Effect of cage surface geometry on load transfer and ranges of motion in a fused lumbar spine model: A comparative finite element analysis

Lumbar degenerative disc diseases (DDDs) are the common causes of low back pain, leading to non-conservative treatments like fusion and non-fusion surgery as a last resort. Fusion surgery is the gold standard for addressing DDDs, where implants such as cages, pedicle screws and rods are used for posterior stabilization. Various finite element (FE) studies have reported using corrugated cage surface textures; some others have used flat textures for virtual implantation. No comparative studies have been reported on the biomechanical effects of fusion surgery under implantation with cages of varying surface textures. The present biomechanical study compares the mechanical behaviour of an L4-L5 segment implanted with cages of different surface textures. The surgical techniques used for implantation are posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion. The virtual surgical models were developed from a previously validated intact lumbar spine FE model and simulated for physiological loading conditions. Compared to the flat cage implantation, a higher magnitude of stress was experienced by the cages and pedicle screw-rod systems under corrugated cage implantation. The maximum von Mises stress generated in the PLIF corrugated cage was 80.69% more than that observed in the flat cage. The maximum stresses in the corrugated cage were higher than those of the flat cage by 38.43%-80.69%, considering all the applied loading conditions. The findings of the study suggest that corrugated cage surface texture and suitable material selection may help in improving the long-term stability of cages.