Subchondral lucencies of the medial femoral condyle in yearling and 2‐year‐old Thoroughbred sales horses: Prevalence, progression and associations with racing performance

Abstract

BackgroundSubchondral lucencies (SCLs) in the distal aspect of the medial femoral condyle (MFC) of young Thoroughbred horses are a source of controversy on presale radiographs. There is limited scientific evidence regarding the risk of progression and impact on future racing performance.ObjectivesTo (1) identify the prevalence of MFC SCLs on sales repository radiographs in yearling and 2‐year‐old Thoroughbreds; (2) identify any association between grade of MFC SCL and future racing performance and (3) monitor changes in MFC SCL grades between yearling and 2‐year‐old sales.Study designProspective cohort study.MethodsRadiographs were obtained with consignor permission from a 2016 yearling sale and five 2017 2‐year‐old sales. Stifle radiographs were evaluated and MFC SCLs graded on a scale of 0–3. Axial MFC lucencies were recorded separately. Maximum MFC grades per horse were analysed for associations with racing performance outcomes, adjusted for sex, to the end of the horses' 4‐year‐old racing year. Analysis was via logistic, negative binomial or linear regression as appropriate, with the threshold for significance set at α = 0.05.ResultsRadiographs from 2508 yearlings (5016 stifles) and 436 2‐year‐olds (872 stifles) were included in the study. MFC SCLs of grades 1–3 were observed in 242 (9.65%) yearlings and 49 (11.2%) 2‐year‐olds. Bilateral MFC SCLs of grades 1–3 were observed in 54 (2.2%) yearlings and 12 (2.8%) 2‐year‐olds. Grade 1 MFC SCLs in yearlings either remained unchanged (14/31), progressed to a grade 2 (6/31) or resolved (11/31) by the 2‐year‐old sale. Grade 2 MFC SCLs in yearlings remained unchanged (6/10), progressed to a grade 3 (2/10) or improved to a grade 1 (2/10). Yearlings with a grade 3 MFC SCL had a 78% probability of starting a race (95% confidence interval [CI] 58.2–89.6%), compared with an 84% probability of racing for grade 0 yearlings (95% CI 82.7–85.8%). Six of the seven yearlings with axial MFC lucencies raced.Main limitationsThis study may underestimate the prevalence of severe lesions in the general yearling population of U.S. Thoroughbreds. However, the convenience sample used is representative of the population of interest at sales. The study design could not address exclusions prior to sale.ConclusionsGrade 1 MFC SCLs are the most common type seen in yearling and 2‐year‐old sales horses. The majority of yearling grade 1 MFC SCLs resolved or remained static by 2‐year‐old sales. It was also possible for grade 2 and 3 MFC SCLs to improve one grade between sales. Fewer sales yearlings with a grade 3 MFC SCL raced, but in those that did race there was no evidence of worse performance compared to unaffected peers. Axial MFC lucencies did not affect racing performance.

Clinical insights: Outcomes of juvenile orthopaedic lesions

“…Overall, 85% of the yearlings raced with no statistical difference between any lucency grades (grade 0 being no lucency and grade 3 having an ovoid cystic lesion). 9 Grade 3 lucencies did have the lowest number of horses that ran, and authors highlighted this was still approximately 10% higher than published Jockey Club data. 6 This group echoed the unpredictability of the MFC lucencies; two thirds of grade 3 lesions improved by one grade and most grade 0-2 remained static.…”

“…6 This group echoed the unpredictability of the MFC lucencies; two thirds of grade 3 lesions improved by one grade and most grade 0-2 remained static. 9 These two studies indicate MFC lucencies seen on sales radiographs may have minimal effect on careers. The financial impact of decisions made at sales related to specific radiographic findings is large and so these data help support the industry.…”

Treatment Comparison for Medial Femoral Condyle Subchondral Cystic Lesions and Prognosis in Yearling Thoroughbred Racehorse Prospects

“…Subchondral cystic lesions (SCL) have a predilection for the medial femoral condyle, with a prevalence of 0.08-9.65% in Thoroughbred yearling repository radiographs, and account for 45.8% of SCL in all locations [1][2][3]. The etiology of SCL is not completely understood; however, trauma or osteochondrosis are likely implicated [4][5][6][7].…”