CT Evaluation of Lumbar Interbody Fusion: A Comprehensive Review with an Integrated Framework for Principle-Based...

Background/Objectives: Computed tomography remains the reference standard for assessing lumbar interbody fusion, yet significant methodological heterogeneity, documented across more than 250 different assessment combinations, directly impacts treatment decisions and outcome reporting. The main challenge is applying uniform criteria to technique-specific anatomical configurations that generate distinct bridging patterns. Methods: This narrative review synthesizes evidence from 2000 to 2025 through PubMed and Google Scholar searches, examining imaging protocols, radiographic criteria validated against surgical exploration and reliability studies, and classification systems with emphasis on clinical application. Results: Modern protocols that incorporate iterative metal artifact reduction and dual-energy imaging substantially improve visualization of the hardware-bone interface. Zone-based evaluation shows that bridging patterns primarily reflect cage configuration and graft placement strategy rather than the surgical approach alone-a key distinction that affects assessment methodology. Validation studies confirm higher inter-observer reliability for extracage zones (ICC 0.79-0.84) compared to intracage regions (ICC 0.70-0.79). Evidence supports three main bridging patterns: graft-dependent consolidation, ungrafted-zone bridging, and accessibility-dependent variation. Assessment at 12 months captures most successful fusions, although 15-16% show delayed progress and require longer follow-up. Conclusions: This review synthesizes current evidence on technical optimization and temporal healing patterns, proposing a principle-based interpretive framework that accommodates technique-specific differences instead of strict categorical criteria. This framework allows personalized assessment correlated with surgical documentation, addressing the documented heterogeneity while enhancing diagnostic consistency.