Bio-Resorbable Orthopaedic Lag Screw With Segmented Torque Geometry
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Solution Overview
Problem
Bioabsorbable ceramic composite screws are mechanically weak and prone to breakage during high rotational forces during insertion, posing a risk of fracture and non-union in small bone fractures.
Innovation Solution
A bioabsorbable screw design featuring a threaded outer section with a square internal geometry extending between 20% to 100% of its length, combined with a circular internal geometry for the remainder, to distribute insertion torque effectively, reducing the risk of breakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ceramic composite material is used for bioabsorbable screw, then biocompatibility and stress shielding are improved, but mechanical strength and resistance to rotational forces deteriorate
Solution Approach 1:
The screw body is segmented into distinct functional zones: a threaded outer section with square internal geometry for torque application, and a shaft portion with circular internal geometry. This segmentation allows the threaded portion to bear the rotational insertion forces while the shaft maintains structural integrity, resolving the contradiction between material biocompatibility and mechanical strength.
Solution Approach 2:
Different internal geometries are applied to different portions of the screw: square internal geometry in the threaded outer section to resist rotational forces during insertion, and circular internal geometry in the shaft portion for smooth insertion through bone. This local differentiation of structural properties allows the screw to simultaneously achieve biocompatibility and resistance to breakage under rotational stress.
2Measurement precision
If fully cannulated design is used for percutaneous insertion, then insertion accuracy is improved, but susceptibility to breakage during insertion worsens
Solution Approach 1:
The screw is segmented into a threaded outer section and a shaft portion, with each having different internal geometries optimized for their specific functions. The threaded section's square geometry provides torque resistance during the critical insertion phase through bone, while the cannulated shaft maintains guidance accuracy, thus resolving the contradiction between insertion precision and breakage resistance.
Solution Approach 2:
The internal geometry is locally optimized: square geometry in the threaded portion where high rotational forces occur, and circular/cannulated geometry in the shaft where smooth passage and positioning accuracy are needed. This local quality differentiation allows the screw to maintain both insertion accuracy and resistance to breakage.
Data Source
AI summary
The present invention relates to a bio-resorbable calcium composite lag screw to achieve compression in small bone fractures. The design features allow for reliable insertion reducing the risk of fracture by having an internal geometry of the screw wherein an inserter or driver used to insert the screw applies force only to the threaded portion of the screw distal from the inserter or driver, reducing the risk of screw breakage on insertion.