Segmented Headless Compression Screw for Controlled Bone Translation
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Solution Overview
Problem
Existing headless compression screws either delay the translation of bone fragments or cause excessive compression once the fragments are joined, failing to provide controlled initial translation and subsequent compression.
Innovation Solution
A headless compression screw design featuring a leading portion with a single or double thread, an unthreaded intermediate portion, and a trailing portion with a single thread of varying pitch or lead, allowing initial bone fragment translation and subsequent controlled compression without significant additional pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the unthreaded central portion spans the fracture in the Herbert screw design, then compression occurs between bone fragments, but longitudinal translation of the distal bone fragment towards the proximal bone fragment is delayed until the threads of the trailing end of the screw begin engaging the proximal bone fragment
Solution Approach 1:
The screw thread is segmented into three distinct portions: a leading threaded portion with a first pitch, an unthreaded intermediate portion, and a trailing threaded portion with a second pitch. This segmentation allows different functional zones along the screw length to perform different operations sequentially - the leading portion initiates translation, the intermediate portion provides compression, and the trailing portion maintains compression while allowing further translation.
Solution Approach 2:
Different portions of the screw are given different local qualities through varying thread pitches. The leading portion has a first pitch optimized for initiating translation, while the trailing portion has a second pitch optimized for maintaining compression. This local differentiation allows each portion to perform its specific function optimally without interfering with other functions.
2Productivity
If a single thread of continuously varying pitch is used along the screw length, then simultaneous translation and compression of separated bones or bone fragments occurs, but controlled initial translation followed by maintenance of gap closure without significant additional compression cannot be achieved
Solution Approach 1:
The continuously varying pitch thread is segmented into discrete portions with specific pitch values. The leading portion has a first pitch for translation, the intermediate unthreaded portion allows gap closure, and the trailing portion has a second pitch for compression. This segmentation provides controlled sequencing of translation and compression operations, allowing the surgeon to achieve gap closure first, then apply compression as needed.
Solution Approach 2:
The thread pitch parameter is changed at specific locations along the screw length. The leading portion has a first pitch value optimized for translation, while the trailing portion has a second pitch value optimized for compression. This parameter change allows the screw to transition from a translation mode to a compression mode, providing controlled operation.
3Force
If the trailing portion thread engages the proximal bone fragment early, then compression occurs between bone fragments, but further advance of the screw while maintaining gap closure without significant additional compression is limited
Solution Approach 1:
The screw is segmented into distinct functional zones that operate in sequence. The unthreaded intermediate portion acts as a buffer zone that allows the screw to advance further into the distal bone fragment without immediately engaging the proximal fragment. This segmentation provides adaptability, allowing the surgeon to control the timing and amount of compression applied.
Solution Approach 2:
The unthreaded intermediate portion serves as an intermediary element between the leading and trailing threaded portions. It mediates the transition from translation to compression by allowing the screw to advance without engaging the proximal bone fragment, thus providing a buffer zone that enables controlled screw advancement while maintaining gap closure.
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
Enables controlled initial translation and final compression of bone fragments, facilitating osteosynthesis while maintaining contact without excessive force between the fragments.
Implementation Method 1
the thread of the leading end portion torqueably engages a distal bone fragment while the thread of the trailing end portion torqueably engages a proximal bone fragment
Implementation Method 2
the fragments are longitudinally translated together and subsequentially compressed as a result of the differential in pitch between the leading thread and the trailing thread
Implementation Method 3
further advance of the screw within the bones or bone fragments while maintaining the gap closure but without significant additional compression between the bones or fragments
Data Source
AI summary
A bone screw for osteosynthesis is provided with screw threads of different pitch or different lead and various diameters in leading, intermediate and trailing ends. The screw may be used to urge together and compress bones or fragments of bone.