The Myth of the Cushioning Disc
Many people fall into the myth of cushioning disc. They assume that intervertebral discs are like a marshmallow between two vertebrae and this cushioning is key to pain relief. Nothing could be further from the truth. Cushioning has nothing to do with pain relief.
The spinal discs contain a non-compressible fluid, mostly made of water mixed with protoglygans and other molecules. This fluid is contained by a very tough membrane called the annulus and it is under considerable pressure. At rest, lying on your bed, a healthy disc is under 30 PSI of pressure about the same pressure as a car tire. For a personal experience try compressing your car tire with upper half of your body weight. In flexion (bending forward) without load the internal disc pressure can go higher than 200 PSI. The only reason it bends at all is the massive leverage the body’s structure gives the muscles to bend the spine. A healthy spine is not a straight spine, but one that has the normal lordotic curve in the cervical and lumbar spine and a kyphotic curve in the thoracic spine..
If you have a healthy back and jump off a roof and land on your feet, by far most of the “cushioning” of the spine will come from the spine flexing (like a leaf spring) in its normal “S” shape, not compression of the discs. In fact, should the discs compress enough to absorb all that energy as if you had a straight and unflexing spine, it would probably paralyze you, by destroying the radicular nerves.
What does give pain relief is the decompression (relief of pressure) of the radicular nerves and facet joints, and the removal of diseased discs. This relief of pressure on the radicular nerves and facet joints comes with the re-establishment of the intervertebral disc space and removal of any troublesome bone spurs. And, of course, the disc is replaced during ADR surgery.
There are other things to consider.
1: There is no controlled center of rotation of the discs. Because the spine has been compromised by degenerative disc disease, it is very likely not conforming to the optimum shape and causing the motion of the spine, particularly the flexion and extension motion, to be irregular. A cushioning disc cannot correct this motion, only one that controls the center-of-rotation. This is what mechanical discs do.
2. What happens if this device fails? A single-piece “cushioning” device failure, will require the endplates to be chiseled out to revise the spinal segment, which puts the endplates of vertebrae at risk. Should the endplates be destroyed, a corpectomy would be required. Not an easy surgery and one with high risks. However, a three-piece mechanical ADR device failure only means the core is replaced without chiseling out the endplates of the ADR and risking the destruction of the vertebrae.