Spinal Fastener Tether Reduces Stress Concentration
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Solution Overview
Problem
Current posterior spinal stabilization systems using pedicle screws and rods cause stress concentrations at the screw-bone interface, leading to complications like proximal junction kyphosis and screw pull-out, especially at the transition from mobile to rigid spinal segments.
Innovation Solution
A spinal bone fastener assembly with a bone fastener, a rod receiving head, and flexible elongate members that connect the bone fastener to the rod receiving head, allowing for adjustable stiffness and distance between the spinal column and the connecting rods, reducing stress concentrations and minimizing tissue damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If rigid pedicle screws and rods are used to stabilize the spinal column, then spinal stability is improved, but stress concentrations occur at the screw-bone interface leading to screw pull-out and junction kyphosis
Solution Approach 1:
The patent changes the mechanical parameter of the connection between pedicle screw and rod from rigid to flexible by introducing a flexible elongate member (tether) that allows relative movement. This parameter change reduces stress concentration at the screw-bone interface while maintaining spinal stability, preventing screw pull-out and junction kyphosis.
Solution Approach 2:
The patent introduces dynamic flexibility into the spinal stabilization system by allowing the rod to move relative to the pedicle screw through the flexible tether. This dynamic capability enables the system to adapt to physiological movements and reduce stress concentrations, contrasting with traditional rigid fixed systems.
2Object-affected harmful factors
If tethers are used to reduce stress on screw-bone interface, then stress concentration is reduced, but surgical complexity and duration increase due to manual tensioning and tying off
Solution Approach 1:
The patent enables the flexible elongate member to self-tension and self-secure automatically when the rod is inserted and positioned. The system uses the insertion process itself to create the necessary tension and locking, eliminating the need for manual tensioning and tying off procedures, thus reducing surgical complexity while maintaining stress reduction benefits.
Solution Approach 2:
The patent performs the tensioning action preliminarily during the rod insertion process itself, rather than requiring separate post-insertion steps. The rod insertion automatically tensions the flexible member and engages the locking mechanism, completing the stress-reduction function before the surgeon needs to perform any additional manual operations.
3Strength
If great forces are applied to fix the rod to the most proximal screw, then rod fixation is achieved, but stresses at the screw-bone interface increase causing screw loosening
Solution Approach 1:
The patent changes the force transmission parameter from direct high-force rigid connection to distributed lower-force flexible connection. The flexible elongate member distributes the fixation forces along its length and reduces peak stresses at the screw-bone interface, preventing screw loosening while achieving adequate rod fixation strength.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The spinal bone fastener assembly reduces stress on the pedicle screw-bone interface, providing a smoother transition from instrumented to adjacent spinal levels, minimizing complications like kyphosis and screw pull-out, and allowing for variable adjustment to accommodate individual anatomical differences.
Implementation Method 1
at least one flexible elongate member (80) connecting or coupling the rod receiving head (30) with the bone fastener (10)
Data Source
AI summary
A spinal bone fastener assembly (1) to be engaged to a posterior spinal bone fastener system comprises a bone fastener (10), a rod receiving head (30), configured to receive a spinal rod (2), a tightening means (60, 70) configured to exert a retaining and/or clamping force between the spinal rod and the rod receiving head, a tether (80) connecting or coupling the rod receiving head (30) with the bone fastener (10). When the bone fastener (10) is introduced into the spine, a spinal rod (2) is positioned in a central pocket (41) of the rod receiving head (30) and a rod tightening means (60; 70) tightens against the spinal rod (2) in the central pocket (41) blocking the position of the tether (80) in the tether retaining means (36) of the rod receiving head (30) at a predetermined distance (X2).