Intramedullary Nail Coupling for Jam-Free Lag Screw Fixation
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Solution Overview
Problem
Conventional intramedullary nails and set screws for femur fractures are cumbersome to assemble, prone to jamming, and provide inadequate mechanical stability due to their complex two-piece structure and inability to prevent uncontrolled medial deviation of the lag screw.
Innovation Solution
An implant system featuring a one-piece coupling member with a drive portion and bone fastener engagement portion, preassembled within the intramedullary nail, which prevents rotation of the bone fastener by engaging its grooves, allowing for simplified assembly and enhanced mechanical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional two-piece set screw structure is used, then the intramedullary nail can be assembled, but the assembly process becomes cumbersome and prone to jamming
Solution Approach 1:
The patent combines the set screw's main body engagement portion and threaded head drive portion into a single integrated one-piece coupling member. This merging eliminates the two-piece structure that caused jamming issues during assembly, while maintaining all necessary functions of guiding, engaging, and securing the bone fastener within the intramedullary nail.
2Ease of operation
If a conventional set screw with guiding structure is used, then the bone fastener can be engaged, but the operation time increases due to additional operation steps
Solution Approach 1:
The one-piece coupling member is preassembled within the intramedullary nail before surgery, with the bone fastener engagement portion already positioned to engage the lag screw groove. This preliminary preparation eliminates the need for complex intraoperative assembly steps, allowing the surgeon to simply drive the coupling member distally to secure the bone fastener, thereby reducing operation time.
3Reliability
If a conventional set screw with prongs or rims is used, then the intramedullary nail structure is maintained, but the lag screw cannot be prevented from uncontrolled medial deviation
Solution Approach 1:
The coupling member features an asymmetric rounded edge at the end of the bone fastener engagement portion that specifically engages with the groove of the bone fastener. This asymmetric geometry prevents uncontrolled medial deviation of the lag screw by providing a mechanical stop, while maintaining a relatively simple one-piece structure without complex multi-component assemblies.
4Ease of manufacture
If a conventional two-piece set screw is preassembled, then the intramedullary nail can be prepared, but the set screw may get stuck or jammed during sliding
Solution Approach 1:
By merging the set screw components into a single one-piece coupling member, the patent eliminates the interface between separate parts that could cause jamming during sliding. The integrated structure ensures smooth movement within the intramedullary nail's axial bore while maintaining all necessary engagement features for securing the bone fastener.
Data Source
AI summary
An implant system for use in orthopaedic surgery for fixation of bone includes an intramedullary nail and a coupling member. The intramedullary nail includes a proximal portion defining a longitudinal axis. The proximal portion includes an axial bore defining an axis substantially parallel to the longitudinal axis of the proximal portion and a transverse bore configured to receive a bone fastener. The coupling member includes a through hole and is movably arranged within the axial bore of the proximal portion. Further, the coupling member includes a drive portion and a bone fastener engagement portion. The drive portion is in one variant non-rotatably coupled to the bone fastener engagement portion. The bone fastener engagement portion is configured to engage the bone fastener penetrating the transverse bore. In one variant the engagement is realized via an extended contact region.