Do intervertebral discs degenerate before they herniate, or after?

Area of Science:

• Orthopedics
• Spinal Surgery
• Histopathology

Background:

• The prevailing clinical assumption is that intervertebral disc degeneration must occur before herniation.
• This belief has significant clinical and medicolegal implications.
• The scientific validity of this assumption is questioned.

Purpose of the Study:

• To investigate whether tissue changes in herniated intervertebral discs differ from those in degenerated discs without herniation.
• To challenge the traditional view that degeneration is a prerequisite for disc herniation.

Main Methods:

• Surgical tissue samples from 21 herniated and 11 non-herniated discs (similar Pfirrmann degeneration grade) were analyzed.
• Histological grading and quantification of specific features (proteoglycan loss, neovascularization, innervation, cellularity, inflammation, matrix-degrading enzymes) using immunofluorescence and confocal microscopy.
• Comparison of tissue types: nucleus, inner annulus, and outer annulus.

Main Results:

• Herniated discs exhibited significantly greater proteoglycan loss in the outer annulus, neovascularization, innervation, and inflammation in the annulus compared to degenerated discs.
• Increased expression of matrix-degrading enzymes was observed in the inner annulus of herniated discs.
• No significant differences were found in the nucleus pulposus between herniated and degenerated discs.

Conclusions:

• The findings challenge the assumption that disc degeneration always precedes herniation, particularly given that degenerative changes typically initiate in the nucleus.
• Specific annular changes in herniated discs (neovascularization, innervation, inflammation) are likely consequences of the herniation event itself.
• This suggests a re-evaluation of the pathophysiology of intervertebral disc herniation is warranted.