Is a central cavity necessary for bioactive glass-ceramic spacers in plated ACDF? A retrospective comparison of solid versus cavity designs

Purpose Traditionally, interbody cages feature a central cavity for graft packing. However, for bioactive glass-ceramic (BGS-7) spacers achieving fusion via surface-mediated osseointegration, this cavity may be biologically redundant and structurally disadvantageous. We compared radiological and clinical outcomes of plated anterior cervical discectomy and fusion (ACDF) using BGS-7 spacers with or without a central cavity. Methods We retrospectively reviewed patients undergoing plated ACDF using solid non-cavity (17 patients, 24 levels) or central-cavity (17 patients, 33 levels) BGS-7 spacers. Radiographic fusion was evaluated using dynamic interspinous distance (primary, ≤ 2 mm) and segmental angular motion (secondary, ≤ 4°), alongside CT-based osseointegration (direct contact ≥ 50%). Subsidence (≥ 2 mm) and clinical outcomes were evaluated at 12 months. Results Both groups demonstrated comparable 12-month clinical improvements ( p > 0.05). Radiographic fusion rates were equivalent between non-cavity and central-cavity groups based on the primary distance (91.7% vs. 84.8%, p = 0.687) and secondary angular criteria (79.2% vs. 63.6%, p = 0.331). The non-cavity group showed a trend toward superior segmental stability, with a smaller dynamic gap distance (0.82 ± 0.64 mm vs. 1.53 ± 1.99 mm, p = 0.064). CT-based fusion perfectly matched (90.5% vs. 90.9%, p = 1.000). Subsidence rates were comparably low (12.5% vs. 12.1%), with no spacer breakage. Conclusions In plated ACDF, adding a central cavity to BGS-7 spacers confers no measurable advantage over the solid design. Solid spacers inherently preserve maximum endplate contact area for optimal load-sharing and surface-mediated fusion. Eliminating the cavity and supplemental grafts avoids logical redundancy, donor-site morbidity, and unnecessary healthcare costs.