Wedge-shaped conformation of the dorsolateral aspect of the third tarsal bone in the Thoroughbred racehorse is associated with development of slab fractures in this site.

Anecdotal evidence suggested that many cases of third tarsal bone (T3) fracture encountered clinically were associated with an abnormal shape to this bone. The radiographs of 10 normal horses and 10 horses affected with slab fracture of T3 were therefore examined to ascertain if any pre-existent radiological abnormality was present in cases of fracture. Measurement of the maximum and minimum width between the proximal and distal articular surfaces of the dorsolateral aspect of this bone was carried out on a standardised dorso-50 degrees medial-palmarolateral radiographic projection of the tarsus of each horse. To avoid artefacts produced by possible image magnification, ratios of these values were used for comparison between horses. The results showed that wedge shaped conformation of T3, in which the articular surfaces of the bone converge and then diverge again on the dorsolateral aspect, was over-represented in the population of horses sustaining T3 fracture when compared to controls. This information may be important in making judgements on the suitability of horses during prepurchase examination for racing.