Variable Angle Bone Screw Groove Alignment and Surface Hardening
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Solution Overview
Problem
Variable angle bone fixation systems face issues with thread engagement between bone screws and plates, leading to burring and reduced fixation strength, which compromises the efficacy of bone stabilization.
Innovation Solution
A bone fixation element with a carburized or nitrided outer surface and grooves on the screw head to align threads, minimizing burring and enhancing the screw-plate interface strength, featuring a shaft with notches for self-tapping and increased surface hardness for improved yield, tensile, and fatigue strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If variable angle screws are used to permit user-selected angle insertion, then adaptability is improved, but thread burring occurs causing loss of fixation strength
Solution Approach 1:
The groove is pre-formed on the screw head at a specific angle relative to the threading. This preliminary geometric feature guides the screw insertion path and ensures proper thread engagement before the actual fastening process begins, preventing burring from misalignment
Solution Approach 2:
The groove is located specifically on the head of the screw at a defined angular position relative to the threading axis. This localized geometric modification creates a preferred insertion path that aligns the threads correctly during variable angle insertion, solving the burring problem while maintaining adaptability
2Ease of operation
If repeated insertion and removal of screws is performed, then ease of operation is improved, but thread sharpening is required maintaining productivity
Solution Approach 1:
The groove is pre-formed on the screw head to establish correct thread alignment before insertion. This preliminary geometric feature ensures that even after multiple insertions and removals, the threads remain properly aligned without requiring sharpening, enabling repeated use while maintaining productivity
3Ease of manufacture
If standard bone screws are used, then ease of manufacture is improved, but surface hardness is insufficient leading to breakage and tissue trauma
Solution Approach 1:
The outer surface of the screw is subjected to carburizing or nitriding treatment, which changes the material parameters by creating a hardened surface layer. This thermal/chemical process increases surface hardness and strength while maintaining the underlying ductile structure, preventing breakage and tissue trauma
Solution Approach 2:
The screw structure becomes composite with a hardened outer surface layer (carburized or nitrided) and a softer core material. This composite structure provides both the surface hardness needed to prevent breakage and the ductility of the base material, solving the strength issue while maintaining ease of manufacture
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a stronger screw-plate interface, reduces galling, and maintains connection strength, allowing for repeated use without sharpening, while the carburized/nitrided surface prevents breakage and minimizes tissue trauma from sharp edges.
Implementation Method 1
an outer surface of the head being one of carburized and nitrided
Implementation Method 2
an outer surface of the head being one of carburized and nitrided
Data Source
AI summary
A bone fixation element includes a threaded head and a shaft extending along a longitudinal axis from a proximal end to a distal end, an outer surface of the head being one of carburized and nitrided and including a first groove extending into an outer surface of the head along a path interrupting the threading and extending along an angle counter to an angle of the threading.