How Degenerative Disc Disease Progresses
Question: If you have degenerative disc disease in one of your discs, does that mean it will spread to your other discs?
— Williamsburg, VA
Degenerative disc disease begins with the effects of wear and tear on your spine in response to years of use, overuse, or misuse. It's part of getting older and part of your individual genetic make-up, so we're all prone to this degenerative process; however, not everyone will have pain because of DDD.
DDD is a slow progression of events, and to understand it and how it can spread from one disc to another, try thinking of it in terms of "if this, then that" statements.
If you're aging, then the basic structure of your intervertebral disc is changing. Discs are made of strands of collagen (a protein), and over time, they can weaken, making it more difficult for the outer portion of the disc (the annulus fibrosus) to contain the inner portion (the nucleus pulposus). At this point, a disc can herniate or rupture as the nucleus pulposus pushes through the weakened annulus fibrosus. A herniated disc can push on a nerve, causing pain. Discs can also start to dehydrate; they lose water and proteoglycan, which together help make the disc an effective cushion for movement.
If your intervertebral disc is changing, then it's harder for the disc to handle movement. Your discs have one main job: to help your spine move safely in various directions. As your disc dehydrates and the strands of collagen weaken, the disc can shrink. It loses height, and that can make the spine unstable. A degenerated disc also can't absorb shock very well.
If your disc thins and can't handle movement as effectively, then the facet joints can become overworked. Facet joints stabilize the spine by controlling movement, but when a disc loses height, the facet joints lose alignment and have to readjust their movement. They can become overworked because the disc isn't doing its part to control the spine's movement—that's a lot of pressure on the facets.
If the facet joints are overworked, then the cartilage can wear away. Cartilage is meant to protect the joint and make movement easier. However, it can degenerate, leading to more facet joint problems. Without cartilage, the facets can move too much; this is called overriding.
If the facet joints are overriding, then bone spurs can develop. Bone spurs are your body's way of trying to protect itself. These bony overgrowths, also called osteophytes, are meant to stop the facets' excessive movement. A side effect of bone spurs, though, is that they can pinch nerves as they grow into the area where the nerves are exiting the spine.
So as you can see, even within one vertebra and disc, degenerative disc disease is a stepladder of events—commonly called a cascade of events. DDD can "spread" from one vertebral level to another in much the same way: weakened structures in one vertebra mean that the vertebrae above and below it are more strained. They can start to wear out, too, and follow the same "if this, then that" pattern.