Do intervertebral discs degenerate before they herniate, or after?

Abstract

The belief that an intervertebral disc must degenerate before it can herniate has clinical and medicolegal significance, but lacks scientific validity. We hypothesised that tissue changes in herniated discs differ from those in discs that degenerate without herniation. Tissues were obtained at surgery from 21 herniated discs and 11 non-herniated discs of similar degeneration as assessed by the Pfirrmann grade. Thin sections were graded histologically, and certain features were quantified using immunofluorescence combined with confocal microscopy and image analysis. Herniated and degenerated tissues were compared separately for each tissue type: nucleus, inner annulus and outer annulus. Herniated tissues showed significantly greater proteoglycan loss (outer annulus), neovascularisation (annulus), innervation (annulus), cellularity/inflammation (annulus) and expression of matrix-degrading enzymes (inner annulus) than degenerated discs. No significant differences were seen in the nucleus tissue from herniated and degenerated discs. Degenerative changes start in the nucleus, so it seems unlikely that advanced degeneration caused herniation in 21 of these 32 discs. On the contrary, specific changes in the annulus can be interpreted as the consequences of herniation, when disruption allows local swelling, proteoglycan loss, and the ingrowth of blood vessels, nerves and inflammatory cells. In conclusion, it should not be assumed that degenerative changes always precede disc herniation. Cite this article: Bone Joint J 2013;95-B:1127-33.

Lumbar Disc Herniation

“…A subset of patients with LDH lack evidence of severe degenerative disc including proteoglycan and water loss in the NP [14]. In these cases, herniation occurs as a result of spinal overloading [15,16].…”

The Role of Cell Clusters in Intervertebral Disc Degeneration and its Relevance behind Repair

“…Two cell types normally populate the adult intervertebral discs: rounded chondrocyte-like cells of the nucleus pulposus and inner annulus fibrosus regions, and the flattened fibroblasts-like cells of the outer annulus fibrosus [30]. Both cell types differ in their developmental origins.…”

“…Fibroblasts divide to form more fibroblasts, but they cannot convert to other cell types and are prone to oxidative DNA damage and senescence [43]. Fibroblast-like cells of the IVDs aggregate in the outer annulus regions (Figure 2) especially during injuries, but they don't form clusters nor differentiate into cluster-like cells [30].…”

“…Both forms of senescence may make the disc cells function inappropriately in such a way that clusters of metabolically active senescent cells could effectively degrade a large surface area due to increased synthesis of matrix-degrading enzymes by these senescent cells and may widen the already existing fissure as cell clusters that produce degradative enzymes tend to aggregate around fissures. In general, matrix-degrading enzymes such as MMP-1, 2, 3, and 9 have been shown to increase with disc degeneration, and MMP's has been suggested to play a pivotal role in degrading the collagenous matrix of the intervertebral discs [30,64,65].…”

Expression of matrix factors in the process of neovascularization of intervertebral disc

“…Although neovascularization has been documented in degenerated discs and in herniated disc content, 17,18 there are no reports in literature that directly assess the paracrine effect of the endothelial cells on the AF cells in a controlled cell culture environment.…”