Stifle Abnormalities in Cutting Horses: Not So Bad, Says Study (AAEP 2010)

Radiographs of a horse's limb joints are an important part of the pre-purchase examination for any performance prospect; the goal is to find any problems that might cause lameness down the road. However, it appears that in cutting horses at least, certain lesions seen on radiographs of the stifle joint just don't hurt a horse's performance as much as many have thought. Myra Barrett, DVM, MS, Dipl. ACVR, a clinical instructor in the radiology department at Colorado State University, discussed the results of a study examining sale repository radiographs and performance records of 432 yearling and 2-year-old cutting horses at the 2010 American Association of Equine Practitioners Convention, held Dec. 4-8 in Baltimore, Md.

Stifle Abnormality

This grade 4 abnormality in the stifle displays well defined lesion in the weight bearing portion of the MFC.

"Radiograph repository studies exist for Thoroughbreds, but results in Thoroughbreds aren't necessarily comparable to Quarter Horses," she began. "Different breeds and disciplines can have distinct orthopedic problems, and the stresses on the horses vary with individual Western performance disciplines."

The research team on this study examined the radiographic characteristics of 432 horses sold for cutting as yearlings and 2-year-olds, specifically focusing on the medial femoral condyle (inner joint surface at the lower end of the femur). Shape and quality of the condyle were graded from 0 (normal) to 4 (lucent lesion extending into the weight-bearing portion of the bone) for the medial femoral condyle (MFC) in each stifle joint on each horse.

The researchers also evaluated performance and earnings data on these horses through their 4-year-old years, and found that surprisingly, no grade of MFC defect significantly reduced performance or earnings. There was a trend between Grade 4 defects and a lower likelihood that the horse would compete, but it was not a statistically significant finding.

Researchers considered whether horses with more severe stifle lesions were weeded out for other uses than cutting, and perhaps this was why their lesions appeared to have no effect on performance. However, they found that only 25% of horses with more severe lesions were used for other purposes, "which seems to show they aren't just being used for other things," Barrett commented.

Interestingly, She reported that the published data in the convention proceedings were no longer accurate by the time of the convention, however. As the study continued, the size of the study group doubled and previously statistically significant findings of MFC defects affecting performance became insignificant.

"This shows how important it is to make sure we have enough horses in our studies, and carefully examine our own and other studies to make sure we have enough horses for significance," said Barrett.

Future study directions for this population might include evaluating lameness, not just performance data, as an outcome of MFC joint pathology.

"Flattening of the medial femoral condyle gets dinged a lot (in purchase evaluations); we know stifles get torn up in cutting horses, but often it's soft tissue damage," commented Wayne McIlwraith, BVSc, PhD, DSc, FRCVS, Dipl. ACVS, director of the Orthopaedic Research Center at Colorado State University and a co-author on the study, following the presentation. "We pretty easily excluded flattening as a knock on a horse (with this study). A lot of changes (bone lesions noted in the current study) are insignificant relative to what horses do to their stifles and injuries they acquire later."

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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