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Functionally Graded Material Vertebroplasty Screws: A Finite Element Biomechanical Study

Authors :

Maryam Rahimi¹ Mohammad Hosein Zadeh-Posti² َAisan Rafiei³ Nima Jamshidi⁴

1- University of Isfahan 2- University of Guilan 3- Iran University Of Science & Technology 4- University of Isfahan

Keywords :

vertebroplasty،functionally graded materials،finite element analysis،hydroxyapatite،biomechanical compatibility

Abstract :

Vertebroplasty is a minimally invasive treatment for osteoporotic vertebral compression fractures (VCFs), yet conventional titanium screws often induce stress shielding and poor load transfer. This study evaluates the biomechanical performance of a novel functionally graded material (FGM) vertebroplasty screw—comprising a Ti-6Al-4V core and hydroxyapatite (HAP) outer layer—using finite element analysis (FEA. A 3D model of the L2 vertebra was reconstructed from CT data and meshed with over 250,000 elements. Two screw types (homogeneous titanium vs. FGM) were simulated under a 300 N axial load. The FGM screw’s radial stiffness gradient was defined by a power-law distribution and implemented via a UMAT subroutine in ABAQUS. Results showed a 14% reduction in peak von Mises stress (12.19 MPa vs. 10.45 MPa) and a 32% decrease in maximum elastic micro-strain (179.9 vs. 121.5) in the FGM screw. Cortical bone stress remained constant (52.20 MPa), while cancellous bone displacement decreased by 36% in the anteroposterior direction (0.02671 mm vs. 0.01702 mm), indicating improved primary stability. Displacement differences between screw types were negligible (<0.00008 mm across all axes), confirming construct integrity. Validation against prior studies showed <10% deviation in stress metrics. The FGM design redistributed internal loads, reduced stress concentrations, and enhanced biomechanical compatibility without compromising cortical integrity. These findings support the potential of graded screws to improve vertebroplasty outcomes by minimizing implant loosening and promoting osseointegration.