Metaplastic proliferative fibrocartilage as an alternative concept to herniated intervertebral disc.

It is hypothesized on the basis of experimental intervertebral disc degeneration that herniated disc is actually newly synthesized proliferative metaplastic fibrocartilage and not herniation of pre-existing disc tissue, particularly that of the nucleus pulposus. Human material in selected surgical tissues was examined to test this concept. Histology revealed evidence for proliferative fronts of fibroblastic cells in herniated discs with hypocellular interiors. Hydroxypyridinium cross-link assay was used to determine the maturity of the collagen. Results indicated, with statistical significance, that herniated disc is a younger tissue than in situ annulus fibrosis, and that herniated disc is not from the nucleus pulposus, thus supporting the hypothesis.