396 - PEEK Rod and Ti Screw Fixation Provides Comparable Construct Stability...

#396 PEEK Rod and Ti Screw Fixation Provides Comparable Construct Stability to Ti Rod and Ti Screw Fixation on Normal Spine

Lumbar Therapies and Outcomes

Poster Presented by: V. Goel

Author(s):

A. Agarwal (1)
M. Kodigudla (1)
D. Desai (1)
A. Agarwal (1)
V. Palepu (1)
V. Goel (1)

(1) The University of Toledo, Bioengineering, Toledo, OH, USA

Abstract

Introduction: Semi-rigid spinal implants that utilize nonmetallic materials and various rod geometries are becoming more prominent to promote fusion by a combination of durability, stability, and intra-and inter-level load sharing. Polyetheretherketone (PEEK) lumbar fusion rods provide semi-rigid fixation and they have recently become accessible for posterior lumbar fusion procedures. Our purpose was to study and compare the PEEK rod system to the traditional titanium (Ti) rod fixation by providing mechanical test data in a cadaveric model.

Material and Methods: Moments were applied to six normal functional spinal units (FSUs) in extension (Ext), flexion (Flex), left and right lateral bending (LB, RB), left and right axial rotation (LR, RR) and the position data was recorded. Tests were also done with a 400 N preload along with moments only in flexion and extension. The stabilized specimens were then tested in the flexion-extension cyclic mode (±75N, at 10 cm from the center of rotation, up to 50,000 cycles at 2 Hz) and moments were applied again to record the change in motion

Results: The range of motion decreased in extension by approximately 58% in Ti screws with PEEK rods while it decreased by 70% in Ti screws with Ti rods. Similar results were observed for other loading modes. The differences were statistically insignificant (P>0.05) in flexion, LR, extension with pre-load, and flexion with pre-load. The ROM in extension decreased by 48% with PEEK rods with cage while it decreased by 65% with Ti rods with cage. Similar results are observed by other loading conditions except in flexion with pre-load where Ti rods with cage had a greater average ROM than PEEK rods with cage. P-values showed, when comparing ROM data of Ti rods with cage to PEEK rods with cage, the difference was statistically insignificant in extension, flexion, and flexion with pre-load. For FSUs with PEEK rods, the ROM increased in extension by 3% post-fatigue. Similar results were seen in all loading conditions except where the ROM stayed the same in flexion with pre-load and the ROM decreased after fatigue in LR. The difference was statistically insignificant, for pre-and post-fatigued FSUs with PEEK rods, in all conditions except flexion. The differences between pre- and post-fatigued FSUs with Ti rods were statistically insignificant in all loading conditions.

Discussion: PEEK rods provided comparable stability to Ti rods in cases with and without a cage. Data also showed PEEK and Ti rods retained their stability after fatigue testing. . A more flexible device will allow for better anterior load sharing, which would improve the results of fusion. The more flexible PEEK rods would also reduce stress on the pedicle screws and reduce the possibility of screw loosening. The clinical advantage of PEEK over Ti is reduced computed tomography and magnetic resonance imaging scatter and artifact.

Conclusion: PEEK rods provided comparable stabilization to Ti rods for fusion, in spite of its flexible nature. PEEK's mechanical profile allows for potential advantages of posterior spinal fusion due to its durability, stability, and load sharing effects.