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TECHNICAL PAPERS: Bone/Orthopedic

Influence of Fixed Charge Density Magnitude and Distribution on the Intervertebral Disc: Applications of a Poroelastic and Chemical Electric (PEACE) Model

[+] Author and Article Information
James C. Iatridis

Dept. of Mechanical Engineering, University of Vermont, Burlington, VT 05405-0084

Jeffrey P. Laible

Dept. of Civil & Environmental Engineering, University of Vermont, Burlington, VT 05405-0084

Martin H. Krag

Dept. of Orthopaedics and Rehabilitation, and Vermont Back Research Center, University of Vermont, Burlington, VT 05405-0084

J Biomech Eng 125(1), 12-24 (Feb 14, 2003) (13 pages) doi:10.1115/1.1537190 History: Received April 01, 2001; Revised August 01, 2002; Online February 14, 2003
Copyright © 2003 by ASME
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References

Figures

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Experimental results (circles, from Drost et al. 1995) and simulation of the PEACE model (curves a,b,c) for a 1 dimensional confined compression study of canine annulus under chemical and mechanical loading. Displacement of anulus fibrosus specimens (d=4 mm diameter, h=1 mm thick) was measured while the NaCl bath concentration c* and load P were varied in 3 stages: 1) Conditioning, c*=0.6 M,P=0.08 MPa, 2) Swelling, c*=0.2 M,P=0.08 MPa and 3) Consolidation, c*=0.2 M,P=0.20 MPa. Curves a, b and c show the PEACE simulation at h=1 mm, 0.5 mm and 0.25 mm, respectively.
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Mesh for plane stress analysis of intervertebral disc slice. The numbers of three nodes are given for reference to the time histories of the loading and fluid flow.
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Fixed charge density distribution for healthy and degenerate intervertebral discs in the sagittal plane. The experimental data was digitized from Urban & Holm, 1986. The healthy and degenerate fixed charge distribution (a) were used to generate a 2-dimensional cF field over our finite element mesh for healthy (b) and degenerate (c) discs. The constant equivalent healthy fixed charge distribution cequivF was taken as the average fixed charge density over the surface of the healthy disc and can be seen as the horizontal plane in (b).
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Time history for the change in water content (-zeta) of the disc slice during the swelling phase and with creep loading for healthy (a) and degenerate (b) discs. The location of nodes 120, 104, and 92 are given in Fig. 2.
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Water displacement vectors for disc slices with (a) healthy fixed charge density (cF), (b) degenerate cF, and (c) constant equivalent healthy cF. All plots are at the same scale with the maximum fluid displacement vector of wmax=0.005 m.
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Change in water content (−ζ) for disc slices with (a) healthy, (b) degenerate, and (c) constant healthy equivalent fixed charge density distributions. Change in water content is measured after both swelling and compression stages of the experiment.
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Fluid (a, b) and solid (c, d) stress distributions for disc slices with healthy and degenerate fixed charge density distributions at equilibrium under compressive loading of −200,000 N/m2 . The fluid stress is equivalent to the negative of the pressure.
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Electric potential fields for (a) healthy and (b) degenerate disc slices subjected to swelling and compression loading immediately after the compressive load was applied.
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Electric potential field with applied potential difference across the right side of the disc slice with (a) healthy and (b) degenerate fixed charge density distribution. For the healthy disc the two potentials at A and B are 0 and −10.75 mV, respectively. For the degenerate disc the two potentials at A and B are 0 and −6.3 mV, respectively.
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Effect of applied electrical potential on water transport (dw/dt) for (a) healthy and (b) degenerated disc slices.

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