The causes of disc degeneration are unknown, but understanding its mechanisms is crucial to advancing treatment. The disc is composed of the nucleus pulposus, a hydrated gel, that is contained by the annulus fibrosus, a highly organized fibrocartilage ring. Under normal conditions a hydrostatic pressure is maintained within the nucleus pulposus, generating tensile stresses within the annulus fibrosus. During the early degenerative process the nucleus pulposus becomes less hydrated and more fibrotic, with mechanical consequences of decreased pressure and increased stiffness within the nucleus. This increases the loading and deformation of the annulus. These early nucleus changes are followed by structural and mechanical changes throughout the disc in more advanced disc degeneration. We hypothesize that increased loads and deformations in the annulus fibrosus, which are brought about by decreased pressure and increased stiffness in the nucleus pulposus, together with cyclic fatigue loading, are important mechanisms in disc degeneration. Altered loading of the annulus fibrosus may mediate degeneration through a direct mechanical fatigue mechanism, through biological processes, or a combination of both. Our study is designed to uncouple the roles of mechanical and biological factors, focusing here upon the mechanical factors. We employ a novel model to alter disc loading in a sheep cadaver that combines a chemonucleolytic agent, chondroitinase-ABC (C-ABC), to decrease pressure, with a collagen crosslinking agent, genipin, to increase stiffness.
Aim 1 Apply a cadaveric model of degeneration that alters the annulus fibrosus loading. Inject the nucleus pulposus according to four groups: C-ABC (to decrease pressure), genipin (to increase crosslinking), a combination of C-ABC and genipin, and sham control. Measure the mechanical and structural changes to A) the nucleus pulposus, and B) the motion segment.
Aim 2 Apply cyclic load to motion segments with modified nucleus pulposus according to the four groups in Aim 1. Measure the mechanical and structural changes to A) the nucleus pulposus and annulus fibrosus, B) the motion segment.
Aim 3 Calculate altered stresses and strains in the annulus fibrosus due to nucleus modification using a finite element model with a fiber-induced constitutive description of the annulus.

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
5R01AR050052-03
Application #
7208974
Study Section
Skeletal Biology Structure and Regeneration Study Section (SBSR)
Program Officer
Tyree, Bernadette
Project Start
2005-02-01
Project End
2009-01-31
Budget Start
2007-02-01
Budget End
2008-01-31
Support Year
3
Fiscal Year
2007
Total Cost
$278,431
Indirect Cost
Name
University of Pennsylvania
Department
Orthopedics
Type
Schools of Medicine
DUNS #
042250712
City
Philadelphia
State
PA
Country
United States
Zip Code
19104
Wright, Alexander C; Yoder, Jonathon H; Vresilovic, Edward J et al. (2016) Theory of MRI contrast in the annulus fibrosus of the intervertebral disc. MAGMA 29:711-22
Peloquin, John M; Elliott, Dawn M (2016) A comparison of stress in cracked fibrous tissue specimens with varied crack location, loading, and orientation using finite element analysis. J Mech Behav Biomed Mater 57:260-8
DeLucca, John F; Peloquin, John M; Smith, Lachlan J et al. (2016) MRI quantification of human spine cartilage endplate geometry: Comparison with age, degeneration, level, and disc geometry. J Orthop Res 34:1410-7
Peloquin, John M; Santare, Michael H; Elliott, Dawn M (2016) Advances in Quantification of Meniscus Tensile Mechanics Including Nonlinearity, Yield, and Failure. J Biomech Eng 138:021002
DeLucca, John F; Cortes, Daniel H; Jacobs, Nathan T et al. (2016) Human cartilage endplate permeability varies with degeneration and intervertebral disc site. J Biomech 49:550-7
Showalter, Brent L; DeLucca, John F; Peloquin, John M et al. (2016) Novel human intervertebral disc strain template to quantify regional three-dimensional strains in a population and compare to internal strains predicted by a finite element model. J Orthop Res 34:1264-73
Suydam, Stephen M; Soulas, Elizabeth M; Elliott, Dawn M et al. (2015) Viscoelastic properties of healthy achilles tendon are independent of isometric plantar flexion strength and cross-sectional area. J Orthop Res 33:926-31
Cortes, Daniel H; Suydam, Stephen M; Silbernagel, Karin Grävare et al. (2015) Continuous Shear Wave Elastography: A New Method to Measure Viscoelastic Properties of Tendons in Vivo. Ultrasound Med Biol 41:1518-29
Showalter, Brent L; Elliott, Dawn M; Chen, Weiliam et al. (2015) Evaluation of an In Situ Gelable and Injectable Hydrogel Treatment to Preserve Human Disc Mechanical Function Undergoing Physiologic Cyclic Loading Followed by Hydrated Recovery. J Biomech Eng 137:081008
Cortes, Daniel H; Magland, Jeremy F; Wright, Alexander C et al. (2014) The shear modulus of the nucleus pulposus measured using magnetic resonance elastography: a potential biomarker for intervertebral disc degeneration. Magn Reson Med 72:211-9

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