Nested Lag Screw Assembly for Fracture Compression and Easy Removal
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Solution Overview
Problem
Current orthopedic fixation devices face challenges such as compression screw breakage, difficulty in removal, and increased risk of nonunion due to fixed lag screws, as well as issues with lateral prominence leading to tissue irritation.
Innovation Solution
The device incorporates a partially threaded compression screw that nests with a lag screw, allowing for easier removal and increased strength, and a telescopic lag screw assembly that slides relative to the IM nail to maintain fracture compression without tissue prominence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fully threaded compression screw is used to engage the lag screw rack, then the compression screw can be rotated to compress the fracture, but the compression screw is prone to breakage and difficult to remove
Solution Approach 1:
The compression screw is divided into two distinct segments: a threaded lateral segment that engages the lag screw rack, and a smooth medial segment that passes through the IM nail. This segmentation allows the threaded portion to provide compression function while the smooth portion enables easy removal and reduces breakage risk
Solution Approach 2:
The threading is extracted from the medial segment of the compression screw, leaving only the lateral segment threaded. This removes the source of breakage and removal difficulty from the critical medial portion while retaining compression functionality at the lateral portion
2Object-affected harmful factors
If the lag screw is fixed to the IM nail to prevent sliding, then lateral prominence and tissue irritation are reduced, but the fracture cannot accommodate secondary collapse and healing
Solution Approach 1:
The lag screw is designed with telescopic capability, allowing it to slide longitudinally within the IM nail. This dynamic adjustment enables the fracture to accommodate secondary collapse and maintain compression during healing, while the lateral head can be contoured to minimize tissue irritation when in its final position
3Strength
If the compression screw diameter is increased to prevent breakage, then the compression screw strength is improved, but the opening in the IM nail must be enlarged or the lag screw diameter reduced
Solution Approach 1:
The compression screw is segmented into threaded and smooth portions, allowing the threaded lateral segment to be optimized for strength and engagement while the smooth medial segment passes through the IM nail opening. This enables the use of a larger diameter compression screw without requiring an enlarged opening
Solution Approach 2:
The compression screw is nested within the IM nail structure, with the smooth medial segment passing through the nail's opening and the lateral segment extending outward to engage the lag screw. This nesting arrangement maximizes the use of available space within the existing opening
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 enhances the strength of the compression screw, facilitates easier removal, and reduces the risk of breakage while maintaining fracture compression and minimizing tissue irritation.
Implementation Method 1
the compression screw 30 is a fully threaded screw which engages a rack 28 on the lag screw 20 to act as a worm gear. Thus arranged, the compression screw 30 is nested (e.g., meshes) with the lag screw 20.
Data Source
Figure 1A~1B
Figure 1C
Figure 2
AI summary
An orthopedic fixation device (e.g., an intramedullary ("IM") nail or bone plate) including a lag screw and a compression screw, the compression screw being nested with the lag screw. In accordance with one or more features of the present disclosure, the compression screw may include a partially non-threaded medial segment, an enlarged diameter, and/or a cannulated bore. In addition, and/or alternatively, the lag screw may be provided as an integrated assembly including a lag screw and an outer sleeve to enable the lag screw to telescope or slide relative to the outer sleeve and IM nail.