Hinged Knee Prosthesis With Eccentric Condyles for Natural Kinematics

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Solution Overview

Problem

Existing hinged knee prostheses fail to accurately replicate normal kinematics, particularly anterior/posterior translation and axial rotation, often leading to increased wear and stress on the implant and surrounding soft tissue.

Innovation Solution

A hinged knee prosthesis design featuring a tibial component with a bearing surface and a femoral component that includes medial and lateral condyles with eccentric sagittal curvature surfaces, allowing for controlled axial rotation and anterior/posterior translation through a range of flexion, guided by a transverse axle hinge pin and sleeved post system.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If a cam mechanism against the joint-linking mechanism is used to force A/P translation, then anterior/posterior translation motion is restored, but wear increases and implant life span decreases

Engineering Contradiction:

ImproveA/P translation motionVSAvoidimplant life span

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent employs curved articular surfaces on the femoral component that articulate with the tibial bearing surface. The curvature of these surfaces naturally guides A/P translation and axial rotation through geometric constraints, replacing the need for cam mechanisms with point/line contact. This distributed surface contact reduces wear while maintaining the desired kinematic motion.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The invention replaces the mechanical cam-and-post system with a geometry-based guidance system. The eccentric curvature of the femoral condyles and the shape of the tibial bearing surface work together to produce the desired A/P translation and rotation through pure geometric interaction, eliminating the need for separate cam mechanisms and reducing contact stresses.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Ease of operation

If a rotating platform is used to address axial rotation, then rotation freedom is allowed, but soft tissue damage occurs when forcing motion

Engineering Contradiction:

Improveaxial rotationVSAvoidsoft tissue damage

Core Design Contradiction:

Ease of operationVSObject-affected harmful factors

Solution Approach 1:

The eccentric curvature of the femoral condyles creates a natural rotation center that is offset from the mechanical hinge axis. This geometric configuration allows the prosthesis to rotate smoothly through axial motion guided by the curved surfaces, reducing the need for soft tissues to force rotation and thereby minimizing soft tissue damage.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The patent changes the rotational parameters by allowing the center of rotation to move relative to the hinge axis through the eccentric curvature design. This dynamic adjustment of the rotation center accommodates natural knee kinematics without requiring excessive force from soft tissues, thus preventing damage.

Inventive Principle:

Principle #35Parameter changes

3Ease of operation

If the femoral component is allowed to translate posteriorly without contact control, then A/P translation occurs, but contact between femoral and tibial components is lost

Engineering Contradiction:

ImproveA/P translationVSAvoidcontact maintenance

Core Design Contradiction:

Ease of operationVSStability of the object's composition

Solution Approach 1:

The curved articular surfaces are designed with specific radii and centers of curvature that ensure continuous contact between the femoral and tibial components throughout the range of motion. The geometry is configured so that as the femur translates posteriorly during flexion, the curved surfaces maintain tangential contact, preventing loss of articulation while allowing natural A/P translation.

Inventive Principle:

Principle #14Spheroidality (Curvature)

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 design achieves kinematically-correct prosthetic motion, reducing wear on the implant and minimizing forces on remaining soft tissue, thereby enhancing the longevity and comfort of the prosthesis.

Implementation Method 1

The medial and lateral condyles have a sagittal curvature surface configured to induce axial rotation on the bearing surface of the tibial component

Methodology Applied

Scientific EffectEccentric curvature geometry: Eccentric

Implementation Method 2

The bearing surface of the tibial component is configured with an anterior portion and a posterior portion. The posterior portion of the bearing surface has a portion configured to guide the medial and lateral condyles of the femoral component

Methodology Applied

Scientific EffectGeometric guidance: Geometry

Data Source

PatentUS12383405B2Anatomical motion hinged prosthesis

Publication Date: 2025.08.12 SMITH & NEPHEW INC

AI summary

A hinged knee prosthesis comprises a tibial component and a femoral component. The tibial component is configured to attach to a tibia. The tibial component has a bearing surface. The femoral component is configured to hingedly attach to the tibial component and rotate relative to the tibial component. The femoral component comprises a medial condyle and a lateral condyle. The medial and lateral condyles have an eccentric sagittal curvature surface configured to rotate and translate on the bearing surface of the tibial component. A method of rotating a hinged knee through a range of flexion is provided. The method fixedly attaches a femoral component to a tibial component. Axial rotation of the femoral component is induced relative to the tibial component when the hinged knee is flexed.