Does the Low-Field MRI Appearance of Intraosseous STIR Hyperintensity in Equine Cadaver Limbs Change when Subjected to a Freeze-Thaw Process?

SIMPLE SUMMARY: Research into the advanced imaging appearance of Thoroughbred racehorse fetlocks is receiving increased attention in an effort to better understand and potentially reduce the occurrence of catastrophic fracture in these horses. Studies in this area commonly use cadaver equine limbs from racehorses and a freeze-thaw process prior to imaging. The low-field magnetic resonance imaging (MRI) appearance of the bones of the fetlock joint is of particular interest in the diagnosis of impending fracture in this location. However, little is known about the effect of the freeze-thaw process on the appearance of certain signal changes (“STIR hyperintensity”) seen commonly in racehorses. This study compares the low-field MRI appearance of short tau inversion recovery (STIR) hyperintensity in the bones of cadaver fetlocks from Thoroughbreds in race training, before and after a freeze-thaw protocol. Fifteen cadaver fetlocks with abnormal bone signal were included in the study. Blinded and unblinded statistical comparisons were made. No overall clinical or statistical difference was detected in intensity and distribution of the STIR signal before and after freeze-thaw. This indicates that the MRI appearance of STIR hyperintensity in freeze-thawed cadaver fetlocks can be considered representative of the appearance of pathology in the recently euthanized horse. This is important information to further advance research in the area of Thoroughbred racing fatality reduction. ABSTRACT: Equine advanced imaging research involving racehorse fetlock pathology commonly uses cadaver limbs and a freeze-thaw process. The presence of short tau inversion recovery (STIR) signal intensity in the distal third metacarpal/metatarsal bone is of particular interest and may be clinically relevant in the diagnosis of horses at risk of fracture. However, little is known about the effect of the freeze-thaw process on the MRI appearance of STIR hyperintensity in these bones. This study compares the low-field MRI appearance of the distal third metacarpal/metatarsal bone from cadaver limbs of Thoroughbreds in race training before and after a freeze-thaw protocol. Blinded and unblinded comparisons were made using objective SNR values and subjective grading. Fifteen cadaver limbs with STIR hyperintensity in the distal third metacarpal/metatarsal bone were included. No overall clinical or statistical significance was detected in STIR signal intensity and distribution after freeze-thaw. Three limbs from one horse had individual changes in STIR hyperintensity that were hypothesized to be attributable to ante-mortem haemodynamic abnormalities caused by anaesthesia. These results indicate that the distribution and intensity of STIR hyperintensity in freeze-thawed cadaver fetlocks can be considered representative of the appearance of pathology in the recently euthanized horse. However, care should be taken with horse selection and handling of the cadaver limbs to ensure reliable appearance of STIR signal after freeze-thaw.