Knee Prosthesis Cam Post Contact Area Design
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Solution Overview
Problem
Existing knee joint prostheses face instability at high flex angles due to insufficient contact area between the cam and post, leading to potential dislocation, as the contact is often restricted to point contact which cannot effectively bear the loads imposed by the cam.
Innovation Solution
A knee joint prosthesis design featuring a concave cam surface that contacts a convex post at high flex angles, increasing the contact area between the cam and post, thereby enhancing load-bearing capacity and stability, with the contact area ratio at high flex angles being significantly larger than at lower angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the cam and post are designed with rod or bar-like shapes for point contact, then the ability to maintain flexibility at lower flex angles is improved, but the load-bearing capacity and stability at high flex angles deteriorate due to insufficient contact area
Solution Approach 1:
The cam surface is designed with different curvatures in different regions: a first curvature (convex) in the region contacting the post at lower flex angles to maintain flexibility, and a second curvature (concave) in the region contacting the post at high flex angles to increase contact area and load-bearing capacity. This local differentiation of geometric properties resolves the contradiction between flexibility and strength requirements.
2Ease of operation
If the contact area between cam and post is minimized to point contact, then the flexibility and range of motion are improved, but the stability and resistance to dislocation deteriorate at high flex angles
Solution Approach 1:
The contact area between cam and post dynamically changes with flex angle. At lower flex angles, the convex cam surface provides point or line contact for maximum flexibility. At high flex angles, the concave cam surface engages with the post to provide a larger contact area for enhanced stability. This dynamic adaptation of contact characteristics resolves the contradiction between range of motion and stability.
3Adaptability or versatility
If the cam surface is convex at the contact point, then the flexibility and ease of rotation are improved, but the area of contact and load distribution deteriorate at high flex angles
Solution Approach 1:
The cam surface incorporates different curvature characteristics in different spatial regions. The convex region facilitates easy rotation at lower flex angles, while the concave region provides increased contact area at high flex angles. This local differentiation resolves the contradiction between ease of rotation and contact area.
4Device complexity
If the post and cam are designed with simple rod shapes, then the device complexity is reduced, but the ability to provide both point contact flexibility and area contact stability deteriorates
Solution Approach 1:
Instead of simple rod shapes, the cam is designed with controlled curvature variations - convex in some regions and concave in others. This curvature-based solution provides the dual functionality of point contact and area contact within the same continuous surface, maintaining structural simplicity while enhancing reliability across different flex angles.
Data Source
AI summary
A knee joint prosthesis which comprises a tibial component (4, 6) and a femoral component (2). The femoral component has condyles (14, 16) which act against the tibial component, directly or indirectly, during flexing of the knee. A cam (20) on the femoral component acts against a post (26) on the tibial component at high flex angles. The surface of the post which is contacted by the cam at high flex angles is convex when the post viewed generally perpendicular to the tibial bone contact and bearing surfaces, and the femoral bearing surface which is provided by the cam, where it contacts the convex surface of the post at high flex angles, is locally concave (32) when viewed along the surface of the post which contacts the cam so that the area of contact between the post and the cam is greater at high flex angles than at lower flex angles.