Threaded Intramedullary Nail Connection with Detent Locking
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Solution Overview
Problem
Existing intramedullary nail insertion systems experience loosening and disengagement of connecting screws due to significant forces applied during nail insertion, requiring retightening.
Innovation Solution
The system employs connecting screws with varying thread pitches or detents to resist disengagement, and includes a cannulated design with a sleeve and T-arm screwdriver for secure attachment, using materials like titanium alloy for the IM nail and stainless-steel alloy for the connecting screw.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a connecting screw is used to attach the intramedullary nail during insertion, then the nail can be inserted into the medullary canal, but the connecting screw loosens and requires retightening
Solution Approach 1:
The connecting screw incorporates a dynamic locking mechanism with movable locking elements that can transition between engaged and disengaged states. The locking elements are biased by springs to automatically engage with corresponding features on the intramedullary nail, maintaining constant pressure and preventing loosening during the dynamic insertion process.
Solution Approach 2:
The connecting screw acts as an intermediary component between the insertion device and the intramedullary nail. It features intermediate locking structures including radial locking elements and axial positioning features that mediate the connection, ensuring stable attachment throughout the insertion procedure without requiring retightening.
2Ease of manufacture
If a standard threaded connection is used between the connecting screw and intramedullary nail, then assembly is simple, but disengagement or loosening occurs under insertion forces
Solution Approach 1:
The threaded connection is segmented into multiple independent locking zones along the length of the connecting screw. Each zone contains separate locking elements that engage with corresponding features on the nail, distributing the mechanical load and preventing single-point failure or loosening under insertion forces.
Solution Approach 2:
The connecting screw utilizes composite construction combining threaded sections for easy assembly with non-threaded locking sections featuring radial and axial locking elements. This composite design integrates the simplicity of threaded connections with the strength of positive locking mechanisms, preventing disengagement while maintaining manufacturability.
Data Source
Figure 1~2
Figure 3A~5
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AI summary
An intramedullary (IM) nail insertion assembly includes an IM nail extending longitudinally from a proximal end to a distal end. A proximal portion of the IM nail has an internal threading. The IM nail insertion assembly also includes a connecting screw extending longitudinally from a proximal end to a distal end. A distal portion of the connecting screw has an external threading for engaging the internal threading of the IM nail. One of the proximal portion of the IM nail and the distal portion of the connecting screw has a feature to resist a disengagement of the proximal portion from the distal portion.