Topological optimization and biomechanical analysis of porous fusion cage with TPMS structures

Porous fusion cages present a promising alternative to traditional solid fusion cages in anterior cervical decompression and fusion surgery (ACDF), offering improved bone in growth through interconnectivity and a reduced elastic modulus, which may reduce the risk of cage subsidence. This study employs an integrated topology optimization approach to design a novel porous fusion cage to minimize the risk associated with cage subsidence and stress shielding. Two innovative porous cervical fusion implants, RPF-G and RPF-D, were proposed through Boolean operations based on optimal topological structures and Triply Periodic Minimal Surfaces (TPMS). After optimizing fusion cages, finite element simulations of ACDF surgeries were performed at C5-C6 segment to evaluate their biomechanical performance. The results showed the range of motion (ROM) in the porous fusion cage model exceeded that of the solid fusion cage model, with maximum intradiscal pressure occurring at the C4-C5 segment in all models. Moreover, stress distribution across the cortical bone surface was more uniform in the porous fusion cages, with the RPF-G and RPF-D cage models exhibiting increased stress at the vertebra C6 cortical bone. Notably, the surface stress on porous cages surpasses solid fusion cages, particularly in flexion loading conditions. The RPF-G model demonstrates superior mechanical stability. In conclusion, the optimized porous fusion cage demonstrates promising mechanical performance and emerges as a potential candidate for fusion surgery. These preliminary investigations guide the design of the fusion cage, potentially offering novel solutions to address the issue of cage subsidence.