Bone Fixation Washer With Elastic Rim
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Solution Overview
Problem
Current bone fixation devices face challenges in stabilizing complex fractures and joints, particularly the sacro-iliac joint, due to screw migration issues and difficulties in removing components post-healing, exacerbated by inadequate screw positioning and limited tool choices.
Innovation Solution
A bone fixation device comprising an elongated member with a proximal head and washer assembly that prevents longitudinal displacement while allowing axial rotation, featuring a central cavity and elastically deformable rims for secure assembly and easy removal, along with a cannulated screw design for enhanced fixation and cement injection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a washer is used to increase retention surface and prevent screw migration into the bone, then screw migration resistance is improved, but the difficulty to remove the washer together with the screw later-on increases
Solution Approach 1:
The washer is designed with a deformable rim that transitions from a locked state during fixation to a releasable state during removal. The rim can be elastically deformed using a specialized tool to break the interference fit, allowing dynamic change in the washer-screw-bone system from stable to removable.
Solution Approach 2:
The removal tool changes the physical state of the washer rim by applying elastic deformation beyond the interference fit threshold. This parameter change (from elastic deformation within limits to plastic deformation or tool-assisted release) enables the washer to be removed after healing.
2Stability of the object's composition
If the washer is firmly attached to the bone to prevent migration, then fixation stability is improved, but the complexity of removing both the migrated screw and attached washer increases
Solution Approach 1:
The deformable rim acts as an intermediary mechanism between the screw and bone. During fixation, it provides stable attachment; during removal, it serves as the target for the removal tool, allowing controlled release without requiring complex extraction procedures for deeply embedded washers.
3Ease of operation
If the proximal rim has a smaller transversal dimension to fit through the bone, then ease of insertion is improved, but the stability of washer-screw attachment deteriorates
Solution Approach 1:
The rim's interference fit creates a dynamic locking mechanism. The slight elastic deformation during insertion accommodates the size constraint, while the resulting interference pressure creates strong attachment. The system transitions from insertion mode (flexible) to fixation mode (rigid).
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 device provides increased screw migration resistance and facilitates secure removal of all components after healing, improving long-term stability and simplifying post-operative procedures by allowing intraoperative assembly and using biocompatible materials for enhanced surgical outcomes.
Implementation Method 1
The proximal rim is configured to be elastically deformable by pressing the proximal head through the proximal rim along the shaft axis and washer axis
Data Source
AI summary
A bone fixation device (1) comprises an elongated member (2) and a washer (3) assembled in a manner to prevent relative longitudinal displacement at the same time allowing axial rotation of the washer (3) with respect of the elongated member (2). The elongated member (2) comprises a proximal head (4) and an elongated shaft (5). The proximal head (4) comprises at least a distal spherical portion (8) having a diameter (D) and defining a maximum transversal dimension (Dh) of the proximal head (4). The washer (3) has a central cavity (14) configured to seat the proximal head (4) and comprising a central spherical portion (15) having the same diameter (D) of the distal spherical portion (8) of the proximal head (4). The central spherical portion (15) extends between a distal rim (16) and a proximal rim (17). The distal rim (16) has a distal transversal dimension (Dd) larger than a maximum transversal dimension (d) of the elongated shaft (5) and smaller than the maximum transversal dimension (Dh) of the proximal head (4). The proximal rim (17) has a proximal transversal dimension (Dw) larger than the maximum transversal dimension (d) of the elongated shaft (5) and slightly smaller than the maximum transversal dimension (Dw) of the proximal head (4). The proximal transversal dimension (Dw) of the proximal rim (17) is larger than the distal transversal dimension (Dd) of the distal rim (16). The proximal rim (17) is configured to be elastically deformable by pressing the proximal head (4) through the proximal rim (17).