Posterior-Stabilized Knee Prosthesis Radii Scaling for Consistent Kinematics
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Solution Overview
Problem
Existing posterior stabilized knee prostheses exhibit size-dependent kinematic behavior inconsistencies due to varying radii of curvature in femoral and tibial components, leading to unpredictable prosthetic movement and roll-back behavior.
Innovation Solution
The radii of curvature in the condyle and bearing surfaces of the femoral and tibial components are designed to increase monotonically with component size, ensuring a homogeneous and predictable kinematic behavior across different component combinations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If differently sized femoral and tibial components are combined to accommodate different patient anatomies, then adaptability is improved, but kinematic behavior consistency deteriorates due to size-dependent variations in radii of curvature
Solution Approach 1:
The patent applies parameter changes by systematically varying the radii of curvature parameters across different component sizes. Specifically, the condyle surface radii (R1, R2, R3) and bearing surface radii (R4, R5) are designed to increase monotonically with component size, ensuring that larger components have proportionally larger radii. This parameter scaling approach maintains consistent kinematic behavior across the full range of component sizes while accommodating different patient anatomies.
Solution Approach 2:
The patent applies local quality by designing different radii of curvature at different locations on the condyle and bearing surfaces. Each surface has multiple radii (R1, R2, R3 for condyle; R4, R5 for bearing surface) that are optimized for their specific functional zones. This local optimization ensures that each region contributes appropriately to the overall kinematic behavior, maintaining consistency across different component size combinations.
2Ease of manufacture
If the radii of curvature vary across different component sizes, then manufacturing flexibility is improved, but prosthetic movement predictability deteriorates
Solution Approach 1:
The patent resolves this contradiction by establishing systematic parameter change rules where radii of curvature increase monotonically with component size. The condyle radii (R1, R2, R3) and bearing surface radii (R4, R5) follow defined progression patterns across sizes S1-S9, allowing manufacturers to produce varied sizes while ensuring predictable roll-back behavior and kinematic consistency through the established parameter relationships.
Solution Approach 2:
The patent applies equipotentiality by creating proportional relationships between radii across different sizes. The monotonic increase pattern ensures that larger components maintain the same kinematic characteristics as smaller ones, effectively creating an 'equipotential' state where kinematic behavior is consistent regardless of size. This allows manufacturing flexibility while preserving movement predictability.
3Stability of the object's composition
If monotonically increasing radii of curvature are used across component sizes, then kinematic behavior homogeneity is improved, but design complexity increases
Solution Approach 1:
The patent manages design complexity through systematic parameter changes where radii (R1-R5) follow monotonic increase patterns across sizes. While multiple radii parameters exist, their relationships are governed by consistent rules (each radius increases with size), which simplifies the design process compared to arbitrary variations. This systematic approach achieves kinematic homogeneity while keeping design complexity manageable through pattern recognition.
Solution Approach 2:
The patent applies universality by creating a standardized radii progression pattern that works across all component sizes (S1-S9) and both femoral and tibial components. The same monotonic increase principle applies to all radii (R1-R5), making the design methodology universal and reusable throughout the product line, thereby reducing overall design complexity despite the multiple parameters involved.
Data Source
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AI summary
The invention relates to a posterior stabilized knee prosthesis system (1), comprising a set (10) of femoral components (100) of different sizes (F1 to F9) configured for attachment to distal femurs of different sizes, each femoral component having a pair of spaced apart condyles (111, 112) defining an intercondylar notch (103) therebetween, and having a posterior cam (104) positioned in the intercondylar notch, wherein at least one of the condyles has a condyle surface (101, 102) curved in the sagittal plane (E) with multiple at least substantially tangential radii of curvature (R0, R1 to R5); and a set (20) of tibial components (200) of different sizes (T1 to T9) configured for attachment to proximal tibiae of different sizes, each tibial component having a bearing surface (201 202) curved in the sagittal plane with multiple at least substantially tangential radii of curvature (AR, PR), and having a post (203) extending upwardly from the bearing surface; wherein each size of femoral component is engageable to at least one size of tibial component to articulate by contact between the condyle surface and the bearing surface and/or by contact between the cam and the post. According to the invention the radii of curvature of the condyle surface each increase monotonically across increasing size of the femoral components, and the radii of curvature of the bearing surface each increase monotonically across increasing size of the tibial components.