Offset Polyaxial Screw Non-Symmetrical Pivoting

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Solution Overview

Problem

Existing multiaxial screws in spinal fixation systems provide limited non-symmetrical pivoting capabilities, making it difficult to achieve favorable angles for retainer movement relative to the screw head, especially when using retainers with non-canted surfaces.

Innovation Solution

A polyaxial screw system with a screw head that has a partial opening or shape offset from the axis of the threaded portion, allowing for non-symmetrical pivoting by varying degrees in different directions, enabling greater mobility and adaptability with various retainer types.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a traditional multiaxial screw with symmetrical pivot capability is used, then the screw can pivot equally in all directions, but it cannot accommodate non-symmetrical pivoting requirements for certain retainer configurations

Engineering Contradiction:

Improvepivoting capabilityVSAvoidachieving favorable angles

Core Design Contradiction:

Adaptability or versatilityVSEase of operation

Solution Approach 1:

The screw head is designed with an offset axis relative to the threaded portion axis, creating non-symmetrical pivoting capability. This asymmetric configuration allows the retainer to pivot at different angles in different directions, enabling favorable angles for various retainer types including those with non-canted surfaces, while maintaining ease of operation through the offset mechanism

Inventive Principle:

Principle #4Asymmetry

2Adaptability or versatility

If the screw head is offset from the threaded portion axis, then non-symmetrical pivoting is enabled, but the device complexity increases

Engineering Contradiction:

Improveangular position adjustmentVSAvoidscrew head geometry

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The offset screw head design implements non-symmetrical pivoting through a relatively simple geometric modification - positioning the screw head axis at an offset from the threaded portion axis. This asymmetric arrangement enables varied angular positions without requiring complex mechanical mechanisms, thus achieving adaptability while keeping the design relatively simple

Inventive Principle:

Principle #4Asymmetry

3Adaptability or versatility

If a polyaxial screw with offset head is used, then greater range of motion is achieved, but manufacturing precision requirements increase

Engineering Contradiction:

Improverange of motionVSAvoidoffset alignment

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The offset screw head design achieves enhanced range of motion through asymmetric geometry that can be manufactured using conventional machining processes. The offset between the screw head axis and threaded portion axis is a fixed geometric parameter that can be controlled during manufacturing, enabling varied angular positions without requiring extremely tight tolerances or complex precision manufacturing techniques

Inventive Principle:

Principle #4Asymmetry

Data Source

PatentUS9198691B2Offset multiaxial or polyaxial screw, system and assembly

Publication Date: 2015.12.01 X SPINE SYSTEMS INC

AI summary

A capless multiaxial screw fixation assembly, including a screw having a threaded portion and a screw head portion positioned at one end thereof and a retainer having a first end, a second end opposite the first end, and a bore for receiving the screw threaded portion so that the screw head portion is seated therein. At least one of the screw and the retainer is configured such that the retainer is able to pivot about the screw head portion in a non-symmetrical manner.