Computed tomography (CT) is increasingly used for evaluation of the fetlock joint in Thoroughbred racehorses.1 However, the CT features and prevalence of fetlock lesions in actively racing Thoroughbred racehorses is unknown.2 This study aimed to identify CT features present within the fetlock joint of an actively racing population of elite, staying Thoroughbred horses. CT features of the fetlock joint were graded and descriptive statistics and univariable logistic regression models were generated to investigate associations between CT features and performance variables.
A total of 406 limbs from 86 horses were scanned; 72 horses were scanned once, 12 horses were scanned twice, and two horses scanned three times. POD was common, present within 74/86 (86.0%, 95% CI 76.9-92.6%) horses and in 231/342 (67.5%, 95% CI 62.3-72.5%) limbs on the first scan. Increasing severity of medial condylar POD in the thoracic limb, and lateral condylar POD in the pelvic limb, was associated with fewer placings per start (thoracic limb P=0.01; pelvic limb P=0.04) and less prizemoney per start (thoracic limb P=0.009; pelvic limb P=0.02). Lysis within the parasagittal groove (PSG) was observed in 16/86 (18.6%; 95% CI 11.0-28.4%) horses and 20/342 (5.8%; 95% CI 3.6-8.9%) limbs on the first scan, whereas fissures in this region were observed in 41/86 (47.7%; 95% CI 36.8-58.7%) horses and 65/342 (19.0%; 95% CI 15.0-23.6%) limbs. CT features consistent with osteoarthritis of the fetlock joint were not commonly observed in this population.
These results demonstrate that POD is common in elite, staying Thoroughbred racehorses. However, increasing severity of POD is associated with poorer performance. The relatively high prevalence of PSG lysis, previously associated with condylar fracture,3 supports CT screening of high-risk populations of Thoroughbred racehorses in fracture risk management. Further work is required to determine if these findings are applicable more broadly to other racing Thoroughbred populations.