Composite Spinal Pedicle Screw for MRI Compatibility
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Solution Overview
Problem
Metallic pedicle screw systems used in spinal surgeries interfere with imaging and radiotherapy, cause biocompatibility issues, and have limitations in fatigue resistance and stress shielding, while non-metal composite materials offer lower stiffness and limited indications.
Innovation Solution
A pedicle screw implant construct kit made of composite materials with reinforcing filaments embedded in a polymer matrix, featuring a collar and locking ring design that allows for radial compression to secure the screw and rod, reducing metal content and enhancing imaging compatibility and fatigue resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If metallic pedicle screw systems are used, then bending and torsion strength is adequate, but imaging compatibility deteriorates and biocompatibility issues arise
Solution Approach 1:
The patent employs carbon fiber reinforced polymer (CFRP) composite materials to manufacture pedicle screws, combining the high strength-to-weight ratio of carbon fibers with the toughness of polymer matrices. This composite approach achieves adequate bending and torsion strength while eliminating metal-induced imaging artifacts and improving biocompatibility, as the polymer-based material is non-corrosive and does not interfere with MRI or CT imaging.
Solution Approach 2:
The patent modifies the material composition parameters by incorporating specific ratios of carbon fibers (e.g., 60-80% by weight) into the polymer matrix, adjusting the composite's mechanical properties to match or exceed metallic implants. This parameter optimization ensures that the composite screws achieve the necessary structural strength for spinal fixation while maintaining the non-metallic characteristics required for imaging compatibility.
2Object-affected harmful factors
If non-metal composite materials are used, then imaging compatibility improves, but stiffness is reduced
Solution Approach 1:
The patent utilizes carbon fiber reinforced polymer composites where the carbon fiber network provides high stiffness and strength, while the polymer matrix binds the fibers together and transfers loads. This composite structure achieves imaging compatibility through its non-metallic composition while recovering adequate stiffness through the high modulus of elasticity of carbon fibers, effectively resolving the contradiction between imaging compatibility and mechanical stiffness.
3Strength
If metallic implants are used, then structural strength is maintained, but fatigue resistance deteriorates
Solution Approach 1:
The patent leverages the inherent fatigue resistance of carbon fiber composites, which exhibit superior fatigue performance compared to metals due to their ability to distribute stress across the fiber network. The composite material maintains structural strength through fiber reinforcement while resisting fatigue failure through the progressive load distribution mechanism, where individual fibers fail without compromising the overall structure, thereby extending implant longevity.
4Strength
If rigid metal implants are used, then implant fracture resistance is improved, but stress shielding phenomena worsen
Solution Approach 1:
The patent adjusts the elastic modulus of the composite implant by varying carbon fiber orientation, volume fraction, and distribution within the polymer matrix. By optimizing these parameters, the implant's stiffness is tuned to better match bone mechanics, reducing the stress shielding effect while maintaining sufficient fracture resistance. The composite structure allows for gradient stiffness design, where different regions of the screw have different fiber concentrations to optimize both strength and stress distribution.
Data Source
AI summary
A pedicle screw implant construct kit, comprising at least one pedicle screw, at least one collar comprising a recess for receiving a rod, the collar configured to be coupled to a head of the pedicle screw, an elongated rod for connecting the collar to one more additional collars to couple between the pedicle screw and one or more additional screws, and a locking ring sized to be positioned over at least a distal portion of the collar to restrain relative movement of the screw head and rod by exerting radial compression force onto the collar. In some embodiments, the components of the kit are comprised of carbon reinforced composite material, optionally with no radiation blocking material. In some exemplary embodiments of the invention, the kit includes two locking rings on a collar, optionally both below the rod.