Morphometric, Biomechanical and Histologic Assessment of Physiologic Ovine Cervical Intervertebral Disc: An Experimental Study and Brief Literature Review

Abstract

The ovine cervical spine model has been established as a representative model of the human cervical spine in the current literature, and is the most commonly used large animal model in studies investigating pathogenesis and treatment strategies for intervertebral disc (IVD) degeneration. However, existing data regarding morphometry, biomechanical profiles and the microscopic features of a physiological ovine cervical IVD remain scarce. Hence, the aim of this study was to perform a multimodal morphometric, biomechanical and histologic evaluation of a normal ovine cervical IVD. For this purpose, nine ovine cervical IVDs were harvested from three female sheep, and subjected to morphometrical, biomechanical and histologic analyses. The biomechanical assessment included the performance of cyclic compression, creepand compressive strength tests in a controlledlaboratory environment. Histological evaluation was performed using hematoxylin–eosin, Masson’s trichrome and Alcian blue staining. The results from the morphometric analysis showed that the range of disc heights was 4–9 mm in all surfaces, featuring a constant increase from cranial to caudal levels. Biomechanical evaluation revealed that cyclic loading for 20 cycles was necessary for preconditioning so that the repeatability of the force–displacement hysteresis response is present. The critical failure point was defined at 15.5 MPa, whereas Young’s modulus of elasticity was 1.2 MPa. The histologic assessment demonstrated the presence of a concentric arrangement of collagen lamellae in external annulus fibrosus, along with the sparsely organized internal nucleus pulposus. Ovine cervical IVD represents a complex structure with distinct features that should be considered by researchers in this field in order to optimize the reliability and validity of testing results.