Clinical findings and prognosis of interference injuries to the palmar aspect of the forelimbs in Standardbred racehorses: a study on 74 cases

BACKGROUND: Information on interference injuries in racehorses is lacking. OBJECTIVE: To describe clinical findings and prognosis of palmar forelimb interference injuries in Standardbreds. STUDY DESIGN: Retrospective cohort study. METHODS: Records of 74 racehorses sustaining palmar forelimb interference injuries were studied, 7 during training, 67 during racing. The number of starts before injury, hind shoeing status, gait penalties, and racing speeds in cases occurring during racing were compared with negative controls, 67 age, sex and speed category matched horses from the same races. The number of starts and racing speed in 30 racing days preceding recruitment were compared with those following recruitment (negative controls) or return to racing (cases). Clinical aspects and outcome in interference-induced superficial digital flexor (SDF) tendinitis were compared with 77 horses with overstrain-induced SDF tendinitis. RESULTS: In 89% of cases, there was SDF tendinitis and this was associated with a longer time to return to racing (6 months vs. 1 months; p<0.001). The presence of gait penalties (odds ratio (OR) 11.13; 95% CI 3.74, 41.64; p<0.001) and unshod hind feet (OR=6.26, 95% CI 2.26, 19.62; p<0.001) increased risk of interference injuries. After recruitment/return to racing, horses with interference injuries participated in a lower number of races (24 starts per racing day, interquartile range (IQR) 20-32) compared to controls (49, IQR 43-55, p<0.0001). Interference-induced tendinitis cases (n=58) had a shorter time to return to racing (245 ± 137 days) than overstrain-induced tendinitis cases (331 ± 118 days, p<0.001). MAIN LIMITATIONS: Data were collected retrospectively, time of ultrasonographic assessment varied and health status of the racing controls is unknown. CONCLUSIONS: SDF tendinitis is common with palmar forelimb interference injuries in Standardbreds and increases time to return to racing. Interference-induced SDF tendinitis has a better prognosis than overstrain-induced tendinitis.