Slab fractures of the third carpal bone in standardbreds and thoroughbreds: 155 cases (1977-1984).

Case records and radiographs of 155 horses with third carpal bone (C3) slab fractures were reviewed. Of these cases, race records were obtained for 72 Thoroughbreds and 61 Standardbreds. Three performance criteria were examined: ability to make 1 start, ability to make 10 starts or earn $2,000 (within 1 year of first start after the fracture), and earnings per start. Treatment distribution (lag screw fixation, fragment excision, or rest) was similar in both breeds. Significant differences between breeds were identified in age and sex distributions, fracture displacement, and postinjury performance. In Thoroughbreds, there was a tendency for fractures to occur in the right C3 (59%); in Standardbreds, forelimbs were affected equally. The dorsomedial aspect of C3 was the site of fracture in 87% (135/155) of the cases. Horses referred for treatment were predominantly 2-year-old Standardbreds and 3-year-old Thoroughbreds. Females of both breeds were less likely to race after injury than males (46 vs 90%). In Standardbreds, all 38 horses with racing starts before fracture were able to race again. Prior racing starts were not related to outcome in Thoroughbreds. The effects of treatment on outcome were not significantly different. Fracture characteristics did not significantly affect outcome, but did influence treatment selection. Convalescent time was not correlated with any of the variables examined (including treatment) or related to outcome; time from admission to first start averaged 11 months. In STandardbreds, 77% of the horses with C3 slab fracture raced after injury; in Thoroughbreds, 65% raced. Earnings per start declined in each breed, but the decline was more pronounced in Thoroughbreds.