Biomechanical Evaluation of a Newly Developed Functional-Grade Composite Material for Pedicle Screws

Abstract

Pedicle screw and rod systems are widely employed in spine surgeries, and loosening due to insufficient mechanical stimulation on the bone is frequently encountered in pedicle screws. This mechanical stimulation problem also arises due to the high rigidity of the implant material. This study aimed to develop new pedicle screws with composite material to solve the pedicle screw loosening problem. The vertebrae and vertebral disk were modeled in 3D using computerized tomography images obtained from a patient. A commercially available pedicle screw was modeled using Fusion software, and all models were assembled in accordance with the surgical procedure. Pedicle screw models were also divided radially and longitudinally to resemble functionally graded materials, which are composite materials. The load was applied to the top of the T12 vertebra, and the screw-vertebral system was fixed to the bottom of the L1 vertebra. The strain results on the vertebrae were examined according to the mechanostat theorem. According to the results, FGM pedicle screw decreased the strain on the vertebral bones, and the positive effects on the bone were determined when using the radially functionally graded screws. The maximum stress values were also examined to determine the strengths of all the models. In conclusion, FGM pedicle screw decreased the strain on the bone which is an important parameter for the loosening failure according to the study. The other important conclusion is that FGM pedicle screw can be the solution to the loosening of the screw but not in all vertebrae.