Effect of compression and anisotropy on the diffusion of glucose in annulus fibrosus.

STUDY DESIGN: Investigation of the effect of static compression and anisotropy on the apparent diffusivity of glucose in bovine annulus fibrosus (AF). OBJECTIVE. To determine the apparent glucose diffusivity in 2 directions (axial and radial) of bovine AF under 3 levels of compressive strain (0%, 10%, and 20%). SUMMARY OF BACKGROUND DATA: Knowledge of diffusivity of small molecules is important for understanding nutritional supply in intervertebral discs and the mechanisms of disc degeneration. However, little is known regarding the strain-dependent and anisotropic behavior of glucose diffusivity in intervertebral discs. METHODS: Apparent glucose diffusivity measurements were performed on 10 axial and 10 radial AF specimens from bovine coccygeal discs. The dependence of diffusivity on compression was determined using 3 levels of strain (0%, 10%, and 20%). RESULTS: The apparent glucose diffusivity (mean +/- standard deviation) of the bovine AF in the axial direction was 1.38 +/- 0.015 x 10 cm/s (n = 10) at 0%, 1.00 +/- 0.070 x 10 cm/s (n = 10) at 10%, and 7.65 +/- 0.552 x 10 cm/s (n = 10) at 20% compression. For radial specimens, the apparent glucose diffusivity was determined to be 9.17 +/- 1.12 x 10 cm/s (n = 10), 7.29 +/- 0.863 x 10 cm/s (n = 10), and 5.43 +/- 1.16 x 10 cm/s (n = 10) for 0%, 10%, and 20% compressions, respectively. A significant decrease in diffusivity with increasing strain was found for both axial and radial specimens [analysis of variance (ANOVA), P < 0.05]. Diffusion in the radial direction was determined to be significantly less than that in the axial direction (ANOVA, P < 0.05). A significant interaction was found between the level of strain and the direction of diffusion (ANOVA, P < 0.05). CONCLUSION: Diffusion of glucose in bovine AF is dependent on strain and the direction of diffusion.