Abstract
Introduction
Herniated disc tissue removed at surgery usually appears degenerated, and MRI often reveals degenerative changes in adjacent discs and vertebrae. This has fostered the belief that a disc must be degenerated before it can herniate, which has medicolegal significance. We hypothesise that degenerative changes in herniated disc tissues differ from those found in tissues that have degenerated in-situ, and are consistent with being consequences rather than causes of herniation.
Methods
Surgically-removed discs were examined using histology, immunohistochemistry and confocal microscopy. 21 samples of herniated tissues were compared with age-matched tissues excised from 11 patients whose discs had reached a similar Pfirrman grade of degeneration but without herniating. Degenerative changes were assessed separately in three tissue types (where present): nucleus, inner annulus, and outer annulus. Mann-Whitney U tests were used to compare ‘herniated’ vs ‘in-situ’ tissues.
Results
Herniated tissues showed significantly greater cellularity (annulus), greater proteoglycan loss (outer annulus), greater neovascularisation (annulus), greater innervation (annulus) as judged by PGP 9.5 staining, greater expression of matrix-degrading enzymes MMP1 and MMP3 (inner annulus), but less cell clustering (outer annulus). Some similar but non-significant differences were seen in nucleus tissues.
Interpretation
Herniated tissues that escape the pressurised confines of the disc are free to swell, lose proteoglycans and come into contact with blood cells. These events could explain most of the differences between herniated tissues and those that degenerated ‘in situ’. Results support our hypothesis, and warn against assuming that degenerative changes always precede (or cause) disc herniation.
No conflicts of interest
No funding obtained
This abstract has not been previously published in whole or in part; nor has it been presented previously at a national meeting.
