Why do some intervertebral discs degenerate, when others (in the same spine) do not?

Area of Science:

• Biomedical Engineering
• Orthopedics
• Spinal Anatomy

Background:

• Intervertebral discs (IVDs) are avascular fibrocartilage pads enabling vertebral movement.
• Human IVDs have low cell density and limited mechanical adaptability.
• Normal aging causes matrix changes (yellowing, brittleness), but intact discs function well.

Purpose of the Study:

• To elucidate the mechanisms driving intervertebral disc degeneration.
• To differentiate between normal disc aging and pathological degeneration.
• To identify factors contributing to disc disruption and associated pain.

Main Methods:

• Review of existing literature on disc structure, aging, and degeneration.
• Analysis of mechanical loading effects on disc tissues.
• Examination of genetic and age-related influences on disc integrity.

Main Results:

• Approximately 50% of aged lumbar discs degenerate pathologically.
• Posterior annulus and lower lumbar discs are most susceptible to degeneration.
• Degeneration involves physical disruption, nerve/blood vessel ingrowth, and inflammation.
• Two degeneration phenotypes exist: endplate-driven (upper/mid-lumbar) and annulus-driven (L4-S1).

Conclusions:

• Excessive mechanical loading is a primary cause of disc degeneration, often without trauma.
• Age and genetics predispose discs to disruption.
• Moderate mechanical loading can strengthen spinal tissues.
• Discogenic pain arises from tissue disruption, inflammation, and infection.