Asymmetrical Cam Knee Prosthesis Reducing Post Height and Wear
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Solution Overview
Problem
Existing knee prostheses struggle to replicate the complex kinematic movements of a natural knee joint, particularly in terms of rolling, sliding, and rotational movements between the femoral condyles and tibia, often requiring high posts to support upward cam movement during flexion, which can lead to increased wear and soft tissue strain.
Innovation Solution
A knee prosthesis design featuring a femoral component with an asymmetrical cam and a tibial component with a post, where the cam's curvature and post interaction allow for rotational movement by engaging at different flexion angles, reducing the need for high posts and enhancing anatomical movement, with the cam moving downward along the post as flexion increases, allowing for more natural kinematic patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high posts are used to support upward cam movement during flexion, then the prosthesis can maintain structural stability, but wear on the tibial post increases and soft tissue strain increases
Solution Approach 1:
The patent inverts the traditional cam movement direction. Instead of the cam moving upward along the post during flexion (as in conventional designs), the cam moves downward along the post. This inversion allows the cam to engage the post at lower positions, eliminating the need for high posts and thereby reducing wear on the tibial post and strain on surrounding soft tissues while maintaining structural stability throughout the flexion arc.
Solution Approach 2:
The patent changes the geometric parameters of the cam, specifically implementing an asymmetrical cam profile with different curvatures on its medial and lateral sides. This parameter change allows the cam to rotate about the post during flexion, enabling the cam to maintain engagement with the post at lower positions throughout the flexion arc, thereby reducing the required post height and associated wear and soft tissue strain.
2Ease of manufacture
If conventional symmetrical cam designs are used, then manufacturing is simplified, but anatomical movement replication is inadequate
Solution Approach 1:
The patent employs an asymmetrical cam design where the cam profile differs on its medial and lateral sides. Specifically, the cam has a first curvature on one side and a second curvature on the other side, with different radii of curvature. This asymmetry enables the cam to replicate the complex anatomical movement patterns of the natural knee, including rollback and rotation, while still being manufacturable using conventional machining processes.
Solution Approach 2:
The patent utilizes curved surfaces on the cam, with specific radii of curvature designed to match anatomical knee kinematics. The cam incorporates a first curvature with a first radius and a second curvature with a second radius, allowing the cam to roll and rotate along the tibial post in a manner that replicates natural knee movement patterns, thereby improving anatomical movement accuracy.
3Reliability
If the cam is designed to move upward during flexion, then engagement with the post is maintained, but the post height must be increased
Solution Approach 1:
The patent inverts the traditional cam movement direction. Instead of the cam moving upward along the post during flexion (as in conventional designs), the cam moves downward along the post. This inversion allows the cam to engage the post at lower positions, eliminating the need for high posts and thereby reducing wear on the tibial post and strain on surrounding soft tissues while maintaining structural stability throughout the flexion arc.
Data Source
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AI summary
A knee prosthesis includes a femoral component (200) having two condyles (201, 202) and an asymmetrical cam (210) extending between the condyles. The cam has a medial end (212) and a lateral end (214). The knee prosthesis also includes a tibial component (100) having bearing surfaces (101, 102) and a post (110) disposed between the bearing surfaces. The femoral component and tibial component are engageable by contact between the femoral condyles and tibial bearing surfaces, and by contact between the cam and post. The cam includes a first curvature (260) defined by a first plane (P1) passing through the cam, and a second curvature (270) defined by a second plane (P2) passing through the cam, the first curvature having a first vertex (261), and the second curvature having a second vertex (271), the distance between the first vertex and a medial plane (222) being greater than the distance between the second vertex and the medial plane.