The accuracy of biomechanics analyses based on the finite element method in biological structures strongly depends on precise geometric modeling and the correct definition of tissue mechanical properties. The aim of this study was to investigate and compare the stress and strain distributions in two types of lumber interbody cages, LAR and RAR, using theoretical analysis and finite element modeling. For three-dimensional reconstruction, lumbar vertebrae were generated from CT scan data, and complete models of the vertebrae and cages were developed. Finite element analysis was performed in MSC Nastran under physiologic loading conditions. The results demonstrated that the LAR cage, due to its polymeric material and geometric design, produced more uniform stress distribution and lower strain in contact regions, offering greater stability compared with the titanium RAR cage. In contrast, the RAR cage exhibited higher stress concentration and a stiffer mechanical response, which may increase the risk of subsidence and mechanical mismatch with the bone. These findings indicate that cage material and geometry play a critical role in load transmission, stress reduction, and improving the mechanical performance of fusion constructs. The results of this study can assist in optimizing the design and selection of interbody cages with improved biomechanical performance and enhanced biocompatibility.
alizadeh et al. (2025) studied this question.