Bottom-Loaded Bone Anchor Shank Head Collet Containment

Solution Overview

Problem

Polyaxial bone screws used in spinal surgery often exhibit a floppy rotation of the head relative to the shank, making it difficult to achieve the desired rotational position of the receiver with respect to the shank, especially when inserting a rod or longitudinal connecting member.

Innovation Solution

A bone screw assembly with a shank, receiver, and a collet-like retainer that includes a compression insert, allowing for non-floppy pivoting by engaging the shank head with a friction fit, and enabling adjustable angle positioning of the shank relative to the receiver through a rotatable retainer mechanism.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a polyaxial bone screw allows loose rotation of the head relative to the shank, then the receiver can be positioned at various angles, but the rotation becomes floppy and difficult to control for achieving the desired rotational position

Engineering Contradiction:

Improveangular positioning capabilityVSAvoidcontrol of rotational position

Core Design Contradiction:

Adaptability or versatilityVSEase of operation

Solution Approach 1:

The retainer is designed to transition from a movable state during insertion to a locked state during operation. During insertion, the retainer can rotate freely to accommodate different angles. Once the desired angle is achieved, the retainer locks into place, providing stability while maintaining the achieved positioning.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The compression insert is pre-loaded to engage the shank head with friction fit before final positioning. This preliminary engagement provides sufficient friction to hold the desired rotational position while still allowing adjustment during the preliminary positioning phase.

Inventive Principle:

Principle #10Preliminary action

2Stability of the object's composition

If the retainer is fixed relative to the receiver, then the structure is stable, but the shank cannot be positioned at adjustable angles

Engineering Contradiction:

Improvestructural stabilityVSAvoidadjustable angle positioning

Core Design Contradiction:

Stability of the object's compositionVSAdaptability or versatility

Solution Approach 1:

The retainer is designed to transition from a movable state during insertion to a locked state during operation. During insertion, the retainer can rotate freely to accommodate different angles. Once the desired angle is achieved, the retainer locks into place, providing stability while maintaining the achieved positioning.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The bone screw assembly is divided into separate components: a fixed receiver, a movable retainer, and a shank. The retainer acts as an intermediate component that can rotate relative to the receiver during positioning, then lock to provide stability, while the shank rotates relative to the retainer for angle adjustment.

Inventive Principle:

Principle #1Segmentation

3Adaptability or versatility

If the retainer is made movable to allow rotation, then angle adjustment is possible, but the retainer may shift or move unintentionally during the procedure

Engineering Contradiction:

Improveangle adjustment capabilityVSAvoidposition stability during procedure

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The compression insert is pre-loaded to engage the shank head with friction fit before final positioning. This preliminary engagement provides sufficient friction to hold the desired rotational position while still allowing adjustment during the preliminary positioning phase.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The retainer is designed to transition from a movable state during insertion to a locked state during operation. During insertion, the retainer can rotate freely to accommodate different angles. Once the desired angle is achieved, the retainer locks into place, providing stability while maintaining the achieved positioning.

Inventive Principle:

Principle #15Dynamics

4Ease of operation

If a friction fit engagement is used between the compression insert and shank head, then non-floppy pivoting is achieved, but the insertion process becomes more complex

Engineering Contradiction:

Improvecontrol during pivotingVSAvoidinsertion process complexity

Core Design Contradiction:

Ease of operationVSDevice complexity

Solution Approach 1:

The compression insert acts as an intermediary component between the retainer and the shank head. It provides the friction fit engagement that controls pivoting, while being simple enough to insert through the retainer using standard insertion tools, thus managing complexity.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 solution provides a stable and adjustable bone screw assembly that allows for precise positioning of the shank relative to the receiver, facilitating easier and more precise spinal alignment during surgical procedures.

Implementation Method 1

engaging the shank head with a friction fit

Methodology Applied

Scientific EffectFriction: Friction

Data Source

PatentUS20240415550A1Bottom-loaded pivotal bone anchor with shank head collet containment

Publication Date: 2024.12.19 JACKSON CORP

AI summary

A receiver assembly of a pivotal bone anchor includes a receiver housing portion, an expandable collet retainer portion, and an outer sleeve member. The receiver housing portion includes a pair of upright arms defining an open channel configured to receive the elongate rod. The collet retainer portion includes an inner surface defining a center through aperture configured to expandingly receive the head of the shank into the collet retainer portion upon the head being uploaded through a lower collet opening. The outer sleeve member is configured for positioning around the collet retainer portion after uploading the head of the shank of the bone anchor into the collet retainer portion through the lower collet opening.