CELL VIABILITY IN SCOLIOTIC DISCS IN RELATION TO LOAD

Abstract

Introduction: Although the cell density of the intervertebral disc is low, cells perform a vital role, being responsible for maintaining and remodelling the extracellular matrix. In animal models of scoliosis, cell viability of epiphyseal chondrocytes was found to be adversely affected. Here we examine cell density and viability of surgical disc specimens.

Method: A total of 41 discs were removed from 13 consenting patients (3M, 9F, 5–40 yrs) during corrective surgery for scoliosis. Control samples were obtained from 3 non-scoliotic discs. These were further dissected to compare the outer annulus of the disc from the more concave and more convex sides of the quadrant removed at surgery. Cell density was measured using a modified Hoechst’s method. Cell viability was determined microscopically in sections using intracellular fluorescent probes.

Results: Cell density was found to be lowest in apical discs, independent of absolute disc level (p< 0.01, Student’s t test). A significantly lower percentage of live cells was found in samples taken from the convex side of the scoliotic curve (p< 0.01, Student’s t test). No significant differences in cell viability were found in either side of control discs.

Discussion: Cell viability was seen to be lower on the convex side of the scoliotic curve, suggesting that it is more difficult for cells to survive under the conditions on the convexity compared with the concavity. This may be due to differences in the mechanical conditions or the diffusion distances across the disc. Cell numbers were lowest in the apical disc, where stresses are thought to be maximal. Fewer viable cells may decrease production of matrix macromolecules, and thus compromise matrix integrity. A delicate balance exists between production and breakdown of matrix macromolecules, and any factor that interrupts this equilibrium state has the potential to affect the structure and function of the intervertebral disc.