Shoulder Prosthesis Baseplate Screw Retention for Variable Diameters
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Solution Overview
Problem
Existing shoulder prosthesis baseplates face challenges in accommodating compressive screws of varying diameters without altering the baseplate's dimensions or affecting compatibility with modular components, particularly when increased thread diameters are required for different bone qualities or anatomical considerations.
Innovation Solution
The through-hole design features a projecting edge with a circular arc shape that allows a compressive screw to be axially retained while accommodating screws of different diameters by providing a free portion for the threaded stem to pass, eliminating the need for helical shaping and maintaining the baseplate's overall geometry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a through-hole with a threaded portion is provided to accommodate an enlarged central screw, then the screw diameter can be increased for better bone anchorage, but the manufacturing complexity increases due to the need for helical shaping and thread correspondence
Solution Approach 1:
The through-hole is segmented into two distinct functional zones: a first portion with a smaller diameter for receiving the screw head, and a second portion with a larger diameter for receiving the threaded stem. This segmentation allows each portion to be optimized independently, simplifying manufacturing while accommodating enlarged screws for better bone anchorage.
Solution Approach 2:
Different portions of the through-hole have different local qualities (diameters) to serve different functions. The first portion has a smaller diameter matched to the screw head, while the second portion has a larger diameter matched to the threaded stem, allowing the screw to pass through and be retained without requiring complex helical shaping throughout the entire hole.
2Adaptability or versatility
If the through-hole diameter is increased to accommodate larger diameter screws, then screws with increased thread diameters can be used for different bone qualities, but the baseplate dimensions and compatibility with modular components are affected
Solution Approach 1:
Instead of increasing the overall through-hole diameter (affecting baseplate shape and modular compatibility), the solution uses a dimensional variation within the through-hole by creating a localized enlarged second portion that allows larger screws to pass through while maintaining the external baseplate geometry and modular component compatibility.
3Reliability
If a threaded portion is provided in the baseplate for screw retention, then screw positioning is improved, but the thread geometry must correspond exactly to the screw thread, limiting versatility
Solution Approach 1:
The second portion of the through-hole serves multiple functions: it allows the threaded stem to pass through, provides retention for various screw types through friction and geometric interference, and does not require a specific thread geometry correspondence. This universal approach allows compatibility with different screw types and thread pitches while maintaining reliable retention.
Data Source
AI summary
A shoulder prosthesis baseplate (100) comprising a through-hole (102) for a compressive screw (101), wherein the through-hole (102) has a circular profile section and comprises a projecting edge (106) arranged internally and perpendicularly to an axis (102j of the through-hole (102), the projecting edge (106) being configured to axially retain a head (103) of the compressive screw (101) inserted in the through-hole (102). The projecting edge (106) has circular are shape and delimits a corresponding free portion (108) of the circular profile section internally to the through-hole (102), the free portion (108) being configured to allow the screwing passage of a threaded stem (104) of the compressive screw (101) to surpass the projecting edge (106).