Knee Prosthesis Intermediate Structure Concave Convex Transition
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Solution Overview
Problem
Current knee prostheses with posterior stabilization limit flexion to about 120°, leading to excessive polyethylene wear and lateral condylar subluxation due to the extreme posterior contact point, and fail to accommodate deeper flexion and condylar rotation, which is undesirable for patients needing higher range of motion.
Innovation Solution
A knee prosthesis design featuring a femoral component with lateral and medial condylar structures and an intermediate structure that transitions from a concave to a convex surface at the contact interface between 120° to 140° flexion, incorporating a post for posterior support to minimize impingement and allow deeper flexion without excessive wear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a posterior stabilized insert is used to provide posterior support, then stability is improved, but range of motion is limited to about 120°
Solution Approach 1:
The insert transitions from a concave surface to a convex surface at a specific flexion angle (120°-140°), changing the geometric parameters of the contact interface to enable deeper flexion while maintaining stability through the post engagement
2Length of moving object
If deeper flexion is allowed beyond 120°, then range of motion is improved, but polyethylene wear increases due to extreme posterior contact
Solution Approach 1:
The convex surface transition is designed to occur before extreme posterior contact would cause excessive wear, preemptively changing the contact geometry to redirect forces away from the posterior edge of the insert
Solution Approach 2:
The post acts as an intermediary structure that provides posterior support and stabilizes the femoral component during deep flexion, preventing unnatural motion that would lead to excessive polyethylene wear at the contact interface
3Length of moving object
If deeper flexion is allowed beyond 120°, then range of motion is improved, but lateral condylar subluxation occurs due to extreme posterior contact
Solution Approach 1:
The convex surface transition occurs before lateral condylar subluxation can occur, preemptively changing the contact geometry to maintain proper alignment during deep flexion
Solution Approach 2:
The post serves as a stabilizing intermediary that prevents lateral condylar subluxation by providing posterior support and constraining unnatural femoral component motion during deep flexion
Data Source
AI summary
A knee prosthesis is provided that allows for increased flexion. The knee prosthesis includes (a) a femoral component adapted to fit on a distal end of the femur which includes a lateral condylar structure and a medial condylar structure and (b) an intermediate structure configured to cooperate with a femoral component of a knee prosthesis. The intermediate structure includes at least one surface for contacting the femoral component and a transition of a sagittal curvature of the at least one contact surface from a concave surface into a convex surface at the contact interface of the femoral component and the intermediate structure when the knee is flexed at approximately 120° to 140°. The knee prosthesis minimizes impingement on the femoral posterior cortex in deep flexion, increases the dislocation safety factor and allows for easier reengagement of the articular surface should the femoral component externally rotate off of the tibial plateau.