• Kirk C McGilvray, Jeremiah Easley, Howard B Seim, Daniel Regan, Sigurd H Berven, Wellington K Hsu, Thomas E Mroz, and Christian M Puttlitz.
• Orthopaedic Bioengineering Research Laboratory, Department of Mechanical Engineering and School of Biomedical Engineering, Colorado State University, 1374 Campus Delivery, 200 W Lake St, Fort Collins, CO 80523, USA. Electronic address: kirkmcg@engr.colostate.edu.
• Spine J. 2018 Jul 1; 18 (7): 1250-1260.

Background ContextThere is significant variability in the materials commonly used for interbody cages in spine surgery. It is theorized that three-dimensional (3D)-printed interbody cages using porous titanium material can provide more consistent bone ingrowth and biological fixation.PurposeThe purpose of this study was to provide an evidence-based approach to decision-making regarding interbody materials for spinal fusion.Study DesignA comparative animal study was performed.MethodsA skeletally mature ovine lumbar fusion model was used for this study. Interbody fusions were performed at L2-L3 and L4-L5 in 27 mature sheep using three different interbody cages (ie, polyetheretherketone [PEEK], plasma sprayed porous titanium-coated PEEK [PSP], and 3D-printed porous titanium alloy cage [PTA]). Non-destructive kinematic testing was performed in the three primary directions of motion. The specimens were then analyzed using micro-computed tomography (µ-CT); quantitative measures of the bony fusion were performed. Histomorphometric analyses were also performed in the sagittal plane through the interbody device. Outcome parameters were compared between cage designs and time points.ResultsFlexion-extension range of motion (ROM) was statistically reduced for the PTA group compared with the PEEK cages at 16 weeks (p-value=.02). Only the PTA cages demonstrated a statistically significant decrease in ROM and increase in stiffness across all three loading directions between the 8-week and 16-week sacrifice time points (p-value≤.01). Micro-CT data demonstrated significantly greater total bone volume within the graft window for the PTA cages at both 8 weeks and 16 weeks compared with the PEEK cages (p-value<.01).ConclusionsA direct comparison of interbody implants demonstrates significant and measurable differences in biomechanical, µ-CT, and histologic performance in an ovine model. The 3D-printed porous titanium interbody cage resulted in statistically significant reductions in ROM, increases in the bone ingrowth profile, as well as average construct stiffness compared with PEEK and PSP.Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.

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