A preliminary case study of the effect of shoe-wearing on the biomechanics of a horse's foot

Abstract

Horse racing is a multi-billion-dollar industry that has raised welfare concerns due to injured and euthanized animals. Whilst the cause of musculoskeletal injuries that lead to horse morbidity and mortality is multifactorial, pre-existing pathologies, increased speeds and substrate of the racecourse are likely contributors to foot disease. Horse hooves have the ability to naturally deform during locomotion and dissipate locomotor stresses, yet farriery approaches are utilised to increase performance and protect hooves from wear. Previous studies have assessed the effect of different shoe designs on locomotor performance; however, no biomechanical study has hitherto measured the effect of horseshoes on the stresses of the foot skeleton in vivo. This preliminary study introduces a novel methodology combining three-dimensional data from biplanar radiography with inverse dynamics methods and finite element analysis (FEA) to evaluate the effect of a stainless steel shoe on the function of a Thoroughbred horse's forefoot during walking. Our preliminary results suggest that the stainless steel shoe shifts craniocaudal, mediolateral and vertical GRFs at mid-stance. We document a similar pattern of flexion-extension in the PIP (pastern) and DIP (coffin) joints between the unshod and shod conditions, with slight variation in rotation angles throughout the stance phase. For both conditions, the PIP and DIP joints begin in a flexed posture and extend over the entire stance phase. At mid-stance, small differences in joint angle are observed in the PIP joint, with the shod condition being more extended than the unshod horse, whereas the DIP joint is extended more in the unshod than the shod condition. We also document that the DIP joint extends more than the PIP after mid-stance and until the end of the stance in both conditions. Our FEA analysis, conducted solely on the bones, shows increased von Mises and Maximum principal stresses on the forefoot phalanges in the shod condition at mid-stance, consistent with the tentative conclusion that a steel shoe might increase mechanical loading. However, because of our limited sample size none of these apparent differences have been tested for statistical significance. Our preliminary study illustrates how the shoe may influence the dynamics and mechanics of a Thoroughbred horse's forefoot during slow walking, but more research is needed to quantify the effect of the shoe on the equine forefoot during the whole stance phase, at faster speeds/gaits and with more individuals as well as with a similar focus on the hind feet. We anticipate that our preliminary analysis using advanced methodological approaches will pave the way for new directions in research on the form/function relationship of the equine foot, with the ultimate goal to minimise foot injuries and improve animal health and welfare.

Keywords: Equine biomechanics; Farriery; Finite element analysis; Horse foot; Inverse dynamics; Locomotion; XROMM.

Figure 1. Image of experimental and virtual set-up.

(A) Experimental set-up of the horse walking on a custom-made platform retrofitted with a forceplate and surrounded by the bi-planar fluoroscopy system. (B) Virtual setup of the horse right forefoot based on the experimental alignment of the X-ray sources and the intensifiers. Images in black frames (right and left) illustrate the projections of the distal foot from the two X-ray cameras.

Figure 2. XROMM model with bone segments and coordinate systems for the metacarpophalangeal (MCP), proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints.

Green, yellow and red arrows represent the Z, Y′ and X″ segment axes respectively.

Figure 3. Ground reaction forces normalised to 100% stance phase for the shod (black lines) and unshod horse (red lines).

For the craniocaudal GRF, cranial and caudal are positive and negative respectively. For the mediolateral GRF, medial is positive and lateral is negative. Solid lines represent the trials used in the subsequent finite element analysis.

Figure 4. Kinematic data.

Degrees of rotation for the proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints, around the flexion (positive)—extension (negative) axes during the stance phase for the shod (black line) and the unshod (red line) conditions. Dotted lines show the individual trials and the bold lines show the mean degrees of rotation for each condition.

Figure 5. Von Mises stress (MPa) distribution results for the shod and the unshod horse foot, in dorsal view.

Bones shown from top to bottom are the P1, P2 and P3. Warm (red) and cold (blue) colours show higher and lower von Mises stresses respectively.

Figure 6. Von Mises stress (MPa) distribution results for the shod and the unshod horse foot, in palmar view.

Bones shown from top to bottom are the P1, P2 and P3. Warm (red) and cold (blue) colours show higher and lower von Mises stresses respectively.