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Incidence of Radiographic Changes in Young Cutting Horses

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In a large population of young cutting horses there was a high prevalence of radiographic lesions, especially in the tarsi and stifles, on pre-sale survey radiographs. Notably, nearly 90% of the 458 included horses had at least one radiographic finding recorded. Changes in the medial femoral condyle (188/454, 41.4%) and osteophytes in the distal tarsus (201/438, 45.9%) were the most common findings.

Background

Radiographic repositories were first established at the Keeneland Thoroughbred yearling sales and due to the success, the National Cutting Horse Association (NCHA) followed suit at the 2005 NCHA Futurity Sales in Fort Worth, Texas. Studies of repository and survey radiographs have reported the prevalence of radiographic changes in various populations, most notably in Thoroughbreds1,2 and Standardbreds3-5. A veterinarian's role is to identify abnormal radiographic changes and correlate them to future performance1,6 which can be challenging without knowledge, or in the absence, of clinical signs6. This problem has been addressed in Thoroughbred and Standardbred populations by studies that correlate radiographic changes with performance7-10. There are no such published studies in Quarter Horses. The objective of this study was to quantify the radiographic changes in survey radiographs of yearling and 2-year-old Quarter Horses intended for cutting. This study has recently been published in the Equine Vet Journal and was done by Drs. Erin Contino, Richard Park and Wayne McIlwraith.

Materials and Methods

Digital radiographs of yearling and 2-year-old horses were obtained from the Western Bloodstock Radiograph Repository at NCHA sales between December 2005 and December 2006. Routine survey radiographs of yearling Quarter Horses foaled between 2003 and 2006 at a private cutting horse farm were also included. One view of each carpus, two views of each fetlock, four views of each tarsus, and two views of each stifle were evaluated. Following categorization of radiographic lesions, the frequency of each lesion was statistically analyzed by limb, by horse, and by age. The prevalence of radiographic lesions between yearlings and 2-year-olds was compared. 

Grading of the stifle: In the stifle, the medial femoral condyle (MFC) was classified as convex in contour (grade 0), flattened without evidence of subchondral bone changes (grade 1), a small defect or change in, without extension through, the subchondral bone (grade 2), a shallow, crescent shaped subchondral lucency that is confluent with the joint surface (grade 3) or a well-defined radiolucency in the middle of the MFC that communicates with the joint (grade 4) (Fig. 1). Abnormalities of the trochlear ridges, trochlear groove and patella were also recorded. 

Grading of the carpus, tarsus, and fetlocks: The carpus was evaluated for the presence of osteophytes, bony fragments, and fractures of the accessory carpal bone. The fetlocks were evaluated for the presence of bony fragments, radiographic evidence of osteochondritis dissecans, palmar/plantar supracondylar lysis, abnormalities of the proximal sesamoid bones, and thickening of the dorsal proximal cortical surface of the middle phalanx (P2). The tarsocrural joint was evaluated for changes of the medial malleolus, distal intermediate ridge of the tibia (DIRT), and the trochlear ridges. The distal tarsal joints were evaluated for radiographic signs consistent with osteoarthritis (OA) including osteophytes, lysis, sclerosis, joint space narrowing, and tarsal bone malformation.

Figure 1 (right) Caudocranial radiographic projections of the femorotibial joint were used to evaluate the medial femoral condyle (MFC). A: The contour of the MFC is flat (Grade 1). B: There is a small defect in, but not extending through, the subchondral bone of the MFC (Grade 2). C: A shallow dome shaped lucency is seen extending through the subchondral bone in the MFC (Grade 3). D: A well defined subchondral bone cyst that communicates with the articular surface is evident in the MFC (Grade 4). Reproduced with permission from Contino et al. (2011).
 

Results

The study included 8,857 radiographs of 3,900 joints in 458 horses (278 yearlings and 180 2-year-olds) of which 408 (89.1%) had at least one radiographic change recorded.

Stifle: Of the 454 horses with stifle radiographs, 202 (44.5%) had a radiographic change, the majority of which (188, 41.4%) were due to changes of the MFC. Of these, 98 (52.1%) were categorized as grade 1, 37 (19.7%) as grade 2, 30 (16%) as grade 3 and 23 (12.2%) as grade 4. The right MFC (157, 34.6%) was affected significantly more than the left MFC (128, 28.2%) (p<0.0001). Six (1.3%) horses had an osteophyte on the medial proximal tibia; all were 2-year-olds which was a significant difference when compared to yearlings (p=0.0033). Of the 433 horses in which evaluation of the femoropatellar joint was possible, 14 (3.2%) had radiographic changes that most commonly involved the lateral trochlear ridge.

Tarsus: Of 438 horses with tarsal films, 304 (69.4%) had at least one finding recorded, most of which were in the distal tarsus. There were 201 (45.9%) horses with osteophytes, 76 (17.3%) with lysis, 30 (6.8%) with malformation, 29 (6.6%) with sclerosis, and 11 (2.5%) with joint space narrowing in the distal tarsus. In the tarsocrural joint, 54 horses (12.3%) had flattening of the medial trochlear ridge and 59 (13.5%) had changes of the DIRT. Two-year-olds had significantly more changes in the DIRT compared to yearlings (p=0.0107).

