Thumb Metacarpal Prosthesis Anchored to MC2 After Trapeziectomy

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Solution Overview

Problem

Existing thumb prostheses for osteoarthritis of the thumb basal joint fail to address arthritis in the scaphotrapeziotrapezoid (STT) joint when the trapezium is removed due to collapse of os metacarpale I, leading to thumb shortening and mobility issues.

Innovation Solution

A prosthesis that attaches to os metacarpale II, diverting tendon forces via the capitate to the proximal carpal row and radius, using a plate or intramedullary rod for attachment, ensuring mobility and stability without relying on the trapezium.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If a cup is placed in os trapezium for CMC1 joint replacement, then thumb mobility is maintained, but the solution becomes inapplicable when os trapezium is removed due to trapeziectomy

Engineering Contradiction:

Improveapplicability of joint replacementVSAvoidadaptability to post-trapeziectomy anatomy

Core Design Contradiction:

Ease of operationVSAdaptability or versatility

Solution Approach 1:

The prosthesis is divided into two separate elements: a first element that attaches to os metacarpale I and a second element that attaches to os metacarpale II. This segmentation allows the prosthesis to function without requiring os trapezium, as the second element directly anchors to MC2, bypassing the need for a trapezium-based cup.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The prosthesis acts as an intermediary structure that transfers forces between os metacarpale I and os metacarpale II. By introducing this intermediate mechanical linkage, the system compensates for the absence of os trapezium and provides stable force transmission without relying on the removed bone.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Force

If axial forces are transmitted through CMC1 and STT joint to radius, then normal tendon function is maintained, but joint strain increases in patients with arthritis

Engineering Contradiction:

Improvetendon force transmissionVSAvoidjoint strain in arthritic patients

Core Design Contradiction:

ForceVSObject-affected harmful factors

Solution Approach 1:

The prosthesis extracts the force transmission pathway from the arthritic STT joint and CMC1 joint by creating a direct mechanical linkage between os metacarpale I and os metacarpale II. This bypasses the damaged joint surfaces and eliminates the harmful strain on arthritic joints while maintaining necessary force transmission for thumb function.

Inventive Principle:

Principle #2Taking out (Extraction)

3Stability of the object's composition

If suspensionplasties are used to prevent secondary collapse after trapeziectomy, then thumb stability is attempted, but results are disappointing with mobility loss

Engineering Contradiction:

Improvethumb stabilityVSAvoidthumb mobility

Core Design Contradiction:

Stability of the object's compositionVSEase of operation

Solution Approach 1:

The prosthesis provides a dynamic solution by allowing controlled movement between the first and second elements while maintaining overall structural stability. The movable connection between elements permits thumb mobility while the rigid attachment to both MC1 and MC2 prevents secondary collapse, achieving both stability and mobility simultaneously.

Inventive Principle:

Principle #15Dynamics

4Stability of the object's composition

If arthrodesis between os metacarpale I and os metacarpale II is performed, then stability is achieved, but high percentage of non-unions occurs and mobility is lost

Engineering Contradiction:

Improvejoint stabilityVSAvoidunion success rate

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The prosthesis replaces the biological arthrodesis process with a mechanical linkage system. Instead of relying on bone healing and fusion (which has high non-union rates), the prosthesis provides immediate mechanical stability through rigid attachment to both bones while maintaining controlled mobility through the movable connection between elements.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentEP4051186B1Prosthesis for movably coupling os metacarpale i of a hand to a second bone of the hand and a kit comprising a prosthesis and a fastening means

Publication Date: 2025.12.03 DE JONG TJEERD RENE

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AI summary

The invention relates to a prosthesis (1) for movably coupling os metacarpale I of a hand to a second metacarpal bone of the hand, which prosthesis comprises a first (2) and a second element (4), wherein the first element comprises a first attachment member (3), which first attachment member is configured for attachment to os metacarpale I, and the second element comprises a second attachment member (5), which second attachment member is configured for attachment to the second metacarpal bone, which first and second element are movable relative to each other, wherein the second metacarpal bone is os metacarpale II of the hand and the second attachment member is configured to be arranged from the radial side of os metacarpale II. The invention also relates to a combination of a prosthesis according to the invention and at least one fastening means (16, 17).