Polyaxial Bone Anchor With Two-Position Saddle Assembly
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Solution Overview
Problem
Conventional pedicle screws are typically pre-assembled, limiting the ability for surgeons to place the threaded screw portion first and then attach the head body, which restricts the polyaxial nature and flexibility during rod insertion and locking.
Innovation Solution
A polyaxial bone anchor with a two-position saddle assembly that allows the head body to be snapped onto the threaded screw portion, maintaining polyaxial freedom, and includes a set screw for locking the rod and securing the saddle assembly in place, enabling both pre-assembled and disassembled configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the pedicle screw is pre-assembled with the head body joined to the threaded screw portion, then the assembly is ready for immediate placement, but the polyaxial nature and flexibility during rod insertion is restricted
Solution Approach 1:
The pedicle screw is divided into separable components: the threaded screw portion and the head body with saddle assembly. The saddle assembly can be detached from the head body, allowing the threaded screw portion to be placed first, then the head body to be attached separately while maintaining polyaxial movement capability for rod insertion.
Solution Approach 2:
The saddle assembly incorporates a movable component that allows the head body to rotate relative to the threaded screw portion within a conical circle, providing dynamic polyaxial movement. This enables the surgeon to insert rods from various angles before final locking, enhancing operational flexibility.
2Adaptability or versatility
If the head body is attached to the threaded screw portion before placement, then the structure is pre-assembled and stable, but the ability to place the threaded screw portion first and then attach the head body is limited
Solution Approach 1:
The device is segmented into the threaded screw portion and the head body with integrated saddle assembly. This segmentation allows the threaded screw portion to be placed in bone first, then the head body to be attached subsequently, providing placement configuration flexibility while maintaining a relatively simple assembly process through the snap-fit and set screw mechanism.
3Reliability
If the saddle assembly is locked into place immediately, then the head body is secured rigidly, but the polyaxial nature is lost and rod insertion flexibility is reduced
Solution Approach 1:
The saddle assembly includes a movable component that allows the head body to rotate within a conical circle relative to the threaded screw portion. This dynamic capability maintains polyaxial movement during rod insertion, and only after the rod is in place does the set screw lock the saddle assembly to secure rigid attachment, ensuring both reliability and operational freedom at the appropriate stages.
Data Source
AI summary
A polyaxial bone anchor assembly, comprising: a threaded screw portion comprising a head end; a head body disposed concentrically about the head end of the threaded screw portion; and a saddle assembly disposed within the head body and selectively engaging the head end of the threaded screw portion; wherein, when the saddle assembly is translated within the head body into a first locked position, the head body is coupled to the threaded screw portion such that disengagement of the head body from the threaded screw portion is allowed; and wherein, when the saddle assembly is translated within the head body into a second locked position, the head body is coupled to the threaded screw portion such that disengagement of the head body from the threaded screw portion is prevented.