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

Abstract

This review suggests why some discs degenerate rather than age normally. Intervertebral discs are avascular pads of fibrocartilage that allow movement between vertebral bodies. Human discs have a low cell density and a limited ability to adapt to mechanical demands. With increasing age, the matrix becomes yellowed, fibrous, and brittle, but if disc structure remains intact, there is little impairment in function, and minimal ingrowth of blood vessels or nerves. Approximately half of old lumbar discs degenerate in the sense of becoming physically disrupted. The posterior annulus and lower lumbar discs are most affected, presumably because they are most heavily loaded. Age and genetic inheritance can weaken discs to such an extent that they are physically disrupted during everyday activities. Damage to the endplate or annulus typically decompresses the nucleus, concentrates stress within the annulus, and allows ingrowth of nerves and blood vessels. Matrix disruption progresses by mechanical and biological means. The site of initial damage leads to two disc degeneration "phenotypes": endplate-driven degeneration is common in the upper lumbar and thoracic spine, and annulus-driven degeneration is common at L4-S1. Discogenic back pain can be initiated by tissue disruption, and amplified by inflammation and infection. Healing is possible in the outer annulus only, where cell density is highest. We conclude that some discs degenerate because they are disrupted by excessive mechanical loading. This can occur without trauma if tissues are weakened by age and genetic inheritance. Moderate mechanical loading, in contrast, strengthens all spinal tissues, including discs.

Effects of sex, age, body height and body weight on spinal loads: Sensitivity analyses in a subject-specific trunk musculoskeletal model

“…According to our findings, slightly higher spinal loads in females (at identical BH, BW and age) combined likely with other risk factors (e.g., psychological factors, physical ability, job assignments (Bielby and Baron, 1986)) could play a role in greater prevalence of low back pain in females reported in some studies (DePalma et al, 2012;Schneider et al, 2006). Although current results suggest that age (in the range of 35-60 years) does not affect spinal loads, ageing could reduce damage tolerance threshold of intervertebral discs making them more susceptible to injury (Adams et al, 2015;Adams and Roughley, 2006 normalized to the mean values at each task at the L5-S1 disc.…”

Anti-inflammatory Chitosan/Poly-γ-glutamic acid nanoparticles control inflammation while remodeling extracellular matrix in degenerated intervertebral disc

“…Pathologies of intervertebral disc (IVD) such as disc degeneration, herniation or cervical radiculopathology are strongly associated with low back pain (LBP) [1,2]. This might be caused by herniation-induced pressure on over-sensitized nerve roots, due to mechanical stimuli, and by molecules arising from the inflammatory cascade [1,3].…”

“…This might be caused by herniation-induced pressure on over-sensitized nerve roots, due to mechanical stimuli, and by molecules arising from the inflammatory cascade [1,3].…”

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

“…changes with age, excessive mechanical loading, and pathologies that weakens the disc tissue [5,6]. These changes are known to increase expression of matrix-degrading enzymes and other catabolic molecules that progressively contribute towards accelerated degradation of the tissue.…”