Objective—To determine whether the bending modulus
and yield strength of the outer stratum medium
(SM) differed from those of the SM zona alba (SMZA)
and to what degree they differed. In addition, a comparison
was made among our values and values
Sample Population—10 normal equine feet.
Procedure—A 3-point bending technique was used
to determine the bending modulus and yield strength
of the outer SM and SMZA. Efforts were made to
minimize biological and technical factors that could
influence the bending modulus.
Results—Bending modulus of the outer SM was
(mean ± SD) 187.6 ± 41.3 MPa, whereas mean value
for the SMZA was 98.2 ± 36.8 MPa. Mean yield
strength was 19.4 ± 2.6 MPa for the outer SM and
5.6 ± 1.7 MPa for the SMZA. Values for bending modulus
and yield strength differed significantly between
the outer SM and SMZA. Significant differences were
not detected when the outer SM was loaded in bending
from the outer or inner surface.
Conclusions and Clinical Relevance—Potentially,
the SMZA could serve as a mechanical buffer zone
between the rigid hoof wall and bone and laminar tissues.
This buffer zone potentially assists the feet of
horses in transmitting a load through the tissues and
prevents the most susceptible tissues from becoming
damaged. More consistency among tissue selection,
preparation, and testing protocols must be
attained before an accurate 3-dimensional finite-element
model of an equine foot can be constructed.
(Am J Vet Res 2001;62:745–751)
Objective—To evaluate patterns of digital cushion
(DC) displacement that occur in response to vertical
loading of the distal portion of the forelimb in horses.
Sample Population—Forelimbs from 10 horses with
Procedure—Patterns of DC displacement induced by
in vitro vertical limb loading were determined. Loadinduced
displacement of the DC was defined as the
magnitude and direction of displacement of 6 radiodense,
percutaneously implanted markers in specific
regions of the DC. The effects of solar support and
nonsupport on displacement of the DC were compared.
Results—Regional displacement of the DC occurred
principally along distal and palmar vectors in response
to vertical loading. Medial or lateral abaxial displacements
were variable and appeared to be dependent
on response of the limb to the applied load.
Displacement of the DC was not affected by the
degree of solar support.
Conclusions and Clinical Relevance—Data indicated
that the biomechanical function of the DC is to act
as a restraint to the displacement of the second phalanx
or as a passive structure that allows flexibility of
the caudal two thirds of the foot. Results did not indicate
that the DC provides a force that induces displacement
of or an active restraint against outward
displacement of the hoof wall capsule. (Am J Vet Res 2005;66:623–629)