Finite Element Analysis and Materials Characterization of Changes Due to Aging and Degeneration of the Human Intervertebral Disc

Intervertebral disc (IVD) degeneration occurs with aging, and may be a major cause of back pain. Alterations in major biochemical constituents of the IVD have been shown to coincide with aging and degeneration, and can subsequently alter the disc's ability to support load. A significant biochemical change that takes place in degeneration is the loss of proteoglycans (PGs) in the nucleus pulposus (NP). PGs work to resist mechanical forces in the NP through hydration of the molecules, providing hydrostatic pressure to the annulus fibrosus (AF).

Poroelastic theory with osmotic swelling, created for the simulation of articular cartilage, is applied to a finite element model (FEM) of a human IVD throughout a daily loading cycle. The model was validated against experimental studies of axial displacement, radial bulge, and fluid volume lost. The incorporation of osmotic swelling allows for the study of the effect of PGs on the mechanics of the IVD.

In this study, the IVD FEM is created and validated, and the response of the model to a diurnal loading cycle is investigated. Various degrees of degeneration are examined, as well as the intervention techniques of a hydrogel NP replacement implant and the restoration of the PG content in the IVD for the restoration of degenerated discs. A NP hydrogel replacement decreases the stresses in the AF, and restoration of the PG content reduces stresses in both the NP and AF, which may lead to deceleration of the degenerative process.

To develop a more reliable and possibly diagnostic tool for the determination of IVD biomolecular components, Fourier transform infrared (FTIR) spectroscopy is investigated for the analysis of IVD tissue. The results of the study suggest FTIR as a dependable method for quantifying degeneration.

The model developed here provides a novel tool for the investigation of IVD tissue mechanics through the diurnal cycle. The incorporation of poroelastic components allows for the investigation of key biomolecular changes that as demonstrated have a marked effect on IVD mechanics. Accurate determination of biomolecular changes in the IVD will allow for a physiologically relevant model to be developed and possible detection of earlier intervention points.

