Cervical Artificial Disc Replacement: What You Need To Know
SpineUniverse: Who are the best candidates for cervical disc replacement surgery?
Patients with neck and arm pain unresponsive to conservative treatment of at least 6 weeks can be further evaluated to see if they meet all the inclusion criteria for surgery.
- To help ensure a good outcome, the patient has to have motion in their bending zone. If not, placing an artificial disc in a severely degenerative disc space is probably not going to help.
- Secondly, a patient can’t have severely degenerative facets because damaged facets limit motion.
- Finally, patients with metabolic bone disease (ie, osteoporosis) are not good candidates; neither are patients with deformity such as kyphosis.
A good surgical candidate would have neck and arm pain, without the aforementioned contraindications. With regard to deformity, there was a recent study that showed good outcomes with the Mobi-C in patients with mild kyphosis, but we don’t know the long-term effects yet. Anyone with significant kyphosis is not a good candidate because the artificial disc permits a degree of unstrained motion. Artificial disc replacement in the kyphotic spine exacerbates existing instability and doesn’t help the situation at all.
Well, the risks are really the same as doing an anterior cervical (neck) fusion, with the exception that there is a remote possibility of device migration (movement). This is extremely rare. In fact, it’s really the only significant risk that comes to mind.
Generally speaking, the risks associated with disc replacement are similar to those associated with fusion, except fusion carries additional risks such as non-healing, plate breakage or migration of hardware. I can state with relative certainty that device failure in disc replacement is not one of those issues we worry about. Artificial discs are tested mechanically to last up to 40 years.
SpineUniverse: Is artificial disc replacement a minimally invasive procedure?
I consider it minimally invasive. Technically, it’s an open procedure, but it’s done through a 2.5 cm or 1-inch incision. You don’t need anywhere near the incision required for a fusion, because you don’t have to put a plate in and have all of that bony surface area exposed.
All we need to do is see the disc space and get in there and get out. I’m always amazed when patients come back post-operatively with a little incision, and I’m saying to myself, I can’t believe I got that in there. Patients are actually amazed, too. They ask, How did you do that? If “minimally invasive” means minimal tissue disruption, then that’s what this surgery is. There is a small incision, but it heals very quickly. These patients go home in less than 24 hours. They’re in what we call “23.5 hours” meaning that the procedure can be done on an outpatient basis, as well.
SpineUniverse: Specifically, where is the incision made?
We try to make it either within in a crease or parallel to a crease in the neck fold. That’s the beauty of doing these neck incisions. Most people come back and it’s hard to see the incision. Were you to make a vertical incision, it would be a different story. Those incisions look pretty ugly.
SpineUniverse: How is the device implanted? Obviously, the old disc comes out.
Correct. The old disc is removed, and depending on the prosthesis, we measure the size of the disc space and custom build the disc for the patient. There are preset device sizes, but what we try to do is restore the normal height of the disc, compared to the levels above and below, and obtain as much endplate coverage as possible. Endplate is the bony surface of the vertebra, so we want to make sure we cover as much of that as we can to prevent the artificial disc from sinking into the bone, or what’s referred to as subsiding.
SpineUniverse: So there isn’t much of the endplate that’s actually removed? Is it preserved in some way?
It’s recommended that you not violate the endplate. You can shape it down, but you don’t want to go through the endplate. And when I say shape it down, I’m talking about a fraction of a millimeter. It’s important not to violate the hard bony surface of the endplate upon which the artificial disc sits. There are certain prostheses, for example, the Bryan disc, where you do shape the endplate to fit the prosthesis, but I’ve not seen any data that says it has significant benefit to do that. I don’t want to mislead anyone by saying that we don’t shape at all, as certain prostheses require some shaping, but in general, we try not to do any shaping at all.
To learn about Dr. Guyer’s practice, click here.