Variable-Angle Bone Plate Screw With Zoned Head Threading

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Solution Overview

Problem

Existing variable-angle screws have a less secure threaded connection between the screw head and the bone plate due to discontinuous contact along the entire length of the screw head, which can lead to loosening over time.

Innovation Solution

A variable-angle screw with a threaded head featuring a double frustoconical geometry and grooves only in the lower region, ensuring a continuous thread contact in the upper region for secure fixation to the bone plate, combined with a less accentuated entry relief for improved tracking.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If grooves are placed along the entire length of the screw head, then variable-angle function is achieved, but threaded connection security deteriorates due to discontinuous contact

Engineering Contradiction:

Improvevariable-angle functionVSAvoidthreaded connection security

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The screw head is segmented into two distinct regions: an upper region with continuous threading for secure plate connection, and a lower region with grooves for variable-angle functionality. This segmentation allows each region to fulfill its specific function without compromising the other.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different parts of the screw head are given different qualities: the upper region has continuous threads for maximum contact and security with the plate, while the lower region has grooves that enable angular adjustment. Each local region is optimized for its specific purpose.

Inventive Principle:

Principle #3Local quality

2Reliability

If continuous threading is provided along the entire screw head, then threaded connection security is improved, but variable-angle function is lost

Engineering Contradiction:

Improvethreaded connection securityVSAvoidvariable-angle function

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The screw head is divided into functional zones where continuous threading in the upper region provides secure connection, while the lower region incorporates grooves to enable angular adjustment. This segmentation resolves the conflict between continuity and variability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The screw head design allows dynamic angular adjustment through the grooved lower region while maintaining secure fixed connection through the continuously threaded upper region, combining flexibility with stability.

Inventive Principle:

Principle #15Dynamics

3Ease of operation

If entry relief is made more accentuated, then easier insertion is achieved, but tracking precision deteriorates

Engineering Contradiction:

Improveinsertion easeVSAvoidtracking precision

Core Design Contradiction:

Ease of operationVSManufacturing precision

Solution Approach 1:

The entry relief geometry is locally optimized to provide sufficient clearance for easy insertion while maintaining precise angular tracking through the frustoconical geometry that guides the screw along the desired insertion path.

Inventive Principle:

Principle #3Local quality

Data Source

PatentEP4483825B1Screw with variable-angle fixation insertable into a threaded hole in a bone plate

Publication Date: 2026.01.14 ASTROLABE FABCAO DE IMPLANTES MEDICOS LDA

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AI summary

The invention refers to a bone fixation screw (P) with variable-angle fixation to be inserted into a threaded hole of a bone plate. This screw (P) features a variable-angle design that facilitates continuous threading of the upper region (1.3.1) of the screw head thread (1.3) into contact with the plate, ensuring enhanced screw (P) fixation. A key advantage lies in the grooves (1.4) of the screw (P), strategically placed only in the lower region (1.3.2) of the screw head thread (1.3) rather than along its entire length. This placement enables the upper part of the head (1) to maintain complete thread fillets without discontinuities. Consequently, when securing the screw (P) into the plate at any angle, the upper thread fillets engage the plate seamlessly, reinforcing secure contact between the plate thread and the screw for a more reliable fixation.