Study design:

Randomized controlled trial.

Objectives:

Lumbar interbody fusion with cages is performed to provide vertebral stability, restore alignment, and maintain disc and foraminal height. Polyetheretherketone (PEEK) is commonly used. Silicon nitride (Si₃N₄) is an alternative material with good osteointegrative properties. This study was designed to assess if Si₃N₄ cages perform similar to PEEK.

Methods:

A non-inferiority double-blind multicenter RCT was designed. Patients presenting with chronic low-back pain with or without leg pain were included. Single- or double-level instrumented transforaminal lumbar interbody fusion (TLIF) using an oblique PEEK or Si₃N₄ cage was performed. The primary outcome was the Roland-Morris Disability Questionnaire (RMDQ). The non-inferiority margin for the RMDQ was 2.6 points on a scale of 24. Secondary outcomes included the Oswestry Disability Questionnaire (ODI), Visual Analogue Scales (VAS), SF-36 Physical Function, patient and surgeon Likert scores, radiographic evaluations for subsidence, segmental motion, and fusion. Follow-up was planned at 3, 6, 12, and 24-months.

Results:

Ninety-two patients were randomized (i.e. 48 to PEEK and 44 to Si₃N₄). Both groups showed good clinical improvements on the RMDQ scores of up to 5-8 points during follow-up. No statistically significant differences were observed in clinical and radiographic outcomes. Mean operative time and blood loss were statistically significantly higher for the Si₃N₄ cohort. Although not statistically significant, there was a higher incidence of complications and revisions associated with the Si₃N₄ cage.

Conclusions:

There was insufficient evidence to conclude that Si₃N₄ was non-inferior to PEEK.