Spiral U-Blade Lag Screw Fixation Stability
Solution Overview
Problem
Current lag screw and U-blade combinations used in hip fracture treatment often experience loss of reduction and rotational failure, necessitating revision surgery due to inadequate fixation performance in the femoral head.
Innovation Solution
A lag screw assembly with a shank featuring helical grooves and a blade with legs that slidably engage these grooves, providing enhanced fixation by allowing the blade to extend along the shank and into the intramedullary nail, thereby improving axial and rotational stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a U-blade and lag-screw combination is used to provide both axial and radial grip, then fixation performance is improved, but loss of reduction and rotational failure occur over time
Solution Approach 1:
The groove in the lag screw shank is configured in a helical (curved) path around the longitudinal axis, allowing the blade leg to follow this curved trajectory. This curvature enables the blade to engage both the lag screw and the intramedullary nail simultaneously, providing rotational constraint while maintaining axial stability, thereby preventing loss of reduction and rotational failure.
Solution Approach 2:
The blade is nested between the lag screw and the intramedullary nail, with the blade leg extending through the groove of the lag screw and engaging the groove in the nail. This nested configuration creates a three-component fixation system where each element contributes to overall stability, preventing both rotational and axial failure modes.
2Force
If a lag screw is used to provide axial grip, then axial stability is improved, but rotational grip is insufficient
Solution Approach 1:
The helical groove adds a rotational dimension to the otherwise axial lag screw. By configuring the groove in a spiral path around the longitudinal axis, the system transforms pure axial engagement into combined axial and rotational engagement, allowing the blade to prevent both axial displacement and rotational movement simultaneously.
3Stability of the object's composition
If opposing blades are used to provide radial grip and rotational stability, then rotational stability is improved, but axial grip is insufficient
Solution Approach 1:
The invention merges the functions of the lag screw (axial grip) and the blade (rotational stability) into a single integrated assembly. The blade leg simultaneously engages the helical groove of the lag screw and the groove in the intramedullary nail, combining axial and rotational fixation capabilities in one component system.
Data Source
AI summary
A lag screw assembly includes a lag screw and a blade. The lag screw includes a shank extending from a proximal end to a distal end along a longitudinal axis, the shank having an outer surface, and the shank having a threaded portion at the distal end. The lag screw further includes a groove formed in the shank and open to the outer surface, the groove extending along the shank between the proximal and distal ends. At least a portion of the groove defines a path that extends around and along the longitudinal axis on the outer surface. The blade has a head and a leg extending therefrom for slidably engaging the groove.