Tensile strength and other material properties of the equine suspensory apparatus of the distal phalanx and the effect of specimen size, tensile load orientation, and freezing on determination of the material properties
Nabors, Benjamin E.
AdvisorLinford, Robert L.
Coyne, Cody P.
Elder, Steven H.
Ryan, Peter L.
Embargo TypeComplete embargo for 1 year
Embargo Lift Date12/15/2020
The suspensory apparatus of the distal phalanx (SADP) is an intricate adaptation of dermal and epidermal tissue that has a specialized role in the horse to absorb concussion while suspending the weight of the horse from within the hoof. The integrity of the hoof-bone connection is critical to the health of the horse and it can be affected by numerous disorders that cause it to fail. Accurate data on the ultimate tensile strength and other material properties of the SADP are important in modeling the behavior of the tissue under load and selecting appropriate prevention and treatment strategies for disorders of the SADP. The tensile load orientation and tissue sample size both have a profound effect on obtaining representative estimates for the material properties of a tissue. Consideration of the collagen fiber axis is important when selecting both. The purposes of this investigation were 1) to morphometrically determine the true collagen fiber axis in the SADP, 2) determine the most appropriate test sample size and tensile load orientation for materials testing, 3) to determine the ultimate tensile strength and other material properties of the SADP in healthy digits of adult horses, 4) to determine the site of tissue failure during testing, and 5) to determine whether freezing the SADP tissue samples prior to testing alters the material properties. Results of this investigation indicated that the true collagen fiber axis of the SADP in the toe region was predominantly vertical, in alignment with gravity. A vertical tensile load most closely matched the collagen fiber axis and was appropriate to model the load in the SADP for standing horses. A radial tensile load was appropriate to model the load in the SADP near the break over portion of the stride. Tissue blocks with a proximal-to-distal dimension of 1 cm tested less than 30% of the vertically oriented collagen fibers during radial tension testing and significantly underrepresented the ultimate tensile strength. The tissue failed in the deep dermis during radial tension testing and at the dermo epidermal junction during vertical tension testing. Freezing the tissue prior to testing significantly reduced the ultimate tensile strength.