Bicondylar Ankle Prosthesis Design for Stability and Bone Preservation

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Solution Overview

Problem

Conventional ankle prostheses face issues such as high rates of loosening, wound problems, limited range of motion, and bone resorption, which affect patient satisfaction and the feasibility of revision surgeries, due to highly constrained designs and cement fixation.

Innovation Solution

A fixed-bearing ankle prosthesis with bicondylar geometry and articular surfaces that allow for varus/valgus stability and anterior/posterior translation, minimizing edge loading and bone stress, while providing a flexible surgical option for resurfacing and reducing bone resection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If highly constrained designs and cement fixation are used in conventional ankle prostheses, then initial stability is improved, but loosening rates increase significantly

Engineering Contradiction:

Improveinitial stabilityVSAvoidloosening rates

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The patent changes the fixation parameter from cement-based to porous-coat bone ingrowth fixation. The tibial and talar components feature porous coats that allow bone ingrowth, transforming the fixation mechanism from chemical/cement-based to biological/bone- ingrowth-based, thereby reducing loosening rates while maintaining initial stability through the press-fit mechanism of the porous structure

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the cement fixation mechanism with a porous-coat bone ingrowth mechanism. Instead of relying on cement to bond the prosthesis to bone, the design uses a porous surface structure that enables direct biological fixation through bone ingrowth, substituting a mechanical/chemical system with a biological system that provides long-term reliability

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Stability of the object's composition

If highly constrained designs are used in conventional ankle prostheses, then varus/valgus stability is improved, but range of motion is limited

Engineering Contradiction:

Improvevarus/valgus stabilityVSAvoidrange of motion

Core Design Contradiction:

Stability of the object's compositionVSEase of operation

Solution Approach 1:

The patent introduces dynamic elements to the prosthesis design, including a mobile bearing that allows anterior/posterior translation and rotation between the tibial and talar components. This dynamic mechanism enables the joint to adapt to physiological movements while maintaining varus/valgus stability through the bicondylar geometry and collateral ligaments

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent segments the articulation into multiple independent surfaces: a fixed bearing surface for varus/valgus stability and a mobile bearing surface for anterior/posterior motion. This segmentation allows different parts of the prosthesis to perform different functions independently, providing both stability and range of motion

Inventive Principle:

Principle #1Segmentation

3Ease of manufacture

If conventional bone resection methods are used, then prosthesis implantation is simplified, but bone stock is lost making revision difficult

Engineering Contradiction:

Improveimplantation simplicityVSAvoidbone stock

Core Design Contradiction:

Ease of manufactureVSLoss of substance

Solution Approach 1:

The patent performs preliminary actions during implantation by using trial components and positioning devices to precisely determine the required bone resection depth and orientation before final implantation. This preliminary planning ensures that minimal bone is removed while still achieving proper prosthesis positioning and alignment

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the bone resection parameters by using a bicondylar resection geometry that follows the natural anatomy of the tibial plateau. This approach allows for more precise and conservative bone removal compared to traditional flat resections, preserving bone stock while ensuring proper implant fit and alignment

Inventive Principle:

Principle #35Parameter changes

4Stability of the object's composition

If conventional prosthesis designs are used, then initial fixation is achieved, but wound complications occur due to bone stress

Engineering Contradiction:

ImprovefixationVSAvoidwound complications

Core Design Contradiction:

Stability of the object's compositionVSObject-affected harmful factors

Solution Approach 1:

The patent changes the fixation mechanism from cement-based to porous-coat bone ingrowth fixation. The porous structure allows for gradual load transfer to the bone as it ingrows, reducing peak stresses on the surrounding bone and soft tissues that would otherwise lead to wound complications

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent provides beforehand cushioning by designing a porous-coat structure that acts as a transition zone between the rigid prosthesis and the bone. This porous layer distributes stresses more evenly and prevents stress concentrations that could lead to bone failure and subsequent wound complications

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Data Source

PatentUS9750516B2Positioning device for ankle joint replacement surgery

Publication Date: 2017.09.05 THE UNIVERSITY OF IOWA RESEARCH

AI summary

A positioning device for ankle joint replacement surgery.