Longitudinal, Objective Fan-Beam Computed Tomographic Evaluation of the Distal Third Metacarpal Bone in 31 Non-Lame Showjumpers

Computed tomography (CT) is increasingly used in equine lameness diagnosis, but no objective CT findings have been documented in the fetlock of sport horses. The aim of this study was to describe the pattern and longitudinal changes of densification in the distal third metacarpal bone (McIII) in non-lame showjumpers using CT measurements. Fan-beam CT examination of both metacarpophalangeal regions was performed in 31 non-lame showjumpers in regular work, at four examinations (times 0–3) on 27, 21 and 10 horses, respectively, with a median interval of 10 months. Mean Hounsfield unit (HU) values were recorded on sagittal reconstructions in the dorsal and palmar halves of the medial and lateral condyles, parasagittal grooves, and in the sagittal ridge. Mean dorsal HU values were highest in the medial condyle (1168.7 ± 67.2 HU at time 0) and lowest in the lateral parasagittal groove (947.0 ± 96.2 HU at time 0). Multivariable linear regression analysis showed that dorsal HU increased with showjumping level (3.12 HU per 5 cm increase in fence height; p = 0.002) and was higher in medial compared with lateral regions (estimate 28.58 HU; p < 0.001). Palmar HU values also increased with competition level (2.27 HU per 5 cm increase; p = 0.003) and examination time (6.22 HU per time point; p = 0.010). Overall, bone densification was greatest in the condyles, particularly medially. In most regions, no significant changes were detected over time, suggesting limited adaptive bone densification in this population of mature showjumpers over the study period.