Total Knee Prosthesis Median Protuberance Design
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Solution Overview
Problem
The existing 'postero-stabilized' total knee prostheses experience significant strain and wear on bone anchorings due to impacts between the femoral and tibial implants, particularly at the protuberance, leading to potential loosening and increased wear over time.
Innovation Solution
The design features curved condylian portions and a median protuberance with a posterior boss and anterior portion that form a smooth transition, providing strong congruence and stability, reducing impact and wear by allowing soft contact during joint extension and hyperextension, and incorporating marked and rounded angles for reinforced guidance without substantial wear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a postero-stabilized prosthesis with a rounded boss and median protuberance is used to prevent anterior luxation, then stability against anterior luxation is improved, but impact strain on bone anchorings and wear at the protuberance increases
Solution Approach 1:
The median protuberance is segmented into distinct functional zones: a posterior boss with convex upper face for guidance, a central recessed area for shock absorption, and an anterior portion with concave upper face for engagement. This segmentation allows each zone to perform its specific function, reducing overall impact strain while maintaining stability.
Solution Approach 2:
The central recessed area with smooth transition is designed beforehand to cushion impacts between the femoral implant's inter-condylian edge and the tibial implant's protuberance. This recessed zone absorbs shock during flexural movement, preventing direct impact transmission to the bone anchorings and reducing wear at the protuberance.
2Stability of the object's composition
If condylian portions and glenoid surfaces are made strongly congruent to improve stability throughout joint movement, then prosthetic stability is improved, but complexity of the implant design increases
Solution Approach 1:
The condylian portions are given a curved shape in both the sagittal plane and transverse plane, matching the natural curvature of the femoral condyles. The glenoid surfaces are correspondingly curved to receive these condylian portions. This spherical/curved geometry naturally provides congruence and stability throughout the range of motion while following anatomical forms, making the design both effective and relatively simple.
Data Source
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AI summary
In this prosthesis the condylian portions of the femoral implant and glenoid surfaces (25) of tibial implant are congruent; the femoral implant comprises an anterior inter-condylian wall forming a lower inter-condylian edge; and the intermediate plate (20) comprises a median protuberance (26); with a posterior boss (30) with a convex upper face in the sagittal plane, which plunges down towards the central area (32) of the protuberance (26), and an anterior portion (31 ) with a concave upper face in the sagittal plane which emerges from this same central area (32), said central area (32) thus having a recess continuously connected to the posterior boss (30), this recess is located so that in an extension or hyperextension of the joint, said lower inter-condylian edge (12) is immediately below it, or slightly engaged on the anterior portion of the posterior boss (30).