The anisotropic hydraulic permeability of human lumbar anulus fibrosus

Influence of age, degeneration, direction, and water content

Weiyong Gu, X. G. Mao, R. J. Foster, M. Weidenbaum, V. C. Mow, B. A. Rawlins

Research output: Contribution to journalArticle

126 Citations (Scopus)

Abstract

Study Design. Experimental investigation to determine the effect of intervertebral disc degeneration on the kinetic behavior of fluid in human anulus fibrosus. Objectives. To measure the hydraulic permeability coefficient of anulus fibrosus specimens in the axial, circumferential, and radial directions to determine the anisotropic permeability behavior of nondegenerate and degenerate human intervertebral discs over a range of ages. Summary of Background Data. Fluid, a major component of normal intervertebral discs, plays a significant role in their load-supporting mechanisms. Transport of fluid through the intervertebral disc is important for cell nutrition and disc viscoelastic and swelling behaviors. The hydraulic permeability coefficient is the most important material property governing the rate of fluid transport. However, little is known about the anisotropic behavior of this kinetic property and how it is influenced by disc degeneration. Methods. Using a permeation testing apparatus developed recently, testing was performed on 306 axial, circumferential, and radial anulus fibrosus specimens from the posterolateral region of 30 human lumbar (L2-L3) discs. A new method, flow-controlled testing protocol, was developed to measure the hydraulic permeability coefficient. Results. The hydraulic permeability coefficient of anulus fibrosus depended significantly on the disc degenerative grade (P = 0.0001) and flow direction (P = 0.0001). For the nondegenerate group (Grade I), the hydraulic permeability was significantly anisotropic (P< 0.05), with the greatest value in the radial direction (1.924 x 10-15 m4/Ns) and the lowest value in the circumferential direction (1.147 x 10-15 m4/Ns). This anisotropic kinetic (flow) behavior of anulus fibrosus varied with disc degeneration. For the Grade III specimen group, there was no significant difference in hydraulic permeability coefficient among the three major directions (P = 0.37). With disc degeneration, the hydraulic permeability coefficient was decreased in the radial direction and increased in the axial and cirCumferential directions. The variations of hydraulic permeability coefficient from nondegenerate discs (Grade I) to mildly degenerate discs (Grade II) in each direction were significant (P< 0.05). However, the changes in permeability from Grade II to Grade III groups were not significant (P > 0.05) except in the circumferential direction (3.8% increase; P < 0.05). Conclusions. The hydraulic permeability of human nondegenerate anulus fibrosus is direction-dependent (i.e., anisotropic), with the greatest permeability in the radial direction. With disc degeneration, the radial permeability of anulus fibrosus decreases, mainly because of decreased water content, and the axial and circumferential permeability coefficients increase, mainly because of structural change, leading to more isotropic permeability behavior for Grade III discs.

Original languageEnglish
Pages (from-to)2449-2455
Number of pages7
JournalSpine
Volume24
Issue number23
DOIs
StatePublished - Dec 1 1999

Fingerprint

Permeability
Water
Intervertebral Disc Degeneration
Intervertebral Disc
Direction compound
Annulus Fibrosus

Keywords

  • Anisotropic
  • Anulus fibrosus
  • Degeneration
  • Hydraulic permeability
  • Intervertebral disc
  • Soft tissue mechanics

ASJC Scopus subject areas

  • Physiology
  • Clinical Neurology
  • Orthopedics and Sports Medicine

Cite this

The anisotropic hydraulic permeability of human lumbar anulus fibrosus : Influence of age, degeneration, direction, and water content. / Gu, Weiyong; Mao, X. G.; Foster, R. J.; Weidenbaum, M.; Mow, V. C.; Rawlins, B. A.

In: Spine, Vol. 24, No. 23, 01.12.1999, p. 2449-2455.

