Tibial Insert Post Geometry for Stable Medial Knee Pivoting
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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, providing stability through a cam-post mechanism and conforming surfaces to mimic natural joint movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a fixed tibial insert is used to limit movement, then stability is improved, but natural kinematics and ease of operation deteriorate
Solution Approach 1:
The tibial insert transitions from a fixed configuration to a dynamic design with a mobile posterior stabilizing cam that can pivot and rotate. This allows the insert to adapt its position and orientation during knee flexion, providing stability when needed while enabling natural kinematic movement when required, thus resolving the contradiction between stability and natural kinematics.
Solution Approach 2:
The mobile posterior stabilizing cam changes its spatial parameters (position, orientation) relative to the tibial insert during knee flexion. By allowing the cam to pivot and rotate, the system dynamically adjusts the articulation parameters to maintain stability while preserving natural movement patterns, addressing both requirements simultaneously.
2Ease of operation
If a mobile tibial insert is used to increase freedom of movement, then ease of operation is improved, but stability deteriorates
Solution Approach 1:
The mobile posterior stabilizing cam provides dynamic stability through its controlled pivoting and rotating motion. The cam maintains contact with the femoral component during flexion while allowing controlled movement, thus providing stability without restricting natural kinematics, resolving the contradiction between freedom of movement and stability.
3Manufacturing precision
If the cam engages the post at a distance greater than 5mm from the anterior surface, then manufacturing precision is improved, but stability deteriorates
Solution Approach 1:
The system allows the cam to pivot and rotate, changing the engagement parameters dynamically. This dynamic engagement maintains stability during knee flexion while accommodating manufacturing tolerances, as the cam can adjust its position within a controlled range rather than requiring precise fixed positioning, thus resolving the contradiction between manufacturing precision and stability.
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.