Posterior Stabilized Knee Prosthesis Saddle Cam Design
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Solution Overview
Problem
Conventional posterior cruciate substituting knee designs remove excessive bone and experience deformation issues in the tibial insert's anterior face, leading to stress concentration and potential mechanical failure.
Innovation Solution
The design modifies the anterior cam surface of the femoral component and the anterior face of the tibial insert to a saddle-shaped configuration, reducing bone removal and stress on these surfaces, with a femoral component intercondylar portion having an increased box angle and a cylindrical shape, and a tibial post with a convex-concave radius curvature mismatch to distribute contact stress evenly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional posterior cruciate substituting knee designs are used, then the prosthesis provides stable knee replacement, but excessive bone is removed from the femur
Solution Approach 1:
The patent modifies the geometric parameters of the intercondylar box, specifically increasing the box angle from conventional values to at least 28 degrees, and changing the shape from rectangular to cylindrical. These parameter changes allow the prosthesis to achieve stable posterior cruciate substitution while reducing bone removal volume by 37% compared to conventional designs.
Solution Approach 2:
The patent transitions from a rectangular intercondylar box shape to a cylindrical shape with curved surfaces. This spheroidality principle applies by replacing sharp corners and flat surfaces with curved geometries, which reduces stress concentration points and allows for more efficient bone preservation while maintaining the mechanical function of the prosthesis.
2Ease of manufacture
If conventional flat cam surfaces are used, then the manufacturing is simple, but stress concentration occurs leading to deformation of the tibial post
Solution Approach 1:
The patent replaces the conventional flat cam surface with a saddle-shaped surface that has curved geometries in both transverse and sagittal directions. This curvature distributes contact stresses more evenly across the cam-post interface, preventing stress concentration that would otherwise lead to tibial post deformation and mechanical failure, while still being manufacturable using standard polishing techniques.
Solution Approach 2:
The saddle-shaped cam surface provides different radii of curvature in different directions (transverse vs. sagittal), creating locally optimized stress distribution. The surface has a first radius of curvature in the transverse direction and a second radius of curvature in the sagittal direction, allowing the cam surface to better match the contact geometry and distribute loads appropriately in each direction.
Data Source
AI summary
A femoral component for a knee joint prosthesis is formed of a body having an anterior side, a posterior side, and pair of laterally spaced condylar portions. The femoral component includes an intercondylar portion that joins the condylar portions and includes a recess. The intercondylar portion has an arcuate shaped roof that extends between a pair of opposing side walls. The arcuate shaped roof is formed so as to be defined by a single radius.