Fetlocks and Carpus: In the hind fetlocks, 155 of 355 horses (43.7%) had at least one radiographic change recorded. Changes of sagittal ridge were recorded in 69 (19.4%) horses and thickening of the dorsal cortex of P2 affected 49 (13.8%) horses. Osteophytes of the dorsal proximal aspect of P2 were recorded in 43 (12.1%) horses and were significantly more common in 2-year-olds than yearlings (p=0.0004). The front fetlocks were evaluated in 361 horses of which 131 (36.3%) had radiographic changes. In 54 (15%) horses, changes of the sagittal ridge were recorded. Palmar supracondylar lysis affected 47 (13.1%) horses, most of which (36, 76.6%) were categorized as mild. Only 27 of 342 (7.9%) horses had changes in the carpus making it the least affected joint examined.

Discussion

There was a high prevalence of MFC changes in this population. A recent study of Thoroughbred yearlings found that MFC lesions had a negative impact on the sale of a horse but did not negatively impact performance11. Flattening of the MFC affected over 20% of the horses in the study. There have been few studies on the prevalence or clinical relevance of this finding and further research is warranted in Quarter Horses to determine the extent to which changes to the MFC, including flattening, affect future performance.

In the fetlocks there was a relatively high prevalence of palmar supracondylar lysis which has been shown to decrease the likelihood of Thoroughbreds to start a race7. Thus, it may be a lesion that proves to negatively affect performance cutting horses. Dorsal cortical thickening of P2 in hind limbs has not been reported in the literature and may be unique to cutting horses. Yearlings were affected as frequently as 2-year-olds suggesting it does not develop in response to training. Osteophytes of P2 were significantly more common in 2-year-olds compared to yearlings suggesting they may form to stabilize the pastern joint in response to the biomechanical stresses of training.

There was a high prevalence of horses with radiographic signs of tarsal OA however, radiographic OA is not a reliable indicator of lameness6. It was interesting that there was no significant difference between the age groups since OA advances with age12. This indicates that training and discipline are clearly not the only factors contributing to the high prevalence of radiographic tarsal OA in this population of horses. Osteophytes, when seen independent of other changes, may be incidental although in Thoroughbreds, they have been associated with fewer race starts7

This study establishes a baseline for what can be expected in the evaluation of pre-sale radiographs of young Quarter Horses. Work is ongoing to evaluate the clinical significance of these individual changes. This work was performed by Drs. Erin Contino, Richard Park, and Wayne McIlwraith.
 

Acknowledgements

This study was funded by the Colorado State University National Cutting Horses Association Stallion Auction Program with additional support from a Colorado State University Research and Scholarly Excellence grant. We wish to thank Jim and Carolyn Ware and Western Bloodstock for facilitating the availability of radiographs.

References

  1. Howard B.A., Embertson R.M., Rantanen N.W., et al. Survey of radiographic changes in Thoroughbred sales yearlings, in Proceedings. Am Assoc Equine Pract 1992;38:397-402.
  2. Kane A.J., McIlwraith C.W., Park R.D., et al. Radiographic changes in Thoroughbred yearlings. Part 2: Associations with racing performance. Equine Vet J 2003;35:366-374.
  3. Sandgren B. Bony fragments in the tarsocrural and metacarpo- or metatarsophalangeal joints in the Standardbred horse – a radiographic survey. Equine Vet J Suppl 1988;6:66-70.
  4. Alvarado A.F., Marcoux M., Breton L. The incidence of osteochondrosis in a Standardbred breeding farm in Quebec, in Proceedings. Am Assoc Equine Pract 1989;35:293-307.
  5. Grondahl A.M. The incidence of bony fragments and osteochondrosis in the metacarpo- and metatarsophalangeal joints of Standardbred trotters: A radiographic study. Equine Vet Sci 1992;12:81-85.
  6. Van Hoogmoed L.M., Snyder J.R., Thomas H.L., et al. Retrospective evaluation of equine pre-purchase examinations performed 1991-2000. Equine Vet J 2003;35:375-381.
  7. Kane A.J., Park R.D., McIlwraith C.W., et al. Radiographic changes in Thoroughbred yearlings. Part 1: Prevalence at the time of the yearling sales. Equine Vet J 2003;35:354-365.
  8. Laws E.G., Richardson D.W., Ross M.W., Moyer W. Racing performance of Standardbreds after conservative and surgical treatment for tarsocrural osteochondrosis. Equine Vet J 1993;25:199-202.
  9. Beard W.L., Bramlage L.R., Schneider R.K., Embertson R.M. Postoperative racing performance in Standardbreds and Thoroughbreds with osteochondrosis of the tarsocrural joint: 109 cases (1984-1990). J Am Vet Med Assoc 1994;204:1655-1659.
  10. Brehm W., Staecker W. Osteochondrosis (OCD) in the tarsocrural joint of Standardbred trotters- correlation between radiographic changes and racing performance, in Proceedings. Am Assoc Equine Pract 1999;45:164-166.
  11. Whitman J., Morehead J., Prichard M., et al. Radiographic lucencies in the medial femoral condyle of thoroughbred sale yearlings: A preliminary investigation of the effect on race records, in Proceedings. Am Assoc Equine Pract 2006;52:416-419.
  12. Axelsson M., Bjornsdottir S., Eksell P., et al. Risk factors associated with hindlimb lameness and degenerative joint disease in the distal tarsus of Icelandic horses. Equine Vet J 2001;33:84-90.
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