Computed tomographic evaluation of protrusion of the superficial layer of the hoof wall and crena marginis solearis in non‐lame horses

Background: There are no published data on density changes of the metacarpal condyles in Thoroughbred racehorses over >1 year.Objectives: To document the pattern and changes in density of the metacarpal condyles in Thoroughbreds during their first 2 years of training and racing, using objective computed tomographic (CT) measurements.Study design: Prospective cohort.Methods: Fan-beam computed tomographic examinations of the metacarpophalangeal regions were performed on 40 non-lame Thoroughbred yearlings (T1), and four more times, approximately 6 months apart (T2-5).Mean Hounsfield Unit (HU) measurements were obtained on sagittal reconstructions in the dorsal and palmar halves of the medial and lateral condyles and parasagittal grooves.Due to loss to follow-up over time, a one-way ANOVA with a posthoc Tukey's Test was used to investigate differences between mean HU measured among examinations and between different regions of interest. Results:The highest HU values were in the dorsal half of the medial condyle at all time points (T1 971.0 73.9, T2 1046.8 67.2, T3 1048.0 69.4,T4 1120.1 63.4,T5 1033.6 87.3).The lowest HU values were in the palmar aspects of the medial and lateral parasagittal grooves at all times.There was an increase in HU values between T1 and T2 at all sites ( p < 0.01) and between T3 and T4 ( p < 0.02), except for the dorsal half of the lateral condyle.Between T4 and T5, a there was a decrease in the dorsal and palmar aspects of the medial condyle ( p < 0.01), the dorsal aspect of the medial parasagittal groove ( p = 0.04) and the palmar aspect of the lateral condyle ( p = 0.02).Main limitations: Some horses were lost to follow-up. Conclusions: Density of most regions of the metacarpal condyles increased with time spent in training, especially the dorsal aspect of the medial condyle, reflecting adaptation to racehorse training and known biomechanical loading patterns.