Intervertebral Disc Explanation | Video
A Spine Surgeon Explains Intervertebral Discs
In this short video, you can hear a spine surgeon's explanation of the intervertebral disc. Lukas Zebala, MD, walks you through the basics of this important part of spinal anatomy.
What Is an Intervertebral Disc?
In your spine, you have bones called the vertebrae, and in between those, you have discs that help cushion your movements. Those are the intervertebral discs, and they are part of what helps you bend, twist, arch, and round your back.
The discs are also the shock absorbers of your spine. Every time you take a step, your body reacts to that pressure, and many parts of your body (including the spine's discs) help absorb and distribute it.
What Are the Parts of an Intervertebral Disc?
The disc has 2 main parts: the annulus fibrosus and the nucleus pulposus.
The annulus fibrosus is the tougher outer layer of the disc. It is made up of interwoven fibers.
The nucleus pulposus is the gel-like inner layer of the disc. This "gel" is made of water and proteoglycans, and it is the part of the disc that most absorbs and cushions your movements.
Several analogies have been used to describe the parts of the intervertebral disc. Two of the more popular ones are:
- Imagine your disc is a jelly-filled donut. The annulus fibrosus is the dough part on the outside, and the nucleus pulposus is the jelly (or cream filling, if you prefer those).
- Imagine your disc is a tire. The annulus fibrosus is the tough, rubbery outside, and the nucleus pulposus is the air inside.
What Can Happen to an Intervertebral Disc? (And Lead to Pain for You)
The intervertebral disc can be a source of back pain or neck pain.
It can start to wear out (or degenerate), perhaps from age, or from misuse or overuse. As with other joints in your body—and the intervertebral discs are part of a joint, since they help your back move—the intervertebral discs can, over time, lose their ability to move well.
For example, the disc can start to thin as you age. As mentioned above, discs are partially made of water and proteoglycans; over time, they can lose that fluid and become less elastic. They are then more susceptible to compression and can become thinner.
When a disc thins, it causes the vertebrae above and below it to become closer together. They can even start to rub on each other, and bone on bone is never a good feeling; that can cause pain and/or difficulty moving.
This degeneration can be called degenerative disc disease.
An intervertbral disc can also herniate: the nucleus pulposus can start to push through the annulus fibrosus, causing a bulging disc. If the nucleus pulposus pushes entirely though the annulus fibrosus, that is a herniated disc.
Both a bulging and a herniated disc can press on spinal nerves or the spinal cord, which can cause pain and other back pain or neck pain symptoms.