Mechanical Behavior of the Human Lumbar Intervertebral Disc With Polymeric Hydrogel Nucleus Implant: An Experimental and Finite Element Study

The origin of the lower back pain is often the degenerated lumbar intervertebral disc (IVD). We are proposing replacement of the degenerated nucleus by a PVA/PVP polymeric hydrogel implant. We hypothesize that a polymeric hydrogel nucleus implant can restore the normal biomechanics of the denucleated IVD by mimicking the natural load transfer phenomenon as in case of the intact IVD.

Lumbar IVDs (n=15) were harvested from human cadavers. In the first part, specimens were tested in four different conditions for compression: Intact, bone in plug, denucleated and Implanted. Hydrogel nucleus implants were chosen to have line-to-line fit in the created nuclear cavity. In the second part, nucleus implant material (modulus) and geometric (height and diameter) parameters were varied and specimens (n=9) were tested.

Nucleus implants with line-to-line fit significantly restored (88%) the compressive stiffness of the denucleated IVD. The synergistic effect between the implant and the intact annulus resulted in the nonlinear increase in implanted IVD stiffness, where Poisson effect of the hydrogel played major role. Nucleus implant parameters were observed to have a significant effect on the compressive stiffness. All implants with modulus in the tested range restored the compressive stiffness. The undersize implants resulted in incomplete restoration while oversize implants resulted in complete restoration compared to the BI condition.

Finite element models (FEM) were developed to simulate the actual test conditions and validated against the experimental results for all conditions. The annulus (defined as hyperelastic, isotropic) mainly determined the nonlinear response of the IVD. Validated FEMs predicted 120-3000 kPa as a feasible range for nucleus implant modulus. FEMs also predicted that overdiameter implant would be more effective than overheight implant in terms of stiffness restoration. Underdiameter implants, initially allowed inward deformation of the annulus and hence were less effective compared to underheight implants.

This research successfully proved the feasibility of PVA/PVP polymeric hydrogel as a replacement for degenerated nucleus. This approach may reduce the abnormal stresses on the annulus and thus, prevent/postpone the degeneration of the annulus. A validated FEM can be used as a design tool for optimization of hydrogel nucleus implants design and related feasibility studies.

