Clinical outcomes for lumbar fusion using silicon nitride versus other biomaterials

In lumbar fusion surgery, intervertebral spacer cages made of silicon nitride (Si₃N₄) ceramic are an available option among other biomaterials. While the surface chemistry of Si₃N₄ is known to favor bone fusion, large-scale clinical studies attesting to its efficacy are lacking. This multicenter retrospective study compared lumbar fusion outcomes for Si₃N₄ cages to previously reported data for other cage materials.

Pre-operative patient demographics, comorbidities, changes in visual analog scale (ΔVAS) pain scores, complications, adverse events, and secondary surgical interventions (SSI) were compiled from the records of 450 patients who underwent Si₃N₄ lumbar spinal fusion at four separate U.S. surgical centers. For comparison, MEDLINE/PubMed and Google Scholar searches identified studies reporting similar outcomes for other biomaterials. A total of 1,025 patients from 26 cohorts reported in 14 publications met inclusion criteria for this control group.

Overall, the mean last-follow-up for all patients was 341±293 days (11.4±9.8 months), with the longest follow-up being 6.4 years. Patients with Si₃N₄ implants were similar in gender and age distribution to the control group but had higher BMI values (30.9±6.1 vs. 25.8±4.1, P<0.01) and lower tobacco use (15.8% vs. 30.0%, P<0.01). Both the Si₃N₄ and control groups showed significant improvements in VAS pain scores from preoperative to last follow-up. For the Si₃N₄ group, ΔVAS was 36.8±35.4 points compared to 37.6±22.5 points (P=0.63) for the metadata group. Complications and reoperations for the Si₃N₄ and the control groups were similar (i.e., 9.8% and 3.1% versus 12.4% and 2.9%, P=0.16 and P=0.84, respectively).

Lumbar fusion with Si₃N₄ spacers compared favorably with the improvements reported with other commonly used biomaterial cages.