Polyaxial Pedicle Screw With Lateral Locking Insert
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Solution Overview
Problem
Current polyaxial pedicle screws in spinal fixation systems face challenges in aligning and locking the shank orientation during minimal invasive surgeries, as existing solutions either restrict rod insertion or limit the surgeon's ability to correct shank orientation after rod placement.
Innovation Solution
A polyaxial pedicle screw design featuring a receiving head with a U-shaped passage and a locking insert that can be externally pressed into a locking position through lateral apertures, allowing independent locking of the shank orientation without hindering rod insertion, using a dedicated instrument with pressing arms to maintain the locking insert in place.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the locking insert is engaged to lock the shank orientation, then the shank orientation is fixed, but the connecting rod cannot be inserted from above
Solution Approach 1:
The locking mechanism is segmented into two independent functions: the locking insert locks the shank orientation through engagement with the bulging end, while the set-screw independently locks the connecting rod through engagement with the U-shaped passage. This segmentation allows each component to perform its specific locking function without interfering with the other, resolving the contradiction between securing shank orientation and enabling rod insertion.
Solution Approach 2:
The locking insert is positioned in a first dimension (engaging the bulging end to lock shank orientation) while the set-screw operates in a second dimension (engaging the U-shaped passage to lock the rod). By distributing the locking functions across different spatial dimensions and operational sequences, the design enables both orientation locking and rod insertion without mutual interference.
2Reliability
If the set-screw is used to clamp the rod, then the rod is locked into position, but the shank orientation cannot be corrected
Solution Approach 1:
The locking mechanism is divided into two independent locking actions: the locking insert secures the shank orientation independently, and the set-screw secures the rod independently. This segmentation allows the surgeon to first lock the shank orientation with the locking insert, then correct any orientation issues while the rod is still being positioned, and finally lock the rod with the set-screw. The independent locking actions enable sequential operations without compromising either function.
Solution Approach 2:
The locking insert is engaged preliminarily to lock the shank orientation before the final rod positioning is completed. This preliminary locking action allows the surgeon to establish and verify the correct shank orientation early in the procedure, then proceed with rod insertion and final locking without being constrained by a pre-locking mechanism that would prevent orientation correction.
3Ease of manufacture
If an outer set-screw is added to tighten the locking insert, then the locking insert can be tightened independently, but the connecting rod cannot be inserted from above
Solution Approach 1:
The locking mechanism is segmented into two independent functional elements: the locking insert that tightens through engagement with the bulging end to lock shank orientation, and the set-screw that independently engages the U-shaped passage to lock the rod. This segmentation eliminates the need for an outer set-screw to tighten the locking insert, as the locking insert self-tightens through its engagement mechanism. The independent functions allow rod insertion from above without interference from an outer set-screw.
Data Source
AI summary
A polyaxial pedicle screw may include a receiving head having a transversal U-shaped passage, and a shank having a threaded portion external to the receiving head, and a bulging end rotatable housed within the receiving head. The polyaxial pedicle screw may include a locking insert housed within the receiving head and matable with the bulging end, for locking it into position, and a set-screw engaged in the distal aperture for locking a connecting rod received within the transversal U-shaped passage. The receiving head of the polyaxial screw may include a lateral aperture, the lateral aperture exposing a contact surface of the locking insert in such a way that external pressing component can act on the contact surface to maintain the locking insert into its locking position.