# Biomechanical Optimization of Lumbar Fusion Cages with a Porous Design: A Finite Element Analysis
## 4 Discussion  
The biomechanical performance of interbody fusion cages is fundamental to achieving postoperative spinal stability and minimizing subsidence risk. Our finite element (FE)  
Figure 8: The stress distribution on the endplates of L3 and L4 surface on six motion modes. Figure 7: The comparison of the maximum stress on endplates for (**a**) L3 and (**b**) L4 on six motion modes. analysis evaluated four distinct cage designs--C-Cage (classic), P-Cage (personalized), G-Cage (Gyroid), and V-Cage (Voronoi)--revealing that the Voronoi-based porous architecture offers superior mechanical and biological compatibility. These findings resonate with the growing emphasis on biomimetic and patient-specific implant designs, providing a framework to enhance clinical outcomes in lumbar interbody fusion. Segmental stability, assessed via ROM, is a critical indicator of fusion success and long-term spinal health. The V-Cage exhibited the lowest ROM across all motion modes, including a 51% reduction in extension compared to the C-Cage. This enhanced stability arises from the interconnected pores of the Voronoi structure, which promote mechanical interlocking with the surrounding bone while retaining controlled flexibility. This behavior reflects the concept of \"balanced stiffness\" where porous implants stabilize spinal segments without imposing excessive rigidity, thus preserving physiological load transfer [34]. In contrast, the C-Cage and P-Cage displayed higher micromotion, which is associated with delayed fusion and pseudarthosis [30]. These findings align with clinical evidence that overly rigid implants may accelerate adjacent segment disease (ASD) by disrupting spinal kinematics, reinforcing the biomechanical advantages of porous designs in maintaining segmental harmony [35]. The V-Cage, inspired by the anisotropic trabecular architecture of natural bone, exhibited exceptional stress dispersion compared to its solid and Gyroid-based counterparts. Its Voronoi porous structure reduced peak von Mises stress by 41.7% in compression and 28.0% in flexion relative to the C-Cage. This improvement stems from the irregular pore geometry, which redistributes mechanical loads more uniformly, mitigating stress concentrations. Such behavior aligns with prior studies demonstrating that Voronoi lattices enhance yield strength by up to 30% over uniform porous designs by mimicking the stress transfer pathways of cancellous bone [36]. In contrast, the G-Cage, with its isotropic Gyroid scaffold, achieved intermediate stress reduction but lacked the anisotropic adaptability of the V-Cage, limiting its ability to fully replicate the mechanical properties of bone. These results underscore the critical role of biomimetic irregularity in optimizing porous cage design, a principle increasingly validated in additively manufactured implants [37]. Effective load distribution across the vertebral endplates is essential to prevent subsidence, a common complication in interbody fusion. The V-Cage significantly lowered endplate stresses, reducing peak values on the L3 and L4 endplates by 51.8% and 63.7%, respectively, under bending modes. This reduction is attributable to the Voronoi structure, which likely provides a larger effective contact area, leading to reduced localized pressure and minimizing the risk of endplate microfractures [38]. Conversely, the classic C-Cage induced pronounced stress concentrations at the cage-endplate interface, consistent with clinical reports linking solid implants to increased subsidence risk [39]. Although the P-Cage improved geometric fit through personalization, it failed to address the stiffness mismatch between the implant and bone, underscoring the limitations of solid designs [32]. The V-Cage's integration of porosity and patient-specific geometry aligns with proposals for using porous materials (such as titanium alloys) that harmonize elastic moduli with native bone, reducing stress shielding and enhancing endplate stability [39].