Abstract
STUDY DESIGN: Microstructural investigation of mechanical load induced acute disc herniation on five animal models. OBJECTIVE: To compare how spinal discs in different animal models herniate under a standardized complex compressive load. SUMMARY OF BACKGROUND DATA: Animal models in disc herniation research offer reduced degeneration-associated variability, lower cost, and greater availability compared to human specimens. However, there is limited consensus regarding which species is best suited for modeling human herniation, making a comprehensive comparison of species-specific herniation mechanisms necessary. MATERIALS AND METHODS: A standardized shear and compressive load, designed to herniate intervertebral discs, was applied to isolated discs of five cadaveric animal models (n = 30, 6 specimens per group): bovine tail, bovine lumbar, ovine lumbar, porcine lumbar, and porcine cervical. The segments were flexed (7°), and a shear-compressive load was applied at a crosshead displacement rate of 40 mm min(-1), until a force drop, or a displacement limit was reached (~80% of disc height). Microstructural analysis was undertaken to identify failure modes. RESULTS: Clinically relevant herniation features were observed in all models-including endplate and annulus fibrosus (AF) tearing, AF delamination, vertebral body (VB) fracture, nucleus pulposus (NP) extrusion into VB, and radial NP movement. Bovine lumbar, porcine cervical, and porcine lumbar segments exhibited high rates of radial NP movement (84%, 100%, and 67%, respectively), with ovine lumbar discs displaying VB fracture (84%) and NP extrusions into the VB (67%). Bovine tail discs showed minimal damage but were characterized by sequential lamellar AF tears (67%). CONCLUSIONS: Porcine cervical, bovine lumbar, and porcine lumbar discs are suitable for annulus-failure herniation research, although porcine cervical discs may be the most appropriate due to exhibiting the highest rate of relevant damages. Ovine lumbar discs are relevant for studying endplate junction failure herniations, and bovine tail discs are appropriate for implant-related studies.