Knee Endoprosthesis Spherical Condyle Rotation
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Solution Overview
Problem
Knee joint endoprostheses with simple hinge joints restrict mobility due to their inability to replicate the complex kinematics of the natural knee joint, leading to patient complaints of limited mobility.
Innovation Solution
A knee joint endoprosthesis design featuring a tibia part, a femur part with spherical condyle surfaces, and a meniscus part with matching curved joint surfaces, allowing for rotational movement about a longitudinal axis in addition to flexion, thereby enhancing congruence and minimizing wear, with optional anti-twist arrangements and snap-action mechanisms for secure fixation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple hinge joint is used for the connecting device, then the structure is simple and easy to manufacture, but the mobility is restricted and cannot replicate complex knee joint kinematics
Solution Approach 1:
The femur condyle surface is designed as a spherical surface section with radius R1, and the meniscus joint surface is designed as a corresponding curved surface with radius R2. This spherical geometry enables the femur part to rotate relative to the tibia part about a rotational axis while maintaining congruent contact, thereby achieving complex knee joint kinematics including rotation in addition to flexion, without requiring a complex multi-axial mechanism
2Ease of manufacture
If a hinge joint is used for the connecting device, then the manufacturing is easy, but the kinematic complexity is insufficient to match natural knee joint movement
Solution Approach 1:
The spherical condyle surface and corresponding curved meniscus joint surface create a ball-and-socket type articulation that is relatively simple to manufacture compared to complex multi-axial mechanisms, yet enables sophisticated kinematics including rotation about a longitudinal axis and flexion, closely matching natural knee joint movement patterns
Solution Approach 2:
The connecting device transitions from a fixed hinge joint to a dynamic articulation where the femur part can rotate relative to the tibia part about a rotational axis. This dynamic capability allows the prosthesis to adapt to varying movement patterns and replicate the complexity of natural knee kinematics while maintaining manufacturing feasibility
3Ease of operation
If the femur condyle surface and meniscus joint surface are formed with spherical geometry, then rotational movement is enabled and mobility is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The femur condyle surface is formed as a spherical surface section with radius R1, and the meniscus joint surface is formed as a corresponding curved surface with radius R2. These spherical geometries are designed to be congruent to each other, enabling smooth rotational movement of the femur part relative to the tibia part while maintaining stable contact. The spherical geometry simplifies the manufacturing process compared to complex freeform surfaces, as spherical surfaces can be produced with standard machining techniques and spherical grinding tools, thereby reducing the actual manufacturing precision requirements despite the improved mobility
Data Source
AI summary
The invention relates to a knee joint endoprosthesis has a tibia part, a femur part, a meniscus part arranged on the tibia part in mutually non-rotatable manner and a connecting device for connecting the tibia part to the femur part in articulated manner. Said femur part comprises at least one femur condyle having a femur condyle surface. Said meniscus part comprises at least one upper surface which faces the femur part and has at least one meniscus joint surface which touches the femur condyle surface of the at least one femur condyle. Said femur part and the tibia part are mounted such as to be rotatable relative to each other about a rotational axis.