The Modulus of Elasticity of Equine Hoof Wall: Implications for the Mechanical Function of the Hoof

Abstract

During normal weight-bearing and locomotion, the equine hoof wall deforms in a consistent pattern; the proximal dorsal wall rotates caudo-ventrally about the distal dorsal border and there is latero-medial flaring posteriorly. The aim of this study is to examine whether there are regional differences in the modulus of elasticity of hoof wall material and whether such differences correlate with the pattern of deformation which occurs in vivo. The modulus of elasticity of equine hoof wall was determined in tension and compression for samples from six forefeet. Samples were tested at the mid-point of the inner and outer halves of the wall thickness at two positions along the proximo-distal axis of the dorsal wall, and from the mid-point of its thickness at the lateral and medial quarters. Test samples were oriented both parallel and perpendicular to the tubules that characterise the microstructure of the wall. The colour of each sample was noted, and the moisture content measured. The range in the mean modulus of elasticity for all samples and tests was 460-1049 MPa, the dorsal outer wall having the highest values, the dorsal inner wall the lowest, and the quarters having intermediate values. The mean value obtained for the quarters was similar to the average of the values for the dorsal inner and outer walls. At all sites, the modulus of elasticity was marginally higher in compression than in tension, possibly owing to microstructural defects. The difference in stiffness between the outer wall and the inner wall was inversely related to moisture content. The difference in stiffness between the dorsal outer and inner walls demonstrates that the equine hoof wall has a comparatively rigid external capsule with a lining of lower stiffness. This arrangement presumably provides some stress protection to the internally adjacent living tissues. The similarity in stiffness between the samples from the quarters and the mean of the two dorsal wall sites suggests that the wall at the quarters has a similar change in stiffness across its thickness as the dorsal wall. However, the reduced thickness of the wall at the quarters compared with the dorsal wall means that, functionally, the quarters are more flexible than the dorsal wall. This will facilitate the flaring of the lateral and medial walls which occurs during weight-bearing. Anisotropy was evident only in tensile tests of the dorsal wall samples. Contrary to popular assertions that white hooves are mechanically inferior, horn pigmentation had no detectable effect on stiffness.

Investigation of forelimb hoof wall strains and hoof shape in unshod horses exercised on a treadmill at various speeds and gaits

“…23 Given the lateral location of the forelimb in relation to the center of a horse' s body, more loading could be expected at the medial quarter and toe. 24 Assuming that both sides of a hoof are morphologically similar and have similar elasticity, 25,26 the higher strains observed on the lateral side of the horses' hooves in the present study suggest that different forces act on each side. However, medial and lateral angles also affect strains in the hoof wall, with decreasing compression as the angle increases, particularly at the lateral side.…”

Shoe configuration effects on third phalanx and capsule motion of unaffected and laminitic equine hooves in-situ

“…Subtle differences in material properties among regions of the hoof result in variable responses to tensile [ 57 – 59 ] and compressive stresses [ 57 , 60 ]. Similar to shoe effects on P3 displacement, hoof capsule deformation also differed between laminitic and unaffected hooves.…”

Photoelastic stress analysis of strain patterns in equine hooves after four-point trimming

“…It also suggests that the hoof wall behaves as an orthotropic material that resists compressive loads better than tensile stresses, and it confirms results of a study on material properties in which it was revealed that the Young modulus of the hoof horn is greater under compressive loads. 30 Although we did not evaluate laminar stresses in this study, it could be assumed that the strain concentration over the pillars as well as the significant increase in shear strain magnitudes following trimming could potentially induce focal disruptive stresses on the laminae. Conversely, providing that laminar integrity is sustained, increases in strains could stimulate growth and, therefore, thickness and strength of the hoof wall, resulting in healthier feet.…”