Technological Advancements in Spinal Fusion Implants: A Summary of the Current Scientifi c and Clinical Research on Titanium Engineered Surfaces

Lumbar interbody fusion is commonly performed by inserting an implant into the disc space. Interbody fusions are benefi cial because they result in high fusion rates, maintain spinal alignment, and allow for indirect decompression of the neuroforamen.1 Currently, the two most commonly used implants are made of polyether ether ketone (PEEK) or allograft bone. Threaded titanium (Ti) cages were used in the past, but many surgeons became concerned about challenges with imaging the fusion around titanium as well as subsidence, and their use declined. These implants were previously used as threaded “standalone” constructs (no pedicle screw fi xation). This was shown to be mechanically inferior and led to more clinical failures due to surgical technique rather than the implant material. A new class of Ti i mplants with nano-roughened (micron-level) surface modifi cations have been shown to induce greater osteoblast differentiation of culture stem cells than PEEK.2 There is an emerging trend in spine surgery to move away from plastic interbody fusion spacers. This trend has stimulated an expanding clinical and scientifi c interest in the surface technology of acid-etched titanium spinal implants. The purpose of this article is to review the scientifi c literature surrounding these unique titanium engineered surfaces and discuss the clinical outcomes to date. Titanium alloys have been extensively studied in the dental literature and have a well-established history of use. Basic science studies have shown that titanium, especially with roughened nano-surface (micron-level) properties, creates a favorable bone-implant contact surface and superior osseointegration with the surrounding bone.3,4,5 In vitro experiments comparing the responses of immature osteoblasts to roughened and smooth titanium surfaces conclude that the differentiation of the cells is greater when the surface has an engineered texture with micron-scale (10 9) roughness. This is the scale on which the mesenchymal stem cells are stimulated. Dual acid etching processes applied to the surface of Ti has been shown to stimulate local, physiologic bone morphogenetic protein (BMP) production, transforming growth factor beta (TGF-β), and vascular endothelial growth factor (VEGF), all of which promote a natural osteogenic environment and may facilitate bone integration with the implant surface.3,4 This is a novel concept that has not been previously examined in the spinal fusion clinical application.