I have a place in my neck where the disc is paper thin and no longer cushioning the spine. As a result, I have chronic neck pain that goes down my arm. Why does a thin disc cause nerve pain and why don't I have this problem at other places in the neck?
Two very good questions. Let's start with the first one: why does degenerative disc disease cause pressure on the spinal nerve root resulting in neck and/or arm pain? The disc is like a gel- or fluid-filled cushion between two vertebrae (spinal bones). Disc act to cushion and disperse load, force, and friction. When it loses its shape and form, the bones collapse toward each other.
Disc disease of this type means the pressure and load on the vertebrae increases. It also means the facet (spinal) joints move closer together. Compression and added load there can cause bone spurs to form as the body responds to the added friction and shear forces.
A smaller space between the vertebrae also affects the spinal ligaments with resultant increase in stiffness of the spine. All of these factors together reduce the size of the foramen (hole through which the spinal nerve travels as it leaves the spinal cord and travels down the arm).
And over time, with thinning of the bones and compression, the front of the vertebral bodies get pushed down. Vertebral compression fractures can develop. These are two more anatomical factors that can contribute to narrowing of the foramen. The final result? Pinching or pressing on the spinal nerve root(s) and cervical radiculopathy.
If it happens in one place, why doesn't this happen at every level of the spine? There isn't a clear-cut answer to that question. We simply don't know. Educated guesses have been made. For example, there may have been known or unknown trauma at that spinal level some time in the past. Over time, the disc has lost fluid and nutrients until it end up being paper thin and not much good for anything.
It's possible that small deviations in posture and alignment have created uneven force and shearing forces at that level with the final result being changes in the disc. There is even some study to suggest disc degeneration at any level (even single levels) has some genetic links.
Finding out what risk factors might predict degenerative disc disease may eventually help us screen for those and prevent future disease. We are still quite a ways away from being there. But efforts are already being made to find treatment that works based on current evidence. Guidelines based on best evidence found so far have been published. Those practice guidelines will be reviewed and revised as new information is discovered.