Post-mortem computed tomography features associated with fracture of the fetlock joint in racing Thoroughbreds.

Background: Post-mortem studies have shown that fractures involving the metacarpophalangeal/metatarsophalangeal or fetlock joint are associated with focal areas of microdamage. Identification of computed tomography (CT) features consistent with microdamage and their association with fracture may aid in identification of horses at risk of fracture.

Objectives: To identify CT features associated with fracture of the metacarpophalangeal/metatarsophalangeal joint.

Study design: Retrospective cohort study.

Methods: Post-mortem CT images of 367 limbs from 157 Thoroughbred racehorses were graded for CT features. Multivariable logistic regression models were generated. Intraclass correlation coefficients of key CT features to assess intra and inter-rater reliability were calculated.

Results: The presence of lysis within the subchondral/trabecular bone underlying the lateral and, or, medial parasagittal groove (PSG) of the distal third metacarpus/tarsus (odds ratio [OR] 9.6; 95% confidence interval [CI] 4.3-21.3; p < 0.001) and sclerosis of the palmar subchondral and trabecular bone underlying the lateral and medial PSG that projected proximoaxially (OR 4.6; 95% CI 1.1-19.02; p = 0.03) were associated with condylar fracture. The presence of a proximal sesamoid bone (PSB) lytic lesion (OR 5.3; 95% CI 1.2-23.6; p = 0.03) and increasing medial PSB density (OR 1.02; 95% CI 1.00-1.03; p < 0.001) were associated with PSB fracture. Palmar osteochondral disease grade was not associated with condylar (p = 0.8) or PSB fracture (p = 0.09). Inter rater reliability was moderate for the presence of PSG lysis (ICC 0.7; 95% CI 0.6-0.8) and shape of sclerosis in the lateral condyle (ICC 0.6; 95% CI 0.5-0.8).

Main limitations: The extent of lysis within the PSG and the volume of the PSB could not be as accurately obtained in limbs with multiple fracture fragments.

Conclusions: CT examination of fetlock joints post-mortem identified changes associated with both metacarpal condylar fracture and PSB fracture in racehorses. These findings show that pre-race CT screening has the potential to reduce fracture rates.