Frictional Polyaxial Spinal Screw With Slotted Collet
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Solution Overview
Problem
Current polyaxial screws in spinal surgery lack effective mechanisms for maintaining the angular position and stability of screws during assembly and handling, leading to potential misalignment and instability.
Innovation Solution
A polyaxial spinal screw assembly featuring a threaded screw with a bulbous head, a receiver, and a slotted collet that creates a three-point bending condition to frictionally retain the screw's angular position, allowing for elastic deformation to accommodate assembly and apply force for retention, while also incorporating fenestration holes to limit resin pillar formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a simple polyaxial screw design with loose pivot is used, then ease of operation is improved, but stability of the screw's angular position deteriorates
Solution Approach 1:
The collet is designed to transition from a loose state during assembly to a locked state during tightening. Initially, the collet allows free movement of the screw head within the receiver for easy positioning. When the locking mechanism is activated, the collet engages with the screw head to fix the angular position, providing stability when needed without compromising ease of assembly.
Solution Approach 2:
The collet serves as an intermediary component between the screw head and the receiver. It mediates the interaction by providing frictional retention of the screw's angular position through controlled contact, allowing the screw to be easily positioned initially while maintaining stability once locked in place.
2Stability of the object's composition
If a frictional retention mechanism is added to maintain angular position, then stability of angular position is improved, but device complexity increases
Solution Approach 1:
The locking function is merged with the existing polyaxial screw structure. The collet is integrated into the receiver and works in conjunction with the screw head, combining the positioning and locking functions into a unified system that does not require separate complex mechanisms.
Solution Approach 2:
The frictional retention mechanism is designed to be self-regulating. The collet automatically adjusts its contact with the screw head to maintain the desired angular position through friction, without requiring additional active control systems or complex adjustment mechanisms.
3Object-affected harmful factors
If fenestration holes are added to limit resin pillar formation, then harmful factors are reduced, but manufacturing precision requirements increase
Solution Approach 1:
The screw shaft is segmented by adding fenestration holes that divide the solid structure into multiple sections. This segmentation allows the bone cement to flow through the holes rather than forming continuous pillars, reducing the harmful effect of resin pillar formation while the holes can be manufactured with standard precision.
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 solution provides enhanced stability and retention of the screw's angular position, reducing the risk of misalignment and facilitating secure locking with a spinal rod, while minimizing the risk of resin pillar formation during surgery.
Implementation Method 1
The collet may be able to elastically bend to accommodate assembly and to apply force to the screw head, in an un-locked condition, for the purpose of creating friction to retain a desired relative position of the screw and the receiver.
Implementation Method 2
The points of contact with the collet, in an un-locked condition, may include a contact point of the screw head against the collet interior that may be at or near a maximum diameter of the screw head... creating friction to retain a desired relative position of the screw and the receiver.
Data Source
AI summary
Various embodiments are provided with a polyaxial spinal screw assembly that comprise a threaded screw having a bulbous or curvate head, and a receiver for receiving the head of the screw, and a slotted collet between the receiver and the screw head. The collet may, in an un-locked condition, bear against the head of the screw to frictionally retain the screw's angular position. The collet may have a lip that may engage with a corresponding internal feature of the receiver. The screw head may be able to be inserted into the receiver through the bottom of the receiver. The screw may be cannulated and also may be fenestrated. Embodiments may also include a bone screw having fenestration holes that include a component in the rotational direction, such as backward-facing with respect to the forward-rotational direction of the screw.