The effect of blocking a nutritional pathway to the intervertebral disc in the dog model.

BACKGROUND

The hypothesis that injecting bone cement adjacent to one or both endplates would bring about degeneration in the intervening disc was tested.

METHODS

In 11 dogs, bone cement was injected just below the superior endplates of L1, L2, and L3 to block the nutritional supply through these endplates to the three intervertebral discs T13-L1, L1-L2, and L2-L3. In one other dog, both the superior and the inferior endplates of the same discs (T13-L1, L1-L2, and L2-L3) were blocked with bone cement. All 12 dogs were euthanized between 31 and 70 weeks after the surgery. The three experimental discs (T13-L1, L1-L2, and L2-L3) and two control discs (T12-T13 and L4-L5) were excised and assessed using enzyme-linked immunosorbent assay (ELISA) and histology.

RESULTS

Radiographs of the lumbar spine at the time of death did not show any signs of disc bulging, disc space narrowing, or peripheral osteophyte formation in any of the 12 dogs. The experimental discs as well as the control discs appeared normal in every dog. After the discs were bisected, they were carefully inspected for any visible signs of degeneration. The experimental discs showed no clear signs of disc degeneration and were not distinguishable from the control discs on a gross level. The numerical results from the ELISA showed that in the experimental discs as opposed to the control discs, there were significant increases in proteoglycan content in both the nucleus (P = 0.033) and annulus (P = 0.01) and clear histologic changes in some of the discs.

CONCLUSION

The results show that injecting bone cement adjacent to one or both endplates for up to 70 weeks does not produce degeneration in any visible form in the intervening disc. There were no disc bulging, no apparent annular fissures, and no disc spacing narrowing. There were, however, increases in protoglycan content in both the nucleus and the annulus and clear histologic changes in some of the discs.