Polyaxial Bone Anchor with Interference Fit Clamping
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Solution Overview
Problem
Current polyaxial bone anchoring devices face challenges in providing improved handling during surgery and ensuring safe fixation, particularly in maintaining adjustable angular positions of bone anchors without locking, which complicates the alignment and insertion of stabilization rods.
Innovation Solution
A polyaxial bone anchoring device featuring a pivotably connected anchoring element with a pressure element that exerts a predefined preload on the head, allowing temporary clamping and adjustable angular positioning without locking, facilitating easy assembly and adjustment of the stabilization rod without additional tools.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the head is completely locked in the receiving part, then the angular position is fixed and stable, but the alignment and insertion of the rod becomes difficult
Solution Approach 1:
The device transitions from a static locked state to a dynamic adjustable state. The head can pivot freely during alignment, then be locked at the desired angle. The pressure element allows the head to be temporarily clamped without complete locking, enabling dynamic adjustment during surgery.
Solution Approach 2:
The head is temporarily clamped in a desired angular position before final locking. This preliminary clamping action allows alignment to be established while maintaining the ability to adjust, and facilitates rod insertion before committing to the final locked position.
2Ease of operation
If the head is not locked, then the receiving part remains adjustable, but the fixation safety is compromised
Solution Approach 1:
The head is temporarily clamped in a desired angular position before final locking. This preliminary clamping action allows alignment to be established while maintaining the ability to adjust, and facilitates rod insertion before committing to the final locked position.
Solution Approach 2:
The device provides visual and tactile feedback to confirm proper alignment and locking. The pressure element's engagement with the head provides feedback on the clamping force, and the locking mechanism provides feedback when the head is securely locked at the desired angle.
3Manufacturing precision
If additional crimp tools are used to secure the head, then the assembly precision is improved, but the device complexity and surgical time increase
Solution Approach 1:
The device is designed to be self-assembling without requiring additional crimp tools. The pressure element and locking mechanism are integrated into the receiving part, allowing the head to be secured through the inherent mechanical interaction between components rather than external tools.
Solution Approach 2:
The pressure element and locking mechanism are merged with the receiving part as integrated components. This consolidation eliminates the need for separate crimp tools and reduces the number of steps required to secure the head, while maintaining assembly precision.
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 enables precise alignment and secure fixation of the stabilization rod, allowing for adjustable angular positioning during surgery and easy assembly without the need for additional crimp tools, enhancing surgical efficiency and safety.
Implementation Method 1
The head is slightly oversized with respect to the head contacting surface to achieve an interference fit such that the head is clamped by friction before it is locked.
Data Source
AI summary
A polyaxial bone anchoring device includesan anchoring element having a shaft and a head;a receiving part having a channel for receiving a rod therein, a coaxial bore and a seat portion for receiving the head;a pressure element having a head contacting surface portion;wherein the head is pivotable with respect to the receiving part and can be fixed at an angle by exerting pressure via the pressure element onto the head, and wherein the head has an oversize with respect to the head contacting surface portion such that an interference fit is achieved that clamps the head by the friction between the head and the head contacting surface portion. The curved outer surface portion has a largest diameter and the head contacting surface contacts the head at least in a region including the largest diameter.