Bone Screw Z-Axis Translation via Segmented Tulip Mechanism
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current bone screw systems in spinal surgery face challenges in achieving precise alignment due to anatomical variations, often requiring anterior/posterior translation which can lead to suboptimal alignment or bone fractures, and existing solutions for z-axis adjustment either weaken the bone-screw interface or are cumbersome to assemble.
Innovation Solution
A modular bone fixation system featuring a bone fastener with an outer receiver, inner receiver, and a screw retainer that allows for variable angle orientation and longitudinal translation, utilizing a spring and locking mechanism to securely lock the bone fastener and connecting rod in place, enabling easy assembly and adjustment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If anterior/posterior translation is performed to align the tulip/receiver with the rod or plate, then alignment is improved, but bone fractures or pullout of the shank portion may occur due to stresses placed on the bone-screw interface
Solution Approach 1:
The invention divides the adjustment function into two independent segments: polyaxial rotation (pitch, yaw, roll) and z-axis translation. The tulip/receiver handles angular orientation while the set screw mechanism handles longitudinal positioning, allowing each to be optimized independently without compromising the bone-screw interface
Solution Approach 2:
The set screw acts as an intermediary mechanism that enables z-axis translation of the tulip/receiver relative to the shank portion without requiring translation of the vertebral body itself. This intermediate adjustment mechanism eliminates the need for harmful persuading forces on the bone-screw interface
2Manufacturing precision
If the screw is partially backed out to allow z-axis adjustment, then alignment is improved, but the bone-screw interface is weakened reducing overall strength
Solution Approach 1:
The set screw serves as a mediator that provides z-axis translation capability while keeping the bone-screw interface intact. Instead of backing out the screw, the set screw mechanism allows the tulip/receiver to be positioned longitudinally without compromising the primary bone-screw anchorage
Solution Approach 2:
The adjustment mechanism is segmented into two independent functions: the bone screw provides secure anchorage while the set screw mechanism provides z-axis translation. This segmentation allows alignment adjustment without weakening the bone-screw interface
3Adaptability or versatility
If manual assembly of the screw and head construct is required during surgery, then z-axis adjustment capability is provided, but surgical time and complexity increase
Solution Approach 1:
The invention merges the z-axis translation mechanism with the existing polyaxial tulip/receiver structure. The set screw is integrated into the tulip/receiver assembly, allowing both angular and longitudinal adjustments to be made as a unified operation rather than separate manual assembly steps
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 system provides secure and adjustable bone fixation with enhanced stability by allowing for precise alignment and adjustment along the z-axis without compromising the bone-screw interface, facilitating easier assembly and reducing the risk of bone fractures during spinal surgery.
Implementation Method 1
a spring disposed between the inner receiver and the outer receiver. The spring is configured to bias the inner receiver proximally relative to the outer receiver.
Implementation Method 2
utilizing a spring and locking mechanism to securely lock the bone fastener and connecting rod in place
Data Source
AI summary
A bone fixation system with variable z-axis translation is provided. The system includes an outer tulip coupled to a bone fastener via a screw retainer. An inner tulip is coupled to the outer tulip such that the inner tulip is longitudinally movably relative to the outer tulip. The inner tulip includes a lock that provides a seat for a connecting rod. The inner tulip together with a seated rod is permitted to translate along the z-axis inside the outer tulip when in an unlocked position. Also in the unlocked position, the bone fastener is free to angulate relative to the outer tulip. The z-axis position of the inner tulip and rod relative to the outer tulip is fixed in a locked position. Also, in the locked position, the bone fastener is locked with respect to the outer tulip. The system may be adjusted between the locked and unlocked positions by way of a set screw.