Knee Prosthesis Hyperbolic Paraboloid Surfaces
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Solution Overview
Problem
Existing total knee prostheses face challenges in achieving optimal tribological and kinematic compatibility, leading to wear issues and discomfort due to unidirectional movements, high pressure points, and instability, particularly during flexion and extension.
Innovation Solution
A novel total knee prosthesis design featuring a femoral implant with convex intercondylar notch and concave glenoid cavities forming complementary hyperbolic paraboloid surfaces, preventing roll-forward phenomena without abutments or cams, and including stabilization reinforcements to maintain stability and unconstrained kinematics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If postero-stabilized configuration with cam and abutment is used, then stability during flexion is improved, but movement becomes unidirectional and constrained causing abutment and repulsion sensations
Solution Approach 1:
The invention removes the cam and abutment elements from the prosthesis design, eliminating the constrained unidirectional movement mechanism while maintaining stability through alternative means (femoral component geometry and polyethylene insert design)
Solution Approach 2:
Instead of using active cam-abutment engagement to enforce stability, the invention inverts the approach by designing passive geometric congruence between the femoral component and polyethylene insert that naturally provides stability through contact surface mating
2Ease of operation
If guiding surfaces configuration without planar contact surfaces is used, then movement freedom is improved, but high pressure points are created accelerating wear
Solution Approach 1:
The invention employs curved, congruent contact surfaces between the femoral component and polyethylene insert, specifically the mating surfaces of the femoral component and the polyethylene insert that form a conformal interface to distribute loads and reduce wear
3Reliability
If high congruence between contact surfaces is used, then wear reduction is improved, but movement adaptability is reduced
Solution Approach 1:
The invention creates a dynamic interface where the femoral component can rotate and translate relative to the tibial component through the polyethylene insert, with the congruent surfaces adapting their contact pattern during movement while maintaining wear resistance
Data Source
AI summary
The present invention relates to a total knee prosthesis. This prosthesis includes a femoral implant (2) including two condyles (8, 9) delimiting between them an intercondylar notch (10), a tibial implant (3) intended to rest on the end of the tibia, and an articular insert (4) interposed between the tibial implant and the femoral implant and the upper surface of which (41) includes two glenoid cavities (18, 19) with an external profile (181, 191) congruent with the external profile (81, 91) of the condyles (7, 8) of the femoral implant and connected together through an interglenoidal connecting surface (20). According to the invention, the intercondylar notch (10) and the interglenoidal connecting surface (20) have congruent contact surfaces (101, 201) which are inscribed in two mating hyperbolic paraboloids and the contact surface (181, 191) of the glenoid cavities (18, 19) have in a horizontal section an ovoid shape and its inclined point (P) is located posteriorly to the line of larger width (L) of the insert.