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- Author or Editor: Harry A. Hogan x
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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 reported elsewhere.
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 normal feet.
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)