NURBS Knee Prosthesis for Natural Motion
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Solution Overview
Problem
Existing total knee replacement prostheses do not accurately replicate the complex motion path of the natural knee, leading to unnatural motion, undue tension, and increased wear and loosening, as they are often designed with simple geometries that fail to account for femoral translation and tibial rotation.
Innovation Solution
A total knee replacement prosthesis utilizing high-order non-rational B-spline surfaces (NURBS) to create articulating surfaces that mimic the natural knee's motion, allowing for flexion, translation, and rotation, with the femoral component and tibial component designed to replicate the complex geometry of the natural knee joint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If simple geometries are used for prosthetic components, then manufacturing is easier and device complexity is reduced, but the prosthesis cannot accurately replicate the complex motion path of the natural knee
Solution Approach 1:
The patent applies high-order NURBS surfaces to define the articulating surfaces of the femoral and tibial components, enabling precise control over complex curvatures and motion paths. This mathematical surface definition allows the prosthesis to replicate natural knee kinematics including femoral translation and tibial rotation while maintaining manufacturability through computer-aided design and manufacturing processes.
2Manufacturing precision
If complex geometries are used to accurately replicate natural knee motion, then motion accuracy is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent uses NURBS surfaces to create a mathematical copy of the natural knee's complex geometry and motion path. By defining the articulating surfaces with high-order mathematical equations that replicate natural knee kinematics, the invention captures the essential motion characteristics without requiring physical copies of anatomical structures, thus reducing manufacturing complexity while maintaining accuracy.
3Device complexity
If simple hinge design is used allowing only pivotal rotation, then device complexity is reduced, but reliability decreases due to high rotational stresses and unnatural motion
Solution Approach 1:
The patent transitions from a static hinge design to a dynamic articulating surface system where the femoral and tibial components have complex curved surfaces that naturally guide motion. The NURBS-defined surfaces enable femoral translation and tibial rotation during flexion, distributing stresses more naturally and reducing peak loads that lead to loosening and failure, thereby improving reliability while maintaining reasonable design simplicity.
Data Source
AI summary
A knee replacement prosthesis comprising a femoral component and a tibial component that enable anterior-posterior translation of the femur relative to the tibia and enable the tibia to rotate about its longitudinal axis during flexion of the knee. The femoral component connects to the distal end of a resected femur and includes medial and lateral condyles having distal, articulating surfaces, and a patellar flange having a patellar articulating surface. The tibial component connects to the proximal end of a resected tibia and includes a proximal bearing surface with medial and lateral concavities that articulate with the medial and lateral condyles. The condylar articulating surfaces and the said concavities are substantially defined by non-uniform, rational B-spline surfaces (NURBS).