A Finite Element Analysis of the Pedicle Screw Displacement on Spine Implant with Varying Frictional Contact

Displacement can occur for a variety of reasons, including pedicle screw detachment from the spine, damaged pedicle screws, the supporting rod detaching from the pedicle screw, and broken supporting rods. The relationship between displacement and screw threads indicates that the displacement of the screw is a measure of thread movement, and the smaller the pitch (the space between the two screw threads), the lower the displacement of the screw. Results from a normal bone simulation using MSC-Marc show that variations in pedicle screws under tensile load result in a displacement of 5.53x10-5 mm for single-threaded conical pedicle implants, with no greater coefficient of friction than single-threaded cylindrical implants, which have a displacement of 1.62x10-6 mm. When a tensile load is applied to an osteopenia bone, a single-threaded conical implant with no coefficient of friction results in a displacement of 3.45x10-5 mm as opposed to a cylindrical implant. The higher contact force reinforces the pedicle screw's interface with the bone, making it less likely to detach due to the pedicle screw's tensile force. When applying tensile forces and bending moments to a single-threaded conical implant with a single-threaded cylindrical implant, the displacement increases as the friction coefficient rises