Expansion Retainer Ring for Polyaxial Bone Screw Locking

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing polyaxial bone screws with contractile locking engagements are weak against pull-out forces during spinal reduction procedures, and they can be difficult to assemble and disassemble, especially when the screw head and receiver are integrated as a unit.

Innovation Solution

A polyaxial bone screw design featuring a resilient expansion-only split retainer ring that is slidingly and pivotally engaged with the shank head and receiver, providing a stronger locking mechanism that resists pull-out forces and allows for independent locking and adjustment, similar to a fixed monoaxial screw, without contractile locking engagements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If contractile locking engagements are used in polyaxial bone screws, then the screw head can be securely locked to the receiver, but the assembly becomes weak against pull-out forces during spinal reduction procedures

Engineering Contradiction:

Improvelocking engagement securityVSAvoidresistance to pull-out forces

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The patent inverts the traditional contractile locking mechanism by using an expansion-only split retainer ring that expands to lock the screw head to the receiver, rather than contracting. This expansion mechanism provides superior resistance to pull-out forces while maintaining secure locking engagement.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes the mechanical parameter of the locking mechanism from contractile (shrinking) to expansive (expanding). The split retainer ring expands radially to engage and lock the screw head, fundamentally altering how the locking force is generated and applied, thereby improving pull-out resistance.

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If the screw head and receiver are integrated as a unit, then the structure is simplified, but assembly and disassembly become difficult

Engineering Contradiction:

Improvestructural integrationVSAvoidassembly and disassembly process

Core Design Contradiction:

Device complexityVSEase of operation

Solution Approach 1:

The patent segments the bone screw system into distinct components: a screw head, a receiver, and a split retainer ring. This segmentation allows the components to be assembled and disassembled independently while maintaining a simplified overall structure when locked together.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The split retainer ring serves as an intermediary component between the screw head and receiver. It facilitates easy assembly by being inserted through the receiver and expanded to lock the components, and enables simple disassembly by compressing it back, without requiring the components to be permanently integrated.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Strength

If a resilient expansion-only split retainer ring is used, then resistance to pull-out forces is enhanced, but the device complexity increases

Engineering Contradiction:

Improveresistance to pull-out forcesVSAvoidnumber of components

Core Design Contradiction:

StrengthVSDevice complexity

Solution Approach 1:

The patent merges multiple functions into the single split retainer ring component: it provides the locking mechanism, resists pull-out forces through its expansion, and enables easy assembly and disassembly. This consolidation achieves enhanced strength without proportionally increasing device complexity.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The split retainer ring is designed as a multi-functional component that simultaneously provides structural support, locking engagement, pull-out resistance, and assembly facilitation. This universality reduces the need for additional specialized components, balancing strength enhancement with acceptable device complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 design enhances the resistance to pull-out forces and simplifies the assembly and disassembly process, providing a more secure and stable fixation of the screw head to the receiver, allowing for flexible angular adjustments and independent locking of the screw mechanism.

Implementation Method 1

a resilient expansion-only split retainer for capturing the bone screw shank head in the receiver member assembly

Methodology Applied

Scientific EffectElasticity: Elasticity

Data Source

PatentUS12016594B2Pivotal bone anchor assembly with temporary positional locking by tooling

Publication Date: 2024.06.25 JACKSON CORP

AI summary

A pivotal bone anchor assembly includes a receiver having a channel configured to receive an elongate rod and communicating with a bottom opening through a central bore, with the central bore having a lower portion configured to receive the capture portion of a bone anchor with the bone anchor being pivotal with respect to the receiver in a non-locked configuration. The assembly further includes a compression insert that is also receivable within the central bore with an upper surface configured for engagement with the elongate rod, a central opening, and upward-facing surfaces on tool engagement structures positioned radially outward from the central opening. The tool engagement structures are configured for direct engagement by tooling to receive a continuously-applied downwardly directed force that temporarily locks the position of the bone anchor with respect to the receiver prior to the elongate rod being secured within the channel in a locked arrangement.