Shoulder Prosthesis Baseplate Hole for Variable Screw 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 bone quality or anatomical considerations.
Innovation Solution
A through-hole design with a projecting edge that allows a compressive screw to pass through, featuring a circular arc shape with a greater diameter locally and a free portion that enables screws of different diameters to be inserted without a helical fit, maintaining the baseplate's overall geometry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a through-hole with a threaded portion is provided in the baseplate to accommodate an enlarged central screw, then the screw can be retained with a helical fit, but the manufacturing complexity increases and only one type of screw with specific thread geometry can be used
Solution Approach 1:
The through-hole is designed with non-uniform geometry: a smaller diameter portion for screw retention and a locally enlarged portion with circular arc shape for thread passage. This local quality variation allows the baseplate to accommodate screws of different diameters without requiring a fully threaded complex structure throughout the entire hole.
Solution Approach 2:
The through-hole is segmented into functionally distinct zones: a retention zone with smaller diameter that holds the screw head, and a passage zone with locally enlarged diameter that allows the threaded stem to pass through. This segmentation enables versatile screw accommodation while keeping each zone's manufacturing relatively simple.
2Reliability
If a threaded portion is added to the baseplate for screw retention, then screw anchorage is improved, but the manufacturing process becomes more difficult
Solution Approach 1:
Instead of threading the entire through-hole, only a localized portion is enlarged with a circular arc shape. This local modification provides sufficient screw retention through the enlarged arc region while avoiding the need for complex threading operations throughout the entire hole, simplifying manufacturing.
Solution Approach 2:
The locally enlarged portion of the through-hole features a circular arc shape rather than a helical thread. This curved geometry provides effective screw retention through geometric interlocking while being significantly easier to manufacture using standard machining or molding processes compared to precision threading.
3Adaptability or versatility
If the through-hole diameter is increased to accommodate larger diameter screws, then screw size versatility is improved, but the baseplate dimensions and compatibility with modular components are affected
Solution Approach 1:
The through-hole maintains a small overall diameter to preserve baseplate dimensions and modular compatibility, but includes a locally enlarged portion with circular arc shape that temporarily accommodates larger diameter screw threads during insertion. This localized enlargement allows versatile screw accommodation without increasing the baseplate's external dimensions.
Solution Approach 2:
The solution addresses the diameter constraint by introducing a dimensional variation in the radial direction at a specific location along the hole's length. The circular arc shaped enlargement creates a localized three-dimensional feature that allows larger screws to pass through without increasing the hole's entry or exit diameter, preserving baseplate compactness.
Data Source
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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 arc 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).