Lumbar (Low Back) Artificial Discs: Spine Technology Update
An Interview with Jack Zigler, MD
SpineUniverse: Please tell us about the history and development of lumbar (low back) artificial discs.
The history of modern lumbar discs started in 1984 in Germany with the implantation of the first Charité artificial disc. The Charité device was developed by Karin Büttner-Janz, an orthopaedic spine surgeon and Kurt Schellnack, an engineer. Doctors Büttner-Janz and Schellnack continued to work together revising the Charité artificial disc and implanting models in patient during the 1980s and 1990s. Prior to that time, there were different designs and even some pilot studies involving patient participants, but those earlier devices were not very successful.
Charité artificial disc was removed from the market in 2012
In France, Dr. Thierry Marnay developed a precursor of the ProDisc® lumbar artificial disc, which he implanted into 64 patients and observed their progress. Therefore, sometime in the late 1990s both the Charité and ProDisc were being developed for potential study by the United States (US) Food and Drug Administration (FDA). In 2000, the Charité IDE study started followed by the ProDisc IDE study in 2001. Approximately 300 patient participants were enrolled in each of the separate multicenter prospective randomized studies. Each clinical trial was supported by about 20 centers.
SpineUniverse: Were both lumbar artificial discs approved for use in the US?
The Charité artificial disc was approved in October 2004 and the ProDisc-L in August 2006. Those were the only two lumbar artificial discs available in the US for several years. However, Charité was removed from the market worldwide in 2012. So, ProDisc is currently the only lumbar artificial disc that is FDA-approved for use in the US.
SpineUniverse: Are there other lumbar artificial discs in the device pipeline?
Yes, in fact, there are several other designs in the FDA’s queue. It takes between five and seven years to obtain FDA approval. The Texas Back Institute has been in an investigative role in several other disc designs in the pipeline, and has been following patients for the companies who sponsor research and development of those artificial disc devices. As yet, no other lumbar artificial disc has received FDA approval.
SpineUniverse: What is the status of new clinical trials for this technology?
There may be some other designs beginning IDE studies within the next year or two for which we’ll be able to recruit patients. However, both the global and US economies, as well as the regulatory environment has really slowed the willingness of companies to start these FDA studies.
Currently, these studies are terribly expensive and many companies don’t want to gamble large sums of money on a process that’s going to take seven years, and then into an unknown market. In general, clinical research has slowed down significantly during the last three to five years.
SpineUniverse: How is the design or construction of the ProDisc different from Charité?
Charité was a very slippery disc. It used a mobile plastic or polyethylene core with almost friction-less surfaces both above and below. In theory, that made for a very good model—and in the lab, it looked like a good model. However, in the body, it didn’t work out as well.
SpineUniverse: Why didn’t the Charité artificial disc work well when implanted?
The Charité offered no internal support to shear, forcing the ligaments and the facet joints to give stability to the vertebral segment. It turned out to be a very finicky disc that needed to be implanted “spot-on.” It didn’t have a very forgiving “sweet spot” and some of the clinical results were just not as good as people had hoped.
SpineUniverse: Please tell us about the ProDisc.
The ProDisc is a bit different, although it’s constructed from the same materials. It’s built with cobalt-chrome alloy endplates and an ultra-high molecular weight polyethylene insert. The insert is locked into the inferior (bottom) metal component creating a ball-and-socket joint. Because the polyethylene insert is locked into the inferior aspect of the artificial disc, it is semi-constrained. Semi-constrained means there is some constraint—limitation of movement within the implant itself to accommodate for extremes of motion—in particular, the extremes of forward shear, which was the problem with Charité (which had no internal constraint). Essentially, we’ve found the ProDisc is more forgiving; implantation offers a wider sweet spot, and patient outcomes are better in general. Because of the ProDisc’s design, it appears to be more protective of the facet joints than Charité.