Sagittal distal limb kinematics inside the hoof capsule captured using high-speed fluoroscopy in walking and trotting horses

Kinematic evaluation of the distal limb of the horse using standard methods is challenging, mainly due to the hoof capsule restricting visualisation, but the recent development of a high-speed fluoroscopy (HSF) system has allowed in vivo cineradiographic assessment of moving skeletal structures at high speeds. The application of this non-invasive method to the equine distal limb is used to describe 'internal' distal limb kinematics including intra-horse and inter-horse variability, and variability between walk and trot. Distal limb kinematic data were collected at walk and trot from six non-lame horses using HSF set over a force plate. The dorsal proximal interphalangeal joint (PIPJ) angle and the dorsal distal interphalangeal joint (DIPJ) angle were measured at toe-on and at 25%, 50% and 75% of stance.The PIPJ and DIPJ showed overall extension through stance. The mean ± SD range of motion (ROM) during stance of the PIPJ was 9.7 ± 2.7° (walk) and 8.7 ± 3.0° (trot) and of the DIPJ was 28.6 ± 4.6° (walk) and 26.5 ± 6.3° (trot) showing significant differences between gaits and changes through stance (P < 0.001). Inter- and intra- horse variations were also significant for both joint angles (P < 0.001). HSF allowed for kinematic assessment of the distal limb within the hoof capsule. The ROM of the PIPJ observed was similar to results published in the literature whilst the ROM for the DIPJ was less than values previously reported. Future studies will use HSF to estimate strain in the tendons and ligaments within the hoof capsule, which are a common site of lameness in the horse.