Spinal Fixation Construct With Variable Stiffness Flexible Member

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Solution Overview

Problem

Current spinal fixation devices often lead to proximal junctional kyphosis (PJK) and adjacent level failure, resulting in pain, neurological deficits, and the need for additional surgeries, due to inadequate restoration of lumbar lordosis and thoracic kyphosis post-surgery.

Innovation Solution

A spinal fixation construct with varying stiffness properties along its length, incorporating a flexible member with reduced stiffness compared to other components, such as a spinal rod and fixation member, to facilitate a transition from a stiff instrumented spine to a more flexible non-instrumented spine, minimizing facet capsule and muscle disruption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If a stiff spinal fixation construct is used to stabilize the spine, then spinal stability is improved, but proximal junctional kyphosis and adjacent level failure occur due to excessive stiffness at the junctional regions

Engineering Contradiction:

Improvespinal stabilityVSAvoidresistance to PJK and adjacent level failure

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The spinal fixation construct incorporates a flexible member with different stiffness characteristics at different locations along its length. The flexible member has reduced stiffness at the proximal and distal ends compared to the central portion, allowing the junctional regions to flex independently while maintaining overall construct stability. This local variation in stiffness properties enables the construct to provide stability where needed while preventing excessive stiffness at the junctional regions that would cause PJK and adjacent level failure.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The flexible member is divided into multiple segments with varying stiffness properties along its length. The proximal and distal segments have lower stiffness than the central segment, creating a segmented stiffness profile. This segmentation allows different portions of the construct to have different mechanical properties, enabling the junctional regions to move independently while maintaining overall spinal stability.

Inventive Principle:

Principle #1Segmentation

2Strength

If the spinal rod and fixation members are made from rigid materials to ensure structural strength, then load-bearing capacity is improved, but stress concentration occurs at adjacent levels leading to deformities

Engineering Contradiction:

Improveload-bearing capacityVSAvoidstress concentration causing deformities

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The flexible member's stiffness parameter varies along its length, with the proximal and distal portions having lower stiffness values than the central portion. This parameter change allows the construct to maintain adequate load-bearing capacity through the rigid spinal rod and fixation members while reducing stress concentration at the junctional regions through the flexible member's variable stiffness profile.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The spinal fixation construct uses composite construction combining rigid materials (spinal rod, fixation members) with a flexible member that has different mechanical properties. This composite approach allows the rigid components to provide overall structural strength and load-bearing capacity while the flexible member reduces stress concentration at adjacent levels, preventing deformities.

Inventive Principle:

Principle #40Composite materials

3Ease of operation

If extensive dissection of paraspinal musculature is performed to access the spinal column, then surgical access is improved, but soft tissue disruption increases leading to accelerated degeneration at adjacent levels

Engineering Contradiction:

Improvesurgical accessVSAvoidsoft tissue disruption causing accelerated degeneration

Core Design Contradiction:

Ease of operationVSObject-generated harmful factors

Solution Approach 1:

The flexible member converts the harmful effect of soft tissue disruption into a beneficial outcome by providing a flexible junctional region that naturally accommodates the loss of paraspinal musculature. The reduced stiffness at the proximal and distal ends of the flexible member allows these regions to flex independently, compensating for the disrupted soft tissues and preventing accelerated degeneration at adjacent levels.

Inventive Principle:

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

Data Source

PatentUS20250143752A1Spinal Fixation Construct And Methods Of Use

Publication Date: 2025.05.08 VB SPINE LLC

AI summary

A spinal fixation construct for aligning vertebral bodies includes a bone screw, a spinal rod, a flexible member, and a fixation member. The spinal rod is disposed within a saddle portion of a housing of the bone screw, and includes an elongated body having a first end and a second end. The spinal rod is formed from a first material having a first modulus of elasticity. The flexible member is coupled to the spinal rod, and includes an elongated body having a first end portion and a second end portion. The flexible member is formed from a second material having a second modulus of elasticity that is different from the first modulus of elasticity. The fixation member includes a threaded body portion and a head portion defining a hole therethrough. A portion of the flexible member extends through the hole of the head portion.