Polyaxial Bone Anchor with Sleeve Insert for Large Pivot Angles
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Solution Overview
Problem
Existing polyaxial bone anchoring devices lack simplicity in design and efficiency in fixation, particularly for applications requiring large pivot angles like cervical spine lateral mass fixation.
Innovation Solution
A polyaxial bone anchoring device with a sleeve-like insert piece and pressure member that allows for a wide pivot angle (≥45°) without flexible parts, providing effective axial pressure locking and a compact design, suitable for top or bottom loading configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If existing polyaxial bone anchoring devices are used to achieve enlarged pivot angle, then the pivot angle can be increased, but the design complexity increases and fixation efficiency decreases
Solution Approach 1:
The device is divided into three main segments: a bone anchoring element (screw or hook), a receiving part (head), and a locking mechanism. This segmentation allows each component to be optimized independently for its specific function while maintaining overall simplicity. The bone anchoring element provides the enlarged pivot angle capability, the receiving part houses the locking mechanism, and the locking mechanism secures the angular position, thereby resolving the contradiction between adaptability and design complexity.
Solution Approach 2:
Instead of using flexible parts to achieve polyaxial movement (which would increase complexity), the invention inverts the approach by using a rigid structure with a locking mechanism that allows angular adjustment before locking. The bone anchoring element is rigidly connected to the receiving part through the locking mechanism, eliminating the need for flexible components while maintaining the enlarged pivot angle capability.
2Adaptability or versatility
If existing polyaxial bone anchoring devices are used to achieve enlarged pivot angle, then the pivot angle can be increased, but fixation efficiency and clamping force decrease
Solution Approach 1:
The locking mechanism is designed to apply axial pressure to lock the angular position of the bone anchoring element relative to the receiving part before final tightening. This preliminary action ensures that the clamping force is effectively applied in the axial direction, securing the enlarged pivot angle position with high fixation efficiency and reliability before the device is fully tightened.
Solution Approach 2:
The invention changes the parameter of pressure application direction by designing the locking mechanism to apply pressure specifically in the axial direction rather than radially or tangentially. This parameter change ensures that the clamping force is optimally directed to maintain the enlarged pivot angle position, thereby improving fixation efficiency and reliability while maintaining the ability to achieve large angular adjustments.
3Adaptability or versatility
If flexible parts are used to achieve polyaxial movement, then the pivot angle can be adjusted, but reliability decreases during multiple angular adjustments
Solution Approach 1:
The invention inverts the conventional approach by eliminating flexible parts entirely and using a rigid locking mechanism instead. The bone anchoring element and receiving part are connected through a rigid structure with a locking mechanism that secures the angular position. This inversion ensures that the device maintains high reliability during multiple angular adjustments, as the rigid structure does not degrade or lose effectiveness with repeated use, unlike flexible parts.
Data Source
AI summary
A polyaxial bone anchoring device includes: an anchoring element having a shaft for anchoring in a bone and a head, the head having a spherically-shaped outer surface portion; a receiving part configured to be pivotably connected to the head, the receiving part having a top end and a bottom end, a longitudinal axis extending through the top end and the bottom end, a channel transverse to the longitudinal axis for receiving a rod, and an accommodation space for accommodating the head, the accommodation space having a lower opening at the bottom end, a sleeve-like insert piece configured to be positioned around a portion of the head and to pivot in the receiving part, the insert piece having a spherically-shaped outer surface portion, wherein a lower edge of the insert piece extends past the lower opening in a direction away from the receiving part when the insert piece is seated in the receiving part in a position in which a central axis of the insert piece is coaxial with the longitudinal axis, and wherein the insert piece has an opening with a diameter greater than or equal to a maximum diameter of the head when the head is not in contact with the insert piece; a pressure member configured to be arranged at least partially in the accommodation space, the pressure member having a lower surface portion configured to contact the head to exert pressure onto the head when the head and the pressure member are arranged in the receiving part; wherein when the head, the insert piece, and the pressure member are arranged in the receiving part, the insert piece is tiltable with respect to the longitudinal axis of the receiving part and with respect to a longitudinal axis of the anchoring element, and wherein the anchoring element and the insert piece can be locked at respective angles relative to the longitudinal axis of the receiving part by exerting pressure with the pressure member onto the head.