3D Print This!
Robin Young • Fri, December 2nd, 2016
It’s not a revolution, but it is changing orthopedics.
It’s not going to lead to customization of implants in the OR.
It’s not going on the mass production line.
But 3D printing is transforming implant design and functionality.
Here, for example, are two titanium implants (see X-rays below). The one on the left is the titanium BAK cage fabricated the old fashioned way. Under X-ray the BAK looks like automobile headlights on high beam staring back at you.
The one on the right is a 3D printed titanium cage (aka: Tritanium) and it generates a very different x-ray image. In this one, unlike the BAK X-ray, the surgeon can see bone growing through the implant.
Why the different X-rays? The titanium implant on the right was fabricated with 60% porosity and an internal structure similar to cancellous bone. Which was only possible because it was both designed and fabricated using a 3D printing system.
And it has become the best-selling new product in the history of Stryker Spine.
It’s called Tritanium.
One more quick data point: 20% of the best new spinal implant technologies for 2016 (as voted on by a blue ribbon panel of top spine surgeons) were 3D printed designs including K2M, Inc.’s CASCADIA™ AN Lordotic-Oblique Interbody System.
3D: What It Is, What It Isn’t
3D printing has been around for 30 years, but it is still a new technology.
Probably the most impactful change over those 30 years was the accelerated deposition rate of 3D printers—which is the speed with which these machines lay down material. Today’s printers, are substantially faster than earlier versions. As a result, they’re commercially viable as fabricating machines for small, comparatively expensive implants like interbody spacers.
At slower speeds, 3D printers are prototyping tools. But even a 3D printed prototype has to be adapted for fabrication on traditional machines. By contrast, today’s faster printers deliver to the surgeon precisely what the engineer envisioned on the computer. That’s a big deal.
Fast 3D printers allow biomedical engineers to dream up highly complex, lightweight geometric designs and actually fabricate them for surgeon use. 3D printing is becoming the catalyst for a new generation of innovative, multi-functional orthopedic and spinal implants.
To 3D print something, an engineer has to create a digital model on the computer—typically with CAD software. When the design is finished, the engineer uses “slicing software” to create hundreds or thousands of cross sectional layers about 0.1mm thick.
These digital slivers then go to a 3D printer which, one layer at a time, builds the part.
The official name for this is “additive manufacturing.”
Conceptually, the most exciting aspect of additive manufacturing is customization. Imagine, for example, using a patient’s MRI digital file to 3D print a custom implant the night before surgery.
But that is probably a long way off. Experts cite quality control issues, FDA concerns and more complexity in the OR as roadblocks. Bottom line, it could take 10 or 20 years for hospitals to “print” their own hips, spinal implants or stents.
3D Printing Titanium
According to market research group CONTEXT, the 500, 000th 3D printer was shipped in 2015. By 2017, that number is expected to double to more than one million.
In 2016 more than 150, 000 Kgs of titanium will be likely consumed for 3D printed medical applications. Industry analysts are writing that this will grow to almost 1.1 million Kg by 2022.
Orthopedic surgery is the #1 driver of this growth.
Additive manufacturing, as contrasted to the more traditional subtractive manufacturing process, improves the osseointegrative properties of titanium implants and, as we saw earlier, post-op X-ray visualization as well.
More Innovation on the Way
The current method for printing a titanium part is known as granular materials binding, which means fusing metal powder granules with a laser or other heat source. Besides titanium, 3D print fabricators can use nylon, wax, bronze, stainless steel or cobalt chrome.
Most interestingly, several new metal 3D printing innovations are coming to market which could change today’s 3D metal printing landscape dramatically. These new, faster, sharper technologies use chemical vapor deposition (CVD, currently used for coating), physical vapors deposition (PVD, which uses a vacuum), liquid metal material jetting or friction stir 3D printing.
In the works at Stryker for more than a decade, the Tritanium Posterior Lumbar Cage is a 3D printed implant, and as we noted, has become the fastest growing new product launch in the history of Stryker Spine.
Stryker’s Tritanium PL cage received 510(k) clearance in November 2015.
Because the Tritanium cage is 3D printed, it is able to mimic the shape and structure of cancellous bone—which means it has fully interconnected pores that span endplate to endplate with an average 60% porosity and a mean pore size of roughly 450um.
The implants large lateral windows and open architecture are the keys to its visualization on both CT and X-ray.
The shape itself is solid-tipped with precise angled serrations on the superior and inferior surfaces. This allows for bidirectional fixation.
Here’s an image of Stryker’s Tritanium PL cage:
Note the large central opening which spans endplate to endplate.
Tritanium vs PEEK vs Titanium Coated PEEK
Stryker sponsored a study which compared the bone in growth and fusion performance of three different materials—PEEK, titanium plasma sprayed PEEK and Tritanium.
The study used 27 mature sheep. The investigators performed spinal fusion surgery at L2-L3 and L4-L5 using the three different types of interbody cages each packed with iliac crest bone graft.
There were ten implants per group for an 8-week time point and eight implants per group for a 16 week time point.
All the implants tested for three primary directions of motion and various quantitative measures of boney fusion. Among those quantitative measures, the investigators also used histomorphometric measurements to quantify the area of new bone in the implant itself, in the graft window and in total (endplate to endplate).
The full study is available on the Stryker Spine website: http://www.stryker.com/builttofuse/media/assets/TRITA-WP-2%20Tritanium%20PL%20Pre-Clinical%20Study%20Summary%20FINAL.pdf
But the blinded third party review of the histologies reported that the Tritanium PL Cage demonstrated a statistically greater bony bridge score at the 16 week time point as compared to the PEEK or PEEK coated with Titanium implant.
Here are the histologies images at 16 weeks.
Different Product, Different Launch
Stryker Spine’s President Brad Paddock met with OTW at NASS and described how Stryker Spine launched the new implant.
Since the Tritanium PL cage is indicated for posterior lumbar fusion in patients with degenerative disc disease (a bread and butter spine surgery) spine surgeons already knew how to implant the cage.
But Stryker Spine’s management decided to require surgeons to come to Allendale, New Jersey, to learn about Tritanium PL cage before being “allowed” to use it.
Allendale is a fine community, but it’s no Las Vegas or Orlando or Cabo San Lucas. So, Stryker was asking its surgeon customers to come to Allendale to hear about a surgery they know extremely well and stay at the local Holiday Inn Express.
Not the most compelling offer.
But a few surgeons agreed. And they learned about the Tritanium 3D printing technology. They learned about the characteristics of the materials, how it would work in the spine and how bone would grow into and through the material.
The training, it turned out, was well worth the trip.
The Future of 3D Printing
Tritanium’s success clearly shows the commercial value of 3D printing for orthopedic implants. And innovative firms like K2M have jumped on the 3D bandwagon as a way to differentiate their products and to innovate multi-functional, better performing implants.
What makes this so exciting is that 3D printing is opening up the creativity of the orthopedic engineers and inventors.
What will they think of next?