Offset Adjustable Prosthesis Stem With Eccentric Bushing
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Solution Overview
Problem
The variability in the position of the intramedullary canal relative to the proximal tibia poses a challenge in centering a tibial stem on the tibial baseplate due to anatomical variations, known as tibial offset, which can lead to interference with the cortex during surgical procedures.
Innovation Solution
A prosthesis system with offset adjustability, comprising a monoblock stem extension and eccentric bushings, where the distal portion of the stem has a second neutral axis offset from the proximal portion, and the bushings have offset neutral axes to allow for adjustable alignment, enabling correction of the tibial baseplate position in the transverse plane.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a tibial stem is centrally located on the tibial baseplate, then the stem structure is simplified and manufacturing is easier, but the stem may interfere with the cortex due to anatomical variation in intramedullary canal position
Solution Approach 1:
The prosthesis system is divided into modular components: a tibial baseplate and a separate stem extension that can be selectively positioned. This segmentation allows the stem to be offset from the baseplate center to accommodate varying intramedullary canal positions while maintaining a simple, centrally-located baseplate structure for ease of manufacture.
Solution Approach 2:
The system provides dynamic adjustability through modular stem extensions that can be selectively attached at different positions and orientations. This allows the stem alignment to be adapted to each patient's specific anatomy rather than being fixed, eliminating cortex interference while maintaining manufacturing simplicity.
2Adaptability or versatility
If modular components with offset adjustability are used, then anatomical variations can be accommodated and surgical alignment is improved, but the device complexity and inventory requirements increase
Solution Approach 1:
The system uses segmented modular components (baseplate and stem extensions) that can be combined in different configurations. This segmentation enables adaptability to various anatomies while keeping each individual component relatively simple in design, balancing versatility with manufacturing simplicity.
Solution Approach 2:
The modular stem extensions are designed with universal features that allow them to be attached to the baseplate in multiple positions and orientations. This multi-functionality enables a single set of standardized components to accommodate a wide range of anatomical variations, reducing the need for highly specialized custom parts.
3Adaptability or versatility
If modular components with offset adjustability are used, then anatomical variations can be accommodated and surgical alignment is improved, but the inventory of parts needed increases
Solution Approach 1:
The modular components are designed with universal attachment features and standardized dimensions that allow a limited set of stem extensions to serve multiple purposes. This universality enables the same components to accommodate various offset requirements through different positioning and orientation configurations, reducing the total inventory needed compared to having separate custom components for each anatomical variation.
Data Source
AI summary
A prosthesis system of the present invention includes a monoblock stem extension including a proximal portion having a first neutral axis; and a distal portion defined by a longitudinal cylindrical shaft having a second neutral axis, wherein the second neutral axis is parallel and offset by a distance α from the first neutral axis; and an eccentric bushing arranged coaxial around the cylindrical shaft of the monoblock stem extension, the eccentric bushing including an external cylindrical shaft having a third neutral axis; and an internal cylinder having a fourth neutral axis that is substantially co-linear with the second neutral axis of the monoblock stem extension, wherein the third neutral axis is parallel and offset by a distance β from the fourth neutral axis.