"Slipped" Disc Fallacy
After having a roaring conversation with a patient about the spine, she said she needed a whole course on this. The least I can do is write a post on the minutiae of one of my favorite parts of the spine, the vertebral disc.
So here we go!
Anatomy: THE BEAN-SHAPED VERTEBRAL DISC IN THREE PARTS.
The annulus fibrosus- the outer ring of the disc
This structure resists tensile load such as twisting or bending because these collagen fibers are arranged in alternate directions obliquely at about 30 degrees from the vertical axis
It is made up of type I collagen.
Type I collagen is made up of fibroblast and chondroblast cells.
The nucleus pulposus
The nucleus resists mostly compression loads such as when we stand or sit.
It is made up of mostly type II collagen
Type II collagen is produced by chondrocyte cells and proteoglycans.
Cartilage end plates
About .6 millimeters thick and separates the vertebral body (the bony part) and is strongly bound to the disc.
Both hyaline and fibrocartilage.
*Fun Fact* Vertebral discs are the largest avascular structures in the body, so they get most of their nutrients from hydrophilic macromolecules (one of which is lovingly coined GAG- glycosaminoglycan). So, water makes up 70-90 percent of the disc!
Now that you understand the anatomy of the disc, I’m going to go ahead and say it, IT DOESN’T SLIP, it tears.
We can think of tears in 2 ways:
Disc degeneration: as we age we have less water in the disc, therefore less nutrition and a lower PH. Things get kinda stiff, the disc absorbs compressional forces differently, and transmission of that load adds to breakdown in the annulus. This leads to tearing, pain, and dysfunction.
Trauma: when we are younger the disc is more malleable, but so is the rest of us. There are many reasons for one segment of the spine to be moving more than another, but when this happens we put undue stress on the annulus and again, it can tear.
After a tear what can happen is some material from the disc can herniate.
What structure herniates you ask?
Research has shown that the structures herniated may depend on the type of tear/injury. Some find that there are portions of the nucleus, end plate and/or annulus being involved.
No matter what, GAG will be a component and GAG imbibes fluid, making the herniation larger.
Why are disc lesions painful?
The annulus fibrosus is innervated with nerves that send pain signals to the brain. If it tears, it will be painful.
Herniation also causes a chemical change in the area outside of the annulus and this inflammatory reaction is painful.
The nerve root that exits nearby (this is a whole other blogpost) can be affected in a variety of ways and nerve pain can become an issue.
What does all this have to do with Physical Therapy?!
So. . . if the main issue is that the annulus tore, we need to start with exercises to heal the tear.
And now that we understand the collagen and structural makeup of the annulus, which are these layers of diagonal collagen tissue, we can appropriately dose exercise for healing.
An example of an exercise for tissue healing of the disc: Small rotations to stimulate fibroblasts in the annulus!
Once the disc starts to heal and the pain decreases, we then start poking around to figure out what other factors may have contributed to it tearing (weakness, mobility issues, coordination etc) and progress exercises for this. The list of exercises at this point is endless and only limited by your own imagination.