Dual Pivot Knee Prosthesis for Stability and Flexion
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Solution Overview
Problem
Existing knee replacement designs fail to effectively stabilize abnormal motion patterns of arthritic knees, leading to high implant and bone stresses, poor durability, and inadequate strength.
Innovation Solution
A dual pivot knee prosthesis design featuring a femoral component with major and minor radii and a tibial component with hemispherical and curved trough recesses, allowing for initial external femoral rotation and later internal rotation, thereby aligning the quadriceps mechanism for strength and preventing bone impingement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional total knee arthroplasty designs are used, then the knee joint can be replaced with femoral and tibial components, but the abnormal motion patterns of arthritic knees are not stabilized, leading to high implant and bone stresses
Solution Approach 1:
The knee prosthesis employs a dynamic dual-pivot mechanism that transitions between lateral and medial pivot points during the flexion cycle. The femoral component features two condyles with different radii of curvature that sequentially engage with corresponding tibial recesses, allowing the pivot point to shift dynamically from lateral to medial compartment as the knee flexes, thereby stabilizing abnormal motion patterns while distributing stress throughout the articular surface
Solution Approach 2:
The femoral component is segmented into two distinct condyles (lateral and medial) with different geometric characteristics. The lateral condyle has a larger radius of curvature for initial engagement during extension, while the medial condyle with smaller radius engages during flexion. This segmentation allows each condyle to handle specific phases of motion, stabilizing abnormal motion patterns without concentrating stress on a single pivot point
2Duration of action of stationary object
If traditional knee replacement designs are used, then basic joint replacement is achieved, but durability is poor due to high stresses and inadequate strength
Solution Approach 1:
The dynamic dual-pivot mechanism distributes mechanical loads throughout the flexion cycle by transitioning between lateral and medial pivot points. This dynamic load distribution prevents stress concentration at any single location, thereby enhancing the durability of the prosthesis while maintaining adequate strength through continuous articular contact
Solution Approach 2:
The femoral condyles feature different radii of curvature designed to match corresponding tibial recess geometries. The lateral condyle with larger radius provides initial stability during extension, while the medial condyle with smaller radius enables controlled flexion. These curved spherical surfaces ensure continuous articular contact throughout motion, distributing stresses to enhance both strength and durability
3Adaptability or versatility
If single pivot point design is used, then the structure is simple, but it cannot accommodate the variable motion patterns required for different knee flexion activities
Solution Approach 1:
The knee prosthesis incorporates a dynamic dual-pivot mechanism that automatically adapts to different flexion activities through the sequential engagement of lateral and medial condyles. During low-flexion activities like walking, the lateral pivot dominates; during high-flexion activities like squatting, the medial pivot becomes active. This dynamic adaptation provides versatility across different activities without requiring complex external control mechanisms
Solution Approach 2:
The dual-pivot femoral-tibial interface serves multiple functions within a single integrated structure: it provides lateral pivoting for extension-phase stability, medial pivoting for flexion-phase motion, and transitions between both modes based on activity level. This multi-functionality achieves adaptability to various knee activities while maintaining a unified prosthesis design rather than requiring separate mechanisms for different motion patterns
Data Source
AI summary
An implantable, asymmetrical right or left knee prosthesis for the arthritic, aging, ligament-deficient knee comprising a femoral component, a tibial component and a patella component, forming three interactive knee compartments mainly the lateral, medial, and femoral patellar compartments, articulating together with a dual, axial pivot knee motion. This dual pivot motion pattern is accomplished by four femoral component radii coacting with four reciprocal proximal tibial surface recesses (in a variety of locations on the tibia based on surgeon choice and patient anatomy), accomplishing initial external femur rotation on the tibia (first pivot location), guiding alignment of the femoral-patellar groove with the patellar quadriceps muscle providing knee strength, durability, and stability. The second pivot point develops with the minor femoral radius in the opposite knee compartment to guide internal rotation of the femur on the tibia to prevent boney impingement of the femur on the tibia and allow deep flexion activities.