An artificial disc is a device placed into the cavity between vertebrae where once the original organic disc functioned. It recreates and provides the support the original disc gave to the positioning of the spine.
Total Disc Replacement
In this procedure, all of the original disc is removed and replaced by a synthetic device. The discs can be made of metal or biopolymer materials. The area of 3D prototyping has been able to make great strides in recreating discs made from a resin that is more flexible than metal, but still retains the structural integrity of metal.
Total disc replacements are usually designed to have two plates. The top plate attaches to the vertebrae above the disc and the bottom plate attaches to the vertebrae below the disc. The two plates may have a cushion material in between the plates to provide bending, movement, cushioning, and flexion. Since the plates are curved slightly, the cushion also allows for the plates to rub smoothly across each other.
Disc Nucleus Replacement
In this procedure, only the central part or nucleus of the disc is replaced. An implant is used that goes directly in the center of the disc. The annulus (outer part) is not removed and left to provide structure to the section being treated.
The nucleus replacement device is also made from biopolymers. Often, surgeons will use a hydrogel that will take on water and expand. This gel is able to be compressed and so functions very much like a normal disc.
This procedure is done in Europe, but does not enjoy the approval of the Food and Drug Administration in America. Most compressive gels like this have simply not undergone extensive study in approved trials.
If you have been diagnosed with spondylolisthesis, osteoporosis, vertebral body fracture, spinal tumor, spinal infection, obesity, changes in the facet joints, allergic reactions to biopolymers, pregnancy, chronic steroid use or autoimmune issues, then you may not be a good candidate for total disc replacement. If you have had abdominal surgery, then you may be excluded from this particular procedure.