Titanium and polyetheretherketone for spinal fusion cages: a comparative narrative review of material behavior, structural design, and clinical translation

Cage material selection in spinal fusion requires a trade-off among biological fixation, mechanical compatibility, subsidence resistance, and postoperative imaging. This structured narrative review compares titanium and polyetheretherketone (PEEK) cages across seven domains: osseointegration, modulus matching, endplate load transfer, surface biofunctionality, imaging, additive manufacturing and personalization, and geometry-guided architecture. Peer-reviewed literature indexed in PubMed/MEDLINE, Scopus, and Web of Science was considered from database inception through May 2026, with emphasis on comparative clinical studies, systematic reviews, meta-analyses, and mechanistic studies directly relevant to cage design. Preclinical studies favor porous and additively manufactured titanium for bone–implant integration, but a consistent fusion-rate advantage in anterior cervical discectomy and fusion (ACDF) has not been established. In lumbar surgery, lower subsidence has been reported in selected lateral lumbar interbody fusion cohorts, while results after transforaminal lumbar interbody fusion remain heterogeneous. PEEK retains advantages in radiolucency and intrinsic modulus matching, while surface-modified and porous PEEK can improve biological performance. Subsidence is not determined by chemistry alone; cage footprint, architecture, endplate preparation, fixation, and bone quality remain major modifiers. Current evidence therefore supports procedure and design-specific selection rather than universal replacement of either platform. Long-term comparative data and standardized definitions of fusion and subsidence remain limited.