Polyaxial Bone Screw Deformable Tab Preload
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing polyaxial screw assemblies for spinal fixation systems face challenges in maintaining sufficient frictional force between the bushing and the rod receiver, which can lead to instability during spinal rod insertion and instrument manipulation, necessitating improved preload mechanisms.
Innovation Solution
A polyaxial screw assembly featuring a deformable tab within the rod receiver or bushing that applies a preload condition to wedge the bushing between the sidewall and spherical head, increasing frictional force, and utilizing plastically deformable tabs to secure the bushing in place, enhancing the interface between the bushing, rod receiver, and spherical head.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a friction fit mechanism is used between the bushing and rod receiver, then the bushing can be retained in place, but insufficient frictional force leads to instability during spinal rod insertion and instrument manipulation
Solution Approach 1:
The deformable tab is pre-loaded against the bushing before the spinal rod is inserted, creating a preload condition that generates frictional force. This preliminary action ensures the bushing is securely retained against the rod receiver before any loading occurs during surgery, preventing instability during rod insertion and instrument manipulation.
Solution Approach 2:
The tab is designed to be plastically deformable, allowing it to change its physical state from a relaxed position to a pre-loaded position. This parameter change in the tab's deformation state directly controls the frictional force generated between the bushing and rod receiver, enabling adjustment of retention strength.
2Reliability
If a deformable tab preload mechanism is implemented, then frictional force is increased to stabilize the assembly, but the device complexity increases
Solution Approach 1:
The deformable tab integrates multiple functions into a single component: it serves as both the retention mechanism and the preload mechanism. The tab is formed as an integrated part of either the rod receiver or bushing, combining the functions of mechanical retention and friction generation without requiring separate components, thereby minimizing device complexity while achieving assembly stability.
Solution Approach 2:
The deformable tab is designed to automatically apply the preload condition through its own elastic or plastic deformation when the bushing is inserted into the rod receiver. The tab self-activates upon assembly, eliminating the need for external actuators, adjustment mechanisms, or additional steps to generate the frictional force, thus maintaining simplicity while ensuring reliable retention.
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 deformable tab mechanism effectively increases the frictional force between components, stabilizing the assembly and facilitating easier insertion of spinal rods and instruments by maintaining a secure preload, thereby improving the overall stability and usability of the polyaxial screw assembly.
Implementation Method 1
A polyaxial screw assembly featuring a deformable tab within the rod receiver or bushing that applies a preload condition to wedge the bushing between the sidewall and spherical head, increasing frictional force, and utilizing plastically deformable tabs to secure the bushing in place
Data Source
AI summary
A polyaxial screw assembly having a threaded shaft, a rod receiver, a bushing, and a deformable tab is provided. The rod receiver includes a side wall forming a proximal end with an interior portion configured to receive a spinal rod and a distal end configured to receive the spherical head. The bushing is disposed between the spherical head and the sidewall of the rod receiver is configured to engage the spinal rod. The deformable tab is within one of the rod receiver and the bushing and engages with the other of the rod receiver and the bushing. The deformable tab may be disposed within the side wall of the bushing. The deformable tab may be configured to apply an axial force along a longitudinal axis of the threaded shaft to increase a friction force between the rod receiver, the bushing, and the spherical head.