Journal of Spine

Accelerated Cervical Fusion of Silicon Nitride versus PEEK Spacers: A Comparative Clinical Study

Abstract

Hieu T Ball, Bryan McEntire and Sonny Bal B

Introduction: The ideal material for the manufacture of cervical fusion cages used in anterior cervical discectomy and fusion (ACDF) is undetermined. Spacers made of polyether-ether-ketone (PEEK) are commonly used, although metal and ceramic devices are also commercially available. This observational study compared outcomes of ACDF using two different biomaterial spacers (i.e., PEEK and silicon nitride, Si3N4).
Methods: Twenty consecutive patients who underwent ACDF with Si3N4 were retrospectively compared to a group previously implanted with PEEK spacers. Patient demographics, neck pain visual analog scale (VAS) and the neck disability index (NDI) scores were recorded for all enrollees. Cervical radiographs, including flexion-extension views, were examined to determine fusion at 3, 6, 12, 24, and 36 months post-operatively.
Results: Patient demographics were essentially identical between groups, except for a slightly higher incidence of worker compensation claims in the PEEK group (p=0.27), and increased prevalence of cervical myelopathy in the Si3N4 group (p=0.12). There were no differences in the number of cervical levels treated (p=0.65) or hospital length of stay (p=0.65). No cage failures or infections occurred in either group. At 3, 6, and 12 months, the average flexionextension angular rotation was lower for the Si3N4 group as compared to the PEEK cohort. However, these data were not statistically significant. Nevertheless, the incidence of fusion was consistently higher in the Si3N4 group at all follow-up visits except 36 months; both groups reached 100% fusion at the 3-year time-point.
Conclusion: By 36 months, there were no differences in ACDF with PEEK or Si3N4 as measured by NDI, VAS, and radiographic fusion of cervical segments. Earlier time points suggested a trend toward enhanced fusion with Si3N4. The interim differences may reflect the enhanced bioactive surface of the silicon nitride spacers and/or the radiographic characteristics of each biomaterial.