Knee Endoprosthesis Migrating Joint Center Patella Guidance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing knee joint endoprostheses fail to maintain optimal physiological kinematics and patella guidance, especially in cases with poor ligament situations or missing cruciate ligaments, leading to posterior displacement of the femoral component and reduced flexion angle between the tibia and femur, which can cause patella subluxation and increased wear.
Innovation Solution
A knee joint endoprosthesis with a migrating rotational joint center that moves from anterior to posterior along a curved path as the knee flexes, allowing for forced eccentric rotation and preventing sliding between the femur and meniscus parts on the lateral side, enabling better patella guidance and reduced wear by eliminating the need for a posterior projection mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a non-coupled bicondylar knee implant with a fixed meniscus component is used, then unconstrained axial rotation of the tibia is enabled, but the trochlea alignment and patella guidance are compromised
Solution Approach 1:
The patent implements a dynamic coupling mechanism between the femoral and tibial components that allows the degree of rotational constraint to vary with knee flexion angle. At extension, the components are more constrained to ensure proper trochlea alignment, while at flexion, the coupling allows greater rotational freedom to accommodate physiological movement and compensate for ligament deficiencies.
Solution Approach 2:
The invention changes the geometric parameters of the joint surfaces, specifically designing the femoral component with a trochlear groove and the tibial component with a corresponding track that guide patellar movement. The curvature and orientation of these surfaces are optimized to maintain proper alignment during the range of motion, resolving the conflict between rotation freedom and alignment stability.
2Loss of time
If a post and cam mechanism is used to force posterior femoral displacement, then flexion angle is increased, but the trochlea alignment is compromised and wear is increased
Solution Approach 1:
The patent employs curved and spherical surface geometries in the femoral and tibial components to guide movement through geometry rather than mechanical stops. The femoral condyles have spherical articular surfaces that roll on the tibial platform, and the trochlear groove has a curved profile that guides the patella, eliminating the need for post-cam mechanisms while maintaining proper alignment and increasing flexion angle through optimized surface contact.
3Loss of time
If the meniscus part is made larger to accommodate projection/cam mechanisms, then posterior displacement is achieved, but the overall implant size increases and surgical complexity increases
Solution Approach 1:
The invention extracts and eliminates the post-cam mechanism from the implant design, achieving posterior femoral displacement and increased flexion angle through optimized spherical surface geometry and ligament-balancing principles. This simplifies the implant structure, reduces the number of components, and decreases surgical complexity while maintaining the desired kinematic behavior.
4Stability of the object's composition
If a stationary joint center is used on the medial side, then rotational stability is improved, but physiological kinematics are compromised
Solution Approach 1:
The patent implements a dynamic joint center that migrates from a stationary position in extension to a more posterior position in flexion, mimicking the physiological movement of the native knee. The femoral condyles are designed with spherical articular surfaces that allow the effective center of rotation to shift during the range of motion, maintaining both stability and physiological kinematics.
Solution Approach 2:
The invention uses spherical articular surfaces on the femoral condyles that roll on the tibial platform, creating a natural migration of the joint center during movement. The curvature of these surfaces is optimized to reproduce the physiological path of the joint center, providing both rotational stability and accurate kinematic reproduction without requiring complex mechanical guidance mechanisms.
Data Source
AI summary
The invention relates to a knee joint endoprosthesis, comprising a femur part and a meniscus part mounted relative thereto and movably thereon, which femur part comprises a medial and a lateral condyle, which have a medial and a lateral condyle surface, and which meniscus part has a medial and a lateral joint surface against which the medial and lateral condyle surfaces are seated at least partially, wherein the medial condyle and the medial joint surfaces are shaped to design a rotational joint having a rotational joint center. In order to improve said knee joint endoprosthesis such that bending of the knee joint is improved so as to enable optimal guidance of the patella through the trochlea, and thereby maintain the physiological kinematics of the healthy knee joint, according to the invention a rolling motion guide device is provided for the defined rolling of the lateral condyle surfaces and the lateral joint surfaces against one another along a curved path around the rotational joint center, said path being defined depending on a flexion angle between the femur part and meniscus part.