Constrained Knee Prosthesis Hinge Post Stability

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Solution Overview

Problem

The challenge is to make the femoral component of a knee salvage prosthesis system compatible with a recently designed constrained prosthetic knee system, which has a tibial bearing component attached to a tibial baseplate rather than the femoral component, risking spin-off and instability.

Innovation Solution

A novel hinge post design and tibial bearing component are created, featuring a well and walls that interact with the hinge post to drive articular surface rotation with increased conformity to the femoral component, and ramps on the hinge post to return to a non-distracted position.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If the femoral component is made compatible with the recently designed constrained prosthetic knee system, then the system can utilize a tibial baseplate with improved stability, but the femoral component risks spin-off from the tibial bearing component

Engineering Contradiction:

Improvestability of knee prosthesis systemVSAvoidrisk of spin-off

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The hinge post is received within a well formed in the tibial bearing component, creating a nested configuration where the femoral component (via hinge post) is positioned within the tibial bearing component. This nesting prevents lateral displacement and spin-off while maintaining the improved stability provided by the tibial baseplate configuration.

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The well and ridge features act as intermediary structures between the hinge post and tibial bearing component. These intermediary features provide mechanical engagement that prevents spin-off while allowing the femoral component to be compatible with the recently designed constrained prosthetic knee system that utilizes a tibial baseplate.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Stability of the object's composition

If the tibial bearing component is attached to the tibial baseplate rather than the femoral component, then improved stability is achieved, but hyperextension control becomes more difficult

Engineering Contradiction:

Improvestability of knee prosthesis systemVSAvoidhyperextension control

Core Design Contradiction:

Stability of the object's compositionVSEase of operation

Solution Approach 1:

The bump stop feature is positioned to preemptively prevent hyperextension before it can occur. When the femoral component approaches excessive extension, the bump stop makes contact with the tibial bearing component, creating a preliminary counter-force that stops the hyperextension motion before it can cause damage or instability.

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

The interaction between the bump stop and the femoral component provides mechanical feedback that limits hyperextension. As the knee approaches the safe range of motion, the bump stop engages to provide resistance, giving immediate feedback to the system to prevent further extension beyond the safe limit.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS20250152372A1Constrained knee joint prosthesis system and assembly

Publication Date: 2025.05.15 ZIMMER INC

AI summary

A prosthesis system for a constrained knee optionally including: a tibial bearing component configured to articulate with a femoral component; and a hinge post configured to couple with the femoral component and configured to be at least partially received by a well of the tibial bearing component. The hinge post includes one or more ramps and the tibial bearing component includes a riding feature configured to interact with the one or more ramps to rotate the hinge post during distraction of the hinge post from the tibial bearing component.