Polyaxial Pedicle Screw Head With Rotatable Temporary Clamping
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Solution Overview
Problem
Existing osteosynthesis devices, such as pedicle screws, face challenges in mounting bone anchors with larger diameters and require additional instruments for maintaining temporary clamping, leading to mechanical stress and limitations in spinal correction maneuvers.
Innovation Solution
A polyaxial pedicle screw design with a U-shaped fork head and internal fixing element that allows temporary clamping of the bone anchor without mechanical load on the pressure piece, enabling modular assembly and increased stability, allowing for larger bone anchors and reduced overall height.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a pressure piece is used to maintain temporary clamping, then clamping force is applied, but the pressure piece is subjected to mechanical stress and requires additional instruments for maintenance
Solution Approach 1:
The patent extracts the pressure piece from the clamping mechanism, allowing the fixing element to clamp the bone anchor directly without mechanical load on the pressure piece. This eliminates the need for additional instruments to maintain clamping and reduces device complexity while preserving clamping force application.
Solution Approach 2:
The fixing element is designed to maintain temporary clamping independently without requiring external instruments or continuous pressure piece engagement. The system serves itself by maintaining the clamping state through the fixing element's geometric configuration and material properties alone.
2Adaptability or versatility
If the outer diameter of the bone anchor shaft is larger than the opening diameter of the clevis, then larger bone anchors can be used, but mounting becomes problematic
Solution Approach 1:
The patent segments the clevis head into multiple functional zones with different diameters: a proximal opening diameter for bone anchor insertion and a distal opening diameter for fixing element engagement. This segmentation allows bone anchors with larger outer diameters to be mounted by inserting them through the proximal opening while maintaining compatibility with the fixing element at the distal end.
Solution Approach 2:
The patent transitions from a single-diameter clevis design to a multi-diameter design by introducing a wall cutout that creates different opening diameters at different locations. This dimensional variation in the clevis structure enables accommodation of bone anchors with varying sizes while maintaining functional integrity.
3Force
If a lever-like actuation is used to generate temporary clamping, then clamping force is generated, but combined compression and bending stress increases on the pressure piece
Solution Approach 1:
The patent removes the lever-like actuation mechanism from the pressure piece, allowing the fixing element to generate clamping force through direct geometric engagement with the bone anchor head. This extraction eliminates the combined compression and bending stress that would otherwise act on the pressure piece while maintaining effective clamping force application.
Solution Approach 2:
The fixing element serves as an intermediary between the bone anchor and the clamping mechanism, transferring forces directly without requiring lever-like actuation. This intermediary component allows clamping force generation while preventing stress transmission to the pressure piece through direct engagement geometry.
4Force
If the pressure piece is mechanically decoupled during temporary clamping, then reserves regarding maximum clamping force are provided, but the clamping mechanism becomes more complex
Solution Approach 1:
The patent extracts the pressure piece from the temporary clamping mechanism, allowing direct clamping of the bone anchor head by the fixing element. This extraction provides mechanical decoupling that reserves maximum clamping force capacity while the simplified direct-engagement geometry actually reduces overall device complexity compared to coupled lever mechanisms.
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
Enables independent maintenance of temporary clamping without additional instruments, providing enhanced stability and flexibility in spinal correction maneuvers, reducing mechanical stress and capital requirements for a diverse screw portfolio.
Implementation Method 1
the fixing element, by introducing a torsional moment about the transverse opening axis, clamps the head region of the bone anchor in the fork head in an angularly stable manner
Data Source
Figure 1
Figure 2
Figure 3a~3b
AI summary
Osteosynthesis device (1) for treating the spinal column, consisting of a fork head (10) which is U-shaped in a side view and has a through-opening (18) and which, in the proximal direction (101), has two fork limbs (11, 12) with an internal thread (16), and in which a connecting rod (50) can be received, and a ball-head receiving region (19) is provided in the fork head (10) in the distal direction (102) in the through-opening (18), and a bone anchor (90) is mounted pivotably therein, characterized in that there is provided on the fork head (10) a transverse opening (13) which communicates (185) with the through-opening of the fork head (10), and a fixing element (30) is mounted in this transverse opening (13) so as to be rotatable about a transverse-opening axis (130), and the fixing element (30), with introduction of a torsional moment about the transverse-opening axis (130), clamps the head region (91) of the bone anchor (90) at a stable angle in the fork head (10).