Research output: Contribution to journalArticle

Gu, Weiyong ; Mao, X. G. ; Foster, R. J. ; Weidenbaum, M. ; Mow, V. C. ; Rawlins, B. A. / The anisotropic hydraulic permeability of human lumbar anulus fibrosus : Influence of age, degeneration, direction, and water content. In: Spine. 1999 ; Vol. 24, No. 23. pp. 2449-2455.
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abstract = "Study Design. Experimental investigation to determine the effect of intervertebral disc degeneration on the kinetic behavior of fluid in human anulus fibrosus. Objectives. To measure the hydraulic permeability coefficient of anulus fibrosus specimens in the axial, circumferential, and radial directions to determine the anisotropic permeability behavior of nondegenerate and degenerate human intervertebral discs over a range of ages. Summary of Background Data. Fluid, a major component of normal intervertebral discs, plays a significant role in their load-supporting mechanisms. Transport of fluid through the intervertebral disc is important for cell nutrition and disc viscoelastic and swelling behaviors. The hydraulic permeability coefficient is the most important material property governing the rate of fluid transport. However, little is known about the anisotropic behavior of this kinetic property and how it is influenced by disc degeneration. Methods. Using a permeation testing apparatus developed recently, testing was performed on 306 axial, circumferential, and radial anulus fibrosus specimens from the posterolateral region of 30 human lumbar (L2-L3) discs. A new method, flow-controlled testing protocol, was developed to measure the hydraulic permeability coefficient. Results. The hydraulic permeability coefficient of anulus fibrosus depended significantly on the disc degenerative grade (P = 0.0001) and flow direction (P = 0.0001). For the nondegenerate group (Grade I), the hydraulic permeability was significantly anisotropic (P< 0.05), with the greatest value in the radial direction (1.924 x 10-15 m4/Ns) and the lowest value in the circumferential direction (1.147 x 10-15 m4/Ns). This anisotropic kinetic (flow) behavior of anulus fibrosus varied with disc degeneration. For the Grade III specimen group, there was no significant difference in hydraulic permeability coefficient among the three major directions (P = 0.37). With disc degeneration, the hydraulic permeability coefficient was decreased in the radial direction and increased in the axial and cirCumferential directions. The variations of hydraulic permeability coefficient from nondegenerate discs (Grade I) to mildly degenerate discs (Grade II) in each direction were significant (P< 0.05). However, the changes in permeability from Grade II to Grade III groups were not significant (P > 0.05) except in the circumferential direction (3.8{\%} increase; P < 0.05). Conclusions. The hydraulic permeability of human nondegenerate anulus fibrosus is direction-dependent (i.e., anisotropic), with the greatest permeability in the radial direction. With disc degeneration, the radial permeability of anulus fibrosus decreases, mainly because of decreased water content, and the axial and circumferential permeability coefficients increase, mainly because of structural change, leading to more isotropic permeability behavior for Grade III discs.",
keywords = "Anisotropic, Anulus fibrosus, Degeneration, Hydraulic permeability, Intervertebral disc, Soft tissue mechanics",
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T1 - The anisotropic hydraulic permeability of human lumbar anulus fibrosus

T2 - Influence of age, degeneration, direction, and water content

AU - Gu, Weiyong

AU - Mao, X. G.

AU - Foster, R. J.

AU - Weidenbaum, M.

AU - Mow, V. C.

AU - Rawlins, B. A.

