Condylar fracture location is correlated to exercise history in Thoroughbred racehorses

Background: Condylar fractures are a major cause of morbidity and mortality in Thoroughbred racehorses. Condylar fractures have a variety of fracture configurations that suggest there may be differences in aetiopathogenesis. Objective: To determine if exercise history differs with condylar fracture location in a population of Thoroughbred racehorses. Study design: Retrospective analysis of clinical and exercise data. Methods: Exercise history of Thoroughbred racehorses that had condylar fracture repair between 1 January 2018 and 28 February 2021 was compared between racehorses that had fractures located radiographically either within the parasagittal groove (PSG) or abaxial to the PSG (non-PSG). Age, sex, and last event (race, timed work) matched control groups were compared between the PSG and non-PSG groups. Additionally, exercise history variables of both groups were each compared with a group-specific control population, each consisting of three control racehorses of equivalent age and sex matched to each affected racehorse by last event (race or official timed work) before fracture. Results: Eighty-two horses with 84 fractures (45 PSG, 39 non-PSG) met inclusion criteria. Age was not different between groups (PSG: 3.4 +/- 1.3 years [mean +/- SD], non-PSG: 3.7 +/- 1.3, p = 0.3). Number of races (PSG: 5.3 +/- 7.1, non-PSG: 11.4 +/- 8.9, p < 0.001), total race furlongs (PSG: 38.2 +/- 54.7, non-PSG: 79.2 +/- 64, p = 0.003), and number of active days (PSG: 304 +/- 224, non-PSG: 488 +/- 314, p = 0.003) before fracture were greater; while mean number of layups was fewer (PSG: 1.0 +/- 1.2, non-PSG: 0.5 +/- 0.7, p = 0.02) in horses with non-PSG fracture. Horses with non-PSG fracture had more differences compared with their respective control group than horses with PSG fractures. Outcomes following fracture repair were not different between groups. Main limitations: Retrospective study, one regional racehorse population, two-dimensional imaging and potential inherent bias for fracture localisation, low statistical power for return to performance analysis. Conclusions: Thoroughbred racehorses with non-PSG condylar fractures have a more extensive exercise history than horses with PSG condylar fractures, suggesting differences in fracture aetiopathogenesis.