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) frac ture 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 rad iological abnormality was present in cases of fracture. Measurement of the maximum and minimum width between the proximal and distal articular surface s of the dorsolateral aspect of this bone was carried out on a standardised dorso-50 degrees medial-palmarolateral radiographic projection of the tars us of each horse. To avoid artefacts produced by possible image magnificati on, ratios of these values were used for comparison between horses. The res ults showed that wedge shaped conformation of T3, in which the articular su rfaces of the bone converge and then diverge again on the dorsolateral aspe ct, was overrepresented in the population of horses sustaining T3 fracture when compared to controls. This information may be important in making judg ements on the suitability of horses during prepurchase examination for raci ng.