Customized Knee Prosthesis Asymmetric Design
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing custom knee implants fail to account for the asymmetric characteristics of femoral condyles and tibial plateau, leading to suboptimal functionality and limited flexion range due to the reliance on symmetric designs and incomplete anatomical data from arthritic knees.
Innovation Solution
A method for customizing knee prostheses using MRI and CT images to identify key landmarks and generate asymmetric implant profiles that mimic the pre-arthritic condition of the knee, incorporating elliptical cam parameters for 3D rotation during flexion and extension.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If symmetric implant designs are used, then manufacturing simplicity is maintained, but anatomical accuracy and functional performance deteriorate
Solution Approach 1:
The patent applies asymmetry by designing implant components that mirror the natural asymmetric geometry of healthy femoral condyles and tibial plateaus. The implant includes asymmetric femoral condyles with different radii of curvature and asymmetric tibial plateaus with non-uniform thickness distribution, matching patient-specific pre-arthritic anatomy rather than using symmetric designs.
Solution Approach 2:
The patent implements local quality by customizing specific regions of the implant to match local anatomical variations. Each femoral condyle has locally adapted curvature and shape, the tibial plateau has region-specific thickness and contour, and the articular surfaces are locally tailored to replicate pre-arthritic geometry, ensuring anatomical fidelity throughout the implant structure.
2Manufacturing precision
If asymmetric implant designs are used, then anatomical accuracy is improved, but device complexity increases
Solution Approach 1:
The patent applies preliminary action by obtaining and analyzing pre-arthritic MRI or CT images before implant design to establish baseline anatomical parameters. The system performs preliminary 3D reconstruction of the patient's native knee geometry, identifies key anatomical landmarks, and calculates asymmetric parameters (AP asymmetry, ML asymmetry, axial asymmetry) before generating the custom implant design.
Solution Approach 2:
The patent implements parameter changes by quantifying specific asymmetric parameters from imaging data and using these parameters to drive implant geometry generation. Key parameters include anterior-posterior asymmetry ratios, medial-lateral asymmetry ratios, axial asymmetry angles, and radii of curvature that are extracted from pre-arthritic anatomy and applied to customize the implant dimensions and shape.
3Reliability
If pre-arthritic joint parameters are used, then functional equivalence is achieved, but data availability deteriorates due to arthritis damage
Solution Approach 1:
The patent applies inversion by working backward from the available post-arthritis anatomy to infer the pre-arthritic geometry. Instead of directly measuring healthy anatomy, the system uses the remaining bone structures, ligament attachments, and joint line orientations in the arthritic knee to reverse-engineer the original asymmetric parameters and reconstruct the pre-arthritic joint geometry for implant design.
Solution Approach 2:
The patent implements copying by creating a digital 3D replica of the patient's pre-arthritic knee anatomy from imaging data. The system generates virtual models of the femur and tibia with accurate asymmetric geometry, which are then used as templates for implant design, allowing the implant to replicate the copied pre-arthritic anatomical features without requiring direct measurement of healthy tissue.
4Ease of operation
If asymmetric implant profiles are generated, then flexion range is improved, but manufacturing complexity increases
Solution Approach 1:
The patent applies dynamics by designing implant articular surfaces with optimized curvature profiles that enable dynamic motion ranges exceeding 140° of flexion. The asymmetric femoral condyles and tibial plateau geometries are specifically configured to facilitate natural knee kinematics through the full range of motion, allowing dynamic adaptation during flexion and extension cycles.
Data Source
AI summary
A computer-aided method, using a pre-operative planning software tool and patient-specific images, establishes implant parameters that customize selection of a total knee replacement prosthesis. The computer system determines from coronal, axial and sagittal image slices of a knee joint a neutral boundary axis, a set of epicondylar and trochlear features that define an elliptical cam, and a medial-lateral tibial slope, then defines from overlapping condylar and trochlear circles an ellipse with eccentricity 0.25 and focal points coincident with the circles. A knee prosthesis has a femoral component as an elliptical cam with dimensions defined by the ellipse, and has tibial and patellar components interacting with the femoral component as cam followers under knee flexion. A prosthesis is selected from a set with differing coronal asymmetry angle α to closely match the patient a as estimated from the images.