34th Annual Scientific Meeting proceedings

Osteochondrosis dissecans (OCD) is a developmental orthopedic disease where there is osteochondral necrosis and separation of an osteochondral fragment from the parent bone following failure of endochondral ossification in the articular-epiphyseal cartilage complex. In horses, OCD most commonly affects the tibiotarsal joint, the metacarpo-(metatarso-) phalangeal joint, and the femoropatellar joint. There is breed predilection for lesion location, with lesions of the tibiotarsal joint commonly diagnosed in Standardbreds and Warmbloods and lesions of the femoropatellar joint commonly diagnosed in Thoroughbreds. Treatment options include conservative management, arthroscopic removal, and reattachment of cartilage flaps with absorbable pins in very select cases.

Racing performance following femoropatellar arthroscopy for OCD has been previously published in Thoroughbreds but not for Standardbreds. The objectives of this work were to evaluate postoperative racing performance of Standardbreds that underwent arthroscopic removal of an OCD lesion of the femoropatellar joint and identify any prognostic indicators. We hypothesized that horses with larger OCD lesions and multiple joint involvement would have poorer racing performance.

Medical records were searched for Standardbreds that underwent femoropatellar arthroscopy between January 2014 and January 2022. OCD lesions were measured from preoperative digital radiographs. Postoperative racing results were obtained from the United States Trotting Association, and follow-up owner surveys were conducted. A control group of contemporaneous paternal siblings free of OCD lesions were selected for comparison of racing performance. Regression analysis was used to determine associations between presence or grade of OCD lesions and performance parameters with sex and gait covariates.

There were 45 affected Standardbreds that met the inclusion criteria. There was no significant difference in proportion of horses starting a race based on OCD lesion grade. Affected racehorses had fewer starts at 3 years of age (IRR = 0.82, p <0.001) but not at 2 years of age, when compared to unaffected siblings. There was also no difference in race wins or earnings between affected and unaffected horses.

Limitations included a small number of affected horses limiting our power to detect true differences between the OCD lesion grades, and there was no conservative treatment group. We examined only short-term performance parameters (through the 3-year-old racing season). It is possible that the true impact of femoropatellar OCD lesions affects athletic longevity rather than poor performance in the first two racing seasons, but this possibility was beyond the scope of the current study. Further work to investigate if there is any difference in racing longevity between affected horses and controls is warranted. Based on the findings in this population, we conclude that arthroscopy is an effective treatment for OCD lesions of the femoropatellar joint in Standardbred racehorses, when performed prior to the start of intensive training, and that lesions treated in this manner can be expected to have no major impact on early racing potential.