Spinal Rod Partial Reduction via Tether Mechanism
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Solution Overview
Problem
Current surgical methods for correcting spinal disorders, such as scoliosis and kyphosis, often result in proximal junctional kyphosis (PJK), a complication that can lead to deformity, pain, and reduced mobility, due to the complete reduction of spinal rods into screw heads, which can cause excessive stress on vertebral levels.
Innovation Solution
The surgical system employs a tether-based reduction mechanism that allows for incomplete or partial reduction of spinal rods, using adjustable tethers and bone screws to resist and prevent PJK by selectively positioning the spinal rod relative to the vertebral levels, thereby reducing stress and maintaining flexibility in the spinal construct.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If complete reduction of spinal rod into screw head is performed, then spinal stability is improved, but proximal junctional kyphosis (PJK) occurs due to excessive stress on vertebral levels
Solution Approach 1:
The patent applies partial reduction by allowing the spinal rod to be reduced only to a selected position relative to the screw head rather than complete reduction. The rod is reduced partially into the implant cavity defined by the fastener, leaving it positioned at a controlled distance from complete seating. This partial action provides spinal stability while avoiding the excessive stress that causes PJK.
Solution Approach 2:
The patent changes the reduction parameter from complete to partial by using a tether-based mechanism that allows controlled positioning. The tether connects the spinal rod to the fastener and enables the rod to be reduced to a selected configuration and position, transforming the binary complete/incomplete reduction into a continuously adjustable parameter that optimizes both stability and stress distribution.
2Strength
If spinal rod is completely reduced into screw head, then fixation strength is improved, but stress on vertebral levels increases causing deformity
Solution Approach 1:
The patent implements partial reduction where the spinal rod is secured to the vertebrae through the fastener but not completely reduced into the screw head. The rod is positioned at a selected distance from complete seating, providing sufficient fixation strength while distributing stress more evenly across the vertebral levels to prevent deformity.
Solution Approach 2:
The tether acts as an intermediary element between the spinal rod and the fastener. It allows controlled transmission of forces while enabling partial reduction, mediating between the need for strong fixation and the need to minimize stress on vertebral levels. The tether provides a flexible connection that maintains fixation strength without transmitting excessive stress.
3Ease of manufacture
If traditional fixation method is used, then surgical simplicity is maintained, but adaptability to prevent PJK is reduced
Solution Approach 1:
The patent introduces dynamic adjustability to the fixation system through the tether-based reduction mechanism. The spinal rod can be reduced to a selected position rather than being fixed in a single predetermined state. This dynamic capability allows the surgeon to adapt the reduction degree to prevent PJK while maintaining relative surgical simplicity through the use of standard fasteners and tethers.
Solution Approach 2:
The fastener system serves multiple functions: it provides traditional fixation capability, defines an implant cavity for partial reduction, and enables tether attachment for controlled rod positioning. This multi-functionality allows the same basic components to achieve both surgical simplicity and adaptability for PJK prevention.
Data Source
AI summary
A method for treating a spine comprising the steps of: connecting at least one first fastener that defines an implant cavity with at least one vertebral level of a first portion of vertebrae; connecting at least one second fastener with at least one vertebral level of a second portion of the vertebrae; manipulating the vertebrae; manipulating a spinal rod to a selected configuration; connecting the spinal rod with the at least one first fastener such that the spinal rod is disposed at a selected position with the implant cavity; connecting a tether to a second fastener and the spinal rod; and reducing the spinal rod to a selected position relative to the second fastener with the tether. Systems, spinal constructs and surgical instruments are disclosed.