Year	Entry
1992	Simon BR. Multiphase poroelastic finite element models for soft tissue structures. Appl Mech Rev. June 1992;45(6):191-218.
2001	Huang C-Y, Mow VC, Ateshian GA. The role of flow-independent viscoelasticity in the biphasic tensile and compressive responses of articular cartilage. J Biomech Eng. October 2001;123(5):410-417.
1994	Best BA, Guilak F, Setton LA, Zhu W, Saed-Nejad F, Ratcliffe A, Weidenbaum M, Mow VC. Compressive mechanical properties of the human anulus fibrosus and their relationship to biochemical composition. Spine. January 15, 1994;19(2):212-221.
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.
1988	Urban JPG, McMullin JF. Swelling pressure of the lumbar intervertebral discs influence of age, spinal level, composition, and degeneration. Spine. February 1988;13(2):179-187.
1985	Urban JPG, McMullin JF. Swelling pressure of the inervertebral disc: influence of proteoglycan and collagen contents. Biorheology. 1985;22(2):145-157.
2004	Sun DD, Guo XE, Likhitpanichkul M, Lai WM, Mow VC. The influence of the fixed negative charges on mechanical and electrical behaviors of articular cartilage under unconfined compression. J Biomech Eng. February 2004;126(1):6-16.
1981	Urban JPG, Maroudas A. Swelling of the intervertebral disc in vitro. Connect Tissue Res. 1981;9(1):1-10.
2005	Johannessen W, Elliott DM. Effects of degeneration on the biphasic material properties of human nucleus pulposus in confined compression. Spine. December 15, 2005;30(24):E724-E729.
1967	Galante JO. Tensile properties of the human lumbar annulus fibrosus. Acta Orthop Scand. 1967;(suppl 100):1-91.
1970	Nachemson A, Lewin T, Maroudas A, Freeman MAR. In vitro diffusion of dye through the end-plates and the annulus fibrosus of human lumbar inter-vertebral discs. Acta Orthop Scand. 1970;41(3):589-607.
1996	Iatridis JC, Weidenbaum M, Setton LA, Mow VC. Is the nucleus pulposus a solid or a fluid? mechanical behaviors of the nucleus pulposus of the human intervertebral disc. Spine. May 15, 1996;21(15):1174-1184.
2003	Wilson W, van Rietbergen B, van Donkelaar CC, Huiskes R. Pathways of load-induced cartilage damage causing cartilage degeneration in the knee after meniscectomy. J Biomech. June 2003;36(6):845-851.
2001	DiSilvestro MR, Zhu Q, Suh J-KF. Biphasic poroviscoelastic simulation of the unconfined compression of articular cartilage, II: effect of variable strain rates. J Biomech Eng. April 2001;123(2):198-200.
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.
1993	Setton LA, Zhu W, Weidenbaum M, Ratcliffe A, Mow VC. Compressive properties of the cartilaginous end-plate of the baboon lumbar spine. J Orthop Res. March 1993;11(2):228-239.
2001	Elliott DM, Setton LA. Anisotropic and inhomogeneous tensile behavior of the human anulus fibrosus: experimental measurement and material model predictions. J Biomech Eng. June 2001;123(3):256-263.
2000	Elliott DM, Setton LA. A linear material model for fiber-induced anisotropy of the anulus fibrosus. J Biomech Eng. April 2000;122(2):173-179.
2002	Elliott DM, Narmoneva DA, Setton LA. Direct measurement of the Poisson’s ratio of human patella cartilage in tension. J Biomech Eng. April 2002;124(2):223-228.
1999	Wilke H-J, Neef P, Caimi M, Hoogland T, Claes LE. New in vivo measurements of pressures in the intervertebral disc in daily life. Spine. April 15, 1999;24(8):755-762.
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.
1988	Miller JAA, Schmatz C, Schultz AB. Lumbar disc degeneration: correlation with age, sex, and spine level in 600 autopsy specimens. Spine. February 1988;13(2):173-178.
2003	Urban JPG, Roberts S. Degeneration of the intervertebral disc. Arthritis Res Ther. 2003;5(3):120-130.
1979	Urban JPG, Maroudas A, Bayliss MT, Dillon J. Swelling pressures of proteoglycans at the concentrations found in cartilaginous tissues. Biorheology. 1979;16(6):447-464.
1983	Adams MA, Hutton WC. The effect of posture on the fluid content of lumbar intervertebral discs. Spine. September 1983;8(8):665-671.
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 1998;31(6):535-544.
1949	Friberg S, Hirsch C. Anatomical and clinical studies on lumbar disc degeneration. Acta Orthop Scand. 1949;19(2):222-242.
1991	Lai WM, Hou JS, Mow VC. A triphasic theory for the swelling and deformation behaviors of articular cartilage. J Biomech Eng. August 1991;113(3):245-258.
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.
1976	Mansour JM, Mow VC. The permeability of articular cartilage under compressive strain and at high pressures. J Bone Joint Surg. June 1976;58A(4):509-516.
1993	Laible JP, Pflaster DS, Krag MH, Simon BR, Haugh LD. A poroelastic-swelling finite element model with application to the intervertebral disc. Spine. April 1993;18(5):659-670.
2005	Wilson W, van Donkelaar CC, van Rietbergen B, Huiskes R. A fibril-reinforced poroviscoelastic swelling model for articular cartilage. J Biomech. June 2005;38(6):1195-1204.
1998	Wu JZ, Herzog W, Epstein M. Evaluation of the finite element software ABAQUS for biomechanical modelling of biphasic tissues. J Biomech. February 1998;31(2):165-169.
1999	Andersson GBJ. Epidemiological features of chronic low-back pain. Lancet. August 14, 1999;354(9178):581-585.
