Computed tomography features of the fetlock joint in elite racing Thoroughbred horses

Computed tomography (CT) is increasingly used for metacarpo/tarsophalangeal or fetlock joint (MC/TPJ) evaluation in Thoroughbred racehorses. CT features and lesion prevalence in competing Thoroughbreds are unknown.

To identify standing CT features within the MC/TPJ of elite Thoroughbred staying racehorses.

Retrospective cohort study.

Computed tomography scans of the MC/TPJ were performed as part of pre-race screening for fracture risk and graded for CT features. Descriptive statistics and univariable logistic regression models were generated to investigate associations with presence of palmar osteochondral disease (POD), parasagittal groove subchondral lysis and fissure.

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, being present in 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 first scan. POD was associated with more career race starts (p = 0.05) but fewer placings per start (p = 0.008). Parasagittal groove (PSG) lysis, previously associated with condylar fracture, 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, which are not associated with fracture, 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. Osteoarthritis of the fetlock joint was uncommon.

Horses travelling from overseas had undergone prior screening of their fetlock joints, predominantly with MRI, likely reducing the prevalence of pathology in these horses.

POD is common in elite staying Thoroughbred racehorses, however, negatively impacts performance. The prevalence of PSG lysis supports the use of 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 generally to other racing Thoroughbreds.