Prosthetic Cervical Discs

It's looking like I'm going to get some surgery to replace a degenerating disc in my cervical spine. One of the ways I'm dealing with the anxiety around this impending surgery is by digging into the research and technology around spinal disc replacement.

Before is even get into the arthroplastic surgery, my first concern is over general anesthesia. Back when I was young and impressionable, I enjoyed reading Robin Cook's medical thriller novels. His writing left me with the impression that general anethesia is the riskiest part of modern medicine. This literature review by Gottschalk et al. from 2011 found that mortality from general anesthesia for patients without major systemic disease was about 0.4 per 100,000. Those odds don't sound so scary to me. Of course there are other possible adverse complications and outcomes, but mortality is the one I'm most concerned about. For some context, about 1 in 100 Americans die in car crashes (and there's about 1 fatality for every 100 million miles driven - we Americans drive a lot!). So I'd have to get a lot of surgeries to make it more likely that I'll die from general anesthesia than from a car crash, and I'm willing to get in my car without a second thought. Of course, I don't drive very much, and I'm unlikely to drive anywhere near 100 million miles in my lifetime. But, still, that's a bit of a relief! As a friend told me, getting this surgery is a two-for-one special for me: I'll regain some function in my right arm, and get over my fear of general anesthesia. Writing this paragraph, I think I've basically accomplished the latter.

As for the cervical arthroplasty, surgeons have been removing discs and then fusing vertebrae for a while. They go in through the front, so the procedure is an anterior cervical discectomy and fusion, or ACDF. But that treatment has poor outcomes. Patients lose mobility, symptoms recur, and then patients need further treatment. Also, putting metal into the spine prevents the future use of MRI as a diagnostic tool.

A relatively recent development has been the implantation of prosthetic cervical discs. The surgeon I'm probably going to have work on my neck uses the Simplify cervical disc made by Globus Medical. You can see an animation of the surgical technique at this link. And the image above is an exploded view of the prosthetic disc - the image is from Globus Medical. This basic approach is usually superior to ACDF. This meta-analysis from 2018 found that outcomes for patients were better in the short term, and out to seven years post-surgery, for patients who had their disc replaced, compared to ACDF. The results of this FDA trial from 2019 showed that patients did significantly and substantially better with replacement rather than ACDF ten years after surgery. Research from 2025 indicates that, at least in the short term, and especially for patients with disc herniation, surgery leads to superior outcomes for patients, as compared to non-surgical interventions. In that study, several patients who started in the non-surgical group later opted for surgery. That certainly tracks for me, as my physical therapy has not helped with my radiculopathy.

This is one of those situations where the technique is totally amazing, right up until I start thinking about the surgeon cutting into the front of my neck to remove my disc and implant a prosthesis. So let's not dwell on that for too long, and instead move right along to thinking about the prosthetic technology and the patents protecting it.

The basic idea behind Globus Medical's Simplify replacement cervical disc is two plates that are separated by a core. The core is rounded so that the plates can move relative to each other, allowing for movement just like the spine: bending forward and back; side to side; and also rotating along the axis of the spine. Recent research shows that having less constraint on the motion of these replacement discs leads to better outcomes for patients, like this meta-analysis from 2024. This replacement disc technology is protected by a suite of patents. The basic idea shows up in patent 9839525, which describes the replacement disc, also called an intervertebral prosthesis. Many of the patents in this family of inventions are expired. It looks like they were allowed to expire as the inventors or assignees obtained patents to superior technologies. The '525 patent expired 2023-04-24.

Some versions of the invention include a metal core, such as patents: 9107762 (that one just expired on 2026-06-24); 8974533 (expired 2024-05-26); 8845729 (expired 2025-11-03); 8062371 (expired 2024-09-27); 8002834 (expired 2024-11-10). One drawback of using a metallic core is that the metal interferes with imaging techniques like x-rays, and precludes the use of MRI. So updated inventions use a ceramic core instead of a metallic core, which is covered in later patents. Patents that cover the prosthesis without specifying a metallic core include 8454698 (active, granted 2013-06-04); 8444695 (active, granted 2013-05-21); and 7753956 (active granted 2010-07-13).

One design idea was to retain the core between the plates by having part of the core extend into a recess in each of the plates, so that once the whole thing is sandwiched together, the core can't slip out. That's covered in patent 7442211. It looks like they came up with a better design for retaining the core between the plates, and this patent was allowed to expire on 2025-02-11.

That better idea for retaining the core between the plates is to instead have a recess in the top and bottom of the core, with protrusions from the plates extending into those recesses. A further innovation was to make different dimension for the prostheses - especially different heights - to accommodate patients of different sizes. Those ideas are covered in many active patents, including: 10441431 (active, granted 2019-10-15); 8808384 (active, granted 2014-08-19); 11911283 (active, granted 2024-02-27); 8764833 (active, granted 2014-07-01); 12414859 (active, granted 2025-09-16); 9439775 (active, granted 2016-09-13); 9421107 (active, granted 2016-08-23).

In its current incarnation, the prosthetic disc is made in a range of heights, starting at 4 mm. The core is alumina coated ceramic. And the plates are polyetheretherketone, coated with titanium plasma. To look at claim construction for these patents, let's delve into the most recently granted patent, which is 12414859. While this is a continuation of several previous patents, the claims and their structure in this single patent are straightforward, and show how the inventors and the assignees are trying to protect their ideas. There are two independent claims in the patent - claims 1 and 8. Claim 1 describes endplates, with a keel on the superior endplate, and a core fitting between them. Claim 8 describes the same device, but with the keel on the lower endplate. Then depending from Claim 1, Claim 2 describes an elongated keel, and Claim 3 describes a keel on the inferior endplate as well. Claims 4 and 5 depend from Claim 3, and describe modifications to the inferior endplate keel. Claims 6 and 7 depend from Claim 5, and describe further modifications to that keel under the inferior endplate. For Claim 8 and its dependent claims, the patent basically does the same thing in reverse, building dependent claims that start with the keel on the inferior endplate, modifying it, adding a keel to the superior endplate, and then modifying that keel. It is an elegant and thorough approach to claim construction, providing narrower fallback claims should the broader claims ever fail. Along with the suite of patents in this family, there should be clear descriptions of the invention with adequate protection for these ideas.

While I'm describing the claim construction in these patents, it's probably a good moment to remind you that I'm not a lawyer, and nothing in this blog post should be taken as legal advice or analysis. While I am a patent agent, nothing in this post is advice for a client. The only way to become my client is sign an engagement letter with me. With that said, if you have questions about patenting your invention, please don't hesitate to reach out!

Another patentable part of these inventions are the methods and tools for inserting the prostheses. As you can see in the animation I linked to near the start of this post, the surgeon needs tools to separate the vertebrae and hold them apart while implanting the prosthesis, as well as tools to install the prosthesis itself. Both the tools and the methods of using them are patented. Patent 7585326 is active, having been granted on 2009-09-08. Its current anticipated expiration date is 2027-06-11, but I'm guessing the assignee will want to pay the fees to extend that expiration date - unless they have an even better, patentable version that's going to be patented before then. These ideas were covered in other expired patents, including: 10130494 (expired 2024-08-06); 10085853 (expired 2025-06-26); 9956091 (expired 2024-08-06); 9839532 (expired 2024-08-06); and 11857438 (expired 2025-07-23).

I hope you enjoyed learning about these intervertebral prostheses and surgical techniques as much as I did! It's amazing what people are able to accomplish with scientific rigor and technical innovation.

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