By Richard D Guyer.
In 1989, Texas Back Institute (TBI) discovered that an orthopaedic surgeon in East Berlin, Karin Buettner-Janz, had been successfully implanting artificial discs in the lumbar spine for several years. That novel approach to treating lumbar disc pain was of great interest to the team, so we embarked on a mission to learn more about these implants.
Upon completion of our discovery phase, we went to task to facilitate the efforts to perform biomechanical testing required by the FDA, and to initiate the first clinical trial in the United States to evaluate the safety and effectiveness of the device in the treatment of disc-related low-back pain.
Scott Blumenthal of TBI implanted the first total disc replacement device, the Charité Artificial Disc, in the United States as part of an FDA trial in March, 2000. The next year, Jack Zigler, also of TBI, was the first in the United States to implant the ProDisc-L as that FDA trial was initiated. In total, our group has participated in FDA-regulated trials for five lumbar and five cervical disc replacements. To date, our 11 surgeons have implanted total disc replacements in almost 1,000 patients since that first Charité in 2000.
In the last nine years, we have learned much about these discs and have been active in sharing our experience with other spine professionals through presentations at national and international spine conferences, publications in medical journals, and by serving as faculty at surgical training courses. In analysing our own data, as well as data combined from multiple centres, we have gained insight into factors that are, and are not, related to outcome.Published results of the large multicentre randomised trials of the Charité and ProDisc-L were both designed as non-inferiority trials in which the devices were compared to lumbar fusion. In both studies, TDR was found to be non-inferior to fusion and superior to fusion on some measures. Data from the five-year follow-up of the Charité patients revealed that there was no diminution of results between the original two-year follow-up and the five-year outcome.
Results of the FDA trials for the other devices have not yet been published.
In analysing our own results as well as in reviewing other studies, there do not appear to be any significant differences in the results achieved by the various TDRs; however, it should be noted that complete direct comparisons are difficult due to slight differences in study protocols.
With the introduction of any new technology, there is concern about the results achieved after the initial FDA-regulated trials. Such trials have well-defined selection criteria and typically involve surgeons with high levels of surgical experience. After approval for marketing is granted, such high selection criteria for patients and surgeons are no longer required. In theory, this results in reduced positive outcomes and increased problems.
However, in a post-approval Charité study, this was not found to be the case. The incidence of complications was similar, and for some categories even less than in the FDA IDE studies. At TBI, in our series of 800 consecutive lumbar TDR patients beginning with the first patient nine years ago, which includes the learning curves of 11 individual surgeons, the reoperation rate was between five and six per cent, over a mean follow-up of 44 months. In only six of these 800 patients was the device explanted or revised.
The rationale for using cervical TDR is similar to that for lumbar – to reduce pain and allow motion of the operated segment. Our experience with cervical disc replacement is not as extensive as with lumbar as these devices were developed years after their lumbar counterparts.
TBI’s first surgery for cervical TDR took place in 2003. Similar to lumbar TDRs, the FDA trials were designed as non-inferiority studies and ProDisc-C as well as the other FDA- approved devices were found to be non-inferior to anterior cervical fusion, and superior to fusion on some outcome measures at various time periods. On none of the outcome measures was TDR found to be inferior to fusion.
The development of total disc replacements signifies a monumental advancement in spine surgery in many years. We are now beginning to see second and third generation designs for these devices. Without a doubt, more will follow. In the overall results for TDR, the clinical outcomes are similar or superior to fusion and they allow motion of the operated segment. They may or may not improve the segment back to normal motion in terms of the extent of motion and the pattern of motion. TDRs functioning as intended may have a protective effect on delaying or reducing the occurrence of adjacent segment deterioration as has been reported in some fusion papers.
While TDR represents a step forward in providing care to patients with back or neck pain, they are by no means a cure-all or a replacement for fusion in all patients. TDRs are not appropriate for use in patients with the following conditions:
- significant facet joint changes
- greater than Grade I spondylolisthesis
- morbid obesity
- prior laminectomy/discectomy where enough bone was removed to compromise the structural integrity of the posterior elements (TDR can be performed in patients with prior laminectomy/discectomy provided the posterior elements are not compromised)
As with any spine surgery, good results are not guaranteed. While overall groups of patients do well following TDR, there are patients who do not benefit, or benefit less than desired, from this surgery.
Richard D Guyer is President, Texas Back Institute, Plano, USA.