PY - 1999/12/1

Y1 - 1999/12/1

N2 - Study Design. Experimental investigation to determine the effect of intervertebral disc degeneration on the kinetic behavior of fluid in human anulus fibrosus. Objectives. To measure the hydraulic permeability coefficient of anulus fibrosus specimens in the axial, circumferential, and radial directions to determine the anisotropic permeability behavior of nondegenerate and degenerate human intervertebral discs over a range of ages. Summary of Background Data. Fluid, a major component of normal intervertebral discs, plays a significant role in their load-supporting mechanisms. Transport of fluid through the intervertebral disc is important for cell nutrition and disc viscoelastic and swelling behaviors. The hydraulic permeability coefficient is the most important material property governing the rate of fluid transport. However, little is known about the anisotropic behavior of this kinetic property and how it is influenced by disc degeneration. Methods. Using a permeation testing apparatus developed recently, testing was performed on 306 axial, circumferential, and radial anulus fibrosus specimens from the posterolateral region of 30 human lumbar (L2-L3) discs. A new method, flow-controlled testing protocol, was developed to measure the hydraulic permeability coefficient. Results. The hydraulic permeability coefficient of anulus fibrosus depended significantly on the disc degenerative grade (P = 0.0001) and flow direction (P = 0.0001). For the nondegenerate group (Grade I), the hydraulic permeability was significantly anisotropic (P< 0.05), with the greatest value in the radial direction (1.924 x 10-15 m4/Ns) and the lowest value in the circumferential direction (1.147 x 10-15 m4/Ns). This anisotropic kinetic (flow) behavior of anulus fibrosus varied with disc degeneration. For the Grade III specimen group, there was no significant difference in hydraulic permeability coefficient among the three major directions (P = 0.37). With disc degeneration, the hydraulic permeability coefficient was decreased in the radial direction and increased in the axial and cirCumferential directions. The variations of hydraulic permeability coefficient from nondegenerate discs (Grade I) to mildly degenerate discs (Grade II) in each direction were significant (P< 0.05). However, the changes in permeability from Grade II to Grade III groups were not significant (P > 0.05) except in the circumferential direction (3.8% increase; P < 0.05). Conclusions. The hydraulic permeability of human nondegenerate anulus fibrosus is direction-dependent (i.e., anisotropic), with the greatest permeability in the radial direction. With disc degeneration, the radial permeability of anulus fibrosus decreases, mainly because of decreased water content, and the axial and circumferential permeability coefficients increase, mainly because of structural change, leading to more isotropic permeability behavior for Grade III discs.

AB - Study Design. Experimental investigation to determine the effect of intervertebral disc degeneration on the kinetic behavior of fluid in human anulus fibrosus. Objectives. To measure the hydraulic permeability coefficient of anulus fibrosus specimens in the axial, circumferential, and radial directions to determine the anisotropic permeability behavior of nondegenerate and degenerate human intervertebral discs over a range of ages. Summary of Background Data. Fluid, a major component of normal intervertebral discs, plays a significant role in their load-supporting mechanisms. Transport of fluid through the intervertebral disc is important for cell nutrition and disc viscoelastic and swelling behaviors. The hydraulic permeability coefficient is the most important material property governing the rate of fluid transport. However, little is known about the anisotropic behavior of this kinetic property and how it is influenced by disc degeneration. Methods. Using a permeation testing apparatus developed recently, testing was performed on 306 axial, circumferential, and radial anulus fibrosus specimens from the posterolateral region of 30 human lumbar (L2-L3) discs. A new method, flow-controlled testing protocol, was developed to measure the hydraulic permeability coefficient. Results. The hydraulic permeability coefficient of anulus fibrosus depended significantly on the disc degenerative grade (P = 0.0001) and flow direction (P = 0.0001). For the nondegenerate group (Grade I), the hydraulic permeability was significantly anisotropic (P< 0.05), with the greatest value in the radial direction (1.924 x 10-15 m4/Ns) and the lowest value in the circumferential direction (1.147 x 10-15 m4/Ns). This anisotropic kinetic (flow) behavior of anulus fibrosus varied with disc degeneration. For the Grade III specimen group, there was no significant difference in hydraulic permeability coefficient among the three major directions (P = 0.37). With disc degeneration, the hydraulic permeability coefficient was decreased in the radial direction and increased in the axial and cirCumferential directions. The variations of hydraulic permeability coefficient from nondegenerate discs (Grade I) to mildly degenerate discs (Grade II) in each direction were significant (P< 0.05). However, the changes in permeability from Grade II to Grade III groups were not significant (P > 0.05) except in the circumferential direction (3.8% increase; P < 0.05). Conclusions. The hydraulic permeability of human nondegenerate anulus fibrosus is direction-dependent (i.e., anisotropic), with the greatest permeability in the radial direction. With disc degeneration, the radial permeability of anulus fibrosus decreases, mainly because of decreased water content, and the axial and circumferential permeability coefficients increase, mainly because of structural change, leading to more isotropic permeability behavior for Grade III discs.

KW - Anisotropic

KW - Anulus fibrosus

KW - Degeneration

KW - Hydraulic permeability

KW - Intervertebral disc

KW - Soft tissue mechanics

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