Spiral-profile knee prosthesis for flexion and misalignment
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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 about 70° to 80° due to their simple hinge-based design, which fails to account for anterior-posterior translation and minor surgical misalignment errors.
Innovation Solution
A knee prosthesis design featuring a femoral component with a spiral-like outer sagittal profile and a tibial component with specific concavities and curvatures that allow for anterior-posterior translation and accommodate rotational misalignments, enabling flexion up to 90°-110° and compensating for surgical errors, thereby mimicking natural knee kinematics.
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 range of flexion is limited to 70°-80°
Solution Approach 1:
The femoral component employs a spiral-like outer sagittal profile with varying radii of curvature along its length, transitioning from a first radius at the anterior end to a second radius at the posterior end. This curved geometry enables the prosthesis to replicate the complex rollback motion of the natural knee, allowing flexion beyond 90 degrees while maintaining a unified component design
Solution Approach 2:
The prosthesis incorporates dynamic motion characteristics through its asymmetric condylar geometry and varying curvature radii, which allow the femoral component to naturally rollback on the tibial platform during flexion. This dynamic behavior replicates physiological knee kinematics without requiring active control mechanisms
2Manufacturing precision
If a fixed geometry design is used, then the manufacturing precision is improved, but the ability to accommodate surgical misalignment errors is reduced
Solution Approach 1:
The femoral component features deliberately varied curvature radii along its sagittal profile, with the first radius at the anterior end differing from the second radius at the posterior end. This parameter variation creates a spiral geometry that provides tolerance to rotational misalignment errors while maintaining precise manufacturing specifications for the implant components
3Device complexity
If anterior-posterior translation is not accommodated, then the device complexity is reduced, but the quality of life after surgery is reduced
Solution Approach 1:
The spiral-like outer sagittal profile with varying radii of curvature enables the femoral component to naturally rollback anteriorly during flexion, accommodating physiological anterior-posterior translation. This geometric design allows greater than 90 degrees of flexion and improves patient quality of life without adding active control mechanisms or increasing device complexity
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 have in sagittal profile a spiral outer surface with increasing anterior-to-posterior radii of curvature, such as radii that follow a Fibonacci sequence ratio per every quadrant. The tibial component is lateral-medial mirror symmetric in coronal profile and 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. The shallow concave condyle surfaces in sagittal profile have sharp radii of curvature near anterior and posterior ends of the condyle surfaces that can accommodate up to 5° anterior and up to 6° posterior misplacement error and up to 4° rotational mismatch between the femoral and tibial components.