Polyaxial Bone Anchor With Threaded Compression Saddle
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Solution Overview
Problem
Conventional pedicle screws are typically pre-assembled, limiting the ability of surgeons to place the threaded screw portion first and then the head body, which restricts the polyaxial nature and flexibility during rod insertion and locking.
Innovation Solution
A polyaxial bone anchor design featuring a threaded screw portion with an externally threaded head end, an internally threaded head body, and an externally threaded compression saddle assembly, allowing for assembly in either a pre-assembled or disassembled configuration, with the compression saddle assembly being securely locked using a set screw to maintain polyaxial freedom and provide compressive force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If pedicle screws are placed in a pre-assembled configuration, then the structural integrity and rigidity are improved, but the flexibility and ease of operation during rod insertion and locking are worsened
Solution Approach 1:
The pedicle screw system is divided into separate components: a threaded screw portion and a head body that can be assembled together. This segmentation allows the surgeon to first implant the threaded screw portion into the vertebra, then subsequently attach the head body containing the rod, providing flexibility during the surgical procedure while maintaining structural integrity when assembled
Solution Approach 2:
The threaded screw portion is prepared and implanted into the vertebra before the head body is attached. This preliminary action allows the screw to be securely positioned in the bone first, then the head body is screwed onto it, maintaining polyaxial freedom during the process and enabling rod insertion before final locking
2Adaptability or versatility
If the head body is screwed onto the threaded screw portion after implantation, then the polyaxial nature is maintained during placement, but the risk of misalignment or improper assembly increases
Solution Approach 1:
A polyaxial collar serves as an intermediary component between the threaded screw portion and the rod. The collar maintains polyaxial freedom while providing a controlled interface for rod insertion and locking, ensuring proper alignment and reducing the risk of assembly errors
Solution Approach 2:
Traditional set screws are replaced with a compression mechanism that uses a compression member and spring to apply axial compression force. This mechanical substitution improves reliability by ensuring consistent, controlled compression without the complexity of traditional set screw assemblies
3Stability of the object's composition
If a compression mechanism is added to secure the head body to the threaded screw portion, then the structural stability is improved, but the device complexity increases
Solution Approach 1:
The compression mechanism is integrated into the head body structure itself, merging the compression function with the existing head body components. This reduces overall device complexity while maintaining structural stability through the compression force applied to the rod and head body assembly
Data Source
AI summary
A polyaxial bone anchor assembly, comprising: a threaded screw portion comprising an externally threaded head end; a head body selectively disposed concentrically about the externally threaded head end of the threaded screw portion, wherein the head body defines an internally threaded hole in a bottom portion thereof; and an externally threaded compression saddle assembly selectively disposed within an interior portion of the head body and selectively engaging the externally threaded head end of the threaded screw portion; wherein the externally threaded compression saddle assembly and the externally threaded head end of the threaded screw portion are selectively disposed within the interior portion of the head body by engaging and passing through the internally threaded hole in the bottom portion of the head body.