2004	Ferguson SJ, Ito K, Nolte L-P. Fluid flow and convective transport of solutes within the intervertebral disc. J Biomech. February 2004;37(2):213-221.
1985	Simon BR, Wu JSS, Carlton MW, Evans JH, Kazarian LE. Structural models for human spinal motion segments based on a poroelastic view of the intervertebral disk. J Biomech Eng. November 1985;107(4):327-335.
2006	Guerin HAL, Elliott DM. Degeneration affects the fiber reorientation of human annulus fibrosus under tensile load. J Biomech. 2006;39(8):1410-1418.
1991	Dillaman RM, Roer RD, Gay DM. Fluid movement in bone: theoretical and empirical. J Biomech. 1991;24(suppl 1):163-177.
2004	Roughley PJ. Biology of intervertebral disc aging and degeneration: involvement of the extracellular matrix. Spine. December 1, 2004;29(23):2691-2699.
1980	Mow VC, Kuei SC, Lai WM, Armstrong CG. Biphasic creep and stress relaxation of articular cartilage in compression: theory and experiments. J Biomech Eng. February 1980;102(1):73-84.
1996	Argoubi M, Shirazi-Adl A. Poroelastic creep response analysis of a lumbar motion segment in compression. J Biomech. October 1996;29(10):1331-1339.
1984	Mow VC, Holmes MH, Lai WM. Fluid transport and mechanical properties of articular cartilage: a review. J Biomech. 1984;17(5):377-394.
1997	Paschalis EP, Betts F, DiCarlo E, Mendelsohn R, Boskey AL. FTIR microspectroscopic analysis of normal human cortical and trabecular bone. Calcif Tiss Int. December 1997;61(6):480-486.
1978	Lin HS, Liu YK, Adams KH. Mechanical response of the lumbar intervertebral joint under physiological (complex) loading. J Bone Joint Surg. January 1978;60A(1):41-55.
1997	Iatridis JC, Setton LA, Weidenbaum M, Mow VC. Alterations in the mechanical behavior of the human lumbar nucleus pulposus with degeneration and aging. J Orthop Res. March 1997;15(2):318-322.
2006	Adams MA, Roughley PJ. What is intervertebral disc degeneration, and what causes it? Spine. August 15, 2006;31(18):2151-2161.
2008	Raj PP. Intervertebral disc: anatomy-physiology-pathophysiology-treatment. Pain Pract. January–February 2008;8(1):18-44.
1976	Kulak RF, Belytschko TB, Schultz AB, Galante JO. Nonlinear behavior of the human intervertebral disc under axial load. J Biomech. 1976;9(6):377-386.
2000	Luoma K, Riihimäki H, Luukkonen R, Raininko R, Viikari-Juntura E, Lamminen A. Low back pain in relation to lumbar disc degeneration. Spine. February 15, 2000;25(4):487-492.
1998	Suh J-K, Bai S. Finite element formulation of biphasic poroviscoelastic model for articular cartilage. J Biomech Eng. April 1998;120(2):195-201.
1997	Iatridis JC, Setton LA, Weidenbaum M, Mow VC. The viscoelastic behavior of the non-degenerate human lumbar nucleus pulposus in shear. J Biomech. October 1997;30(10):1005-1013.
1980	Bowen RM. Incompressible porous media models by use of the theory of mixtures. Int J Eng Sci. 1980;18(9):1129-1148.
1996	Ebara S, Iatridis JC, Setton LA, Foster RJ, Mow VC, Weidenbaum M. Tensile properties of nondegenerate human lumbar anulus fibrosus. Spine. March 15, 1996;21(4):452-461.
1992	Osti OL, Vernon-Roberts B, Moore R, Fraser RD. Annular tears and disc degeneration in the lumbar spine: a post-mortem study of 135 discs. J Bone Joint Surg. September 1992;74B(5):678-682.
1995	Drost MR, Willems P, Snijders H, Huyghe JM, Janssen JD, Huson A. Confined compression of canine annulus fibrosus under chemical and mechanical loading. J Biomech Eng. November 1995;117(4):390-396.
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.
1999	Gu WY, Mao XG, Foster RJ, Weidenbaum M, Mow VC, Rawlins BA. The anisotropic hydraulic permeability of human lumbar anulus fibrosus: influence of age, degeneration, direction, and water content. Spine. December 1, 1999;24(23):2449-2455.
1981	Lai WM, Mow VC, Roth V. Effects of nonlinear strain-dependent permeability and rate of compression on the stress behavior of articular cartilage. J Biomech Eng. May 1981;103(2):61-66.
2004	Wilson W, van Donkelaar CC, van Rietbergen B, Ito K, Huiskes R. Stresses in the local collagen network of articular cartilage: a poroviscoelastic fibril-reinforced finite element study. J Biomech. March 2004;37(3):357-366.
1990	White AA III, Panjabi MM. Clinical Biomechanics of the Spine. 2nd ed. Philadelphia, PA: J.B. Lippincott Company; 1990.
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.
1992	McNally DS, Adams MA. Internal intervertebral disc mechanics as revealed by stress profilometry. Spine. January 1992;17(1):66-73.
2001	DiSilvestro MR, Zhu Q, Wong M, Jurvelin JS, Suh J-KF. Biphasic poroviscoelastic simulation of the unconfined compression of articular cartilage, I: simultaneous prediction of reaction force and lateral displacement. J Biomech Eng. April 2001;123(2):191-197.
2003	Gu WY, Yao H. Effects of hydration and fixed charge density on fluid transport in charged hydrated soft tissues. Ann Biomed Eng. November 2003;31(10):1162-1170.
2000	Carden A, Morris MD. Application of vibrational spectroscopy to the study of mineralized tissues (review). J Biomed Opt. July 2000;5(3):259-268.
1995	Buckwalter JA. Aging and degeneration of the human intervertebral disc. Spine. June 1995;20(11):1307-1314.
2002	Boos N, Weissbach S, Rohrbach H, Weiler C, Spratt KF, Nerlich AG. Classification of age-related changes in lumbar intervertebral discs. Spine. December 1, 2002;27(23):2631-2644.

