Bone Implant Screw Wedging via Conical Head and Radial Notch

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Solution Overview

Problem

Existing bone implantation assemblies restrict screw placement direction and are prone to unscrewing over time, leading to potential defective positioning and instability.

Innovation Solution

A cylindrical hole with radial notches and a conical screw head with specific thread pitch and depth ratios, allowing for multiple screw placement directions and effective wedging to prevent unscrewing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a smooth cylindrical hole is used in the implantable part, then the screw can be implanted in multiple directions, but the risk of screw protruding at the articular surface increases

Engineering Contradiction:

Improvescrew implantation direction flexibilityVSAvoidrisk of screw protruding at articular surface

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The hole is provided with a radial notch that creates local structural differentiation. The notch allows the bone to deform locally in a controlled manner, enabling multi-directional screw insertion while maintaining overall structural integrity and preventing screw protrusion at the articular surface.

Inventive Principle:

Principle #3Local quality

2Reliability

If a thread engagement system is used between the hole and screw head, then the screw is securely fixed, but the implantation direction is restricted to a single direction

Engineering Contradiction:

Improvescrew fixation securityVSAvoidscrew implantation direction flexibility

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The radial notch creates a localized area of controlled deformation in the bone structure. This local modification allows the threaded hole to accommodate screws at various angles while the threading provides secure fixation, resolving the contradiction between fixation security and directional flexibility.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The bone structure around the radial notch is designed to deform dynamically during screw insertion. The notch allows the bone to yield and adapt to different screw angles, while the threaded engagement maintains secure fixation regardless of the insertion direction.

Inventive Principle:

Principle #15Dynamics

3Reliability

If axial screw retention systems are used to prevent unscrewing, then the risk of unscrewing is reduced, but the manufacturing cost increases significantly

Engineering Contradiction:

Improveresistance to unscrewingVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The conical screw head with specific thread pitch ratio (0.33-0.5) creates a self-wedging mechanism. As the screw is tightened, the conical geometry causes the threads to wedge together progressively, generating increasing friction and mechanical interference that prevents unscrewing without requiring additional retention components.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The invention changes the geometric parameters of the screw-head-thread interface. By specifying that the screw head thread pitch is 0.33-0.5 times the hole thread pitch and the head depth is 0.5-0.67 times the hole thread depth, the system creates optimal wedging conditions that prevent unscrewing through geometric self-locking rather than additional mechanical features.

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

Enables flexible screw placement and secure anchoring, reducing the risk of unscrewing and defective positioning, while maintaining stability and versatility across various anatomical applications.

Implementation Method 1

the head of the screw is conical in shape, having an apex angle between 15 and 25°, and the pitch of the thread of the head of the screw is between one third and one half of the pitch of the thread forming the thread of the hole

Methodology Applied

Scientific EffectWedge: Wedge

Implementation Method 2

effective wedging of the head of the screw in the hole, such as to oppose any risk of unscrewing

Methodology Applied

Scientific EffectFriction: Friction

Implementation Method 3

the hole is cylindrical in shape and comprises at least one radial notch opening out at least in the proximal face of said implantable part, that is to say in the face of this implantable part through which the screw is intended to be engaged in the hole, this radial notch providing an interruption of the tapping that the hole comprises

Methodology Applied

Scientific EffectDeformation: Deformation

Data Source

PatentEP2529685B1Assembly comprising an implantable part to be secured to one or more bones or bone parts to be joined, and at least one screw for securing said implantable part to said one or more bones

Publication Date: 2014.04.16 COMPAGNIE FINANCIERE & MEDICALE

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AI summary

The assembly (1) has an implantable part (2) comprising a cylindrical threaded hole (4) having a radial notch emerged on a proximal face of the part. A fixing screw (3) is engaged with the hole through the face. The notch realizes interruption of tapping comprising the hole. The screw has a conical threaded head possessing apex angle ranging between 15 and 25 degree. Thread pitch of the head ranges between one-third and half of a thread pitch forming the tapping of the hole. Depth of the thread of the head ranges between half and two-third of depth of the thread pitch forming the tapping.