Knee Prosthesis Box-Post Geometry for Constrained Natural Articulation
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Solution Overview
Problem
Existing knee replacement implants do not provide a high degree of constraint while preserving natural interaction between femoral and tibial components over a range of motion, and modifying constraint levels is costly and tedious.
Innovation Solution
A versatile knee implant kit and prosthesis that includes a femoral component with a central box and a tibial component with a complementary post, allowing for constrained articulation and adjustable constraint levels through complementary concave and convex curved surfaces, enabling rotation about a single axis over a range of motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a hinge-based constraint implant is used to provide high constraint, then stability is improved, but natural interaction between femoral and tibial components is lost
Solution Approach 1:
The implant uses a dynamic box-post interface where the post can move within the box boundaries. The curved surfaces allow the post to rotate and translate along defined paths, providing constraint when needed while permitting natural motion ranges. This dynamic constraint adapts to the physiological range of motion rather than imposing fixed mechanical constraints.
Solution Approach 2:
The implant changes the constraint parameters through the geometry of curved surfaces. The box central surface and post central surface have specific curvature radii that define the arc of motion. By adjusting these geometric parameters, the implant provides constraint within a controlled range while preserving natural articulation outside that range.
2Stability of the object's composition
If a more constrained implant is required, then a new implant must be obtained, but this increases cost and complexity
Solution Approach 1:
The implant is designed with universal adaptability through the box-post interface that can accommodate different constraint requirements. The same basic implant structure can provide varying degrees of constraint depending on the surgical situation, eliminating the need for multiple specialized implant types and simplifying inventory and selection.
Solution Approach 2:
The implant is segmented into modular components including the femoral component with box, tibial component with post, and interchangeable inserts. This segmentation allows selective replacement or modification of specific components to adjust constraint levels without replacing the entire implant system.
3Ease of manufacture
If ligaments are sacrificed to address bone loss or trauma, then bone removal is enabled, but more constraint is required in the knee implant
Solution Approach 1:
The box-post interface acts as an intermediary constraint mechanism that compensates for lost ligamentous stability. The curved surfaces provide a mechanical mediator that guides and controls motion, replacing the function of sacrificed soft tissues while allowing the surgical approach needed for bone reconstruction.
Data Source
AI summary
A knee joint prosthesis includes a femoral component and a tibial component. The femoral component includes a medial condylar articulation surface, a lateral condylar articulation surface and a central box therebetween, the central box being enclosed on a bone-facing side of the femoral component and open on a tibial-facing side of the femoral component. The tibial component including a medial tibial articulation surface, a lateral tibial articulation surface and a post therebetween, the post being disposed within the central box of the femoral component. A concave curved surface portion of the box travels along a convex curved surface portion of the post over a range of motion of the tibial component relative to the femoral component such that an axis of rotation of the box of the femoral component and the post of the tibial component is coincident over the range of motion.