Corrective shoeing is used to change hoof angulation with the intention to influence the angulation of the digital joints to reduce strain on associated tendons. The objective of this study is to examine how gradual changes in hoof angulation affect the dorsal metacarpophalangeal joint (DMPJ) angulation and cross-sectional areas (CSAs) of the deep digital flexor tendon (DDFT) and superficial digital flexor tendon (SDFT) concerning the individual toe conformation. Forelimbs of 30 horses were examined barefoot and equipped with 5°, 10° and 20° toe wedges (TWs) and heel wedges (HWs). Phalangeal angulation and lengths were measured in lateromedial radiographs of the digit. CSAs of both flexor tendons was calculated in sonographic images. Significant effects on the DMPJ and CSA of the DDFT/SDFT were measured with 10° and 20° HWs or 20° TWs. Both flexor tendons showed increasing CSA after heel elevation. Significant interindividual variations occurred. Phalangeal angulation and length influenced the responsivity of the parameters to a changed hoof angulation. Significant impact of corrective shoeing on the DMPJ and flexor tendons is related to a distinct change in hoof orientation and varies with individual toe conformation. Similar response of the DDFT and SDFT to raised and lowered hoof orientation needs further investigation for a more specific application of therapeutic shoeing.

Ultrasound imaging of the distal limb enables veterinarians to determine morphological characteristics like the size and degree of changes in tissue conformation of the flexor tendons. To date, no study has validated the accuracy and precision of repeat follow-up ultrasound examinations for quantitative measurements of the cross-sectional area (CSA) of both flexor tendons. So this study was perforemed evaluate the accuracy and precision of ultrasound image acquisition and analysis to evaluate the cross-sectional areas of the equine deep and superficial digital flexor tendons of the forelimbs. In 10 consecutively obtained transverse images the CSA of both flexor tendons at 3 levels was examined in 5 horses by one operator. To examine the agreement of repeat image analysis, the CSA of the SDFT and DDFT at 3 levels on the left forelimb of 12 sound warmblood horses was repeatedly measured 10 times in the obtained ultrasound images by the same experienced operator. For all examinations the overall concordance correlation coefficient (OCCC) was calculated. The OCCC of the repeated image acquisition at the SDFT was very high at all levels (≥ 0.98 -≥ 0.99) and at the DDFT, a substantial or modest agreement for level 2A (0.98) and 2B (0.94) and a poorer agreement at level 1B (0.84) was shown. Repeat image analysis of the CSA showed an extremely high agreement between all measurements of the cross-sectional area at all levels of both tendons (≥ 0.99). The results show that the acquisition and analysis of transverse ultrasound images of the SDFT and the DDFT to measure the cross-sectional areas at different levels can be stated as a technique to perform quantitative examinations with high precision and accuracy for scientific purpose or as follow-up examinations of clinical cases.

The angulation of the equine fetlock determines the load of associated tendons and probably their predisposition for injuries. However, it is questionable how the individual toe conformation and tendon properties interact with the dorsal metacarpophalangeal joint angle (DMPJ). Data are needed for a tangible evaluation of the equine limb conformation for more specific orthopaedic treatment. The aim was to evaluate the correlation between the DMPJ, toe conformation and cross-sectional area (CSA) of both flexor tendons; the superficial digital flexor tendon (SDFT) and deep digital flexor tendon (DDFT). Thirty Warmblood horses were available for the study. Lateromedial radiographs of the toe and fetlock and transverse ultrasound images of both flexor tendons were obtained from three zones. The DMPJ, length and angle of the phalanges and CSA SDFT/DDFT were measured. In addition, hoof angle, wither height, age, and sex were documented. Correlations were calculated using Pearson’s test. A paired t-test was used to evaluate left–right differences. Length and angle of the proximal and middle phalanx were significantly associated with the DMPJ (r = -0.28 – -0.45, p<0.001-0.04). Neither the angle of the hoof and distal phalanx nor the CSA SDFT/DDFT, showed a noticeable correlation with the DMPJ. Significant left–right differences occurred for the DMPJ (p<0.002) and the angle of the proximal and middle phalanx (p<0.01 – 0.002). A moderate negative correlation was shown between the DMPJ and wither height (r = - 0.31, p=0.04). Results represent only a specific population. The study provides only a static evaluation of a dynamic situation. In a clinical context, it might be useful to focus on the angulation and length of the pastern to evaluate the individual load affecting the DMPJ and its associated structures. These findings might be relevant for orthopaedic treatments and shoeing recommendations.