Developmental Lateral Patellar Luxation in Standardbred Yearlings: Understanding the Condition

Objective To report the incidence, and clinical and pathological findings of developmental lateral patellar luxation in Standardbred yearlings diagnosed with femoropatellar dysplasia (FPD) and demonstrate that osteochondral lesions in the lateral trochlear ridge (LTR) of the femur observed in the affected horses are osteochondral lesions related to patellar maltracking. Study Design Retrospective case series. Medical records were retrospectively reviewed for Standardbreds <12 months of age diagnosed with FPD between 2017 and 2023. Results A total of 10 Standardbred yearlings developed FPD (incidence 6.4 cases per 1,000 foals). Patellar instability and femoropatellar joint effusion were observed between 3 and 9 months of age. Six horses developed severe lameness at walk within 6 months from diagnosis. Radiography revealed abnormal patellar tilt in all cases, flattening and osteochondral lesions in the LTR in nine cases, flattening of the intertrochlear groove and patellar ridge in three horses, and patellar displacement in two cases. The condition deteriorated in six cases, leading to euthanasia, while four horses were retired to pasture. Conclusion FPD is not uncommon in Standardbred yearlings and clinical signs are visible under 12 months of age. The condition is career-limiting and affected horses have poor prognosis despite treatment as racehorses.