Bone Screw Thread Termination Surface Design

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Solution Overview

Problem

Conventional bone screw thread forms become excessively thin as they approach the neck portion, leading to disadvantageous thinning and reduced turns, which compromises the screw's effectiveness in penetrating bone tissue.

Innovation Solution

The bone screw incorporates a thread-termination surface that abruptly transitions into the shank over less than a half turn, preventing thinning and maximizing the number of turns by truncating the thread form, which includes a face oriented approximately 90° to the central axis, thereby maintaining thread thickness and pullout force.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Duration of action of moving object

If the angled faces are made closer to 90° to the central axis to maximize thread turns, then the number of thread turns is increased, but the thread form becomes excessively thin near the neck portion

Engineering Contradiction:

Improvenumber of thread turnsVSAvoidthread form thickness

Core Design Contradiction:

Duration of action of moving objectVSStrength

Solution Approach 1:

The patent extracts the angled face termination approach and replaces it with a thread-termination surface that abruptly ends the thread form. This removes the problematic gradual thinning effect while preserving the benefit of increased thread turns through the near-90° angled face configuration.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The thread form is preliminarily configured with a near-90° angled face to maximize the number of turns before the thread-termination surface abruptly ends it. This preliminary configuration ensures adequate thread engagement length without allowing the thread to become excessively thin.

Inventive Principle:

Principle #10Preliminary action

2Length of moving object

If the shaft length is reduced to create a shorter bone screw, then the implant size is minimized, but the number of thread turns is reduced

Engineering Contradiction:

Improveshaft lengthVSAvoidnumber of thread turns

Core Design Contradiction:

Length of moving objectVSDuration of action of moving object

Solution Approach 1:

The patent changes the geometric parameters of the thread form, specifically using a near-90° angled face configuration that allows more turns to be packed into a shorter shaft length. The thread-termination surface further optimizes this by abruptly ending the thread form to maintain thickness while maximizing turn count.

Inventive Principle:

Principle #35Parameter changes

3Duration of action of moving object

If the thread form is allowed to extend further toward the neck portion to increase turns, then the number of thread turns is increased, but the pullout force is reduced due to thinning

Engineering Contradiction:

Improvenumber of thread turnsVSAvoidpullout force

Core Design Contradiction:

Duration of action of moving objectVSForce

Solution Approach 1:

The patent converts what would normally be a harmful gradual thinning process into a beneficial abrupt termination. The thread-termination surface creates a sharp cutoff that prevents the thread from becoming thin, while the near-90° angled face configuration ensures maximum thread turns are achieved before this abrupt termination.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Data Source

PatentUS11419652B2Thread form for bone screw

Publication Date: 2022.08.23 WARSAW ORTHOPEDIC INC

AI summary

A bone screw including a head portion, a neck portion, and a shaft portion is provided. The shaft portion includes a first end, an opposite second end, a helical thread form, and a shank. The first end of the shaft portion is attached to the neck portion, and the helical thread form extends around the shank between the first end and the second end. The thread form terminates at a thread-termination surface adjacent the first end of the shaft portion, where the thread-termination surface affords an abrupt transition into the shank.