Nov 8, 2016 | By Alec
3D printing is doing much to improve the quality of implant surgeries already, but even most 3D printed implants cause significant discomfort and will erode over time. But as a new study by McGill University professor Damiano Pasini revealed, that could be down to material conventions. Rather than relying on very solid materials, Pasini has developed a very porous 3D printed femoral stem implant that resembles the porousness of actual bone and ‘tricks’ the remaining host bone to continue doing its job. As a result, hip replacements will last much longer, and will even create fewer problems for the patients relying on them.
Pasini is a professor of mechanical engineering at MicGill University, and he and his research team just published their findings in The Journal of Orthopaedic Research. The article is entitled “Fully Porous 3D Printed Titanium Femoral Stem to Reduce Stress-Shielding Following Total Hip Arthroplasty”, with Sajad Arabnejad serving as main author.
As they revealed, the biggest issue with existing hip replacements is that they are too rigid and too strong. They take some stress off the living bone, causing it to ‘give up’, weaken and deteriorate. Over time, this leads to painful joints and a new hip replacement – made more difficult by the fact that there’s very little good bone left to graft on to. The counterintuitive solution therefore calls for implants that are less solid, effectively forcing the existing bone structures to continue doing their job.
In a way, these 3D printed femoral stem designs thus also encourage the body to regenerate. “So because the implant loosely mimics the cellular structure of the porous part of the surrounding femur, it can 'trick' the living bone into keeping on working and staying alive,” Pasini explained. “This means that our implant avoids many of the problems associated with those in current use.”
While these 3D printed implants are not the most dramatic and life-saving medical applications we’ve seen, they are thus a common sense solution for an increasingly common surgical problem. The entire medical system is already buckling under an aging population, and it won’t help if elderly people need new surgeries every few years. At this pace, these new implant solutions could be reaching patients within the next three to five years.
The 3D printed femoral stem implants themselves feature a pyramid-like pattern on its surface, and are used to connect the living femur to the artificial implant. “What we’ve done throughout the femoral stem is to replicate the gradations of density found in a real femur by using hollowed-out tetrahedra,” the professor says of the design. “Despite the fact that there are spaces within the tetrahedra, these forms are incredibly strong and rigid so they’re a very efficient way of carrying a load. Just think of the lattice-work in the legs of the Tour Eiffel.”
The concept itself has been under development for about six years, and Pasini has gone through multiple versions over that time – all in an attempt to force existing bone structures to cooperate. “So because the implant loosely mimics the cellular structure of the porous part of the surrounding femur, it can “trick” the living bone into keeping on working and staying alive. This means that our implant avoids many of the problems associated with those in current use,” he says.
This has now finally been achieved, and the current implant will provide the living femur with sufficient stress to stimulate cell formation. A perfect solution for bone deterioration, a problem that orthopedic surgeons are seeing more and more frequently. “Because people engage in various sports where they may be injured more than they did in the past, we see younger people needing hip replacements more frequently,” says Dr. Michael Tanzer from the Jo Miller Orthopaedic Research Laboratory at McGill and part of this research. “And because people are also living longer, they often need to have the same hip replaced a second time. Unfortunately, I’ve seen many cases where people simply don’t have enough living bone for that to work easily. We are optimistic that this implant will reduce these kinds of problems.”
So far, the implant has been successfully tested various times and the researchers have even filed patents for this 3D printed innovation. They further said that their design is fully compatible with existing surgical technology for hip replacements, and they are hopeful that this will make it easier to receive FDA approval.
Posted in 3D Printing Application
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Phil wrote at 11/8/2016 3:12:26 PM:
I'm interested to learn how the powder is removed from the dense porous structure, and how they are certain there is none remaining. Cleanliness is a serious consideration for these types of porous structures on implants. Furthermore, I'd be interested to learn how this implant performs under fatigue loading. HIP stems undergo significant fatigue, and this continues to be a big factor when designing stems for production via additive manufacturing. I foresee this design having serious challenges in fatigue performance when testing for FDA clearance.