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What Does the Research Show About Results with Disc Replacement for the Neck?

Posted on: 11/17/2010
A sensation of the head "clunking" with movement, headaches, and neck pain that go down the arm are symptoms of an unstable upper cervical spine. Neck and arm pain with numbness and tingling down the arm are more indicative of lower cervical spine problems. And some patients report difficulty swallowing or the sensation of a lump in the throat when there are disc protrusions as part of the mix.

Most of these symptoms go away with conservative care to address the contributing postural components, muscle weaknesses or imbalances, and other soft tissue issues. But with degenerative conditions that don't respond to nonoperative treatment, surgical intervention to stabilize the unstable segment(s) may be necessary.

In the past, the only real choice was neck fusion. And that worked "okay" (pain and other symptoms are relieved, the neck is stabilized) but there are problems with this approach. The biggest drawback is the fact that the patient loses neck motion at the fused level.

The subsequent problem is the increased load and force placed on the spinal segment above and below the fused level. The added stress speeds up wear and tear and can cause a condition called adjacent-segment degeneration. What's the answer to this dilemma?

Well, the next development in this area has been an artificial disc replacement. The procedure is referred to as a cervical disc arthroplasty or CDA. In theory, the implant is designed to stabilize the neck AND maintain motion without transmitting load to the adjacent segments.

How well is that working? That's what the investigators of this article set out to determine. They researched all the studies reported so far on the results of cervical disc arthroplasty (CDA).

This type of report is a technological overview using a systematic review. In reviewing all articles on the topic, they found over 2,000 on the subject. That number tells us there is enough published data now to conduct a systematic review and see what's what.

They posed four questions and tried to see what the study results showed to answer these questions. Results for cervical disc arthroplasty were compared with cervical fusion for each of the following four questions:

  • Are there ways to predict success with CDA? In other words, are there certain patient characteristics that are linked with a good result? These factors could be anything like age, gender, smoking status, use of narcotics or other pain relievers, or work status.
  • Are results better, same, or worse for patients who get the implant (compared to patients who have a fusion). All patients had one or the other of these two procedures because of neck pain (with or without arm pain) from a herniated disc.
  • What about complications and failures requiring a second (revision) surgery? How do these figures compare between artificial disc replacement and fusion?
  • And what about costs? Is one procedure more cost effective than the other? Length of hospital stay and time to return-to-work are the main ways to assess the economics of these two procedures.

    All good questions -- so, what did they find? Well, first the "bad" news. Most of the studies didn't even look at predictive factors for patients (question number one). Most of the studies didn't come to any real conclusions about results (referred to as clinical outcomes) [question number two].

    Most studies did use the same measures (pain, neck motion, function) to assess the results. But the results were all over the map -- some studies showed better results with fusion. Others reported the opposite. Many studies found no (statistically significant) difference in results from one procedure to the other.

    Basically, the quality of the studies was not enough to base recommendations on for the first two questions. When quality standards are not present, the level of evidence gets downgraded.

    There weren't much better or more specific answers to questions three and four. It's a bit easier to track complications and revision surgeries. But not everyone defined the criteria for complications or adverse events the same.

    So, it can be a bit like comparing apples to oranges -- same category of information but different ways to look at it. For example, some researchers included problems that occurred during the operation and for a short period after surgery. Others extended the postoperative period much longer.

    And there are different ways to calculate whether or not data collected is statistically significant or not. Using one method over another can make a difference in how the data is interpreted.

    Using the American Academy of Orthopaedic Surgeons calculations, the authors of this review reported that there were many studies with "unreliable" or "inconclusive" results (as they put it). The level of evidence for questions three and four was downgraded based on the way the researchers collected and analyzed the data.

    Two results were consistently reported: there was no difference in the length of hospital stay between the two procedures. And patients who had the artificial disc instead of the fusion procedure were able to get back to work sooner.

    In summary, conducting systematic reviews of this type on new treatment techniques is important. It's great to have a new device like the cervical disc arthroplasty. But what if it doesn't really give better results than the current standard treatment (fusion)? Then the added time and expense to learn and practice the new approach may not be worthwhile for the surgeon.

    By examining the best available evidence from time-to-time (on any procedure), the standard of care can be challenged and treatment guidelines developed. Selecting patients for success is a much better way to choose the right plan of care (as opposed to just going with the latest technique developed). Identifying factors that can predict success remains an important future goal of research.

  • References:
    Michael Zindrick, MD, et al. Cervical Disc Arthroplasty. In Journal of the American Academy of Orthopaedic Surgeons. October 2010. Vol. 18. No. 10. Pp. 631-637.

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