Year	Entry
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.
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.
1975	Maroudas A, Stockwell RA, Nachemson A, Urban J. Factors involved in the nutrition of the human lumbar intervertebral disc: cellularity and diffusion of glucose in vitro. J Anat. September 1975;120(1):113-130.
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.
1993	Mizrahi J, Silva MJ, Keaveny TM, Edwards WT, Hayes WC. Finite-element stress analysis of the normal and osteoporotic lumbar vertebral body. Spine. October 15, 1993;18(14):2088-2096.
1967	Galante JO. Tensile properties of the human lumbar annulus fibrosus. Acta Orthop Scand. 1967;(suppl 100):1-91.
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.
1951	Virgin WJ. Experimental investigations into the physical properties of the intervertebral disc. J Bone Joint Surg. November 1951;33B(4):607-611.
1960	Roaf R. A study of the mechanics of spinal injuries. J Bone Joint Surg. November 1960;42B(4):810-823.
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.
1991	Crisco JJ III, Panjabi MM. The intersegmental and multisegmental muscles of the lumbar spine: a biomechanical model comparing lateral stabilizing potential. Spine. July 1991;16(7):793-799.
1986	Shirazi-Adl A, Ahmed AM, Shrivastava S. A finite element study of a lumbar motion segment subjected to pure sagittal plane moments. J Biomech. 1986;19(4):331-350.
1996	Antoniou J, Steffen T, Nelson F, Winterbottom N, Hollander AP, Poole RA, Aebi M, Alini M. The human lumbar intervertebral disc: evidence for changes in the biosynthesis and denaturation of the extracellular matrix with growth, maturation, ageing, and degeneration. J Clin Invest. August 15, 1996;98(4):996-1003.
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.
1986	Shirazi-Adl A, Ahmed AM, Shrivastava SC. Mechanical response of a lumbar motion segment in axial torque alone and combined with compression. Spine. November 1986;11(9):914-927.
1979	Schultz AB, Warwick DN, Berkson MH, Nachemson AL. Mechanical properties of human lumbar spine motion segments, I: responses in flexion, extension, lateral bending, and torsion. J Biomech Eng. February 1979;101(1):46-52.
1949	Friberg S, Hirsch C. Anatomical and clinical studies on lumbar disc degeneration. Acta Orthop Scand. 1949;19(2):222-242.
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.
1991	Brinckmann P, Grootenboer H. Change of disc height, radial disc bulge, and intradiscal pressure from discectomy: an in vitro investigation on human lumbar discs. Spine. June 1991;16(6):641-646.
2000	Adams MA, Freeman BJC, Morrison HP, Nelson IW, Dolan P. Mechanical initiation of intervertebral disc degeneration. Spine. July 1, 2000;25(13):1625-1636.
1970	Farfan HF, Cossette JW, Robertson GH, Wells RV, Kraus H. The effects of torsion on the lumbar intervertebral joints: the role of torsion in the production of disc degeneration. J Bone Joint Surg. April 1970;52A(3):468-497.
1994	Natarajan RN, Ke JH, Andersson GBJ. A model to study the disc degeneration process. Spine. February 1, 1994;19(3):259-265.
1954	Hirsch C, Nachemson A. New observations on the mechanical behavior of lumbar discs. Acta Orthop Scand. 1954;23(4):254-283.
1955	Hirsch C. The reaction of intervertebral discs to compression forces. J Bone Joint Surg. December 1955;37A(6):1188-1196.
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.
1979	Berkson MH, Nachemson A, Schultz AB. Mechanical properties of human lumbar spine motion segments, II: responses in compression and shear; influence of gross morphology. J Biomech Eng. February 1979;101(1):53-57.
1960	Nachemson A. Lumbar intradiscal pressure: experimental studies on post-mortem material. Acta Orthop Scand. 1960;31(suppl 43):1-104.
1957	Brown T, Hansen RJ, Yorra AJ. Some mechanical tests on the lumbosacral spine with particular reference to the intervertebral discs: a preliminary report. J Bone Joint Surg. October 1957;39A(5):1135-1164.
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.
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.
1982	Reuber M, Schultz A, Denis F, Spencer D. Bulging of lumbar intervertebral disks. J Biomech Eng. August 1982;104(3):187-192.
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.
1979	Andersson GBJ, Schultz AB. Effects of fluid injection on mechanical properties of intervertebral discs. J Biomech. 1979;12(6):453-458.
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.
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	White AA III, Panjabi MM. Clinical Biomechanics of the Spine. 2nd ed. Philadelphia, PA: J.B. Lippincott Company; 1990.
1983	Brinckmann P, Frobin W, Hierholzer E, Horst M. Deformation of the vertebral end-plate under axial loading of the spine. Spine. November–December 1983;8(8):851-856.
1992	McNally DS, Adams MA. Internal intervertebral disc mechanics as revealed by stress profilometry. Spine. January 1992;17(1):66-73.
1995	Buckwalter JA. Aging and degeneration of the human intervertebral disc. Spine. June 1995;20(11):1307-1314.

Year

Entry

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.

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.

1975

Maroudas A, Stockwell RA, Nachemson A, Urban J. Factors involved in the nutrition of the human lumbar intervertebral disc: cellularity and diffusion of glucose in vitro. J Anat. September 1975;120(1):113-130.

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.

1993

Mizrahi J, Silva MJ, Keaveny TM, Edwards WT, Hayes WC. Finite-element stress analysis of the normal and osteoporotic lumbar vertebral body. Spine. October 15, 1993;18(14):2088-2096.

1967

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

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.

1951

Virgin WJ. Experimental investigations into the physical properties of the intervertebral disc. J Bone Joint Surg. November 1951;33B(4):607-611.

1960

Roaf R. A study of the mechanics of spinal injuries. J Bone Joint Surg. November 1960;42B(4):810-823.

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.

1991

Crisco JJ III, Panjabi MM. The intersegmental and multisegmental muscles of the lumbar spine: a biomechanical model comparing lateral stabilizing potential. Spine. July 1991;16(7):793-799.

