Ultrasound tissue characterisation of the superficial digital flexor tendons in juvenile Thoroughbred racehorses during early race training

BACKGROUND: Injuries to the superficial digital flexor tendon (SDFT) are one of the leading causes of Thoroughbred (TB) wastage. Increasingly, the aim is to prevent injury rather than treat it. Conventional ultrasonography is not sufficiently sensitive to accurately monitor tendon and predict injury. Ultrasound tissue characterisation (UTC) is a relatively new technique, which improves tendon characterisation by providing a 3‐dimensional (3D) SDFT reconstruction and objective calculation of fibre alignment by classifying fibres into one of 4 echo‐types. OBJECTIVES: To report a reference range of echo‐types in a population of normal juvenile TB racehorses. It was hypothesised that: UTC would be easy to use on juvenile TB racehorses in a field setting; that results would be repeatable; that the UTC would demonstrate a physiologic response of the tendon and, finally, that the technique would allow monitoring of the SDFT for early detection of degenerative changes. STUDY DESIGN: Prospective longitudinal cohort pilot study. METHODS: Thirty‐two TB yearling racehorses were recruited. UTC measurements of bilateral forelimb SDFTs were taken every 60–90 days. The proportion of 4 echo‐types were quantified as a relative percentage at specific zones over the length of the SDFT. Relationships were assessed by paired T tests or Wilcoxon signed rank tests. RESULTS: Mean percentage for echo‐type I fibres were >85%; echo‐type II fibres were <15%, with negligible echo‐type III and IV. Significant right to left limb, zonal, and temporal differences in echo‐type were identified. MAIN LIMITATIONS: No control group of untrained horses, limiting ability to differentiate whether findings were training‐related as opposed to age‐related changes. CONCLUSIONS: Changes in SDFT characterisation over the first 6 months of training were identified. UTC may provide useful objective information when assessing juvenile SDFTs. The Summary is available in Spanish – see Supporting Information