Asymmetrical Condylar Knee Prosthesis for Enhanced Flexion
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Solution Overview
Problem
Current knee prostheses for total knee replacement surgeries do not adequately replicate the complex motion of the natural knee joint, limiting flexion to 70° to 80° due to simple hinge-based designs that fail to accommodate translation and lateral rotation, and are not adaptable to minor surgical positioning errors.
Innovation Solution
A knee replacement prosthesis with a femoral component and tibial component design that enables anterior-posterior translation and longitudinal rotation of the tibia, featuring asymmetrical medial and lateral condyles and curvatures to mimic natural knee motion, accommodate placement errors, and provide stability across a wider range of flexion, including beyond 90°, by utilizing specific curvatures and radii that allow for axial rotation and anterior-posterior translation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple hinge-based design is used, then the device complexity is reduced, but the knee flexion range is limited to 70° to 80°
Solution Approach 1:
The prosthesis employs dynamic condylar curvatures that vary along the articulating surfaces, allowing the knee joint to transition from hinge-like motion at low flexion angles to more complex rotational and translational motion at higher flexion angles. This dynamic geometry enables the joint to adapt its motion characteristics based on the flexion angle, achieving greater flexion range without requiring an overly complex mechanical structure.
Solution Approach 2:
The invention introduces anterior-posterior translation and longitudinal rotation as additional degrees of freedom beyond simple hinge rotation. By allowing motion in multiple dimensions (sagittal plane rotation, longitudinal axis rotation, and anterior-posterior translation), the prosthesis achieves enhanced flexion capability while maintaining reasonable structural complexity through integrated condylar design.
2Length of moving object
If asymmetric curvatures are introduced in condyles, then the knee can accommodate translation and lateral rotation for greater flexion, but the manufacturing precision requirements increase
Solution Approach 1:
The prosthesis utilizes systematically varied curvature parameters along the condylar articulating surfaces. By defining specific radius of curvature values at different locations (medial vs lateral condyles, anterior vs posterior surfaces), the design achieves natural knee motion characteristics. These parameter variations are engineered to compensate for surgical positioning errors while maintaining manufacturability through standardized precision requirements.
3Adaptability or versatility
If the prosthesis is designed to accommodate surgical positioning errors, then the adaptability improves, but the device complexity increases
Solution Approach 1:
The asymmetric condylar curvatures and geometric configuration are designed in advance to accommodate expected surgical positioning variations. The medial and lateral condyles feature different curvature radii that create inherent tolerance to minor rotational and positional errors during implantation. This built-in accommodation allows the prosthesis to function reliably despite typical surgical precision limitations without requiring complex error-correction mechanisms.
Data Source
AI summary
A knee prosthesis for total knee replacement has femoral and tibial joint components. The femoral component has a medial condyle, a lateral condyle and an intercondylar recess between the condyles. The condyles in sagittal profile both have spiral outer surfaces, wherein the increasing anterior-to-posterior radii of curvature for the medial condyle is smaller than the corresponding radii of curvature for the lateral condyle. The tibial component has shallow concave medial and lateral condyle surfaces for receiving corresponding condyles of the femoral component as bearing surfaces when the femoral and tibial components are biased together under applied tension by ligaments. Posterior portions of each femoral condyle that contact the corresponding tibial condyle up to 90° flexion are substantially spherical in shape, with gradually increasing radii in coronal profile as flexion increases, while the anterior portions beyond 90° flexion are substantially elliptical in shape in coronal profile.