European spine journal : official publication of the European Spine Society, the European Spinal Deformity Society, and the European Section of the Cervical Spine Research Society
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The intervertebral disc (IVD) annulus fibrosus (AF) is composed of concentric lamellae with alternating right- and left-handed helically oriented collagen fiber bundles. This arrangement results in anisotropic material properties, which depend on local fiber orientations. Prior measurements of fiber inclination angles in human lumbar and bovine caudal IVDs found a significantly higher inclination angle in the inner AF than outer, though it is currently unknown if this pattern is conserved in smaller mammalian species. Additionally, the physical mechanism behind this pattern remains un-determined. ⋯ Trends in AF fiber orientation are conserved between mammalian species. Modeling results suggest that the AF tissue microstructure is more likely to be driven by adjacent vertebral body growth than adapted for optimal mechanical performance.