Stress/strain behaviour of the equine laminar junction.

The equine laminar junction plays a vital role in transferring the forces of weight-bearing between the epidermal hoof wall and the bone of the third phalanx, but the way in which it performs this function is poorly understood. Using samples from sites varying proximodistally and circumferentially around the hoof, the stress/strain behaviour of this tissue was characterised in three directions: radial tension and proximodistal and mediolateral shear. The influences of toe angle and length were also examined. For all three test directions, the modulus of elasticity increased with increasing strain magnitude. The mean modulus of elasticity in tension was 18.25+/-5.38 MPa (mean +/-1 S.D., N=116; mean strain 0. 25). In proximodistal shear, the mean shear modulus was 5.38+/-1.49 MPa (N=76; mean shear strain 0.48) and in mediolateral shear 2. 57+/-0.91 MPa (N=66; mean shear strain 0.81). In many cases, the individual hoof or horse from which the samples were taken significantly affected the value of the modulus, suggesting that mechanical history may affect the material properties of this tissue. Few biologically significant variations with location, toe length or toe angle were unambiguously demonstrated, suggesting that the material properties of the laminar junction are independent of position, despite apparent regional variations in function, and that foot shape is not a major determinant of material properties.