Poly-axial Pedicle Screw Assembly for Spinal Fixation Stability
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Solution Overview
Problem
Conventional spinal fixation devices face screw loosening issues due to the inability of top portions to rotate, requiring surgeons to adjust the entire screw orientation, which complicates proper placement of rods and leads to instability post-surgery.
Innovation Solution
A poly-axial pedicle screw assembly with a tulip head, washer, and set screw that allows for rotational adjustment of the pedicle screw, enabling secure rod placement and locking without screw loosening, featuring a knurled head, threaded inner surfaces, and a semi-circular washer for enhanced stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the top portion of the device is made fixed, then the device structure is simple, but the screw loosening problem occurs and rod placement becomes difficult
Solution Approach 1:
The patent applies the dynamics principle by making the top portion of the pedicle screw rotatable relative to the shaft. The tulip head can rotate about a first axis and the washer can rotate about a second axis, allowing the device to adapt its orientation dynamically. This rotational capability eliminates screw loosening by maintaining proper engagement between the rod and screw head while simplifying rod placement procedures.
2Ease of operation
If the entire screw orientation is changed to accommodate rod placement, then the rod can be placed in slots, but screw loosening problems occur
Solution Approach 1:
The patent applies segmentation by dividing the screw assembly into distinct rotatable segments: the tulip head (with rod receiving slots) and the washer (with engagement surfaces). These segments can rotate independently relative to the shaft, allowing the rod to be placed in slots while maintaining secure engagement. The set screw then locks these segmented portions in their final positions.
3Manufacturing precision
If poly-axial rotation is added to the screw, then screw placement precision is improved, but device complexity increases
Solution Approach 1:
The patent implements poly-axial rotation through the tulip head and washer components that can rotate about different axes. The tulip head rotates about a first axis to allow rod insertion, while the washer rotates about a second axis to engage with the rod. This dynamic rotational capability achieves precise screw placement without requiring excessive structural complexity.
Solution Approach 2:
The patent uses the washer as an intermediary component between the tulip head and the rod. The washer receives the rod and provides engagement surfaces that interface with the rod's outer surfaces. This intermediary element enables precise positioning and rotation independent of the tulip head structure, simplifying the overall design while maintaining placement 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 poly-axial design allows for precise screw placement and secure locking of rods, reducing screw loosening and enhancing the stability of spinal fixation, facilitating easier surgical procedures and post-operative stability.
Implementation Method 1
The washer has a semi-circular opening configured to receive a rod and a knurled inner surface configured to engage the knurled head of the pedicle screw
Implementation Method 2
The set screw has threaded outer walls capable of engaging the threaded inner surfaces of the opposing walls of the tulip head
Data Source
AI summary
A pedicle screw assembly including a pedicle screw, a tulip head, a set screw, and a washer; a packaging assembly for a pedicle screw; a pedicle screw screwdriver assembly; and a set packaging assembly are disclosed.