240. A subtractive biomimetic titanium surface promotes bony ongrowth in an ovine lumbar interbody fusion model

Abstract

BACKGROUND CONTEXT Osseointegration, direct functional contact between bone and an implant surface, is a key process in achieving a rigid fusion and ultimately a successful clinical outcome following interbody fusion surgery. Surface properties of an implant (chemistry, topography, roughness) directly affect the healing response at the bone-implant interface. Surface modifications may enhance osseointegration on implants compared to those that have machined surfaces. A number of techniques exist that can provide macro- and microscale modifications to implant surfaces. Laser-etching is a subtractive technique that allows for controlled, intentionally designed features to be imparted on a surface. An implant surface that mimics the natural osteogenic environment with pores inspired by osteoclast resorption pits may trigger osteoblast cellular signaling, leading to positive downstream effects like implant osseointegration. PURPOSE The purpose of this study was to compare osseointegration of lumbar interbody fusion devices made from polyetheretherketone (PEEK), smooth titanium-alloy (sTAV), and laser-etched biomimetic TAV (rTAV) in a preclinical ovine model. STUDY DESIGN/SETTING In vivo ovine animal study. PATIENT SAMPLE N/A OUTCOME MEASURES Microcomputed tomography (microCT) and histomorphometric analyses were performed to quantify bone volume (BV) within the spacers (ingrowth) and total bone growth onto the surface of the spacer (ongrowth), respectively. BV was measured as the sum of the volume of bone in the central and both lateral graft windows. Bone ongrowth was assessed as the bone apposition ratio (BAR), the percent of the total length of the implant with direct bony contact on the interbody surface (linear apposition). Only superior and inferior surfaces of the implants were considered in BAR analysis, as the laser-etching treatment was only applied to these sides. METHODS Eighteen mature female sheep underwent two-level (L2–L3 and L4–L5) lateral interbody fusion using either PEEK, sTAV, or rTAV spacers (n=6 levels per group per time point). Animals were sacrificed at 6 and 12 weeks postoperatively. BV and BAR were evaluated at the two postoperative time points. RESULTS The rTAV implants demonstrated a trend towards higher BV than PEEK and sTAV implants at the 6-week postoperative time points (179.5±70.7 mm3, 116.9±43.0 mm3, and 108.7±15.2 mm3, respectively) (0.05≤p 0.05). At 6 weeks, the rTAV implants had significantly greater BAR than sTAV (24.9%±17.6% and 3.4±2.6%, respectively) (p CONCLUSIONS Bony ongrowth during interbody fusion is necessary for optimal implant fixation. Interbodyspacers with a biomimetic, laser-etched surface treatment demonstrated more bony ongrowth when compared to sTAV at the initial 6-week time point and continued to demonstrate robust bony ongrowth at 12 weeks. Although a small sample size limited this study's statistical power, these results demonstrate that implants with biomimetic surface modifications may promote robust bony ongrowth and ingrowth. FDA DEVICE/DRUG STATUS SINTROS (Globus Medical) (Approved for this indication)