Utility of bioactive glasses as fusion substrates for cervical and lumbar fusion: a systematic review

There has been a continued search for synthetic graft materials to replace iliac crest bone graft and allograft in spinal fusion. Recently, there has been interest in bioactive glasses (BGs) as graft substitutes, but a confusing landscape of current literature creates difficulty in evaluating their clinical effectiveness. As such, we conducted an updated systematic review on BG use in cervical and lumbar spinal fusion.

A systematic review of the MEDLINE, Cochrane, Embase, and Web of Science databases was conducted on March 26^th, 2024. Studies were included if they pertained to BGs and spine fusion. Risk of bias for included studies was assessed using the Cochrane risk-of-bias tool for randomized trials (RoB 2). Only prospective clinical studies and randomized controlled trials were ultimately included. Data were analyzed narratively.

Five studies with low bias, four with some concerns for bias, and three with high bias were included in the final review. Sample sizes ranged from 17-74 patients, and BG types included BGS-7, S53P4, 45S5, Chitra-HABg, and apatite- and wollastonite-containing glass-ceramic (AWGC). Procedures included posterolateral lumbar fusion (PLF), posterior lumbar interbody fusion (PLIF), anterior lumbar interbody fusion (ALIF), and anterior cervical discectomy and fusion (ACDF). When BGs were used as standalone grafts, fusion rates ranged 0-70.6% at >1-year follow-up. In one study of PLF, grafts composed of AWGC and autograft mixtures resulted in fusion rates between 81.8-83.3%. 45S5 showed comparable fusion to autograft at 1 year postoperatively in ALIF. When BGS-7 was used as a cage material, fusion rates varied from 75.0-95.0% at >1-year follow-up, compared to 65.4-100% for titanium, allograft, or polyether ether ketone (PEEK) cages.

When used as standalone fusion grafts in PLF, pure Chitra-HABg and S53P4 are ineffective compared to autograft. However, grafts made of 45S5 or mixtures of AWGC with autograft show fusion rates comparable to autograft alone. BGS-7 cages showed noninferior fusion rates to titanium, allograft, and PEEK cages. Additional prospective studies with quality methodologies are necessary to validate these results.