General Session: Spinal Innovation
Presented by: J.K. Burkus - View Audio/Video Presentation (Members Only)
J.K. Burkus(1), B. Torstrick(2), R. Guldberg(2), K. Gall(3)
(1) Hughston Clinic, Spine Service, Columbus, GA, United States
(2) Georgia Institute of Technology, Parker H. Petit Institute for Bioengineering and Bioscience, Atlanta, GA, United States
(3) Duke University, Department of Mechanical Engineering and Materials Science, Atlanta, GA, United States
Purpose: Current interbody fusion devices (i.e. cages) are primarily made from polyetheretherketone (PEEK) due to its high strength, radiolucency and similar stiffness to bone. However, smooth-surfaced PEEK cages have been associated with fibrous encapsulation and implant migration, thus stimulating the development of alternative technologies. This study aims to directly compare the in vitro and in vivo bone response to 2 clinically available PEEK alternatives: porous PEEK (Porous; 300µm pore size, 66% porosity, 99% interconnectivity; Sa=0.45±0.06µm) and plasma-coated titanium on PEEK (TiPEEK; Sa=7.02±0.33µm).
Methods: MC3T3 cells were grown on smooth PEEK (Smooth; Sa=0.01±0.002µm), Porous, and TiPEEK discs for 14 days in osteogenic media (n=5). Osteocalcin and calcium are late markers of osteogenic differentiation and are associated with culture mineralization. Osteocalcin content of cell lysates was measured using an ELISA and normalized to DNA measured using a Picogreen dsDNA assay. Calcium content was determined by a colorimetric Arsenazo III reagent assay. For in vivo studies, cylindrical implants were implanted into an established rat tibial defect model with the Porous and TiPEEK surfaces located on the bottom implant face. At 8 weeks, animals were euthanized and each bone-implant interface was subjected to µCT scanning and biomechanical pullout testing (n=3-5). All data were reported as mean±SE. Comparisons were calculated using a 1-way ANOVA followed by a Tukey multiple comparisons test.
Results: Cultures on Porous surfaces contained greater amounts of calcium and osteocalcin than Smooth and TiPEEK cultures (p< 0.01). µCT scans revealed a thin layer of mineralized tissue near the bottom face of Smooth implants and substantial mineralized tissue within the porous architecture of Porous implants. µCT evaluation of TiPEEK implants was obscured by imaging artifact. Porous implants exhibited greater pullout failure loads than Smooth and TiPEEK implants (p< 0.05). (Fig.1) Fig1: (A-C) µCT sections of Smooth, Porous and TiPEEK implants at 8 weeks. (D) Calcium and (E) osteocalcin content of MC3T3 cultures at 14 days in osteogenic media. (F) Pullout failure loads of implants at 8 weeks post-implantation.
Conclusions: Overall, Porous was associated with a more differentiated bone cell phenotype in vitro and greater implant fixation in vivo compared with Smooth and TiPEEK suggesting porous PEEK is a clinically viable alternative for improving osseointegration. Comparing the results between Smooth and Porous suggests not all PEEK implants generate a fibrous response, but rather surface topography might play a larger role than implant chemistry, with macro-porous features exhibiting improved osseointegration compared to smooth and micro-scale rough surfaces. Interestingly, TiPEEK and Smooth performed similarly in vitro and in vivo, which is in contrast to previous reports of rough titanium surfaces inducing a greater osteogenic response than smooth PEEK. Future work is focused on systematically decoupling the effects of surface chemistry (Ti vs. PEEK) and topography.