Polyaxial Bone Anchor Insert for Non-Floppy Locking

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Solution Overview

Problem

Existing polyaxial bone screws suffer from floppy rotation of the receiver relative to the shank, making surgical procedures difficult, and the modular designs are weak against pull-out forces due to contractile locking engagements.

Innovation Solution

A polyaxial bone screw assembly with a split retainer ring that provides expansion-only locking engagement, featuring a friction fit between the shank head and retainer, ensuring secure fixation without floppy rotation, and enhanced resistance to pull-out forces.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If contractile locking engagement is used in modular polyaxial screws, then the receiver can be easily attached to the shank, but the assembly becomes weak against pull-out forces

Engineering Contradiction:

Improveease of attachmentVSAvoidresistance to pull-out forces

Core Design Contradiction:

Ease of operationVSStrength

Solution Approach 1:

The patent inverts the traditional contractile locking mechanism by using an expansion-only locking mechanism. The retainer ring expands outward to engage with the receiver, rather than contracting inward. This inversion transforms the weak contractile engagement into a strong expansion-based locking that resists pull-out forces while maintaining ease of attachment through the expansion action.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes the mechanical parameter of the locking mechanism from contraction to expansion. By using an expansion-only retainer ring that expands outward to lock into the receiver, the system achieves both easy attachment (through the expansion action) and high strength (through the expanded locked state), resolving the contradiction between ease of operation and resistance to pull-out forces.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If polyaxial bone screws allow floppy rotation of the head, then the receiver can be positioned at various angles, but the procedure becomes more difficult

Engineering Contradiction:

Improverotational positioning capabilityVSAvoiddifficulty of surgical procedure

Core Design Contradiction:

Adaptability or versatilityVSEase of operation

Solution Approach 1:

The patent introduces a dynamic locking mechanism where the retainer ring can be selectively locked into the receiver. Before locking, the system allows controlled movement for positioning. After locking, the connection becomes fixed to prevent floppy rotation. This dynamic transition from movable to fixed state provides both adaptability during positioning and ease of operation during the surgical procedure.

Inventive Principle:

Principle #15Dynamics

3Ease of operation

If the bone screw shank is inserted separate from the receiver, then the shank can be manipulated more easily, but the assembly complexity increases

Engineering Contradiction:

Improvemanipulation easeVSAvoidassembly complexity

Core Design Contradiction:

Ease of operationVSDevice complexity

Solution Approach 1:

The patent segments the bone screw assembly into separate components: the shank and the receiver with retainer ring. This segmentation allows the shank to be inserted and manipulated independently, improving ease of operation. The receiver and retainer ring remain as a separate assembly that can be attached later. This modular segmentation reduces assembly complexity by allowing independent manipulation of components.

Inventive Principle:

Principle #1Segmentation

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 assembly offers a secure, non-floppy connection and improved resistance to pull-out forces, allowing for easier surgical manipulation and enhanced stability during spinal correction procedures.

Implementation Method 1

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 2

friction fit resilient expansion-only split retainer for capturing the shank head

Methodology Applied

Scientific EffectFriction: Friction

Data Source

PatentUS20250359895A1Bone anchor assembly with tool deployment of insert into an unlocked configuration

Publication Date: 2025.11.27 JACKSON CORP

AI summary

A pivotal bone anchor assembly includes a receiver having a lower cavity for receiving the partial spherical head of a shank and an upper channel for receiving an elongate rod. The cavity extends upward from a bottom opening through the channel to the top of the receiver to define a central bore having upper and lower receiver abutment structures extending at least partially circumferentially around the central bore. The assembly also includes an insert having exterior upper and lower insert abutment structures configured to have simultaneously overlapping arrangements with the upper and lower receiver abutment structures when positioned in a first position. Upon positioning the shank head into the cavity, the inset is forcibly downward displaced within central bore by tooling such that the insert is inhibited from moving back up within the central bore while the shank remains pivotable with respect to the receiver until the bone anchor assembly is locked with the closure top