Intramedullary Nail Insert for Locking Screw Alignment
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Solution Overview
Problem
Intramedullary nails experience target inaccuracy issues with locking screws, leading to play between the nail and bone fragments, which is clinically undesirable, especially in metaphyseal fragments, and existing solutions like plastic inserts are prone to displacement.
Innovation Solution
A surgical nail with a transverse bore and an insert having a longitudinal slot, made of a material with lower modulus of elasticity than the nail, providing a congruent fit and optional stable-angle locking, allowing for precise screw alignment and adjustable holding power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the outside diameter of the locking screw is undersized in relation to the diameter of the transverse bore to accommodate target inaccuracy, then the locking screw can be passed through the transverse bore despite target error, but play is created between the locking screw and the transverse bore
Solution Approach 1:
A plastic insert is introduced as an intermediary component between the locking screw and the transverse bore. This insert fits tightly within the transverse bore and provides a precise guiding surface for the locking screw, eliminating play while still accommodating target inaccuracies during insertion.
Solution Approach 2:
The insert changes the effective parameters of the transverse bore by providing a precise internal surface that defines the locking screw's position. The insert's dimensions are specifically designed to eliminate clearance while maintaining ease of screw insertion despite target errors.
2Stability of the object's composition
If plastic inserts are used in the transverse bore to reduce play, then guidance effect and holding power are improved, but the plastic inserts can easily be pushed in or forced out, causing loss of function
Solution Approach 1:
The solution uses a composite construction where a plastic insert is combined with a metal nail. The plastic material provides the necessary compliance and friction characteristics to prevent displacement, while the metal nail provides structural strength. The plastic insert's material properties are specifically selected to maintain position while allowing controlled insertion.
Solution Approach 2:
The insert is designed with specific local properties: a tight-fit outer surface that engages with the transverse bore walls to prevent displacement, and an inner surface with appropriate friction characteristics that guide the locking screw without being forced out during normal operation.
3Ease of operation
If the locking screw has play in relation to the transverse bore to accommodate target error, then the locking screw can be inserted without precise alignment, but the bone fragments are able to move in relation to the nail
Solution Approach 1:
The plastic insert acts as a mediator that provides a precise guiding surface for the locking screw during insertion, allowing the screw to be passed through despite target inaccuracies, while simultaneously preventing play between the screw and the insert, thereby eliminating bone fragment movement.
Data Source
AI summary
An intramedullary nail comprising a central axis and a transverse borehole, provided with an insert which can be introduced into the transverse borehole, said insert also containing a longitudinal slit.