Year

Entry

1992

Simon BR. Multiphase poroelastic finite element models for soft tissue structures. Appl Mech Rev. June 1992;45(6):191-218.

2001

Huang C-Y, Mow VC, Ateshian GA. The role of flow-independent viscoelasticity in the biphasic tensile and compressive responses of articular cartilage. J Biomech Eng. October 2001;123(5):410-417.

1994

Best BA, Guilak F, Setton LA, Zhu W, Saed-Nejad F, Ratcliffe A, Weidenbaum M, Mow VC. Compressive mechanical properties of the human anulus fibrosus and their relationship to biochemical composition. Spine. January 15, 1994;19(2):212-221.

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.

1988

Urban JPG, McMullin JF. Swelling pressure of the lumbar intervertebral discs influence of age, spinal level, composition, and degeneration. Spine. February 1988;13(2):179-187.

1985

Urban JPG, McMullin JF. Swelling pressure of the inervertebral disc: influence of proteoglycan and collagen contents. Biorheology. 1985;22(2):145-157.

2004

Sun DD, Guo XE, Likhitpanichkul M, Lai WM, Mow VC. The influence of the fixed negative charges on mechanical and electrical behaviors of articular cartilage under unconfined compression. J Biomech Eng. February 2004;126(1):6-16.

1981

Urban JPG, Maroudas A. Swelling of the intervertebral disc in vitro. Connect Tissue Res. 1981;9(1):1-10.

2005

Johannessen W, Elliott DM. Effects of degeneration on the biphasic material properties of human nucleus pulposus in confined compression. Spine. December 15, 2005;30(24):E724-E729.

1967

Galante JO. Tensile properties of the human lumbar annulus fibrosus. Acta Orthop Scand. 1967;(suppl 100):1-91.

1970

Nachemson A, Lewin T, Maroudas A, Freeman MAR. In vitro diffusion of dye through the end-plates and the annulus fibrosus of human lumbar inter-vertebral discs. Acta Orthop Scand. 1970;41(3):589-607.

1996

Iatridis JC, Weidenbaum M, Setton LA, Mow VC. Is the nucleus pulposus a solid or a fluid? mechanical behaviors of the nucleus pulposus of the human intervertebral disc. Spine. May 15, 1996;21(15):1174-1184.

2003

Wilson W, van Rietbergen B, van Donkelaar CC, Huiskes R. Pathways of load-induced cartilage damage causing cartilage degeneration in the knee after meniscectomy. J Biomech. June 2003;36(6):845-851.

2001

DiSilvestro MR, Zhu Q, Suh J-KF. Biphasic poroviscoelastic simulation of the unconfined compression of articular cartilage, II: effect of variable strain rates. J Biomech Eng. April 2001;123(2):198-200.

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.

1993

Setton LA, Zhu W, Weidenbaum M, Ratcliffe A, Mow VC. Compressive properties of the cartilaginous end-plate of the baboon lumbar spine. J Orthop Res. March 1993;11(2):228-239.

2001

Elliott DM, Setton LA. Anisotropic and inhomogeneous tensile behavior of the human anulus fibrosus: experimental measurement and material model predictions. J Biomech Eng. June 2001;123(3):256-263.

2000

Elliott DM, Setton LA. A linear material model for fiber-induced anisotropy of the anulus fibrosus. J Biomech Eng. April 2000;122(2):173-179.

2002

Elliott DM, Narmoneva DA, Setton LA. Direct measurement of the Poisson’s ratio of human patella cartilage in tension. J Biomech Eng. April 2002;124(2):223-228.

1999

Wilke H-J, Neef P, Caimi M, Hoogland T, Claes LE. New in vivo measurements of pressures in the intervertebral disc in daily life. Spine. April 15, 1999;24(8):755-762.

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.

1988

Miller JAA, Schmatz C, Schultz AB. Lumbar disc degeneration: correlation with age, sex, and spine level in 600 autopsy specimens. Spine. February 1988;13(2):173-178.

