The Science of Degenerative Disc Disease
Degenerative disc disease represents the natural aging process of your intervertebral discs, though it can occur prematurely due to various factors. Your discs are composed of an outer fibrous ring (annulus fibrosus) and an inner gel-like core (nucleus pulposus) that normally acts as a shock absorber between vertebrae. As discs age, they lose water content and the nucleus pulposus becomes less gel-like, reducing the disc's ability to distribute loads evenly. This dehydration process leads to decreased disc height and can result in small tears in the annulus fibrosus. When the disc loses height, it alters the biomechanics of the entire spinal segment. The facet joints, which normally share load with the discs, begin to bear a greater proportion of the forces passing through that level of the spine. This can lead to accelerated wear of these joints and may contribute to the development of bone spurs and other arthritic changes. Despite the name, degenerative disc disease isn't truly a disease but rather a description of the structural changes that occur over time. It's important to understand that these structural changes don't always predict pain levels - many people have significant disc degeneration visible on imaging scans but experience no symptoms whatsoever. Conversely, some individuals with minimal structural changes may have considerable pain. This disconnect between imaging findings and symptoms highlights why treatment focuses on function and symptoms rather than structural abnormalities.
Contributing Factors
Your spine functions as an integrated system where each level works with adjacent levels to allow movement while maintaining stability. When disc degeneration occurs, this system becomes altered in ways that can contribute to symptoms.
The disc and two facet joints at each level form what we call the three-joint complex. Normally, the disc bears approximately 80% of the compressive load, while the facet joints guide movement and prevent excessive rotation. When disc height decreases due to degeneration, the facet joints begin to bear more load than they're designed for - sometimes up to 50% of the total force.
This increased load on the facet joints can lead to inflammation and pain. Additionally, loss of disc height can narrow the spaces where nerve roots exit the spine, potentially causing nerve-related symptoms. The supporting muscles often respond to these changes by increasing tension to provide additional stability, which can contribute to muscle-related pain and stiffness.