Knee Prosthesis Rotation Limiting Device
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Solution Overview
Problem
Knee joint endoprostheses often experience undesired rotation of the meniscus part relative to the tibia part, particularly by 90°, which can lead to instability and interaction with surrounding soft tissues.
Innovation Solution
A rotation limiting device is introduced, featuring a stop member that protrudes anteriorly from the pivot bearing, with a second bearing pin option and a coupling device using first and second coupling members for non-rotatable coupling, allowing limited rotation and modular design for activation or retrofitting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a rotation limiting device is added to restrict meniscus part rotation, then rotational stability is improved, but device complexity increases
Solution Approach 1:
The rotation limiting device is segmented into separate components: a stop member with bearing pins that can be independently mounted on the tibia part, and corresponding bearing surfaces on the meniscus part. This modular segmentation allows the rotation limiting function to be added without redesigning the entire prosthesis system, thus improving rotational stability while minimizing the increase in overall device complexity.
Solution Approach 2:
Bearing pins and bearing surfaces act as intermediary elements between the tibia part and meniscus part to limit rotation. These intermediaries provide a simple mechanical constraint through contact surfaces, achieving rotational stability without complex locking mechanisms or additional actuation systems.
2Volume of moving object
If the stop member protrudes anteriorly from the pivot bearing, then the prosthesis becomes more compact and avoids soft tissue interaction, but manufacturing precision requirements increase
Solution Approach 1:
The stop member protrudes in the anterior direction (a different spatial dimension relative to the pivot bearing axis) rather than extending radially outward. This dimensional change allows the prosthesis to achieve a more compact profile in the radial direction while avoiding posterior soft tissue structures, with the anterior protrusion being contained within the tibial component footprint.
Solution Approach 2:
The bearing pins and bearing surfaces are designed with predetermined geometric features (cylindrical pins matching cylindrical recesses, or planar surfaces with defined contact areas) that establish precise rotational limits before implantation. This preliminary geometric constraint ensures consistent rotational limitation across all implants, reducing the need for intraoperative adjustment and lowering actual manufacturing precision requirements during production.
3Adaptability or versatility
If the rotation limiting device is made detachably connectable, then adaptability is improved, but reliability may worsen due to potential loosening
Solution Approach 1:
The connection system transitions from a static fixed connection to a dynamic detachable connection that can be selectively engaged or disengaged. The bearing pins are mounted on the tibia part with threaded or press-fit connections that allow surgical installation and removal, enabling the rotation limiting function to be activated or deactivated based on individual patient needs while maintaining connection reliability through proven fastening mechanisms.
Data Source
AI summary
In order to improve a knee joint endoprosthesis system comprising a tibial component, a meniscus component rotatably mounted on the tibial component, and a femoral component cooperating with the meniscus component to form a knee joint endoprosthesis, such that rotation of the meniscus component relative to the tibial component is only permitted to a limited extent, it is proposed that the system include a rotation limiting device to restrict rotational movement of the meniscus component relative to the tibial component and that the rotation limiting device be detachably connected, at least partially, to the tibial component and/or the meniscus component.