2003

Urban JPG, Roberts S. Degeneration of the intervertebral disc. Arthritis Res Ther. 2003;5(3):120-130.

1979

Urban JPG, Maroudas A, Bayliss MT, Dillon J. Swelling pressures of proteoglycans at the concentrations found in cartilaginous tissues. Biorheology. 1979;16(6):447-464.

1983

Adams MA, Hutton WC. The effect of posture on the fluid content of lumbar intervertebral discs. Spine. September 1983;8(8):665-671.

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 1998;31(6):535-544.

1949

Friberg S, Hirsch C. Anatomical and clinical studies on lumbar disc degeneration. Acta Orthop Scand. 1949;19(2):222-242.

1991

Lai WM, Hou JS, Mow VC. A triphasic theory for the swelling and deformation behaviors of articular cartilage. J Biomech Eng. August 1991;113(3):245-258.

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.

1976

Mansour JM, Mow VC. The permeability of articular cartilage under compressive strain and at high pressures. J Bone Joint Surg. June 1976;58A(4):509-516.

1993

Laible JP, Pflaster DS, Krag MH, Simon BR, Haugh LD. A poroelastic-swelling finite element model with application to the intervertebral disc. Spine. April 1993;18(5):659-670.

2005

Wilson W, van Donkelaar CC, van Rietbergen B, Huiskes R. A fibril-reinforced poroviscoelastic swelling model for articular cartilage. J Biomech. June 2005;38(6):1195-1204.

1998

Wu JZ, Herzog W, Epstein M. Evaluation of the finite element software ABAQUS for biomechanical modelling of biphasic tissues. J Biomech. February 1998;31(2):165-169.

1999

Andersson GBJ. Epidemiological features of chronic low-back pain. Lancet. August 14, 1999;354(9178):581-585.

2004

Ferguson SJ, Ito K, Nolte L-P. Fluid flow and convective transport of solutes within the intervertebral disc. J Biomech. February 2004;37(2):213-221.

1985

Simon BR, Wu JSS, Carlton MW, Evans JH, Kazarian LE. Structural models for human spinal motion segments based on a poroelastic view of the intervertebral disk. J Biomech Eng. November 1985;107(4):327-335.

2006

Guerin HAL, Elliott DM. Degeneration affects the fiber reorientation of human annulus fibrosus under tensile load. J Biomech. 2006;39(8):1410-1418.

1991

Dillaman RM, Roer RD, Gay DM. Fluid movement in bone: theoretical and empirical. J Biomech. 1991;24(suppl 1):163-177.

2004

Roughley PJ. Biology of intervertebral disc aging and degeneration: involvement of the extracellular matrix. Spine. December 1, 2004;29(23):2691-2699.

1980

Mow VC, Kuei SC, Lai WM, Armstrong CG. Biphasic creep and stress relaxation of articular cartilage in compression: theory and experiments. J Biomech Eng. February 1980;102(1):73-84.

1996

Argoubi M, Shirazi-Adl A. Poroelastic creep response analysis of a lumbar motion segment in compression. J Biomech. October 1996;29(10):1331-1339.

1984

Mow VC, Holmes MH, Lai WM. Fluid transport and mechanical properties of articular cartilage: a review. J Biomech. 1984;17(5):377-394.

1997

Paschalis EP, Betts F, DiCarlo E, Mendelsohn R, Boskey AL. FTIR microspectroscopic analysis of normal human cortical and trabecular bone. Calcif Tiss Int. December 1997;61(6):480-486.

1978

Lin HS, Liu YK, Adams KH. Mechanical response of the lumbar intervertebral joint under physiological (complex) loading. J Bone Joint Surg. January 1978;60A(1):41-55.

1997

Iatridis JC, Setton LA, Weidenbaum M, Mow VC. Alterations in the mechanical behavior of the human lumbar nucleus pulposus with degeneration and aging. J Orthop Res. March 1997;15(2):318-322.

2006

Adams MA, Roughley PJ. What is intervertebral disc degeneration, and what causes it? Spine. August 15, 2006;31(18):2151-2161.

2008

Raj PP. Intervertebral disc: anatomy-physiology-pathophysiology-treatment. Pain Pract. January–February 2008;8(1):18-44.

1976

Kulak RF, Belytschko TB, Schultz AB, Galante JO. Nonlinear behavior of the human intervertebral disc under axial load. J Biomech. 1976;9(6):377-386.

