Development of a porous interbody cage with random pore distribution for lumbar spinal fusion

Porous Ti-alloy interbody cage reduces implant-bone stiffness mismatch and facilitate favorable osteoblast adhesion and differentiation, thereby enhancing stability for improved spinal fusion surgery outcome. Sponge replication is a promising method for fabricating Ti-alloy scaffolds with controlled pore structures using powder metallurgy. The present study aimed to develop a porous interbody cage with interconnected pores, having a random distribution to promote bone fusion. Porous Ti6Al4V scaffolds were prepared by templating sacrificial foam using powder metallurgy and physically characterized to confirm its suitability for spinal load-bearing applications. Samples with ~75% porosity and pore sizes ranging from 390–440 µm exhibited a compressive strength of 36 MPa and an elastic modulus of 120 MPa. The cytotoxicity of the porous Ti scaffold was evaluated through in vitro experiments using the MTT assay with the L929 cell line. Subsequently, a porous interbody cage was fabricated adopting the sponge replica method. The maximum stress generated in the porous cage model was ~21 MPa, which was well below the measured yield strength. Maximum cage subsidence of 0.123 mm and dislodgement of 0.038 mm were observed, indicating minimal risk of cage migration and subsidence. An equivalent FE model of the porous interbody cage exhibited improved mechanical behavior as compared to the solid design in terms of stress distribution, subsidence, and cage dislodgement in the implanted lumbar spine. These findings demonstrate the feasibility of using the foam templating technique to fabricate spinal interbody cages with random pore distribution.