Rotatable Post Knee Prosthesis for Posterior Stability
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Solution Overview
Problem
Conventional knee prosthetics often fail to adequately replace and compensate for non-articulating tissues like the anterior cruciate ligament, posterior cruciate ligament, tendons, and muscles, leading to instability and pain, especially under natural loading conditions.
Innovation Solution
A method of assembling a knee joint prosthesis that involves rotatably coupling a post to an extension portion of an insert from a bearing member, threadably coupling a retention member to limit post movement, and articulating a femoral component with a tibial tray, allowing the post to rotate within an opening of the femoral component to mimic natural joint motion and compensate for tissue deficiencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional knee prosthesis replaces only the articulating portions, then the articulation function is restored, but the soft tissues cannot withstand natural loading causing instability and pain
Solution Approach 1:
The prosthesis is divided into separate functional components: a tibial baseplate with insert, a femoral component, and a rotatable post mechanism. This segmentation allows each component to address specific functional requirements - the articulating surfaces restore joint motion while the post mechanism independently provides posterior stabilization to compensate for deficient soft tissues
Solution Approach 2:
The rotatable post acts as an intermediary mechanism between the femoral and tibial components. It provides posterior constraint through a cam-post interaction that mimics natural ligament function, bridging the gap between rigid prosthetic components and the absent soft tissues
2Stability of the object's composition
If a fixed post is used to constrain posterior movement, then posterior stability is achieved, but the prosthesis cannot accommodate natural range of motion variations
Solution Approach 1:
The post is designed to rotate about an axis perpendicular to the articulation plane rather than being fixed. This dynamic capability allows the post to adapt its orientation during flexion and extension, maintaining effective posterior constraint throughout the range of motion while accommodating natural variations in joint kinematics
3Reliability
If a rotatable post is coupled to the bearing member, then posterior movement is constrained and range of motion is maintained, but the post may move excessively along the axis away from the bearing member
Solution Approach 1:
A retention member is threaded onto the extension portion of the insert before final assembly, positioned to limit the rotational travel of the post. This preliminary constraint ensures the post remains within appropriate bounds during operation, preventing excessive movement while allowing sufficient rotation for effective posterior constraint
Data Source
AI summary
A method of assembling a knee joint prosthesis for replacing a portion of a knee joint. The method includes rotatably coupling a post to an extension portion of an insert extending from a bearing member, and coupling a femoral component for articulation on the bearing member.