Can we use subchondral bone thickness on high‐field magnetic resonance images to identify Thoroughbred racehorses at risk of catastrophic lateral condylar fracture?

REASONS FOR PERFORMING STUDY Fractures of the lateral condyle of the third metacarpus (MC3) are a significant welfare concern in horseracing worldwide. OBJECTIVES The primary aim of this work was to identify magnetic resonance (MR) image-detectable prefracture markers that have the potential for use as a screening tool to identify horses at significant risk of catastrophic fracture. STUDY DESIGN Case-control study of bone-level risk factors for fracture in racehorses. METHODS A total of 191 MC3s from horses, with and without lateral condylar fracture of MC3, were subjected to MR imaging. The depth of dense subchondral/trabecular bone was measured at several sites around the distal end of the bone and regression analyses were conducted to identify differences in this depth between horses with and without lateral condylar fracture. RESULTS Greater depth of dense subchondral/trabecular bone in the palmar half of the lateral parasagittal groove of distal MC3 was associated with an increased likelihood of being from a horse that had sustained a fracture. Receiver operator characteristic analysis was used to identify the optimal cut-off in the depth of dense subchondral/trabecular bone at this site to best discriminate fracture status. Positive and negative predictive values were calculated using the prevalence of fracture within the current study and also a prevalence estimate for the wider racehorse population. CONCLUSIONS There is a requirement to identify suitable prescreening test(s) to eliminate many true negative horses and increase the prevalence of prefracture pathology in the sub population that would be screened using MR imaging, in turn maximising the positive predictive value of this test.