The authors of this review of surgical treatment for painful cervical disc disease describe their work as “structured” and “rigorous.” And it is truly both! Using a series of carefully layed out tables, they walk us through what they found. They did a very thorough review of published studies comparing the results of cervical spine (neck) fusion with total disc replacement.
Their search was for information on radiographic (X-ray) results and clinical pathology after these two treatment approaches. The specific focus was on adjacent segment disease (ASD) that sometimes comes after this type of treatment for degenerative disc disease.
With ASD, there is an increase in motion above and below the fused level. This occurs because when one segment doesn’t move (the fused segment), the vertebrae above and below the fused area take on more stress and load. Over time the result can be increased wear and tear in the adjacent areas of the spine.
With disc replacement, motion is preserved but adjacent segment disease (ASD) can still develop if the center of rotation for those vertebrae is altered. If the implant is not placed so that normal vertebral motion is restored, uneven wear on the spinal joints and discs can occur.
Comparing the outcomes of these two procedures by looking at the pathology that occurs in the adjacent segments is one way to guide surgeons in making treatment decisions for their patients. Studies like this that take a close look at previous studies and summarize what we know so far are very helpful. The strength of evidence can be presented along with recommendations based on that evidence.
Here’s a quick summary of the information presented through a series of five carefully constructed tables. Each study that was reviewed had to meet the criteria listed in Table one. For example, only studies with adults who had surgery for cervical degenerative disease (e.g., disc herniation, spinal stenosis, pressure on the spinal nerves or spinal cord) were included. If trauma, infection, tumors, or deformities were present in the study subjects, then those studies were excluded (left out of the review). Case series, case reports, and studies using cadavers were not included.
Table two presented more details about each study included. Number of patients, percentage by sex (male or female), follow-up length of study, and level of evidence for each study was listed in table form. There was a total of 14 studies selected based on the criteria listed in Table one.
Table three is a comparison of risks comparing total disc replacement with fusion. Table four shows the risks based on different types of disc replacement implants (e.g., Bryan disc replacement, ProDisc-C disc replacement). These two tables really highlight one of the conclusions the authors made: the studies currently published are low-quality with very few actually comparing radiographic and/or clinical results after these two different procedures. In most of the studies, the information was either not recorded or incomplete.
The fifth and final table is a summary showing the strength of evidence from these 14 studies. Three pieces of information are conveyed: 1) evidence that disc replacement has a lower risk of pathology (i.e., adjacent segment disease) compared with fusion; 2) evidence that other types of surgeries (not fusion and not disc replacement) yield better results with less pathology; and 3) evidence that there is less risk of adjacent segment disease with one type of disc replacement over another.
Their conclusions? First and foremost, studies comparing fusion versus disc replacement for cervical spine degenerative disc disease come up short. Many of these studies are conducted by companies that make the disc replacement devices. So there is a clear need for independent research. Independent means the research isn’t carried out by (or paid for) by companies manufacturing these implants.
There is a moderate amount of evidence that no difference exists in short-term or medium-length follow-up results between fusion and disc replacement. In other words, the development of adjacent segment disease is about the same after either type of treatment. But no specific recommendation can be made to guide the selection of treatment without further studies with stronger evidence.
Likewise, they were unable to offer any firm conclusions about the value or benefit of one disc replacement system over another. There just isn’t enough evidence or enough strong evidence to make such a statement. They do point out that it is difficult to perform a blind study, which would be more objective.
In a blind study, the outcomes would be measured without patients or physicians knowing who had which treatment. Since X-rays are one of the main ways to assess results, it is always clear what type of treatment was provided each patient.
And they also mention that it is not clear whether or not painful symptoms or loss of function experienced by patients after surgery necessarily comes from the adjacent segment disease. There could be other factors or variables at work that we just don’t know about or recognize yet.
This report is very valuable. By critically reviewing studies comparing results of cervical spine fusion with disc replacement, the gaps in current research show up. Recognizing the need for high-quality research with short- to long-term results measured is an important step in moving forward in developing better future studies. Developing evidence-based recommendations or treatment based on patient outcomes is next.