Polyaxial Bone Anchoring Device with Asymmetric Receiving Part
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Solution Overview
Problem
Conventional polyaxial bone anchoring devices have limitations in providing a low profile and allowing for a large pivot angle of the bone anchoring element relative to the rest of the device, which is essential for applications like cervical spine surgery and pediatric procedures.
Innovation Solution
A polyaxial bone anchoring device design featuring a cap and locking element that secures and fixes a rod and head of the bone anchoring element, preventing splaying of the receiving part, with a modular system allowing for various shank diameters and pivot angles, enabling a pivot range of up to 360°, particularly suitable for applications requiring small-sized devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a conventional receiving part design is used to secure the bone anchoring element, then the device can provide adequate structural support, but the profile height and diameter increase, and the pivot angle is limited
Solution Approach 1:
The receiving part is divided into multiple functional segments: a head receiving portion with a seat for the bone anchoring element head, and a separate body portion with a U-shaped channel for the rod. This segmentation allows each part to be optimized independently - the head receiving portion can provide polyaxial movement while the body portion maintains a low profile, resolving the contradiction between compact shape and versatile pivot angle capability.
Solution Approach 2:
The receiving part incorporates dynamic characteristics by allowing the bone anchoring element head to pivot polyaxially within the head receiving portion before final locking. The asymmetric construction of the free end edge creates a counter-sunk region that enables increased angulation in specific directions, providing adaptability while maintaining a compact overall structure.
2Adaptability or versatility
If the receiving part is designed to allow large pivot angles, then the bone anchoring element can pivot at enlarged angles, but the receiving part splaying occurs when tightening the locking element
Solution Approach 1:
The free end edge of the receiving part is constructed asymmetrically with a counter-sunk region that is deeper on one side than the other. This asymmetric geometry allows the bone anchoring element to pivot at enlarged angles toward the counter-sunk region while the opposite side provides structural support that prevents splaying when the locking element is tightened, thus resolving the contradiction between pivot angle capability and structural integrity.
3Adaptability or versatility
If a modular system with various shank diameters and pivot angles is implemented, then clinical flexibility and cost-effectiveness improve, but device complexity increases
Solution Approach 1:
The receiving part is designed as a universal component that can accommodate multiple types of bone anchoring elements with different shank diameters, thread forms, and head configurations. The standardized head receiving portion with its asymmetric counter-sunk region provides polyaxial capability for various anchoring elements, while the U-shaped channel accepts different rod configurations. This multi-functionality allows a single receiving part design to serve multiple clinical needs, increasing flexibility without proportionally increasing complexity.
Data Source
AI summary
A polyaxial bone anchoring device includes a bone anchoring element having a shank and a head, a head receiving part having a first end, an open second end, and a hollow interior portion in communication with the open second end for receiving the head therein, the head receiving part being flexible for clamping the head, a locking ring configured to be mounted around the head receiving part and having a rod receiving portion, a cap configured to be connected to the head receiving part, and a locking element configured to extend from the cap to engage an inserted rod, wherein the head is pivotable in and the cap and the locking ring are rotatable relative to the head receiving part, and wherein when the locking element is tightened, an inserted rod and an angular position of the bone anchoring element are locked relative to the head receiving part.