Articulating Knee Spacer with Hinge Assembly

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Solution Overview

Problem

Current temporary knee spacers for infected total knee arthroplasty have limited mobility and functionality, and may become permanent in unfit patients, such as the elderly, leading to reduced mobility and complications.

Innovation Solution

A prosthetic knee implant with a hinged design comprising a femoral and tibial component connected via a unique hinge assembly, allowing for rotational motion of at least 60 degrees and adjustable length through nesting spacers, manufactured from PEKK using selective laser sintering, enabling partial weight bearing and natural range of motion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a static PMMA block spacer is used, then the infection treatment is simplified, but the patient mobility is severely limited and functionality is reduced

Engineering Contradiction:

Improvesimplicity of spacer implementationVSAvoidpatient mobility

Core Design Contradiction:

Ease of manufactureVSEase of operation

Solution Approach 1:

The patent transforms the static PMMA block spacer into a dynamic articulating spacer with a hinge assembly that allows controlled rotation between the femoral and tibial components. This enables the knee joint to move through a range of motion while maintaining the spacer's infection treatment function, thus resolving the contradiction between simplicity and mobility.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The spacer is divided into separate femoral and tibial components connected by a hinge, rather than a single monolithic block. This segmentation allows independent movement of each component while maintaining structural integrity and antibiotic delivery function, improving patient mobility without compromising the treatment simplicity.

Inventive Principle:

Principle #1Segmentation

2Reliability

If a well-fixed prosthesis is removed for infection treatment, then the infection can be addressed, but native bone stock is lost and patient morbidity increases

Engineering Contradiction:

Improveinfection eradication capabilityVSAvoidbone stock loss

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The articulating spacer serves as an intermediary device that maintains the joint space and delivers antibiotics locally without requiring removal of the well-fixed prosthesis. This intermediate solution allows infection treatment while preserving the original implant and associated bone stock, avoiding the harmful effects of prosthesis removal.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Ease of operation

If simple antibiotic suppression is used, then surgical risks are avoided, but infection eradication is unlikely and symptoms persist

Engineering Contradiction:

Improveavoidance of surgical complicationsVSAvoidinfection eradication rate

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The spacer is designed with porous structure that allows high-concentration antibiotic elution directly into the joint space. This localized drug delivery system achieves effective infection eradication while avoiding the systemic side effects and surgical complications associated with prolonged IV antibiotic therapy.

Inventive Principle:

Principle #31Porous materials

4Reliability

If current temporary spacers are used, then infection treatment is provided, but mobility and functionality remain limited

Engineering Contradiction:

Improveinfection treatment effectivenessVSAvoidpatient functionality

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The patent introduces a hinge assembly with rotational capability into the temporary spacer design, transforming it from a static to a dynamic structure. This allows the spacer to provide both infection treatment functionality and improved patient mobility, enabling natural range of motion during the treatment period.

Inventive Principle:

Principle #15Dynamics

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The implant provides improved mobility and functionality as a temporary or permanent solution, allowing for partial weight bearing and natural range of motion, while maintaining soft tissue and joint space, and can be secured with antibiotic-loaded bone cement for infection treatment.

Implementation Method 1

manufactured from PEKK using selective laser sintering

Methodology Applied

Scientific EffectSelective laser sintering: Selective Laser Sintering

Data Source

PatentUS10966838B2Articulating knee spacer and method of manufacture

Publication Date: 2021.04.06 OXFORD PERFORMANCE MATERIALS INC

AI summary

A joint implant for temporary or permanent use has a femoral component and tibial component. The femoral component has a base and rod extending therefrom and defines a pin. The tibial component has a base and rod extending therefrom and defines a bore in which the pin is seated so that the femoral component is rotatable relative to the tibial component.