Polyaxial Bone Anchor Frictional Clamping Mechanism
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Solution Overview
Problem
Current polyaxial bone anchoring devices face challenges in handling during surgery, particularly in complex clinical applications where multiple bone anchors need to be connected to a stabilization rod, due to the difficulty in aligning the receiving part and inserting the rod when the head is freely pivotable before locking.
Innovation Solution
A polyaxial bone anchoring device that allows temporary clamping of the head in a desired angular position without locking, enabling adjustable alignment and insertion of the rod, with a mechanism that exerts a preload on the head using a pressure element and crimp bores to maintain the head in a frictional engagement, facilitating easier handling and manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the head is freely pivotable with respect to the receiving part before locking, then the bone anchoring device provides polyaxial adjustment capability, but the alignment of the receiving part and insertion of the rod becomes difficult in complex clinical applications
Solution Approach 1:
The frictional engagement mechanism is activated before the rod insertion step to preliminarily stabilize the head-receiving part assembly. This preliminary action maintains the receiving part in an adjustable angular position, allowing surgeons to align multiple bone anchors with the rod before actual insertion, thereby resolving the contradiction between polyaxial adjustability and alignment difficulty
Solution Approach 2:
The frictional engagement between the pressure element and the head acts as an intermediary mechanism. It provides temporary stabilization without complete locking, serving as a mediator between the freely pivotable state (needed for polyaxial adjustment) and the fully locked state (needed for stable rod insertion). This intermediary frictional state enables easier alignment while preserving adaptability
2Reliability
If a pressure element is used to exert pressure onto the head to lock the angle, then the head can be maintained in a desired angular position, but the device complexity increases
Solution Approach 1:
The pressure element is designed to be retained within the receiving part through its own geometric features (U-shaped cross-section fitting into grooves) without requiring separate retention mechanisms. The crimping operation simultaneously achieves both retention and frictional engagement, allowing the pressure element to serve multiple functions (pressing, retaining, and frictional engagement) thereby maintaining reliability while minimizing added complexity
Solution Approach 2:
The patent combines multiple functions into the pressure element: it provides the pressing force for angular position maintenance, serves as a retention element through its U-shaped geometry, and creates frictional engagement with the head. By merging these functions into a single component rather than using separate elements, the device achieves reliable angular position stability without proportionally increasing complexity
3Reliability
If crimping through bores is used to fix the pressure element position, then the pressure element is retained in the receiving part, but additional manufacturing steps are required
Solution Approach 1:
The crimping operation is performed as a preliminary action during assembly before final locking. The bores are pre-positioned in the receiving part design, and the crimping process simultaneously achieves retention of the pressure element and preparation for frictional engagement. This preliminary retention action ensures reliability while integrating the retention feature into the existing manufacturing workflow rather than adding separate complex retention 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
The device simplifies the alignment and insertion process during surgery, allows for adjustable rod positioning without complete loosening, and can be manufactured at low costs with fewer parts and without redesigning existing components, ensuring safe and efficient surgical handling.
Implementation Method 1
the pressure element frictionally clamps the head to maintain a desired angular position before locking
Data Source
Figure 1~2
Figure 3
Figure 4a~5b
AI summary
A polyaxial bone anchoring device is provided including an anchoring element (2) having a shaft (3) for anchoring in a bone and a head (4); a receiving part (5) having a top end (51) and a bottom end (52), a channel (56) for receiving a rod therein and a passage (53, 54) extending from the top end (51) to the bottom end (52) and including a seat (54) for receiving the head (4); a pressure element (6) which is arranged in the passage (53) and configured to exert pressure onto the head (4), wherein the head is pivotable with respect to the receiving part (5) and can be locked at an angle by means of the pressure element (6); the pressure element (6) comprising at least one recess (600a, 600b; 610a, 610b; 620a, 620b) facing the inner wall of the receiving part; the receiving part comprising at least one protrusion (502a, 502b) provided at its inner wall, and wherein, when the pressure element is inserted into the receiving part and rests on the head, the protrusion (502a, 502b) engages the lower edge (601a, 601b; 611a, 611b; 621a, 621b) such that by the engagement a force is exerted by the pressure element onto the head (4) to maintain the head at an angular position by friction before locking the head.