General Session: Spinal Innovation
Presented by: R. Guyer - View Audio/Video Presentation (Members Only)
R. Guyer(1), J.-J. Abitbol(2), D. Ohnmeiss(3), C. Yao(4)
(1) Texas Back Institute, Plano, TX, United States
(2) California Spine Group, San Diego, TX, United States
(3) Texas Back Institute Research Foundation, Plano, TX, United States
(4) Nanovis, Columbia City, IN, United States
Introduction: For interbody fusion cages, PEEK has favorable loading properties, but is biologically inert. Various methods for putting a titanium surface to promote osseointegration onto PEEK have been pursued. However, coatings introduce potential wear debris from abrasion and osseointegration may vary with surface properties. The purpose of this study was to compare surface abrasion and implant-bone interface strength, as a measure of osseointegration, of implants with titanium plasma spray (TPS) coating on PEEK vs. a deeply porous titanium scaffold surface on PEEK.
Methods: The mass of each test sample was measured before and after testing. Reduction in mass after testing was considered the amount of surface abrasion. Mean abrasion was compared for the two surface types (TPS coated PEEK vs. deeply porous scaffold, Nanovis, Inc.). Testing was conducted at 7 different loads ranging from 100N to 1,000 N in 150N increments. An abrasion block was placed approximately 2.5 mm from the edge of the sample pad. Axial load was applied while horizontally displacing the abrasion block across each sample. The block was cycled horizontally between 0 and 25 mm using a sine waveform with a frequency of 0.1 Hz. Ten horizontal displacement cycles were completed on each sample to simulate abrasion. For push out testing, holes 4 mm in diameter and 10 mm deep were drilled into the os frontale region of a swine. Implants were press-fit into the holes. After 5 weeks, animals were euthanized and skull sections containing implants harvested. Push out testing was performed using an MTS machine with a push rate of 6 mm/min. Maximum force (N) and shear strength (MPa) were recorded as the bonding strength between each implant and surrounding bone. When calculating shear strength, maximum force was normalized by the actual implant surface area in contact with bone.
Results: The mean abrasion for TPS coated PEEK ranged from 14% to 84%, varying with the test load applied (Figure 1). The mean abrasion for the scaffold was < 1% regardless of applied load. Figure 2 shows a TPS sample with 36.7% abrasion after testing at a load of 250N. In the swine model, mean push-out strength of scaffold pins was significantly greater than that of TPS coated PEEK pins (10.2 MPa vs. 5.6 MPa, p< 0.05).
Discussion: PEEK with a deeply porous titanium scaffold had significantly less abrasion and significantly greater push out strength that TPS on PEEK. These results suggest that the scaffold may have greater osseointegration properties with significantly less risk of coating abrasion than PEEK devices with a titanium plasma spray coating.
Figure 1. Abrasion testing results.]
Figure 2. Example of abrasion of TPS on PEEK.]