Hybrid Bone Screw With Threaded Head for Early Fracture Compression
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Solution Overview
Problem
Existing headless compression screws do not initiate compressive forces across the fracture site until the screw head is buried in the bone, limiting compressive forces to the length of the threads, particularly problematic in small bones like those in the foot and ankle.
Innovation Solution
A hybrid compression screw design featuring a threaded head with a larger diameter than the shaft, combined with a non-threaded buttress section that gradually increases in diameter, and varying or constant pitch threads to enhance compressive force distribution and bone fragment alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a headless compression screw is used to minimize hardware profile and improve aesthetics, then the screw head is buried in the bone, but compressive forces are limited to the length of the threads only
Solution Approach 1:
The screw is divided into distinct functional segments: a threaded head portion for initial compression and tool engagement, a non-threaded buttress portion for structural support and force distribution, and a threaded shaft portion for bone engagement. This segmentation allows each segment to contribute differently to compression, enabling compressive forces to initiate at the head before the threads engage the bone, thereby extending the compression zone beyond just the threaded length.
2Force
If the threaded head with larger diameter is used to provide earlier compressive forces, then compressive force distribution is improved, but the overall device complexity increases
Solution Approach 1:
The invention merges the functions of the screw head (for compression and tool engagement) with the threaded shaft (for bone engagement) into a single integrated structure. The threaded head combines the compressive function typically separated in headed screws with the bone-engagement function of threaded shafts, creating a unified component that reduces overall device complexity while achieving earlier compressive force initiation.
Solution Approach 2:
The screw features localized thread placement: threads are present on the head portion for early compression and on the shaft portion for bone engagement, but absent from the intermediate buttress portion. This local differentiation of properties (threaded vs. non-threaded zones) optimizes each region's function while maintaining overall structural simplicity.
3Stability of the object's composition
If a non-threaded buttress section with gradually increasing diameter is used to distribute compressive forces, then bone fragment alignment is improved, but manufacturing precision requirements increase
Solution Approach 1:
The non-threaded buttress portion with gradually increasing diameter is designed to preliminary distribute compressive forces from the threaded head to the threaded shaft before the threads fully engage the bone. This preliminary force distribution action stabilizes bone fragments during the transition from insertion to full thread engagement, improving alignment while the gradual diameter change allows for tolerable manufacturing variations.
Data Source
AI summary
A compression screw includes an elongate shaft having a shaft length extending between a proximal and distal tip portions, the shaft having: a cannula extending coaxially through the shaft and opening through the shaft tip portion; a shaft threaded section having a length with major and minor diameters, the threaded section having screw threads positioned in a spiral pattern on an outer shaft surface and extending from a leading tip portion of the shaft to a shaft trailing portion. A buttress connects a shaft proximal portion to a threaded head with a head length with major and minor diameters with screw threads of constant pitch positioned in a spiral pattern on a head outer surface, such that MH>MT and mH>mT, the threaded head accommodates a rotational tool. A diameter of the buttress gradually increases from the proximal portion of the shaft towards the head.