Pedicle Screw Detachable Polyaxial Head

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Solution Overview

Problem

Existing pedicle screw systems with detachable polyaxial heads face issues such as screw over-tightening, improper seating, and weak attachment due to threading or collet mechanisms, leading to potential complications like screw migration and failed fusion.

Innovation Solution

A pedicle screw system with a polyaxial head that attaches under the bone screw head, featuring a vertical screw head channel, spherical screw head aperture, and retaining tabs, along with a rod slot and locking screw mechanism to secure the bone screw, providing a stable and secure attachment without relying on threading or collets.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a polyaxial head is attached by threading onto the pedicle screw, then the head can be securely connected to the screw, but this can drive the screw further into the pedicle causing dangerous consequences or prevent proper seating

Engineering Contradiction:

Improveattachment securityVSAvoidscrew over-tightening and improper seating

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The attachment mechanism is divided into separate functional components: a recess in the polyaxial head, a protrusion on the screw head, and a locking screw. This segmentation allows the head to be positioned without threading that could over-tighten, while the locking screw provides secure attachment independently of the positioning process.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The locking screw acts as an intermediary element that secures the polyaxial head to the pedicle screw. Instead of direct threading between head and screw, the locking screw mediates the attachment, allowing controlled securing without the harmful effects of direct threading over-tightening.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of operation

If a collet is used to attach the polyaxial head to the bone screw, then the head can be connected through elastic deformation, but this creates a weak point that can reopen unexpectedly

Engineering Contradiction:

Improveattachment mechanismVSAvoidattachment stability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The attachment system is segmented into the collet for initial positioning and a locking screw for final securement. This division allows the collet to provide ease of operation for attachment while the locking screw provides the reliability needed to prevent unexpected reopening, eliminating the weak point in the original design.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The locking screw provides beforehand cushioning against the potential failure mode of collet reopening. By pre-establishing this secondary securing mechanism, the design compensates for the inherent weakness in the collet-only approach, preventing unexpected attachment failure.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Reliability

If threading is used to attach the polyaxial head, then connection is achieved, but the threads on the bone screw head can deform preventing proper rigid fixation

Engineering Contradiction:

Improveconnection establishmentVSAvoidthread deformation

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The locking screw serves as an intermediary that establishes the connection between head and screw without deforming the screw head threads. The mediator approach allows connection establishment while preserving the manufacturing precision of the original screw components.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The harmful threading operation is extracted from the attachment process. Instead of threading the head directly onto the screw (which causes deformation), the design extracts this step and replaces it with a recess-protrusion interface secured by a locking screw, eliminating the source of thread deformation.

Inventive Principle:

Principle #2Taking out (Extraction)

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

This configuration ensures proper seating and secure fixation of the polyaxial head on the bone screw, preventing screw migration and enhancing fusion stability, while allowing for easy removal post-surgery without causing additional complications.

Implementation Method 1

A pedicle screw system with a polyaxial head that attaches under the bone screw head... a horizontal screw head channel connecting between the vertical screw head channel and the spherical screw head aperture

Methodology Applied

Scientific EffectElasticity: Elasticity

Data Source

PatentUS11589904B2Pedicle screw with detachable polyaxial head

Publication Date: 2023.02.28 BERRY BRET MICHAEL

AI summary

A pedicle screw device for fixating at least two adjacent vertebral bodies is presented. The device consists of a bone screw which is implanted into the pedicle of a vertebral body. A second bone screw is implanted into the pedicle of a second vertebral body. A polyaxial head is then inserted over each bone screw. The polyaxial heads can then be slid into a retaining position on the bone screw, allowing them to rotate about the spherical portion of the bone screw. The polyaxial heads are then attached to one another with a rod. Finally, a locking screw is inserted into the polyaxial heads to force the rod against the bone screw as well as the polyaxial head, locking them in place. The rod also serves to prevent the polyaxial head from disconnecting from the bone screw.