Radiological findings in the proximal sesamoid bones of yearling and 2-year-old Thoroughbred sales horses: Prevalence, progression and associations with racing performance.

Abstract: Radiological findings in the proximal sesamoid bones (sesamoids) are a persistent source of controversy at Thoroughbred sales, due to inconsistent classification and conflicting assignment of potential clinical importance. Objective: To define the prevalence of sesamoid findings on sales repository radiographs in yearling and 2-year-old Thoroughbreds and to analyse associations with racing performance. To track the changes in sesamoid findings between 1 and 2 years of age in horses that present for sale at both ages. Methods: Prospective cohort study using an enrolled sample. Methods: Horses were enrolled from a 2016 yearling sale and five 2017 2-year-old sales with consignor permission. Radiological findings relating to sesamoid vascular channel appearance, abaxial contour changes and sesamoid fragments were examined. Associations between sesamoid findings and racing performance from 2 to 4 years of age were examined using multivariate regression analyses. Clinical follow-up was sought to ascertain why horses that did not race never started. Results: A total of 2508 yearlings and 436 2-year-olds were included for evaluation. Interobserver agreement using the new grading system was substantial. Yearling findings associated with a significantly reduced probability of starting a race were: Grade 3 vascular channels in forelimb sesamoids (0.52, P < 0.001, 95% confidence interval (CI): 0.37-0.67), abaxial new bone in forelimb sesamoids (0.62, P = 0.01, 95% CI: 0.49-0.73), apical or abaxial fragments in forelimb sesamoids (0.55, P = 0.005, 95% CI: 0.37-0.72). For affected horses that did race, Grade 3 vascular channels in forelimb sesamoids were associated with fewer race starts (9.9 starts, P = 0.03, 95% CI: 8.0-12.2) and Grade 3 vascular channels in hindlimb sesamoids were associated with a delayed start to racing careers (54 days, P = 0.01, 95% CI: 20-89). Abaxial new bone in forelimb sesamoids was associated with a 54% reduction in total earnings (P = 0.003, 95% CI: 24-72) and a 46% reduction in earnings per start (P = 0.002, 95% CI: 21-64). Abaxial concavity occurred predominantly in yearling medial forelimb sesamoids, had no impact on racing performance and mostly resolved by 2-year-old sale. Conclusions: These findings are applicable to horses presented for sale at public auction and may underestimate the prevalence of severe lesions in non-sales horses. Conclusions: Grade 3 vascular channels, forelimb sesamoid abaxial new bone and forelimb sesamoid fragments are important findings in sales repository radiology. The new grading scale assigns a numerical grade for vascular channel appearance that matches the number of enlarged vascular channels evident in a given sesamoid. Abaxial contour changes, when present in sesamoids that are Grade 0 for enlarged vascular channels, are noted separately as either abaxial new bone or abaxial concavity. Fragments are also noted and interpreted separately. 背景:近端籽骨(近籽骨)的放射学检查结果一直是纯血马销售中争议的热点，原因由于分类不一致，以及潜在临床重要性的指标冲突， 目的:确定周岁驹和两岁纯血马买前检查X线片中，近籽骨病变发现的普遍程度，并分析其与比赛成绩的关联。追踪周岁至两岁出售的纯血马的籽骨变化。 研究设计:对登记样本进行前瞻性队列研究。 方法:经委托方许可，从 1个2016 年周岁马拍卖会和 5个2017 年两岁马拍卖会上招募马匹。检查了与近籽骨血管通道形态、远轴轮廓变化和近籽骨碎片相关的放射学结果。使用多元回归分析检查籽骨发现与其两岁至四岁比赛表现之间的关联。临床随访，以确定未出赛马匹的情况。 结果:2508 匹周岁驹和 436匹两岁马被纳入评估。经过兽医的一致意见使用新的评分系统。周岁驹中，与参加比赛的概率显著降低相关的发现为:前肢近籽骨中的 3 级血管通道(0.52，P<0.001，95% 置信区间 (CI) 0.37-0.67)，前肢近籽骨中的远轴新骨生成(0.62，P=0.01，95% CI 0.49-0.73)，前肢近籽骨中的顶端或远轴碎片(0.55，P=0.005，95% CI 0.37-0.72)。对于参加比赛的受影响马匹中，前肢近籽骨中的 3 级血管通道与生涯出赛次数减少相关(9.9 次出赛，P=0.03，95% CI 8.0-12.2)，后肢近籽骨中的 3 级血管通道与延迟初赛相关。(54 天，P=0.01，95% CI 20-89)。前肢近籽骨的远轴新骨可能导致总奖金减少 54%(P=0.003，95% CI 24-72)，以及每次出赛奖金收入减少 46%(P=0.002，95% CI 21-64)。远轴面凹陷主要发生在周岁驹前肢内侧近籽骨中，对比赛表现没有影响，大部分在两岁时改善。 主要局限性:这些发现适用于公开拍卖出售的马匹，可能低估了非出售马匹中严重病变的患病率。 结论:3级血管通道、前肢近籽骨远轴新骨生成和前肢近籽骨碎片是买前检查放射学中的重要发现。新的指标为血管通道形态指定了数字等级，与该近籽骨中明显扩大的血管通道的数量相匹配。当近籽骨血管通道 为0 级时，远轴轮廓变化独立记录为远轴新骨或远轴凹面。碎片也被单独注释和解释。.