The Surgeon’s Perspective
We checked in with one of the orthopedic spine surgeons at the Rothman Orthopaedics Institute, Kris Radcliff M.D. Dr. Radcliff is an associate professor in the Department of Orthopedic Surgery at Thomas Jefferson.
When we asked him how the new truss-based implants have a qualitatively different way of interacting with boney interface and fusion bone growth, he immediately started talking about motion—or lack thereof
“I learned early in my orthopedics residency about the importance of motion to bone healing. There was tremendous euphoria when locking plates for periarticular fractures emerged during my orthopedic residency. However, with early locking plates, there were problems with nonunion due to excessive rigidity. Our specialty took a step back and realized that you have to have some controlled micromotion for bone healing.”
“Compared to traditional cages, truss implants permit controlled micromotion. One of the unique features of additive manufactured implants is that they exploit strain distribution creating small, localized deflections that help bone grow.”
“The truss thickness can be engineered for a specific bony strain. It is an established principle in orthopedic surgery that small amounts of controlled strain or deflection stimulates bone growth.”
We asked Dr. Radcliff if there was something innate in this architecture that makes this interface more “bone friendly” than other implants.
“Implants,” Radcliff pointed out, “are, in essence, about two basic properties—the material they are made from and their structure. Modulus is a material property that is dependent on whatever the implant is made of—whether carbon fiber, titanium, PEEK, or even PMMA. Each one has a specific unique set of properties.”
“Rigidity is a structural property which can be independent of the material. Additive manufacturing has allowed for the development of really unique, smart structures. For example, some of these new designs (and I use 4WEB’s Truss design) distribute compressive and tensile forces evenly throughout the implant.”
“Let’s say the left side of the cage is being loaded more than the right side and disc space is a little bit tighter on the left. The implant’s struts redistribute the load throughout the rest of the web structure, even on the right side of the implant and thereby help to normalize forces throughout the implant.”
Can 3D printed implants reduce biologics use?
It occurred to us as we were talking with Dr. Radcliff that these new truss-based 3D-printed implants, by creating a new kind of bone/metal interface, could affect the need for advanced biologics. We posed the question to Dr. Radcliff and here is what he said.
“Yes, I think it does, indeed, enable me to use kind of a simpler, less expensive biologic. There is an increasing resistance from the payers and hospital value analysis committees about biologics. I regularly get insurance denials of cellular biologics. Since the 4WEB cage is actively involved in stimulating bone differentiation, I feel much more comfortable with just a simple DBM [demineralized bone matrix] biologic or local bone in many of my cases.”
“I’ve been using these implants for about probably 5-6 years in the cervical spine. I was an allograft user before I switched to 3D-printed truss-based cages. The problem with allografts is that every now and then there would be an allograft that would not fuse properly. You wonder what exactly is going on there. I like the fact that these additive manufactured implants not only provide the structural support but will also transmit mechanical stimuli to improve and potentially accelerate bone growth.”
“We just completed a study that was accepted to SMISS [Society for Minimally Invasive Spine Surgery] that compares markers of osteoblast differentiation with titanium discs manufactured with the 4WEB process versus smooth titanium and PEEK. Even without any mechanical loading the 4WEB surface showed a significant increase in gene expression. So, the surface roughness alone is stimulating a cellular response and then that response is amplified through the mechanobiologic properties of the truss implant design.”
“I’m especially impressed with 4WEB Medical’s truss design because it can deliver compression and tension forces throughout the entire construct. In many ways, the design optimizes the bones biologic response.”
