THEY DO NOT SLIP! They bulge, they herniate, they sequester or extrude, they degenerate, but they most definitely do not slip no matter how many times people tell me they have a disc out. Patients telling me this is not their fault of course, because at some point either a friend, family member or a misguided yoga website (here) have told them this condition exists; it does not. Patients often attribute low back pain with referral to the back of the leg to a disc problem and this is often known as sciatica.
Anatomy of a disk
Intervertebral discs are found in between each unfused vertebrae in the spine with the notable exception of the space between your atlas and axis. The first thing is to realize that your discs are not like poker chips. They are not rigid, solid and immovable. Discs would be more accurately thought of as a really stale jelly donut. The main role of the discs is for shock absorption in the spine, to help dissipate axial forces and to form a fibrocartilagenous joint with its adjacent vertebrae. The individual joints allow a small amount of movement between each vertebra and all these joints combined allow for much greater range of motion.
They have two main distinct anatomical parts. The outside covering of the disc is known as the annulus and the inside portion (or the jelly of the donut) is the nucleus pulposus. The annulus is the tough shell of the disc, which is sort of like rubber. It is somewhat pliable and is thin layers of fibrocartilage that provides the stability and structure to the disc. The annulus itself can degenerate, be damaged and be a pain generator in the back all by itself without anything like a bulge or herniation. This can be acute or what is known as degenerative disc disease. A bulging disc is when the annulus is pushing outward beyond its normal anatomy but the annulus itself has not ruptured. The pulposus is the jelly of the donut and while it is much firmer than jelly its main purpose is to help with the shock absorption functions of the disc and when well hydrated helps to provide the height (or normal disc space) to the disc. When a disc gets damaged and you get a herniation or sequestration, it is the pulposus that gets pushed through the annulus.
MRI’s and CT Scans
It is important to keep in mind that while these conditions can certainly be painful, they are not always and that many, many people are out there going about their normal everyday activities with these conditions with no symptoms at all. With findings like these that would be viewable through an MRI or CT-scan, they have to be clinically relevant to what the patient is experiencing. For more on MRI and their limitations with disc injuries, you can view one of my previous columns here. Another informative column is here regarding how these findings on advanced imaging does not necessarily mean a surgical intervention is warranted and that disc herniations can and do resolve with conservative treatment.