Polyaxial Bone Anchoring Device Cap and Locking Ring Design
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Solution Overview
Problem
Conventional bone anchoring devices face issues with splaying of receiving parts during tightening, which limits their application in smaller bone structures and requires a lower profile for cervical spine and pediatric use, while also increasing stockholding costs due to limited modularity.
Innovation Solution
A polyaxial bone anchoring device featuring a cap and locking element that secures and fixes a rod to a bone anchoring element, preventing splaying and allowing for a lower profile, combined with a modular system of preassembled head receiving parts, locking rings, and caps with various bone anchoring elements of different shanks, diameters, and thread forms for customizable clinical applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional bone anchoring devices are used, then the receiving part can secure the bone anchoring element, but the receiving part splaying occurs during tightening which limits application in smaller bone structures
Solution Approach 1:
The device is divided into separate functional components: a head receiving part for receiving the bone anchoring element head, a locking ring mounted around the head receiving part for coupling the stabilization rod, and a cap with locking element for securing and locking. This segmentation allows each component to perform its specific function without interfering with others, preventing splaying while maintaining security.
Solution Approach 2:
The locking ring acts as an intermediary component between the head receiving part and the stabilization rod. It is mounted around the head receiving part and provides a stable interface for rod coupling, preventing direct contact and potential splaying of the head receiving part during tightening operations.
2Adaptability or versatility
If conventional bone anchoring devices are used, then the bone anchoring element can be secured, but the device profile is too large for cervical spine and pediatric applications
Solution Approach 1:
The locking ring is mounted around the head receiving part, and the cap is placed over the assembly, with the locking element received within the cap. This nested arrangement allows multiple components to occupy overlapping spatial volumes, significantly reducing the overall axial profile height of the device while maintaining all necessary functional capabilities for cervical spine and pediatric applications.
3Ease of manufacture
If conventional bone anchoring devices are used, then the device structure is simple, but the modularity is limited which increases stockholding costs
Solution Approach 1:
The head receiving part is designed as a universal component that can receive different types of bone anchoring element heads. The locking ring and cap assembly serves multiple functions: coupling the rod, providing a bearing surface for the locking element, and enabling polyaxial locking. This universality allows a limited set of standard components to be used across multiple applications, enhancing modularity while reducing the need for specialized variants and lowering stockholding costs.
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 for receiving the head therein, 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, the cap having a central axis and two opposite legs extending in a direction of the central axis, and a locking element configured to extend from the cap to lock relative positions of the bone anchoring element and an inserted rod relative to the head receiving part, wherein the cap is rotatable relative to the head receiving part between a first position in which the cap is movable and a second position in which the legs engage the head receiving part.