Cervical artificial disc replacement

Motion-sparing procedures is one of the current trends in spine surgery and likely will continue to prevail in the future. Among them, the cervical disc replacement is one of the best-developed and studied techniques. Let me give a quick overview of the surgery and who may benefit from it.

Background: Why was the disc replacement developed?

While intuitively it just makes sense to preserve motion where nature created it, there are good scientific reasons for trying to avoid spinal fusion.

Once the spinal bones in the neck are fused together (a procedure known as ACDF), the adjacent level in the spine will try to compensate for the lost motion. This leads to overload and faster deterioration of this level causing neck pain and pinched nerves. This is called the adjacent level disease and may require additional surgery in up to twenty percent of patients within ten years.

The general idea behind the disc replacement is to preserve motion across the diseased disc and prevent development of the adjacent level disease.

Cervical disc replacement (CDR) is known under other names: total disc replacement (TDR) and cervical disc arthroplasty (CDA).

Figure 1 Implanted artificial disc implant on an x-ray

Indications: Who is the right candidate for the disc replacement?

An artificial disc is used to restore the space between the spine bones after removal of the disc. It may be used instead of a more traditional anterior cervical fusion (ACDF).

An important point to remember is that the artificial disc is used to preserve motion across the disc segment in order to prevent degeneration of the adjacent spinal levels. It will not restore the lost motion and as such, is not recommended for cases of arthritis in the spine.

I recommend the disc replacement in a very specific group of patients: young people with a disc herniation producing pressure on the spinal cord (myelopathy) but otherwise with no significant spine arthritis.

Figure 2 A disc herniation causing pressure on the spinal cord

What are the limitations of the disc replacement?

It is important to remember that the artificial disc is not going to restore lost function. It may only preserve present function. Any degenerative changes, either bone spurs or arthritis in the facet joint (small joint on the back of the spine), may be the source of neck pain and may negatively affect the results the disc replacement.

How is the procedure performed?

Surgical approach to the cervical disc replacement is very similar to ACDF. A small horizontal incision is made in front of the neck and the internal organs are retracted to the side exposing the surface of the spine. The diseased disc is removed relieving pressure from the nerves.

The bone surfaces are then prepared to match the shape of the implant. The artificial disc is positioned into the disc space and secured to the bone. Proper position of the disc is confirmed with an intraoperative x-ray.

Figure 3 Implantation of the artificial disc

What is recovery like after CDR?

The patient spends one night in the hospital to ensure there are no problems with swallowing and breathing. There is no need for a collar. Unlike ACDF, disc replacement does not require limitations in physical activity since it is not a fusion procedure. It is okay to take anti-inflammatory medications (Naproxen, Ibuprofen etc.), which are typically not recommended after fusion.

What are the risks of the disc replacement?

As with any surgery, there is a risk of infection, injury to the nerves, leak of spinal fluid and risks of anesthesia. Surgery on the neck may cause difficulties with swallowing and breathing, changes in voice. The implant may move out of place.

Long-term, there is a chance the bone grows over the implant blocking motion. After all, even in the best-selected patients, the procedure may not help the symptoms. This list is not comprehensive but shows that with likely benefits, you need to remember about potential risks with any surgery.

What are the results of the research studies? Does the replacement prevent development of the adjacent level disease?

We currently have long-term results in patients, who underwent the disc replacement seven-to-ten years ago. They have lower rate of adjacent level disease. What still remains unknown is how the CDA performs over the very long time. Since it is mostly used in young patients, we still don’t know how it will behave after, let’s say, fifty years of use.

How much better is disc replacement compared to spine fusion (ACDF)?

Even though disc replacement demonstrated decreased rates of adjacent level disease, ACDF is still a very good procedure. The immediate results are pretty much the same in the two procedures. For this reason, we still recommend ACDF in most patients, especially when there are signs of arthritis in the spine.

Figure 4 An example of ACDF, Anterior Cervical Discectomy and Fusion

I have neck pain. Will disc replacement help me?

This is one of the most common questions from the patients. Unfortunately, there is no definitive answer to it. Studies show that CDA is very effective for treating nerve compression, but success with neck pain is roughly 50:50. For this reason, it is not typically recommended to treat neck pain.

Can artificial disc be used at any level in the spine?

Currently, artificial discs are approved for use in cervical and lumbar spine. Results are most promising in the cervical spine. While some surgical centers in Texas will offer a disc replacement in the lower back, I only offer the cervical disc replacement.

Are there any other motion-preserving surgical options?

Cervical disc replacement, although arguably the most sophisticated, is not the only motion preserving surgery for the neck. The other examples are laminoplasty and foraminotomy.

Are any of the available disc implants better than others?

Even though there are some theoretical benefits of certain implants over the others, we have not seen significant differences between the implants approved by FDA at this point.

Are there any concerns with the disc replacement or any unanswered questions?

The main concern is the longevity of the artificial disc after many years of use. Since it is recommend for use in young people, the implant will have to function for a longer period of time. One of the possible problems is wearing of the polyethylene seen, for example, in knee and hip replacement. While the hardware is engineered to last, there are no very-long-term clinical trials that give a definitive answer to it’s longevity.

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