Cross-Threaded Cannulated Screw Assembly for Metacarpal Stability

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing intramedullary screws used for metacarpal fractures are prone to loosening due to rotational instability, leading to complications such as malunion and nonunion, while more stable fixation devices like plates compromise the range of motion and recovery rate.

Innovation Solution

A screw assembly comprising a cannulated screw with a first thread and a blocking screw with opposite handedness, forming an interweaving thread pattern that locks the screws in place, providing rotational and translational stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If a single intramedullary screw is used for metacarpal fracture fixation, then the procedure benefits from limited dissection and preserved range of motion, but the screw becomes loose due to rotational instability

Engineering Contradiction:

Improverange of motionVSAvoidrotational stability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent employs a nested screw configuration where a second screw is inserted through the hollow interior of the first screw. The second screw has threads that engage with the inner surface of the first screw, creating a nested arrangement. This nested structure provides rotational stability by preventing the first screw from rotating within the bone while maintaining the minimally invasive benefits of intramedullary fixation.

Inventive Principle:

Principle #7Nested doll (Nesting)

2Reliability

If a plate fixation device is used to achieve rotational stability, then the screw becomes secure, but the range of motion and recovery rate are compromised

Engineering Contradiction:

Improverotational stabilityVSAvoidrange of motion

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The nested screw design allows the second screw to pass through the hollow body of the first screw, with its threads engaging the inner surface. This nested arrangement provides rotational stability comparable to plate fixation while maintaining the advantages of intramedullary screws including limited dissection and preserved range of motion.

Inventive Principle:

Principle #7Nested doll (Nesting)

3Device complexity

If a single screw is used for fracture fixation, then the procedure is simple and quick, but the screw loosens leading to malunion or nonunion

Engineering Contradiction:

Improvefixation device structureVSAvoidfracture healing outcome

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The nested screw configuration involves inserting a second screw through the hollow interior of the first screw. The threads of the second screw engage with the inner surface of the first screw, creating a mechanically interlocked assembly. This increases reliability by preventing screw loosening and promoting fracture healing, while adding minimal complexity to the overall procedure.

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The fixation device is segmented into two distinct screw components rather than a single monolithic screw. The first screw provides primary fixation, while the second screw provides rotational stability. This segmentation allows each component to perform its specific function optimally, resulting in improved fracture healing outcomes.

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS20260053539A1Screw Assembly

Publication Date: 2026.02.26 STRYKER EUROPEAN OPERATIONS LIMITED

AI summary

A screw assembly and a method of inserting the assembly into a bone are described herein. The screw assembly includes a cannulated screw having a first thread with a first handedness and a blocking screw with a second thread having an opposite handedness creating a cross-working thread assembly.