Lumbar Interbody Cages: Design Characteristics, Biomaterials, Biomechanical Performance, Clinical Challenges, and Emerging Innovations

Lumbar interbody cages have evolved significantly in recent decades through advances in biomaterials, geometric design, and surface modifications, all aimed at improving fusion and reducing complications. However, issues such as subsidence, migration, and pseudarthrosis continue to pose significant challenges in spinal practice. This narrative review synthesizes current data on lumbar cage design, biomaterials used, biomechanical performance, clinical outcomes, and recent innovations. Current evidence suggests that 3D-printed porous titanium implants achieve higher fusion rates than polyetheretherketone and are associated with lower rates of subsidence and reintervention, although differences in patient-reported clinical outcomes remain small. Expandable cages offer radiographic advantages, especially in the restoration of disc height, but without a clear clinical superiority over static ones. Overall, the choice of material, implant geometry, and surface properties significantly influence the performance of the cage. Innovations such as additive manufacturing, porous architectures, customized implants, and bioactive surfaces are promising, but long-term prospective studies are needed to more clearly define their role in individualized implant selection.