Tibial Insert Post Geometry for Stable Medial Pivot Knee Motion
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Solution Overview
Problem
Existing orthopaedic knee prostheses experience unnatural anterior translation and instability due to soft tissue forces during flexion, leading to undesirable motion and kinematic issues.
Innovation Solution
An orthopaedic system with an insert featuring asymmetric articular surfaces and a post configuration that allows for controlled medial pivoting of the femoral component, utilizing a cam mechanism to provide stability through controlled contact points and conforming surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional symmetric tibial insert is used, then the structure is simple and easy to manufacture, but the femoral component exhibits unnatural anterior translation and instability during flexion
Solution Approach 1:
The patent applies asymmetry by designing the tibial insert with asymmetric articular surfaces where the medial articular surface has a different geometry than the lateral articular surface. Specifically, the medial surface includes a post that extends into the femoral component's cam, while the lateral surface has a different configuration. This asymmetric design allows the femoral component to pivot medially during flexion, preventing unnatural anterior translation and improving stability.
Solution Approach 2:
The patent segments the tibial insert into distinct functional zones: a medial articular surface with a post, a lateral articular surface with different geometry, and an anterior lip structure. This segmentation allows each zone to perform its specific function - the post provides medial pivot stability, the lateral surface allows lateral movement, and the anterior lip controls anterior translation, collectively resolving the stability-complexity contradiction.
2Ease of operation
If soft tissue forces are allowed to act freely on the femoral component, then the prosthesis maintains ease of operation and natural movement, but unwanted anterior translation and paradoxical motion occur
Solution Approach 1:
The patent introduces the post on the medial articular surface as an intermediary element between the femoral component and the tibia. This post acts as a mediator that controls and guides the interaction between soft tissue forces and the femoral component, allowing natural movement while preventing unwanted anterior translation by providing a stable pivot point during flexion.
Solution Approach 2:
The patent implements dynamic control by designing the asymmetric articular surfaces to adaptively respond to loading conditions. During flexion, the cam-femoral component engages with the post, dynamically changing the kinematic behavior from anterior translation to medial pivot. This dynamic adaptation allows the prosthesis to maintain ease of operation while improving control over femoral component motion.
Data Source
AI summary
An orthopaedic system includes a tibial insert and a femoral component configured to articulate on the tibial insert. The tibial insert includes a pair of articular surfaces spaced apart by a post. The femoral component includes a pair of femoral condyles spaced apart by a notch in which a cam is located. During flexion, the cam of the femoral component is configured to contact the post of the tibial insert. The dwell point of the medial articular surface of the tibial insert is located, relative to the contact point between the post and tibial insert, to improve stability of the femoral component.