Subchondral lucencies of the medial femoral condyle-What does it means for racing?

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

Frances J. Peat, Christopher E. Kawcak, C. Wayne McIlwraith, David P. Keenan, Jeffrey T. Berk, Daniel S. Mork

Background
Subchondral lucencies (SCLs) of the medial femoral condyle (MFC) in young Thoroughbred horses can appear on presale radiographs, raising concerns about their progression and impact on future racing performance. This study aimed to determine the prevalence and natural history of MFC SCLs and assess their associations with racing outcomes.

Methods
A prospective cohort study was conducted using radiographs from 2508 yearlings at the 2016 Keeneland September Yearling Sale and 436 2-year-olds from subsequent 2017 sales. Radiological findings were graded (0–3) based on severity, and changes between yearling and 2-year-old sales were tracked. Racing performance was measured using data up to the end of the horses' 4-year-old season, analyzing variables like race starts, earnings, and performance caliber.

Results
Prevalence: MFC SCLs (grades 1–3) were present in 9.65% of yearlings and 11.2% of 2-year-olds.

Progression:
-Grade 1 SCLs mostly remained static (45.2%) or resolved (35.5%) by 2 years.
-Some Grade 2 SCLs improved (20%), while others remained static (60%) or progressed to Grade 3 (20%).
-Grade 3 SCLs either improved (66%) or remained unchanged (33%).

Impact on Racing:
-Yearlings with Grade 3 SCLs had a slightly lower probability of starting at least one race (78%) compared to those with Grade 0 SCLs (84%), but this difference was not statistically significant.
-There was no significant association between MFC grade and the number of starts, earnings, or career-best performance.
-Axial MFC lucencies (present in 0.3% of yearlings) did not negatively affect racing performance.

Limitations
The study relied on sales horses, which may underrepresent severe lesions in the general Thoroughbred population.
Potential confounding factors, such as clinical interventions between sales, could not be fully controlled.

Conclusions
MFC SCLs are relatively common in sales Thoroughbreds but rarely progress or significantly affect racing performance. Grade 1 lesions frequently resolve or stabilize, while Grade 3 lesions may slightly reduce the likelihood of racing. Axial lucencies were not associated with performance deficits. These findings provide valuable guidance for assessing radiographic findings in sales horses

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