Treatment Comparison for Medial Femoral Condyle Subchondral Cystic Lesions and Prognosis in Yearling Thoroughbred Racehorse Prospects

Simple Summary Subchondral cystic lesions (SCL) are a common finding in young Thoroughbreds intended for racing. Although the complete etiology is not fully understood, it is believed that SCL is a form of osteochondrosis that can also be induced by trauma. Several treatments have been studied to improve soundness or athletic prognosis. The objectives of this study were to compare the athletic prognosis of four current treatments performed in Thoroughbred yearlings, to compare auction value and athletic ability with maternal siblings without medial femoral condyle SCL, and to detect if the size of the SCL would have a negative effect on the racing prognosis. The treatments studied were intralesional injection of corticosteroids, SCL debridement through the joint with a drill bit, translesional cortical screw placement, and absorbable hydroxyapatite implant placement. The price paid at an auction for horses treated for SCL was significantly lower than that of their siblings. Horses treated for SCL had significantly lower chances to start in a race than their siblings free of pathology (59% and 74%, respectively). Wider SCL negatively affected the chances of starting in at least one race and the earnings as a 2-year-old racehorse. Horses with SCL treated with a bioabsorbable implant had a higher median in starts as 3-year-olds than horses treated with debridement of the SCL with a drill bit. In conclusion, Thoroughbred yearlings treated for a medial femoral condyle SCL had lower auction prices and decreased ability to start a race compared to siblings; wider cysts had worse prognosis to start a race and might affect earnings as 2-year-olds; and horses treated with bioabsorbable composite implant placement had more starts as 3-year-olds than other techniques.Abstract Subchondral cystic lesions (SCL) in the medial femoral condyle are a usual finding in Thoroughbred survey and auction repository radiographs. Several treatments with different outcomes have been studied over the years to improve soundness and racing prognosis. Our objective was to report the racing prognosis in Thoroughbred yearlings intended for racing that were diagnosed with SCL in the medial femoral condyle and were treated using four current and different techniques: intralesional injection of corticosteroids, SCL debridement through the joint with a drill bit, translesional cortical screw placement, and absorbable hydroxyapatite implant placement. Data from 182 Thoroughbred yearlings treated for SCL in the medial femoral condyle were collected from 2014 to 2020. Limb affected, age at surgery, sex, and radiographic measurements of the SCL were recorded. Auction price and racing performance were collected for treated horses and compared to 154 maternal siblings free of medial femoral condyle SCL. Analyses were conducted to assess if racing prognosis was affected by SCL size, to detect differences in auction price and selected flat racing outcome parameters between cases and controls, and to compare racing prognosis between the studied treatments. Mares and lesions located in the right stifle were significantly overrepresented. The auction price of treated horses was significantly lower than that of their siblings. Horses treated for SCL had significantly lower chances to start in a race than controls (59% vs. 74% respectively). Wider SCL negatively affected the chances to start at least in one race, and negatively affected the earnings made in the 2-year-olds' racing year. Horses with SCL treated using a bioabsorbable implant had a significantly higher median in starts as 3-year-olds (seven starts) than horses that had the SCL debrided with a drill bit (three starts). In conclusion, Thoroughbred yearlings treated for a medial femoral condyle SCL had lower auction prices and decreased ability to start a race compared to siblings' wider cysts had worse prognosis to start a race and might affect earnings as 2-year-olds; and horses treated with bioabsorbable composite implant placement had more starts as 3-year-olds than with other techniques.