The intervertebral disc is z cartilaginous structure which functions to support and distribute load and to provide motion and flexibility to the spine. The anulus fibrosus of the intervertebral disc consists of several lamellae in which the collagen fiber bundles are oriented at approximately 30° to the transverse plane, with the fiber angles in adjacent lamella alternating above and below the plane. The highly oriented structure of the anulus fibrosus gives rise to anisotropic material behaviors of the tissue.
In this study, a material model for fiber-induced anisotropy in the anulus fibrosus was proposed which described the solid matrix using an explicit representation of the collagen fiber orientations. A linear elastic strain energy formulation was proposed based on material and geometric parameters of the fibers and matrix. The engineering constants were experimentally determined in non-degenerate human lumber disc tissue by evaluating the stress-strain response at equilibrium for samples in five orientations and at two sites. The interlamellar fiber angle was measured.
At outer sites, the average linear moduli were 14.0, 0.7 and 0.4 MPa for samples which were oriented in the circumferential, axial and radial directions, respectively. At inner sites, the moduli were 4.6 and 1.0 MPa for samples oriented in the circumferential and axial directions. At outer sites, the Poisson's ratios ν₁₂, ν₁₃, ν₂₁, ν₂₃ and ν₃₁ were 1.7, 0.3, 0.6, 0.2 and 0.5, respectively. At inner sites the Poisson’s ratios ν₁₂, ν₁₃ and ν₂₁ were 1.6 ,0.8 and 1.4.
The fiber-induced anisotropic model and the experimentally measured engineering constants and fiber angles together provided a complete and unique representation of the material behaviors of the human anulus fibrosus in tension. Parametric studies were performed to determine the sensitivity of the material properties to the measured variation in the engineering constants. Model predictions were compared to independently measured values for model validation. The mechanisms underlying structure-function relationships in the anulus fibrosus were investigated by examining the distribution of the strain energy attributed to the different terms in the model. These results suggest that fiber-fiber interactions are important contributors to the material behaviors of the anulus fibrosus in tension.
|1995||Goel VK, Monroe BT, Gilbertson LG, Brinckmann P. Interlaminar shear stresses and laminae separation in a disc: finite element analysis of the L3-L4 motion segment subjected to axial compressive loads. Spine. March 15, 1995;20(6):689-698.|
|1945||Coventry MB, Ghormley RK, Kernohan JW. The intervertebral disc: its microscopic anatomy and pathology, I: anatomy, development, and physiology. J Bone Joint Surg. January 1945;27(1):105-112.|
|1967||Galante JO. Tensile properties of the human lumbar annulus fibrosus. Acta Orthop Scand. 1967;(suppl 100):1-91.|
|1999||Setton LA, Elliott D., Mow VC. Altered mechanics of cartilage with osteoarthritis: human osteoarthritis and an experimental model of joint degeneration. Osteoarthritis Cartilage. January 1999;7(1):2-14.|
|1951||Virgin WJ. Experimental investigations into the physical properties of the intervertebral disc. J Bone Joint Surg. November 1951;33B(4):607-611.|
|1990||Thompson JP, Pearce RH, Schechter MT, Adams ME, Tsang IK, Bishop PB. Preliminary evaluation of a scheme for grading the gross morphology of the human intervertebral disc. Spine. May 1990;15(5):411-415.|
|1984||Shirazi-Adl SA, Shrivastava SC, Ahmed A. Stress analysis of the lumbar disc-body unit in compression: a three-dimensional nonlinear finite element study. Spine. March 1984;9(2):120-134.|
|1989||Cassidy JJ, Hiltner A, Baer E. Hierarchical structure of the intervertebral disc. Connect Tissue Res. 1989;23(1):75-88.|
|1998||Iatridis JC, Setton LA, Foster RJ, Rawlins BA, Weidenbaum M, Mow VC. Degeneration affects the anisotropic and nonlinear behaviors of human anulus fibrosus in compression. J Biomech. June 1, 1998;31(6):535.|
|1974||Belytschko T, Kulak RF, Schultz AB, Galante JO. Finite element stress analysis of an intervertebral disc. J Biomech. May 1974;7(3):277-285.|
|1993||Fung YC. Biomechanics: Mechanical Properties of Living Tissues. 2nd ed. New York, NY: Springer-Verlag; 1993.|
|1978||Lin HS, Lui YK, Ray G, Nikravesh P. Systems identification for material properties of the intervertebral joint. J Biomech. 1978;11(1-2):1-14.|
|1998||Puso MA, Weiss JA. Finite element implementation of anisotropic quasi-linear viscoelasticity using a discrete spectrum approximation. J Biomech Eng. February 1998;120(1):62-70.|
|1992||Lavaste F, Skalli W, Robin S, Roy-Camille R, Mazel C. Three-dimensional geometrical and mechanical modelling of the lumbar spine. J Biomech. October 1992;25(10):1153-1164.|
|1960||Nachemson A. Lumbar intradiscal pressure: experimental studies on post-mortem material. Acta Orthop Scand. 1960;31(suppl 43):1-104.|
|1988||Eyre DR, Dickson IR, Van Ness K. Collagen cross-linking in human bone and articular cartilage: age-related changes in the content of mature hydroxypyridinium residues. Biochem J. June 1988;252(2):495-500.|
|1996||Ebara S, Iatridis JC, Setton LA, Foster RJ, Mow VC, Weidenbaum M. Tensile properties of nondegenerate human lumbar anulus fibrosus. Spine. March 25, 1996;21(4):452-461.|
|1997||Fujita Y, Duncan NA, Lotz JC. Radial tensile properties of the lumbar annulus fibrosus are site and degeneration dependent. J Orthop Res. November 1997;15(6):814-819.|
|1990||Marchand F, Ahmed AM. Investigation of the laminate structure of lumbar disc anulus fibrosus. Spine. May 1990;15(5):402-410.|
|1995||Acaroglu ER, Iatridis JC, Setton LA, Foster RJ, Mow VC, Weidenbaum M. Degeneration and aging affect the tensile behavior of human lumbar anulus fibrosus. Spine. December 15, 1995;20(24):2690-2701.|
|1994||Skaggs DL, Weidenbaum M, Iatridis JC, Ratcliffe A, Mow VC. Regional variation in tensile properties and biochemical composition of the human lumbar anulus fibrosus. Spine. June 1994;19(12):1310-1319.|
|1967||Hirsch C, Galante J. Laboratory conditions for tensile tests in annulus fibrosus from human intervertebral discs. Acta Orthop Scand. 1967;38(2):148-162.|
|2000||LeRoux MA. Altered Mechanics of the Meniscus With a Healing Tear: Experimental Testing and Biphasic Finite Element Analysis [PhD thesis]. Duke University; 2000.|
|2009||O'Connell GD. Degeneration Affects the Structural and Tissue Mechanics of the Intervertebral Disc [PhD thesis]. Philadelphia, PA: University of Pennsylvania; 2009.|