Adjustable Spinal Fixation With Flexible Tether for Junctional Stress

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Solution Overview

Problem

Existing spinal fixation systems often lead to adjacent segment pathology, such as proximal junctional kyphosis, due to rigid constructs causing excessive strain and stress on non-instrumented spinal segments, which can result in debilitating conditions like kyphotic shifts and loss of structural integrity.

Innovation Solution

Incorporation of a non-rigid portion, such as a flexible tether assembly, telescoping rod, or dampening rod, to transition from rigid fixation to a more flexible support structure, allowing modulation of tension and resistance to compression through mechanisms responsive to remote signals, particularly magnetic fields.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If a rigid spinal fixation system is used to stabilize the spine, then spinal alignment and stability are improved, but adjacent segment pathology occurs due to excessive strain and stress on non-instrumented segments

Engineering Contradiction:

Improvespinal stabilityVSAvoidadjacent segment pathology

Core Design Contradiction:

Stability of the object's compositionVSObject-affected harmful factors

Solution Approach 1:

The spinal fixation system is divided into multiple segments: rigid fixation components (pedicle screws, rods, plates) for instrumented segments and a flexible tether assembly for non-instrumented adjacent segments. This segmentation allows different mechanical properties in different regions, stabilizing the instrumented spine while protecting adjacent segments from excessive stress.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the spinal system are assigned different mechanical qualities. The instrumented segments receive rigid fixation with high stiffness, while the adjacent non-instrumented segments are protected by a flexible tether assembly with adjustable tension. This local differentiation of mechanical properties resolves the contradiction between overall stability and local stress protection.

Inventive Principle:

Principle #3Local quality

2Shape

If a rigid fixation construct is implemented to correct spinal deformities, then spinal alignment is improved, but kyphotic shifts and loss of structural integrity occur at proximal and distal junctions

Engineering Contradiction:

Improvespinal alignmentVSAvoidjunctional integrity

Core Design Contradiction:

ShapeVSReliability

Solution Approach 1:

The flexible tether assembly is installed beforehand in the adjacent non-instrumented segments to cushion and absorb stresses that would otherwise be transmitted to the proximal and distal junctions. This preventive measure protects the junctions from kyphotic shifts and structural failure before they occur.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The flexible tether assembly acts as an intermediary element between the rigid fixation construct and the adjacent vertebral segments. It mediates the transmission of forces, allowing the rigid construct to maintain spinal alignment while preventing excessive stresses from reaching the junctions, thereby protecting against kyphotic shifts.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If spinal fixation is performed to treat primary pathology, then patient quality of life is improved, but secondary junctional disease develops at adjacent segments

Engineering Contradiction:

Improvespinal functionVSAvoidjunctional disease

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The harmful stress transmission to adjacent segments is extracted and isolated by the flexible tether assembly. The tether captures and absorbs the excessive forces that would otherwise be transmitted to the proximal and distal junctions, preventing the development of junctional disease while maintaining the therapeutic benefits of spinal fixation.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The flexible tether assembly converts the potentially harmful stresses and forces acting on adjacent segments into a beneficial protective mechanism. By absorbing and distributing these forces, the tether transforms what would be damaging loads into a protective cushion, preventing junctional disease while allowing the rigid fixation to perform its stabilizing function.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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

Reduces the occurrence and severity of adjacent segment pathology by distributing stress more evenly across the spine, maintaining spinal alignment and reducing the risk of kyphotic shifts and other debilitating conditions.

Implementation Method 1

an adjustable tensioner comprising a magnet mounted to rotate in response to a magnetic field thereby increasing or decreasing tension on the flexible tether depending on a direction of rotation of the magnet

Methodology Applied

Scientific EffectMagnetic field interaction: Magnetic Field

Data Source

PatentUS12433642B2Post-operatively adjustable spinal fixation devices

Publication Date: 2025.10.07 NUVASIVE INC

AI summary

A system for spinal fixation with a non-rigid portion at least one of the caudal or cephalad terminus. Various devices and techniques are described for transition from a rigid fixation construct to a less rigid support structure applied to a “soft zone” that helps share the stress created on the spinal levels caused by the fixed levels below. In some embodiments, the soft zone is provided by terminating the construct with one of a flexible tether or a dampening rod.