Clinical outcomes for anterior cervical discectomy and fusion with silicon nitride spine cages: a multicenter study

Intervertebral spacers made of silicon nitride (Si₃N₄) are currently used in cervical and thoracolumbar fusion. While basic science data demonstrate several advantages of Si₃N₄ over other biomaterials, large-scale clinical results on its safety and efficacy are lacking. This multicenter retrospective study examined outcomes for anterior cervical discectomy and fusion (ACDF) using Si₃N₄ cages. Results were compared to compiled metadata for other ACDF materials.

Pre-operative patient demographics, comorbidities, changes in visual analog scale (VAS) pain scores, complications, adverse events, and secondary surgical interventions were collected from the medical records of 860 patients who underwent Si₃N₄ ACDF at four surgical centers. For comparison, MEDLINE/PubMed and Google Scholar searches were performed for ACDF using other cage or spacer materials. Nine studies with 13 cohorts and 736 patients met the inclusion criteria for this control group.

Overall, the mean last-follow-up for all patients was 319±325 days (10.6±10.8 months), with the longest follow-up being 6.5 years. In comparison to the metadata, patients from the Si₃N₄ groups were older (57.9±12.2 vs. 56.8±11.1 y, P=0.06) and had higher BMI values (30.0±6.3 vs. 28.1±6.5, P<0.01), but gender and smoking were not different. The Si₃N₄ patients reported significant improvements in VAS pain scores at last follow-up (i.e., pre-op of 71.0±22.1 vs. follow-up of 36.4±31.5, P<0.01). Although both preoperative and last-follow-up pain scores were higher for Si₃N₄ patients than the control, the overall change in scores (ΔVAS) was similar. From pre-op to last-follow up, ΔVAS values were 35.4±34.3 for patients receiving the Si₃N₄ implants versus 34.4±27.3 for patients from the meta-analysis (P=0.56). The complication and reoperation rate for the Si₃N₄ and the metadata were also comparable (i.e., 7.39% and 0.31% versus 9.79% and 0%, P=0.17 and 0.25, respectively).

ACDF outcomes using Si₃N₄ implants matched the clinical efficacy of other cage biomaterials.