POSTOPERATIVE RACING PERFORMANCE IN STANDARDBREDS AND THOROUGHBREDS WITH OSTEOCHONDROSIS OF THE TARSOCRURAL JOINT - 109 CASES (1984-1990)

Medical records for 64 Thoroughbred and 45 Standardbred horses with os teochondrosis dissecans (OCD) of the tarsocrural joint that were treat ed by means of arthroscopic removal of the fragments before 2 years of age and before beginning racing were reviewed. Lesion site was record ed for all horses. The other foals from the dams of these surgically t reated horses (siblings) were identified from mare progeny records. Ra cing data, including number of starts and money won during the 2- and 3-year-old racing years were obtained from the Jockey Club and the Uni ted States Trotting Association for affected horses and their siblings . Statistical analysis was performed to test the hypothesis that there was no difference between the racing performance of horses with OCD o f the tarsocrural joint that were surgically treated by means of arthr oscopic removal of the fragments prior to racing and that oi their sib lings. One hundred and seventy-four lesions were recorded in 109 horse s. The distribution of lesions was similar to that previously reported . For the Standardbreds, 22% of chose that had surgery raced as 2 year olds and 43% raced as 3 year olds, compared with 42 and 50% of the si blings that raced as 2 year olds and 3 year olds, respectively. For th e Thoroughbreds, 43% of those that had surgery raced as 2 year olds an d 78% raced as 3 year olds, compared with 48% and 73% of the siblings that raced as 2 year olds and 3 year olds, respectively. The median nu mber of starts for surgically treated horses was decreased, compared w ith median number of starts for siblings, for all groups except 3-year -old Thoroughbreds, The distribution of starts was different between s urgically treated and sibling horses only for 2-year-old Standardbreds . Median earnings were lower for affected horses than for siblings for both breeds and both age groups. Among affected horses, ability to st art at least 1 race was not associated with lesion location or unilate ral vs bilateral involvement. There was a tendency for horses with mul tiple lesions to be less likely to start a race than horses with only a single lesion; however, the difference was significant only for 2-ye ar-old Standardbreds. Affected Standardbreds and Thoroughbreds were le ss likely to race as 2 year olds than were their siblings.