Cruciate Replacing Artificial Knee with Segmented Ligament
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Solution Overview
Problem
Current total knee replacement (TKR) prostheses inadequately substitute the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL), leading to reduced functionality and difficulty in mimicking normal knee kinematics, which limits patient mobility and participation in physical activities.
Innovation Solution
A knee joint prosthesis design featuring two rounded posts and cams, with the posts mimicking the ACL and PCL, allowing for more accurate simulation of the ligaments' function, and an artificial ligament that replicates the anatomy and attachment points of the ACL and PCL, enabling better kinematic simulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a crude cam and post mechanism is used to substitute the ACL, then the device complexity is reduced and ease of manufacture is improved, but the manufacturing precision and functional reliability are worsened because it provides only partial substitution (0-20 degrees flexion contact) and inadequately simulates normal knee kinematics
Solution Approach 1:
The artificial ligament is segmented into distinct functional zones: a first portion with a first radius of curvature for simulating ACL function, and a second portion with a second radius of curvature for simulating PCL function. This segmentation allows each portion to be optimized for its specific kinematic role while maintaining overall ligament continuity.
Solution Approach 2:
Different portions of the artificial ligament are given different local qualities through varying radii of curvature. The first portion has a specific radius optimized for anterior cruciate ligament mechanics, while the second portion has a different radius optimized for posterior cruciate ligament mechanics, enabling anatomically correct replacement throughout the full range of motion.
2Device complexity
If the ACL is removed entirely to simplify the TKR design, then the device complexity is reduced, but the reliability and functionality are worsened because normal knee kinematics cannot be achieved without proper ACL-PCL interplay
Solution Approach 1:
The artificial ligament serves multiple functions within a single component: it replaces both the ACL and PCL, provides anterior and posterior stability, enables full range of motion, and simulates normal knee kinematics. This multi-functionality eliminates the need for separate cam and post mechanisms while achieving complete ligament replacement.
Solution Approach 2:
The artificial ligament with varying radii of curvature dynamically adapts its mechanical properties throughout the range of motion. The transition between the first and second portions occurs at a specific flexion angle, allowing the ligament to naturally shift between ACL-dominant and PCL-dominant mechanics, reproducing the dynamic behavior of a native knee.
3Ease of manufacture
If a cable-like material is used to replace the PCL, then the ease of manufacture is improved, but the manufacturing precision and functional accuracy are worsened because it cannot adequately replace the ACL function
Solution Approach 1:
The artificial ligament incorporates parameter changes along its length, specifically varying the radius of curvature from the first portion to the second portion. This parameter variation enables the single ligament structure to provide different mechanical characteristics appropriate for ACL replacement in extension and PCL replacement in flexion, achieving functional accuracy that uniform cable materials cannot provide.
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3A~3B
AI summary
A knee joint prosthesis is capable of moving between an extended position and a flexion position. The knee joint prosthesis includes a femoral component that is configured to be mounted to a femur, a tibial component that is configured to be mounted to a tibia, a first and second post fixedly connected to one of the femoral component and the tibial component, and a first and second cam recess defined on the other of the femoral component and the tibial component that is configured to be engaged by the post in either the extended position or the flexion position of the knee joint prosthesis.