interesting to see similar studies done with Warmbloods or performance Quarter horses or other breeds. Perhaps specific problems and areas of concern could be identified in these breeds as well. The tendencies noted in this study can be beneficial to all veterinarians however, and some simple take-home lessons are available.

Take-home lessons

Horses with fragments in various joints did not do well in training and many had problems. Many of these animals needed surgery, but these horses were expected to start races at levels comparable to horses without such problems. This indicates that if horses with joint fragments are identified early and surgery is done before those joints are severely damaged, then they can indeed have acceptable athletic careers.

Hind fetlocks should be more carefully evaluated in the young horse. Not all radiographic changes are important and, perhaps most significantly, an experienced veterinarian still matters. Kane summarizes this report by stating, "It is best to apply these analytical results in parallel with your clinical impressions." Perhaps that "educated guess" is not so bad after all, especially if it becomes more education and less guesswork.