2000

Luoma K, Riihimäki H, Luukkonen R, Raininko R, Viikari-Juntura E, Lamminen A. Low back pain in relation to lumbar disc degeneration. Spine. February 15, 2000;25(4):487-492.

1998

Suh J-K, Bai S. Finite element formulation of biphasic poroviscoelastic model for articular cartilage. J Biomech Eng. April 1998;120(2):195-201.

1997

Iatridis JC, Setton LA, Weidenbaum M, Mow VC. The viscoelastic behavior of the non-degenerate human lumbar nucleus pulposus in shear. J Biomech. October 1997;30(10):1005-1013.

1980

Bowen RM. Incompressible porous media models by use of the theory of mixtures. Int J Eng Sci. 1980;18(9):1129-1148.

1996

Ebara S, Iatridis JC, Setton LA, Foster RJ, Mow VC, Weidenbaum M. Tensile properties of nondegenerate human lumbar anulus fibrosus. Spine. March 15, 1996;21(4):452-461.

1992

Osti OL, Vernon-Roberts B, Moore R, Fraser RD. Annular tears and disc degeneration in the lumbar spine: a post-mortem study of 135 discs. J Bone Joint Surg. September 1992;74B(5):678-682.

1995

Drost MR, Willems P, Snijders H, Huyghe JM, Janssen JD, Huson A. Confined compression of canine annulus fibrosus under chemical and mechanical loading. J Biomech Eng. November 1995;117(4):390-396.

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.

1999

Gu WY, Mao XG, Foster RJ, Weidenbaum M, Mow VC, Rawlins BA. The anisotropic hydraulic permeability of human lumbar anulus fibrosus: influence of age, degeneration, direction, and water content. Spine. December 1, 1999;24(23):2449-2455.

1981

Lai WM, Mow VC, Roth V. Effects of nonlinear strain-dependent permeability and rate of compression on the stress behavior of articular cartilage. J Biomech Eng. May 1981;103(2):61-66.

2004

Wilson W, van Donkelaar CC, van Rietbergen B, Ito K, Huiskes R. Stresses in the local collagen network of articular cartilage: a poroviscoelastic fibril-reinforced finite element study. J Biomech. March 2004;37(3):357-366.

1990

White AA III, Panjabi MM. Clinical Biomechanics of the Spine. 2nd ed. Philadelphia, PA: J.B. Lippincott Company; 1990.

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.

1992

McNally DS, Adams MA. Internal intervertebral disc mechanics as revealed by stress profilometry. Spine. January 1992;17(1):66-73.

2001

DiSilvestro MR, Zhu Q, Wong M, Jurvelin JS, Suh J-KF. Biphasic poroviscoelastic simulation of the unconfined compression of articular cartilage, I: simultaneous prediction of reaction force and lateral displacement. J Biomech Eng. April 2001;123(2):191-197.

2003

Gu WY, Yao H. Effects of hydration and fixed charge density on fluid transport in charged hydrated soft tissues. Ann Biomed Eng. November 2003;31(10):1162-1170.

2000

Carden A, Morris MD. Application of vibrational spectroscopy to the study of mineralized tissues (review). J Biomed Opt. July 2000;5(3):259-268.

1995

Buckwalter JA. Aging and degeneration of the human intervertebral disc. Spine. June 1995;20(11):1307-1314.

2002

Boos N, Weissbach S, Rohrbach H, Weiler C, Spratt KF, Nerlich AG. Classification of age-related changes in lumbar intervertebral discs. Spine. December 1, 2002;27(23):2631-2644.

Year	Entry
2011	Sarkar S. Synthesis and Characterization of a Chondroitin Sulfate Based Hybrid Bio/synthetic Biomimetic Aggrecan Macromolecule [PhD thesis]. Drexel University; September 2011.
2013	Jamison D IV. Mechanical Characterization of the Human Lumbar Intervertebral Disc Subjected to Impact Loading Conditions [PhD thesis]. Drexel University; August 2013.

Year

Entry

2011

Sarkar S. Synthesis and Characterization of a Chondroitin Sulfate Based Hybrid Bio/synthetic Biomimetic Aggrecan Macromolecule [PhD thesis]. Drexel University; September 2011.

2013

Jamison D IV. Mechanical Characterization of the Human Lumbar Intervertebral Disc Subjected to Impact Loading Conditions [PhD thesis]. Drexel University; August 2013.