An Immunological and Biomechanical Comparison of PEEK-Zeolite and PEEK Interbody Fusion Devices.

Abstract

A laboratory study comparing PEEK-zeolite and PEEK spinal implants in an ovine model. This study challenges a conventional spinal implant material, PEEK, to PEEK-zeolite using a non-plated cervical ovine model. Although widely used for spinal implants due to its material properties, polyether ether ketone (PEEK) is hydrophobic, resulting in poor osseointegration, and elicits a mild non-specific 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. 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 two cervical disc levels. The study involved two survival timepoints (12 and 26wk) and biomechanical, radiographic, and immunological endpoints. One sheep expired from complications not related to the device or procedure. Biomechanical evaluation was based on measures of segmental flexibility, using a six-degrees-of-freedom pneumatic spine tester. Radiographic evaluation was performed using microCT scans in a blinded manner by three physicians. Levels of the pro-inflammatory cytokines interleukin-1β, interleukin-6, and tumor necrosis factor alpha at the implant were quantified using immunohistochemistry. PEEK-zeolite and PEEK exhibited equivalent range of motion in flexion extension, lateral bending and axial torsion. Motion was significant reduced for implanted devices at both time points as compared to native segments. Radiographic assessments of fusion and bone formation were similar for both devices. PEEK-zeolite exhibited lower levels of interleukin-1β (P=0.0003) and interleukin-6 (P=0.0300). 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.