Sunday, October 11, 2009

Silicon Nitride - Is it all an Illusion?

With the upcoming NASS Meeting in San Francisco on November 10-14th, 2009, TSB was reviewing products and companies to identify any innovation and emerging technology. While reading OTW, I was fascinated by an advertisement that says; "Silicon Nitride Proven Under Such High Stress Conditions as the Space Shuttle, Jet Engines, Race Cars and now Spine!" So we decided to perform some due diligence on Amedica and their products.

First and foremost, what is Silicon Nitride (Si3N4)? It is a hard ceramic with an exceptional modulus of elasticity, it is inherently resistant to fracture and has superior wear resistance. It has been used in gas turbines, automobile engine components, and has been used in the main engine of the NASA Space Shuttle. This material has a ceramic substrate, a substance acted upon an enzyme, that produces a chemical change, acting as a catalyst, mimicking natural cancellous bone.

Amedica's claim to fame is developing Si3N4 for a Spinal Spacer that is 20% stronger than PEEK, it is radiolucent, and does not produce MRI or CT artifact. But the question must be asked; Has anyone in the industry had a problem with PEEK? If anything, INVIBIO needs competition to drive down the cost of their license, which is an estimated $225k over a three year period and material? Up until this point, they have had a monopoly. So what challenges does a company like Amedica face?

First of all, their product portfolio is made up of "me-too" products. Does the industry need another pedicle screw and cervical plate? Probably not! Though their interbody devices are manufactured with Silicon Nitride, to our knowledge, no one has complained about the performance of PEEK interbody spacers. There could be a potential financial advantage that this product could offer if this material is cheaper than PEEK. The TSB would be interested in knowing what the comparative cost is between these materials.

In closing, the rumor on the street, and that is strictly a rumor, is that this company has been challenged in developing traction in the marketplace. TSB is not sure that the newest addition to this company, Ben Shappley has the firepower to get the job done. The TSB wants to know what its readers know about this product and what they think?


  1. The whole point of PEEK is that is has a modulus of elasticity close to bone, which helps to prevent subsidence. Also, under high compression, PEEK will slowly deform prior to complete failure.

    Ceramics like silicon nitride are rock hard with essentially zero elasticity. They carry a risk of subsidence and are even harder than titanium. They also tend to have almost no ductility - the ability to deform before shattering like glass.

    Ceramics do have potential in joint bearings due to their hardness and wear qualities. Maybe I'm missing something but as an interbody spacer I just dont see the benefit.

  2. As a side note, Solvay now has some devices FDA approved using its PEEK. I agree that Invibio needs some market competition.

    Invibio will play the consistency and history card as its arguing point over why someone should use Invibio vs. the newcomer. That is standard practice for companies that are starting to see competition when it comes to raw material providers.

    They better have a clear reason (250k worth) of why their product is substantially better than Solvay.

  3. 25 years ago reconstructive surgeons noticed the growth of fibrous tissue around polymer hip stems. 25 years later they've learned that intimate bone contact, not material, is the greatest deterrant to fibrous tissue formation and non-union. As I see it, the greatest advantage to a material like silicon nitride, or barium doped PEEK for that matter, is the ability to improve placement and increase the surface contact area between bone and implant. As we spend more time looking at histologies of non-unions, and less time staring at nearly radio markers, we'll see this borne out in spine as well. The only other benefit of a ceramic material is that it is more conducive to bony attachment than polymers, which are inherently hydrophobic.

    The elasticity argument is a moot point, and is a carry over myth from a poorly designed Brantigan study developed to move CFRP cages. The greatest determinant of subsidance is surface area, not stiffness. Furthermore, PEEK is not a marshmallowly material that gives and deflects to preserve the endplate. It is used in high load industrial applciations specifically because it is stiffer than most thermoplastics. It's just one more line we've swallowed courtesy of the device companies.

    As a side note, without knowing the specifics at Amedica, ceramics processing is a complex, multi-step, read expensive, process. There is no way it is cheaper than simply machining PEEK bar stock.