Polyaxial Bone Anchoring Device Pressure Member Preload
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Solution Overview
Problem
Existing polyaxial bone anchoring devices lack simplicity in design and handling, despite providing enlarged angulation.
Innovation Solution
A polyaxial bone anchoring device with a pressure member that exerts a preload force on the head of the bone anchoring element, allowing temporary clamping in a desired angular position without locking, facilitated by an interference fit connection and radial forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a polyaxial bone anchoring device is designed to provide enlarged angulation, then the adaptability for different insertion angles is improved, but the device complexity increases
Solution Approach 1:
The device is divided into functionally independent segments: a receiving part with a bore for the bone anchoring element, a separate pressure member for applying preload, and a locking mechanism. This segmentation allows each component to be optimized for its specific function while maintaining overall polyaxial capability, resolving the contradiction between adaptability and complexity.
Solution Approach 2:
The pressure member is designed to be movable along the bore axis, transitioning between a first position for applying preload and a second position for locking. This dynamic design enables the device to adapt to different operational phases (temporary clamping vs. final locking) without requiring multiple static components, thereby maintaining simplicity while providing enlarged angulation capability.
2Manufacturing precision
If a pressure member is designed to exert precise preload force on the head, then the manufacturing precision is improved, but the device complexity increases
Solution Approach 1:
The pressure member is pre-configured with a predefined force application mechanism that exerts a specific preload onto the head when moved to the first position. This preliminary action ensures precise and reproducible preload force without requiring complex real-time control systems, as the force characteristics are determined during manufacturing and assembly.
Solution Approach 2:
The pressure member utilizes the inherent mechanical properties of the device structure and material elasticity to generate and maintain the predefined preload force. The interaction between the pressure member and the head, combined with friction forces, automatically maintains the desired preload without requiring external control systems or additional components, thereby achieving manufacturing precision without increasing device complexity.
3Ease of operation
If the head is temporarily clamped with friction before locking, then the ease of operation is improved, but the reliability of the clamping mechanism decreases
Solution Approach 1:
The pressure member transitions dynamically between a first position where friction provides temporary clamping for easy handling and alignment, and a second position where mechanical locking provides reliable fixed positioning. This dynamic design allows the device to leverage the advantages of both friction-based clamping (ease of operation) and mechanical locking (reliability) at different stages of the procedure.
Solution Approach 2:
The friction-based temporary clamping acts as a cushioning mechanism during the alignment and insertion phase, providing sufficient holding force for easy handling without requiring immediate mechanical locking. This preliminary frictional engagement protects against inadvertent movement during operation while maintaining the ability to achieve precise positioning before final locking, thus balancing ease of operation with adequate reliability.
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 solution enables precise and reproducible preload application, simplifies device handling, and allows for enlarged pivot angulation, making it suitable for applications like lateral mass fixation in the cervical spine.
Implementation Method 1
a pressure member having a first surface for engaging the head and a second surface on which the rod acts. The receiving part includes an accommodation space for accommodating the head and a bore being in communication with the accommodation space, the bore having a bore axis, The pressure member is configured to assume a first position in which it exerts a preload onto the head that results from friction between the first surface and the head
Implementation Method 2
The predefined axial force can be maintained by an interference fit connection, by radial forces which act on the pressure member
Data Source
AI summary
A polyaxial bone anchoring device includes a bone anchoring element having a head and a shaft, a receiving part having a head receiving portion, a rod receiving portion, and a bore having a bore axis, and a pressure member movable in the bore and having a first surface for engaging the head, wherein the pressure member is movable to a first position where friction between the first surface and the head generates a preload on the head to maintain the shaft at a temporary angular position relative to the receiving part, and wherein the pressure member is configured to engage the receiving part to generate a holding force for holding the pressure member at the first position without a positive lock, and wherein the pressure member is movable in and out of the first position by applying an axial force on the pressure member greater than the holding force.