Total Stabilized Knee Prosthesis Flared Surface Constraint
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Solution Overview
Problem
Current posterior stabilized and total stabilized knee prostheses do not adequately address the varied soft tissue balancing needs of patients with compromised soft tissue conditions, leading to surgical compromises and negative clinical results.
Innovation Solution
A total stabilized knee prosthesis design featuring a femoral component with condylar elements and a tibial component with articular surfaces that allow relative rotational movement and varus-valgus constraint through a post and compartment engagement, with flared inner and outer surface portions to reduce constraint during deep flexion, enabling better soft tissue balancing and stress distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If femoral cam surfaces are engaged by tibial post follower surfaces to prevent femoral anterior subluxation, then stability is improved, but relative rotational movement between femur and tibia is reduced
Solution Approach 1:
The cam surface and follower surface are designed to dynamically adapt their engagement throughout the range of motion. During deep flexion, the flared surfaces allow disengagement to permit rotation, while during extension they engage to provide stability. This dynamic behavior resolves the contradiction between maintaining stability and allowing rotational movement.
Solution Approach 2:
The geometry of the cam and follower surfaces changes along their engagement path. The surfaces are flared outwardly at specific regions to alter the engagement parameters, allowing the mechanism to transition between constrained and unconstrained states based on the knee's flexion angle, thus resolving the contradiction between stability and rotational freedom.
2Stability of the object's composition
If the medial and lateral width of the femoral compartment and tibial post are controlled to limit varus-valgus movement, then stability is improved, but the range of relative rotation is reduced
Solution Approach 1:
The compartment and post dimensions are designed to create a dynamic constraint system that adapts to flexion angle. At extension, the full width provides varus-valgus stability, while at deep flexion, the flared surfaces reduce engagement to allow rotation, resolving the contradiction between stability and rotational range.
Solution Approach 2:
Different regions of the compartment and post have different functional qualities. The central region provides stability through controlled width, while the flared outer regions at deep flexion allow rotational movement. This local differentiation resolves the contradiction between stability and rotation.
3Stability of the object's composition
If constraint is provided against uncontrolled relative rotational movement and varus-valgus movements, then stability is improved, but stress on articular surfaces increases
Solution Approach 1:
The flared cam and follower surfaces act as intermediaries that redistribute constraint forces. Instead of concentrating stress at a single point, the flared geometry distributes forces across a larger surface area during deep flexion, reducing peak stresses while maintaining overall stability through the constraint mechanism.
Solution Approach 2:
The contact area and force distribution parameters change throughout the range of motion. During extension, constraint forces are concentrated for maximum stability. During deep flexion, the flared surfaces increase contact area and reduce force concentration, lowering stress on articular surfaces while maintaining constraint.
Data Source
AI summary
An improvement in a total stabilized knee prosthesis wherein stabilization against uncontrolled relative rotation between a femoral component and a tibial component about a longitudinal axis, during articulation of the knee prosthesis, is attained by the engagement of a femoral stabilizing compartment with a tibial stabilizing post, the improvement including profile contour configurations on inner surface portions of condylar surfaces and on corresponding outer surface portions of tibial articular surfaces, the profile contour configurations being flared outwardly, in directions away from an intermediate sagittal plane, along posterior aspects of the condylar surfaces and the tibial articular surfaces engaged through deep flexion for providing an engagement between the profile contour configurations sufficient to establish a desired level of constraint against relative rotational movement between the femoral component and the tibial component about the longitudinal axis enabling a decrease in the level of constraint provided by the engagement between the post and the compartment during articulation through deep flexion.