The effect of pedicle screw angle on stress distribution in lumbar spine fixation: an optimization approach based on finite element analysis

BACKGROUND: Pedicle screw fixation is widely used for lumbar spine stabilization, and technical parameters such as screw insertion angle may influence the biomechanical behavior of the implant-bone construct. OBJECTIVE: This study aimed to evaluate the effect of different transverse pedicle screw insertion angles (25°, 30°, 35°, and 40°) on stress distribution in the L4-L5 segment using three-dimensional finite element analysis (FEA). METHODS: A three-dimensional finite element model of the L4-L5 lumbar segment was developed from computed tomography data of a healthy adult subject. Titanium alloy (Ti-6Al-4 V) pedicle screws (6.5 mm diameter) were modeled at four predefined insertion angles. A 400 N axial compressive load was applied to simulate physiological loading conditions. Stress distributions were analyzed using von Mises criteria within the ANSYS Workbench environment. RESULTS: Maximum von Mises stress values varied across insertion angles. The highest stress (399.26 MPa) was observed at 25°, primarily at the screw head-rod junction and screw-bone interface. The lowest stress (297.86 MPa) was recorded at 40°. A decreasing trend in stress values was observed with increasing insertion angle. CONCLUSION: Pedicle screw insertion angle affects stress distribution in the L4-L5 segment. Higher insertion angles were associated with lower stress values, suggesting a potentially more favorable biomechanical environment. These findings indicate that insertion angle may be an important parameter in pedicle screw fixation planning.