A preliminary study into the correlation of stiffness of the laminar junction of the equine hoof with the length density of its secondary lamellae

Abstract

Summary Reason for performing study: The relationship between mechanical behaviour and microscopic structure of the laminar junction of equine hooves under testing conditions requires elucidation. Objectives: To determine mechanical parameters and 2D length density of profiles of secondary lamellae of the laminar junction in the dermal region and to assess possible correlations. Methods: Specimens (25 samples in total) of the laminar junction were taken from front, quarter and heel parts from 3 equine hooves and exposed to a uniaxial tensile test until rupture to obtain Young's moduli of elasticity, ultimate stress and strain. Neighbouring specimens to those used for the biomechanical experiment were processed histologically to assess the length density of laminar junction basement membrane using stereological grids. Results: The estimated median (interquartile range) length density of the laminar junction basement membrane was 0.024 (0.020–0.027)/µm. Young's modulus of elasticity was 0.15 (0.11–0.35) MPa in the small deformation region, and 7.58 (6.14–8.68) MPa in the linear region was. The ultimate stress was 1.67 (1.41–2.67) MPa, and the ultimate strain was 0.50 (0.38–0.70). The Young's modulus of elasticity in the region of small deformations has a moderate correlation with the length density of the laminar junction basement membrane. Conclusions: As with most soft biological tissues, the laminar junction has a nonlinear mechanical behaviour. Within the range of small deformations, which correspond to physiological loading of the laminar junction, a higher length density of the laminar junction basement membrane is correlated with a higher resistance of the laminar junction against high stresses transmitted from the distal phalanx to the hoof wall. Potential relevance: The condition of the laminar junction apparatus may be easily quantified as the length density of profiles of secondary dermal lamellae. This quantification provides a simple tool that could be used for comparing the proneness of the various parts of the laminar junction to initial stages of laminitis.

Ex vivo effects of insulin on the structural integrity of equine digital lamellae

“…Studies using normal horses have been performed to quantify the biomechanical behaviour of lamellar explants . It has been concluded that location‐dependent variation exists in the density of secondary lamellae leading to a greater surface area for basement membrane attachment resulting in greater structural integrity of the explant .…”

“…Studies using normal horses have been performed to quantify the biomechanical behaviour of lamellar explants . It has been concluded that location‐dependent variation exists in the density of secondary lamellae leading to a greater surface area for basement membrane attachment resulting in greater structural integrity of the explant . The experimental design used in this study attempted to circumvent that potential variation in explant structural integrity by randomly assigning explants to a control and treatment group independent of location within the digit.…”

“…However, in this study the tensile force was applied perpendicular to the distal phalanx for consistency with biomechanical testing. Previous studies examining lamellar tissue free of disease chose an elongation rate (500 mm/min) comparable to what a horse experiences at a gallop . However, the goal of this study was to develop an ex vivo model to study hyperinsulinaemia‐induced lamellar failure.…”

“…However, the unique structure of the hoof provides challenges when evaluating biomechanical stress on the equine digit. Stress at the lamellar dermal‐epidermal junction has been studied in normal horses through biomechanical testing of lamellar explants . In addition, effects of matrix metalloproteinase activators on the structural integrity of the equine lamellar tissue have been evaluated describing the location of lamellar failure at the basement membrane between the dermal‐epidermal junction .…”

The management of equine acute laminitis

“…The third phalanx is supported or slung inside the hoof capsule by interlocking dermal and epidermal lamellae (within the stratum internum). In an adult horse, there are between 550 and 600 primary dermal and epidermal lamellae, 39 each with between 100 and 200 secondary lamellae. 40 These lamellae form a tight connection between the internal portion of the hoof wall and the third phalanx.…”