Sessions

Standing computed tomography (CT) is commonly used for assessment of the equine distal limb and allows detailed evaluation of the navicular bone without superimposition of adjacent anatomical structures. Published literature is available on radiographic findings of the navicular bone in both lame and non-lame horses, but information on longitudinal CT changes in the palmar cortical thickness of the navicular bone in non-lame sport horses is lacking.

The aim of this study was to establish a standardized CT measurement protocol and reference ranges for palmar cortical thickness of the navicular bone in non-lame showjumpers. Initially, 53 hooves from 28 non-lame showjumpers in full training and regular competition were included in the study. At the three follow-up examinations, CT examinations were available for 48, 27 and 14 forelimbs respectively, with a median interval of 10.1 months between consecutive examinations. Available standing fan-beam CT examinations of both forelimbs were evaluated retrospectively. Measurements were obtained at proximal and distal locations on sagittal reconstructions and at medial, midsagittal and lateral locations on transverse reconstructions. Differences between examination time points were assessed using Kruskal–Wallis test, followed by post hoc Dunn’s tests with Bonferroni correction. Differences between the left and right forelimbs and between measurement sites were evaluated using Wilcoxon signed-rank test or paired t-tests, depending on the distribution of paired differences. Possible associations with age, sex, bodyweight, height, bodyweight-to-height ratio, examination time point, forelimb, and level of showjumping were investigated using linear mixed-effects regression models.

No significant differences in palmar cortical thickness were identified between examination time points. When measurements from all examinations were pooled, proximal thickness was significantly greater in the left forelimb than in the right forelimb (p=0.026), medial measurements were significantly greater than lateral measurements (p=0.019) and distal measurements were significantly greater than proximal measurements (p<0.001). Lateral palmar cortical thickness was significantly greater in stallions than in mares (p=0.043). Distal thickness was negatively associated with height (p=0.006), whereas midsagittal thickness was positively associated with bodyweight-to-height ratio (p=0.030). No significant associations were identified with age, bodyweight or level of showjumping.

Palmar cortical thickness remained stable over the study period but differed between anatomical locations and left and right forelimbs. The associations with sex, height and bodyweight-to-height ratio indicate that signalment should be considered when interpreting quantitative CT measurements. The results provide reference data on palmar cortical thickness of the navicular bone in non-lame showjumping horses and aid interpretation of clinical CT examinations.