Who is the ideal candidate for anterior cervical disk replacement surgery?
More than ten years ago, when I was a clinical investigator in the early medical trials for artificial replacement discs, the FDA approved the first set of rules for physicians on the selection criteria for patients. To be perfectly honest, there were no surprises: the FDA included people who experience chronic neck pain and arm pain from diagnosed degenerative herniated discs and pinched nerves in the neck that failed “conservative management.”
In 2007, the FDA approved cervical (neck) artificial disc replacement for one disc. More recently, the artificial disc has been approved for “two-level” cervical application – where two adjacent herniated discs are replaced. The patient protocol is about the same: patients with chronic pain in the neck and arm with weakness, numbness, or tingling. And again, we see the caveat: in cases where conservative treatment methods have failed.
What does the FDA mean by “conservative management”? About six weeks of physical therapy, medications, and other nonsurgical intervention. I’ve gone through most of the possible treatments in previous blog posts. If none of them help, then surgery is the next option.
One of the most common among surgical treatments for cervical disc herniation (herniated disc) is anterior cervical discectomy and fusion (or ‘spinal fusion’). Spinal fusion is where the surgeon removes the herniated disc and bone spurs so that they no longer compress and irritate nerves that emanate from the spinal cord. A graft of bone or synthetic material placed within the space where the disc used to be between two vertebrae, then locked down with a plate and screws. This treatment is considered “conservative” because it is established by more than 70 years of treatment history. I agree that fusion is sometimes necessary, but I consider it a “last resort” because it will limit flexibility of the treated area thus limiting patient movement.
Another procedure often recommended is posterior cervical microdiscectomy, performed with a microlaminotomy from the back of the neck, the surgeon creates a small opening in the bone (lamina of the vertebra) to gain access to the nerve area so that it is decompressed by making more room for the nerve. This procedure is not as favored as anterior cervical microdiscectomy where the approach is via the front of the neck.
The first advantage of the anterior approach is that it is more direct because when a disc herniates it’s usually the front (anterior) side that pushes into the nearby nerve. Moreover, the disease itself emanates from the disc or from the portion of the junction of the joint on the anterior side (front) of the vertebra where bone spurs grow. Therefore, the posterior approach, from the back of the neck, may remove the immediate cause of pain (via a pinched nerve) yet the pathology of the disease is frequently left behind.
This brings us back to anterior cervical disc replacement surgery, now as an alternative to the other treatments I have mentioned. I must be very clear that placing an artificial disc in the cervical spine is technically challenging. First, the herniated disc must be completely removed. After the nearby nerves are cleared of any disc material or bone spurs, I prepare implantation with some bony cuts into the vertebrae and gently insert the artificial disc. This usually requires some light tapping with a small mallet to push the disc into the space the herniated disc once occupied. Sounds easy enough, and it seems like an ideal treatment for just about any patient. But we have another issue to consider: the health of the “facet joints” of the spine.
Facet joints are literally the back of the spine. Every vertebra (level) of the spine has a disc in the front and two of these facet joints in the back. During the FDA clinical trials, we had to ensure that these bones were healthy – that there was no pathology present (e.g., arthritis) which is critical for successful disc replacement. This parameter turned out to be tough to quantify for individual patients.
I developed my methodology for evaluation. First I often obtain CAT scans to examine the joints very carefully. Then I order three x-ray studies: flexion, extension, and lateral bending of the spine from a standing position. Finally, as added precaution, I order an MRI scan. If all of these studies show that the facet joints are intact and healthy, then the patient is indeed a good candidate for disc replacement.
Over the years, having now implanted about 3,000 cervical artificial discs, my tolerance for some facet joint arthritis has increased. I have seen patients who have some degeneration of the facet joints and have had excellent results. I know that some surgeons believe that if the disc has severely degenerated, the patients are not a good candidate for disc replacement. I have found that this is not true. I have treated patients with severely collapsed discs. As long as there is no severe arthritis in the facet joints, I can repair the damage with an artificial disc, decompress the nerves, and regain the patient’s original height while also recovering full movement of the spine.
Of course, every patient must be assessed individually. Everything depends on a thorough examination of the health of the patient and careful reading of clinical studies. The most important factor of all is the benefit to the patient. Success is always measured by outcomes!