An Immunologic and Biomechanical Comparison of Polyether Ether Ketone-Zeolite and Polyether Ether Ketone Interbody Fusion Devices

Abstract

Study Design. A laboratory study comparing polyether ether ketone (PEEK)-zeolite and PEEK spinal implants in an ovine model. Objective. This study challenges a conventional spinal implant material, PEEK, to PEEK-zeolite using a nonplated cervical ovine model. Summary of Background Data. Although widely used for spinal implants due to its material properties, PEEK is hydrophobic, resulting in poor osseointegration, and elicits a mild nonspecific foreign body response. Zeolites are negatively charged aluminosilicate materials that are hypothesized to reduce this pro-inflammatory response when used as a compounding material with PEEK. Materials and Methods. Fourteen skeletally mature sheep were, each, implanted with one PEEK-zeolite interbody device and one PEEK interbody device. Both devices were packed with autograft and allograft material and randomly assigned to one of 2 cervical disc levels. The study involved 2 survival time points (12 and 26 weeks) and biomechanical, radiographic, and immunologic endpoints. One sheep expired from complications not related to the device or procedure. A biomechanical evaluation was based on measures of segmental flexibility, using 6 degrees of freedom pneumatic spine tester. Radiographic evaluation was performed using microcomputed tomography scans in a blinded manner by 3 physicians. Levels of the pro-inflammatory cytokines, interleukin (IL)-1β, IL-6, and tumor necrosis factor-alpha at the implant, were quantified using immunohistochemistry. Results. PEEK-zeolite and PEEK exhibited an equivalent range of motion in flexion extension, lateral bending, and axial torsion. A motion was significantly reduced for implanted devices at both time points as compared with native segments. Radiographic assessments of fusion and bone formation were similar for both devices. PEEK-zeolite exhibited lower levels of IL-1β (P = 0.0003) and IL-6 (P = 0.03). Conclusion. PEEK-zeolite interbody fusion devices provide initial fixation substantially equivalent to PEEK implants but exhibit a reduced pro-inflammatory response. PEEK-zeolite devices may reduce the chronic inflammation and fibrosis previously observed with PEEK devices.