Orthopaedic Research Center, C. Wayne McIlwraith Translational Medicine Institute, Colorado State University, Fort Collins, Colorado, USA.
Matamata Veterinary Services, Matamata, New Zealand.
Equine Vet J. 2024 Jan;56(1):99-109. doi: 10.1111/evj.13945. Epub 2023 Jun 22.
Subchondral 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.
To (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.
Prospective cohort study.
Radiographs 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.
Radiographs 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.
This 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.
Grade 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.
在年轻的纯血马的股骨内侧髁远端（MFC）的软骨下透光区（SCLs）是在销售前的射线照片上存在争议的一个来源。关于进展的风险和对未来比赛表现的影响，科学证据有限。
（1）确定在周岁和 2 岁的纯血马销售库射线照片上 MFC SCL 的流行率；（2）确定 MFC SCL 等级与未来比赛表现之间的任何关联，（3）监测 MFC SCL 等级在周岁和 2 岁销售之间的变化。
前瞻性队列研究。
在 2016 年周岁马销售和 2017 年五个 2 岁马销售中，在获得寄售人许可的情况下获得了膝关节射线照片。对 MFC SCL 进行分级，评分为 0-3 级。单独记录了轴向 MFC 透光区。对每匹马的最大 MFC 等级进行分析，以评估其与比赛表现结果的关联，性别调整，直至马的 4 岁比赛年度结束。分析采用逻辑、负二项或线性回归，显著性阈值设为 α=0.05。
研究包括 2508 匹周岁马（5016 个膝关节）和 436 匹 2 岁马（872 个膝关节）的射线照片。在 242 匹周岁马（9.65%）和 49 匹 2 岁马（11.2%）中观察到 MFC SCL 为 1-3 级。在 54 匹周岁马（2.2%）和 12 匹 2 岁马（2.8%）中观察到双侧 MFC SCL 为 1-3 级。周岁马的 MFC SCL 1 级要么保持不变（31 例中的 14 例），要么进展为 2 级（31 例中的 6 例），要么在 2 岁马销售时缓解（31 例中的 11 例）。周岁马的 MFC SCL 2 级要么保持不变（10 例中的 6 例），要么进展为 3 级（10 例中的 2 例），要么改善为 1 级（10 例中的 2 例）。MFC SCL 3 级的周岁马开始比赛的概率为 78%（95%置信区间[CI]为 58.2%-89.6%），而 MFC SCL 0 级的周岁马比赛的概率为 84%（95%CI 为 82.7%-85.8%）。7 例有轴向 MFC 透光区的周岁马中有 6 例参加了比赛。
本研究可能低估了美国纯血马一般周岁马群中严重病变的流行率。然而，所使用的方便样本代表了销售中的感兴趣人群。研究设计无法解决销售前的排除问题。
1 级 MFC SCL 是周岁和 2 岁马销售中最常见的类型。大多数周岁马的 1 级 MFC SCL 在 2 岁马销售时缓解或保持不变。2 级和 3 级 MFC SCL 也有可能在销售之间提高一个等级。MFC SCL 3 级的销售周岁马参赛人数较少，但在参赛的马中，与未受影响的马相比，没有证据表明其比赛表现更差。轴向 MFC 透光区并不影响比赛表现。
