Influence of osmotic pressure changes on the opening of existing cracks in 2 intervertebral disc models.
METHODS
An experimental hydrogel model and a numerical mixture model were used to investigate why the disc herniates while osmotic pressure is decreasing.


OBJECTIVE
To investigate the influence of decreasing osmotic pressure on the opening of cracks in the disc.


BACKGROUND
In the degeneration process, the disc changes structure (i.e., cracks occur, and osmotic pressure decreases). Disc herniation typically develops when hydration declines, but, on the other hand, it is said that the anulus of a highly hydrated disc has a high risk of rupture. We hypothesized that disc herniation is preceded by the opening of cracks as a result of decreasing osmotic pressure.


METHODS
The osmotic pressure was changed in hydrogel samples with a crack, which was visualized with a confocal laser scanning microscope (Zeiss, Göttingen, Germany). A 2-dimensional finite element mixture model simulated a decrease in osmotic pressure around a crack in a swelling material.


RESULTS
Experiments and simulations show that a decrease in osmotic pressure results in the opening of cracks. The simulations show high effective stress concentrations around the crack tip, while the overall stress level decreases, indicating an increased risk of crack growth.


CONCLUSIONS
Decreasing osmotic pressure in a degenerating intervertebral disc enhances the opening of existing cracks, despite the concomitant decrease in anular stresses.
Wognum
Silvia
S
Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands.
Huyghe
Jacques M
JM
Baaijens
Frank P T
FP
D004487:Edema / Q000150:complications*; D006801:Humans; D007403:Intervertebral Disc / Q000293:injuries*; D009997:Osmotic Pressure; D013122:Spinal Diseases / Q000150:complications*; D016103:Spinal Fractures / Q000209:etiology*