Polyaxial Pedicle Screw Tulip Assembly for Spinal Fixation Stability
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Solution Overview
Problem
Existing bone screw designs for spinal stabilization lack improved designs, instruments, and methods for efficient placement and assembly, particularly in treating spinal irregularities caused by trauma, tumor, disc degeneration, and disease.
Innovation Solution
The development of orthopedic fixation devices featuring a tulip with cooperating threads, a saddle, and a ring system that allows for secure attachment of a polyaxial pedicle screw to a spinal rod, including variations with multiple threads, half-clips, torsion clips, and compression clamps to enhance stability and ease of assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional single-thread screws are used for spinal fixation, then the device structure is simple, but the stability and resistance to toggling and pull-out are insufficient
Solution Approach 1:
The screw thread is segmented into multiple independent threads (first thread and second thread) that are offset from each other. This segmentation allows each thread to engage with bone independently, distributing the load and increasing resistance to toggling and pull-out forces while maintaining a relatively simple overall screw structure.
Solution Approach 2:
The patent introduces a second thread offset from the first thread in the axial direction, adding a dimensional element to the thread configuration. This multi-dimensional thread arrangement increases the surface area of bone engagement and creates more complex load paths, thereby enhancing stability without requiring a completely different screw architecture.
2Adaptability or versatility
If modular fixation heads (tulips) are added after screw insertion, then the adaptability and ease of assembly are improved, but the device complexity increases
Solution Approach 1:
The fixation system is divided into separate modular components: the screw can be inserted independently, followed by the tulip head and rod. This segmentation allows for staged assembly and provides versatility in surgical approaches while keeping each individual component relatively simple in design.
Solution Approach 2:
The tulip head is designed to receive and nest the screw shaft, creating a hierarchical assembly where smaller components fit within larger ones. This nesting arrangement allows the modular components to compactly assemble into a stable fixation structure without requiring complex external fastening mechanisms.
3Strength
If multiple threads are added to the screw, then the resistance to toggling and pull-out is increased, but the manufacturing complexity increases
Solution Approach 1:
The thread is segmented into multiple discrete threads rather than a continuous single thread. This segmentation can be achieved through standard CNC machining or thread rolling processes by making multiple passes, using conventional manufacturing equipment without requiring specialized multi-thread cutting tools.
Solution Approach 2:
The patent varies the parameters of existing threads (such as pitch, diameter, and axial position) to create multiple threads. By adjusting these parameters within standard manufacturing tolerances and using conventional thread formation processes, the multi-thread design can be produced without significantly increasing manufacturing complexity.
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 improved stability and ease of assembly, enhancing the ability to stabilize the spine by increasing the number of threads and using modular components that securely attach to the screw head, reducing the risk of toggling and pull-out.
Implementation Method 1
cooperating threads disposed on mutually facing sides of each arm
Implementation Method 2
a pedicle screw having a tulip head for coupling the screw to the elongate spinal rod
Implementation Method 3
the screw head clampable within the tulip body interior cavity in a position between the saddle and the ring when the saddle is urged in a distal direction towards the tulip ledge
Implementation Method 4
forming a curved surface on the saddle distal end sized and dimensioned to conformingly receive the screw head
Data Source
AI summary
An orthopedic fixation device for affixing the screw head of a polyaxial pedicle screw has a tulip, a saddle, and a ring. The tulip has an interior cavity and two opposed threaded arms and a lower ledge. The saddle is inserted into the tulip body, and has a U shaped groove for receiving a spinal fixation rod. The ring has a diameter that is smaller than the widest diameter of the screw head, and is formable into a diameter larger than the widest diameter of the screw head when the screw head is pushed into the ring. The ring has a connection portion that mates with a connection portion of the saddle. The screw head is clamped within the tulip body between the saddle and the ring when a cap is threaded between the tulip arms.