Pivotable Bone Anchor Assembly With Independent Insert Locking

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Solution Overview

Problem

Existing polyaxial bone screws suffer from floppy connections between the receiver and shank, making spinal surgery procedures difficult, and the prior art's contractile locking mechanisms are weak against pull-out forces.

Innovation Solution

A polyaxial bone screw design featuring a split retainer ring with a radiused surface and expansion-only locking mechanism, providing a secure, non-floppy engagement between the shank and receiver, using a friction fit and winged arm portions for manipulation and stabilization.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If a contractile locking mechanism is used in polyaxial bone screws, then the shank can be locked into the receiver, but the connection becomes weak against pull-out forces

Engineering Contradiction:

Improveresistance to pull-out forcesVSAvoidconnection stability

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

Instead of using a contractile locking mechanism that constricts onto the shank, the patent employs an expansion-only mechanism where the retainer ring expands outward against the receiver's inner surface to create locking engagement. This inverted approach provides superior resistance to pull-out forces by distributing load across a larger contact area within the receiver cavity.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The retainer ring is designed as a split, segmented structure that can be compressed axially to allow insertion through the receiver opening, then expands to engage with the receiver's inner surface. The segmentation allows the retainer to be inserted and locked independently, providing reliable connection without requiring complex contractile mechanisms.

Inventive Principle:

Principle #1Segmentation

2Ease of operation

If a polyaxial bone screw assembly is designed with a receiver and shank connection, then the screw can be inserted into bone, but the connection becomes floppy and difficult to control during surgery

Engineering Contradiction:

Improvecontrol during spinal surgeryVSAvoidconnection stability

Core Design Contradiction:

Ease of operationVSStability of the object's composition

Solution Approach 1:

The retainer ring provides dynamic control during surgery by allowing the shank to be inserted and positioned within the receiver, then locked into a stable configuration. The expansion-only mechanism enables the connection to transition from a loose, adjustable state during insertion to a rigid, controlled state during surgery, eliminating floppiness while maintaining ease of operation.

Inventive Principle:

Principle #15Dynamics

3Strength

If a split retainer ring with expansion-only locking is used, then the connection strength is improved, but the device complexity increases

Engineering Contradiction:

Improveresistance to pull-out forcesVSAvoidretainer ring structure

Core Design Contradiction:

StrengthVSDevice complexity

Solution Approach 1:

The retainer ring utilizes parameter changes in its radial expansion capability to provide locking engagement. By changing the radial dimension from a compressed insertion state to an expanded locking state, the simple expansion-only mechanism achieves strong connection without complex contractile components, reducing overall device complexity while improving strength.

Inventive Principle:

Principle #35Parameter changes

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 offers enhanced resistance to pull-out forces and allows for secure, stable fixation of the shank to the receiver, enabling easier and more reliable spinal correction techniques.

Implementation Method 1

a friction fit resilient expansion-only split retainer for capturing the shank head in the receiver lower cavity

Methodology Applied

Scientific EffectFriction: Friction

Implementation Method 2

a friction fit resilient expansion-only split retainer for capturing the shank head in the receiver lower cavity

Methodology Applied

Scientific EffectElasticity: Elasticity

Implementation Method 3

a top drop and turn in place lower compression insert

Methodology Applied

Scientific EffectCompression: Compression

Implementation Method 4

The shank is finally locked into a fixed position relative to the receiver by frictional engagement between the insert and a lower split ring-like portion of the retainer

Methodology Applied

Scientific EffectFriction: Friction

Data Source

PatentUS12440245B2Pivotable bone anchor assembly with independent provisional locking by insert compressing member

Publication Date: 2025.10.14 JACKSON CORP

AI summary

A pivotal bone screw assembly includes a threaded shank body having an integral upper portion receivable in a receiver, with the receiver having an upper channel for receiving a longitudinal connecting member and a lower cavity cooperating with a lower opening. The assembly also includes a downloadable compression insert with a side arm extension for engagement and compression by a vertically-translating insert side compressing member so as to lock the assembly independent of the closure top.