SpineUniverse: When were artificial discs invented? More specifically, could you give us some background information about the development of cervical artificial discs?
Artificial disc replacement began in Europe in the 1980s. At the time, there was a lot of interest in lumbar disc replacement. As technology advanced, clinicians and industry shifted their attention to the development of an artificial disc for the cervical spine. The process took over a decade. It wasn’t until the mid-1990s that Bristol Hospital in England came out with the first modern day cervical disc.
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SpineUniverse: How has the technology changed since the ‘early days’?
When it was first released, the Bristol disc was a metal-metal disc. It subsequently went through some revisions. Medtronic brought it to the United States (US) under the name of Prestige© Cervical Disc and received approved by the US Food and Drug Administration (FDA) in 2007. Two years later, Medtronic released the Bryan© Cervical Disc, a polymer with metal endplates, whereas the Prestige was metal-metal. Others soon followed. The ProDisc-C© came out, and then there was a little bit of a hiatus before the PCM, the Secure©-C, and now the Mobi-C© were developed. The newest cervical artificial disc to be FDA-approved is a metal/ceramic composite called the Prestige© LP. All were approved by the FDA within the last year or so. Now we have a choice of seven cervical artificial discs in the US, in contrast to just one lumbar artificial disc. It’s like a breath of fresh air.
Below is an example of a cervical artificial disc implanted in a patient's neck.
I’ve had experience with all of them to varying degrees, but the two I use the most are the ProDisc-C and the Mobi-C.
SpineUniverse: What are some of the differences between the ProDisc-C and the Mobi-C?
Artificial discs are typically categorized as “constrained” or “semi-constrained.” This, of course, refers to the amount of motion the disc allows. The ProDisc is a little more constrained than the Mobi-C. The Mobi-C allows more motion due to its design and the movement of the polyethylene within the endplates. For example, the ProDisc-C is more of a ball-in-socket, whereas the polyethylene of the Mobi-C actually moves around a little bit within the bottom tray. Most of the artificial discs are made of metal and polyethylene. There are newer devices like the M6, which is about to go under FDA study soon, that has a polymer within the endplates that allows a little shock absorption and motion, thus simulating the natural disc. To some extent, the Bryan does that, as well. With these variations from metal-metal, to plastic-on-metal, to metal on some type of polymer come slight differences in the degree of motion allowed. But when all is said and done, the differences are minimal. The more modern devices can absorb shock and perform more like a natural disc, as opposed to the limitations imposed by metal-on-metal or plastic-on-metal.
SpineUniverse: How do the differences in these discs influence your device selection for patients?
I want a device that is reproducible in my hands. For example, many surgeons love the Bryan disc. To them, that device is reproducible. I didn’t have a whole lot of experience with the Bryan disc, but I do have a lot of experience with the ProDisc-C. I think it’s important for surgeons to pick the disc they believe they can master and get reproducible results. The devices all look very good. There are subtle variations between them. It’s like having a bunch of different car manufacturers. You might like the fact that this one has this benefit, or that another one is a little less constrained, but ultimately, you’re looking to produce good outcomes in your patient. The cervical spine is very forgiving, and studies show that the performance of the artificial discs on the market today are rather uniform.