The navicular bone (NB) and the deep digital flexor tendon (DDFT) are common sites of lameness. Greater knowledge of foot mechanics will aid in understanding of the aetiopathogenesis and may provide new opportunities for treatment and prevention. It was hypothesised that changes in the distal interphalangeal joint (DIPj) and movement of the NB and DDFT during the stance phase will lead to changes in the moment arm of the DDFT around the DIPj.
Internal hoof kinematics were determined using a high-speed fluoroscopy system. Six horses were walked and trotted over a raised platform consisting of four force plates, through the field of view of the fluoroscopy system. The angles of the DIPj and the DDFT around the navicular bone and the moment arm of the DDFT were measured. Changes in these parameters during stance and differences between strides, gaits and horses were assessed using an ANOVA or paired T-test as appropriate (P<0.05).
The range of motion (ROM, mean ± SD) during stance of the DIPJ was 28.6 ± 4.6° (walk) and 26.5 ± 6.3 (trot) with significant differences between gaits, strides and horses (P<0.001). The angle change of the DDFT around the NB was 21.9 ± 6.0° in walk and 26.6 ± 6.5 in trot. The change in moment arm of the DDFT around the DIPj was 3.7 ± 1.3 mm in walk and 4.1 ± 2.2 mm in trot. There were no significant differences between the different time points during stance or between gaits.
High-speed fluoroscopy is a novel method that allows assessment of internal foot kinematics. The observed changes between gaits during stance may result in altered stress distribution in the DDFT. Further studies will evaluate the effect of farriery intervention on internal foot kinematics.