1986

Shirazi-Adl A, Ahmed AM, Shrivastava S. A finite element study of a lumbar motion segment subjected to pure sagittal plane moments. J Biomech. 1986;19(4):331-350.

1996

Antoniou J, Steffen T, Nelson F, Winterbottom N, Hollander AP, Poole RA, Aebi M, Alini M. The human lumbar intervertebral disc: evidence for changes in the biosynthesis and denaturation of the extracellular matrix with growth, maturation, ageing, and degeneration. J Clin Invest. August 15, 1996;98(4):996-1003.

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.

1986

Shirazi-Adl A, Ahmed AM, Shrivastava SC. Mechanical response of a lumbar motion segment in axial torque alone and combined with compression. Spine. November 1986;11(9):914-927.

1979

Schultz AB, Warwick DN, Berkson MH, Nachemson AL. Mechanical properties of human lumbar spine motion segments, I: responses in flexion, extension, lateral bending, and torsion. J Biomech Eng. February 1979;101(1):46-52.

1949

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

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.

1991

Brinckmann P, Grootenboer H. Change of disc height, radial disc bulge, and intradiscal pressure from discectomy: an in vitro investigation on human lumbar discs. Spine. June 1991;16(6):641-646.

2000

Adams MA, Freeman BJC, Morrison HP, Nelson IW, Dolan P. Mechanical initiation of intervertebral disc degeneration. Spine. July 1, 2000;25(13):1625-1636.

1970

Farfan HF, Cossette JW, Robertson GH, Wells RV, Kraus H. The effects of torsion on the lumbar intervertebral joints: the role of torsion in the production of disc degeneration. J Bone Joint Surg. April 1970;52A(3):468-497.

1994

Natarajan RN, Ke JH, Andersson GBJ. A model to study the disc degeneration process. Spine. February 1, 1994;19(3):259-265.

1954

Hirsch C, Nachemson A. New observations on the mechanical behavior of lumbar discs. Acta Orthop Scand. 1954;23(4):254-283.

1955

Hirsch C. The reaction of intervertebral discs to compression forces. J Bone Joint Surg. December 1955;37A(6):1188-1196.

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.

1979

Berkson MH, Nachemson A, Schultz AB. Mechanical properties of human lumbar spine motion segments, II: responses in compression and shear; influence of gross morphology. J Biomech Eng. February 1979;101(1):53-57.

1960

Nachemson A. Lumbar intradiscal pressure: experimental studies on post-mortem material. Acta Orthop Scand. 1960;31(suppl 43):1-104.

1957

Brown T, Hansen RJ, Yorra AJ. Some mechanical tests on the lumbosacral spine with particular reference to the intervertebral discs: a preliminary report. J Bone Joint Surg. October 1957;39A(5):1135-1164.

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.

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.

1982

Reuber M, Schultz A, Denis F, Spencer D. Bulging of lumbar intervertebral disks. J Biomech Eng. August 1982;104(3):187-192.

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.

1979

Andersson GBJ, Schultz AB. Effects of fluid injection on mechanical properties of intervertebral discs. J Biomech. 1979;12(6):453-458.

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.

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

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

1983

Brinckmann P, Frobin W, Hierholzer E, Horst M. Deformation of the vertebral end-plate under axial loading of the spine. Spine. November–December 1983;8(8):851-856.

1992

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

1995

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

Year	Entry
2006	Thomas JD. Development of Injectable Hydrogels for Nucleus Pulposus Replacement [PhD thesis]. Drexel University; June 2006.
2019	Yang B. Simulating Intervertebral Disc Mechanics Using Finite Element Method [PhD thesis]. Berkeley, CA: Berkeley, University of California; 2019.

Year

Entry

2006

Thomas JD. Development of Injectable Hydrogels for Nucleus Pulposus Replacement [PhD thesis]. Drexel University; June 2006.

2019

Yang B. Simulating Intervertebral Disc Mechanics Using Finite Element Method [PhD thesis]. Berkeley, CA: Berkeley, University of California; 2019.