What causes loss of intervertebral disc height, aging or injury?

Loss of Intervertebral Disc Height: Aging and Injury

Both aging and injury contribute to loss of intervertebral disc height, but contrary to common belief, age-related changes in vertebral bodies rather than disc thinning are the primary cause of height loss in normal aging.

The Aging Process and Disc Height

Age-related changes affecting the spine include:

• Vertebral body changes: With aging, there is progressive increase in vertebral end-plate concavity associated with decreased bone density 1
• Trabecular bone changes: Decreased number of horizontal trabecular "cross braces" leads to fracture of vertical weight-bearing "beams" supporting the vertebral endplate 1
• Disc expansion: Intervertebral discs tend to expand centrally and become increasingly convex with age 1

Importantly, research shows that in normal aging, loss of stature is primarily attributable to loss in vertebral height rather than loss in disc height 1. Only a minority of lower lumbar discs from elderly subjects show significant thinning and degeneration.

Injury-Related Disc Height Loss

Traumatic injuries can cause acute disc height loss through:

• Direct trauma: Spinal cord injuries from falls, motor vehicle accidents, or sports injuries 2
• Central cord syndrome: Common in older persons with spondylotic or congenitally narrow canals following hyperextension injuries 2
• Compression fractures: Particularly in those with osteoporosis or decreased bone mineral density 2

Threshold for Pathological Changes

Recent research has identified a critical threshold for disc degeneration:

• At deviations of up to 1.5 standard deviations below normative disc height, disc function is largely maintained 3
• Once disc compression exceeds this 1.5σ threshold, major pathological changes occur concurrently, including significant drops in apparent diffusion coefficient and normalized T2 intensity 3

Risk Factors for Accelerated Disc Height Loss

Several factors can accelerate the loss of disc height beyond normal aging:

• Decreased nutrition: Impaired disc nutrition allows accumulation of cell waste products and degraded matrix molecules 4
• Cellular changes: Loss of viable cells, cell senescence, and cell death due to pH changes 4
• Matrix degradation: Accumulation of degraded matrix molecules and fatigue failure of the matrix 4
• DNA damage: Evidence suggests DNA damage negatively impacts proteoglycan synthesis, accelerating disc degeneration 5

High-Risk Populations

Certain populations are at higher risk for accelerated disc height loss:

• Adults over 65 years of age 2
• Individuals with osteoporosis or low bone mineral density 2
• Patients with spinal cord injuries 2
• Those with genetic predispositions to accelerated aging or disc degeneration 5
• Individuals with history of falls from greater than standing height 2

Clinical Implications

When evaluating loss of intervertebral disc height:

• Distinguish between normal age-related changes and pathological degeneration
• Consider both vertebral body changes and disc alterations
• Use appropriate imaging modalities:
  • DXA for bone mineral density assessment 2
  • MRI for evaluating soft tissues, ligaments, discs, and neural elements 6
  • CT for identifying fractures (94-100% sensitivity for thoracolumbar fractures) 6

Conclusion

While both aging and injury contribute to loss of intervertebral disc height, research indicates that normal aging primarily affects vertebral bodies rather than causing significant disc thinning. Traumatic injuries can directly impact disc height through mechanical damage. Understanding this distinction is crucial for proper clinical assessment and management of patients with spinal conditions.