Tibial Insert Post Recess for Knee Rotation
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Solution Overview
Problem
Current total knee replacement (TKR) designs fail to replicate the natural kinematics of the knee joint, particularly in terms of longitudinal rotation, due to limited space between the tibial insert post and the femoral box wall, which impairs the natural motion of the replaced knee.
Innovation Solution
The design incorporates a tibial insert post with a recess on its medial or lateral side, allowing for clearance during flexion and extension, enabling relative femoral and tibial rotation, while maintaining the width of the post to ensure strength and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the space between the insert post and the box walls is limited to increase insert post strength and contact area, then the insert post strength and contact area are improved, but the ability of the post to rotate longitudinally is impeded
Solution Approach 1:
The post is designed with non-uniform width: wider at the posterior end to maximize contact area and strength with the box wall, and narrower at the anterior end to enable longitudinal rotation. This local variation in geometry allows different regions of the post to serve different functions simultaneously.
Solution Approach 2:
The post is segmented into distinct regions with different widths along its length. The posterior portion maintains full width for strength, while the anterior portion is narrowed to create clearance for rotation, allowing the single post structure to perform multiple functions through spatial segmentation.
2Ease of operation
If the post width is reduced to allow longitudinal rotation, then the rotational motion is improved, but the contact surface between the post and posterior cam is reduced, leading to increased post deformation or wear
Solution Approach 1:
The post geometry is optimized with local quality variations: the posterior end maintains maximum width to ensure large contact surface area with the posterior cam for load-bearing, while the anterior end is narrowed to enable rotational clearance, allowing each region to be optimized for its specific function.
Solution Approach 2:
The solution moves from a uniform one-dimensional post design to a three-dimensional variable-cross-section design, where the width varies along the longitudinal dimension, enabling different functional requirements to be met at different positions along the post.
3Ease of operation
If the post width is reduced to allow rotation, then the rotational freedom is improved, but the strength and stability of the post are compromised
Solution Approach 1:
The post is designed with non-uniform cross-sectional dimensions along its length, maintaining full width at the posterior end for strength and stability, while narrowing at the anterior end to enable rotation, allowing the structure to be strong where strength is needed and flexible where rotation is required.
Solution Approach 2:
The post is functionally segmented into a strong posterior region for load transmission and a narrower anterior region for rotational clearance, allowing the single structural element to simultaneously provide both strength and rotational capability through spatial differentiation.
Data Source
AI summary
Tibial inserts and tibial femoral systems are provided for improved knee reconstruction systems. External rotation of a knee joint implant is enhanced by modifications to the post, providing a recess that allows clearance of the post against the corners of a box wall within the femoral component. The rotation provides for a more natural knee joint motion of the implant. The depth, size, and location of the post relief may be modified for certain applications to provide both improved rotational motion and constraint against undesirable motion of the knee.