Orthopedic Fastener Thread Transition for Cortical and Cancellous Bone

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Solution Overview

Problem

Existing orthopedic fasteners face limitations in securely attaching to bone structures without damaging the threads or loosening, particularly due to the difference in hardness between cortical and cancellous bone.

Innovation Solution

An orthopedic fastener design featuring a shank with a leading end for self-tapping threads in cancellous bone and a trailing end with larger diameter threads for cortical bone, utilizing cutting grooves at the intermediate transition to create secure attachment without damaging the bone threads.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a single thread configuration is used for the entire shank, then the fastener can be manufactured simpler, but it cannot securely attach to both cancellous and cortical bone without thread damage or loosening

Engineering Contradiction:

Improvethread configuration simplicityVSAvoidattachment security

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The shank is divided into two distinct threaded portions: a first threaded portion with a first thread configuration optimized for cancellous bone, and a second threaded portion with a second thread configuration optimized for cortical bone. This segmentation allows each portion to independently optimize its thread design for the specific bone type it encounters, resolving the contradiction between manufacturing simplicity and attachment reliability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different thread configurations are applied to different portions of the shank based on the local bone type requirements. The first threaded portion has threads designed for softer cancellous bone, while the second threaded portion has threads designed for harder cortical bone. This local differentiation ensures optimal attachment security for each bone type without compromising the other.

Inventive Principle:

Principle #3Local quality

2Reliability

If larger diameter threads are used for cortical bone, then attachment security in hard bone is improved, but the fastener cannot effectively engage softer cancellous bone first

Engineering Contradiction:

Improvecortical bone attachmentVSAvoidinsertion process

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The threaded shank is segmented into a first threaded portion with smaller diameter threads for cancellous bone and a second threaded portion with larger diameter threads for cortical bone. During insertion, the smaller threads engage the softer cancellous bone first, allowing smooth initial engagement, while the larger threads engage the harder cortical bone later, providing secure final attachment. This resolves the contradiction between cortical bone attachment security and ease of insertion.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The first threaded portion with smaller diameter threads performs the preliminary action of engaging the softer cancellous bone first during insertion. This preliminary engagement creates a pathway and initial stability, allowing the second threaded portion with larger diameter threads to subsequently engage the harder cortical bone without resistance, thus facilitating smooth insertion while ensuring secure cortical attachment.

Inventive Principle:

Principle #10Preliminary action

3Reliability

If cutting grooves are added at the intermediate transition, then thread damage is prevented, but the fastener design becomes more complex

Engineering Contradiction:

Improvethread integrityVSAvoidshank structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

Cutting grooves are extracted and placed specifically at the intermediate transition region between the first and second threaded portions. These grooves act as stress relief features that prevent thread damage by reducing stress concentration at the transition zone. The grooves are strategically positioned only where needed, adding minimal complexity while effectively protecting thread integrity.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The cutting grooves at the intermediate transition serve as intermediary features that mediate between the first and second threaded portions. They provide a transition zone that reduces stress concentration and prevents thread damage caused by the abrupt change in thread configuration. This intermediary structure resolves the contradiction by protecting thread integrity with minimal added complexity.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS10893897B2Orthopedic fastener

Publication Date: 2021.01.19 SPINAL ELEMENTS INC

AI summary

An orthopedic fastener has a head and a shank. The shank has a leading end portion adjacent a distal tip and a trailing end portion adjacent a head. An intermediate portion is positioned between the leading and trailing end portions. At the intermediate portion, the shank increases in diameter. The leading end portion has a first thread which includes one or more self-tapping cutting grooves extending adjacent the distal tip and through a plurality of the first threads. The intermediate portion has second threads extending toward the head from the leading end portion. The second threads of the intermediate portion are larger in outer diameter than the first threads in the leading end portion. The intermediate portion has one or more cutting grooves traversing at each of a leading transition at the leading end portion and at a trailing transition.